Search

Mid-air imaging, a visual display technology for augmented reality (AR) that enables multiple people to view images simultaneously without the need for special eyewear, involves the formation of real images in mid-air through various optical elements. This paper presents a novel mid-air imaging optical plate, termed the truncated cylindrical array plate (TCAP). TCAP is composed of transparent cylinders with obliquely truncated ends and mirrors, specifically designed to address issues such as stray light and limited viewing angles in existing mid-air imaging optical elements. We evaluated TCAP through computer simulations and by fabricating a prototype optical element. Ray tracing simulations and stereo matching algorithms demonstrated that mid-air images are symmetrically formed on the side opposite of the light source relative to the TCAP. Furthermore, the simulations indicated that a bright, stray-light-free mid-air image could be achieved within a horizontal viewing angle of approximately ± 40 ∘ . Experimental evaluation using a handcrafted prototype further confirmed the plane symmetry of mid-air image formation, validating its functionality as a mid-air imaging element. The proposed method is advantageous in systems where stray light is problematic, such as mid-air image interaction systems or optical systems utilizing mid-air imaging elements. [ABSTRACT FROM AUTHOR]

This research project envisions using a lunar observation platform to measure the full-wave (0.2~100 μm) and shortwave (0.2~4.3 μm) radiation of the Earth, achieving an accurate estimation of the overall radiation budget of the Earth. Based on the lunar platform, the system analyzes Earth's radiation characteristics and geometric attributes, as well as the sampling properties of observation times. Informed by these analyses, an Earth-facing optical radiation measurement system tailored to these specifications is designed. The optical system adopts an off-axis three-mirror configuration with a secondary image plane, incorporating a field stop at the primary image plane to effectively suppress solar stray light, scattered lunar surface light, and background radiation from the instrument itself, ensuring the satisfactory signal-to-noise ratio, detection sensitivity, and observation duration of the instrument. At the same time, stringent requirements are imposed for the surface treatments of instrument components and temperature control accuracy to further ensure accuracy. Simulation analyses confirm that the design satisfies requirements, achieving a measurement accuracy of better than 1% across the entire optical system. This Moon-based Earth-radiation measurement system, with capabilities for Earth-pointing tracking, radiation energy detection, and stray-light suppression, furnishes a more comprehensive dataset, helping to advance our understanding of the mechanisms driving global climate change [ABSTRACT FROM AUTHOR]

Nuclear fusion is a potential source of energy that could supply the growing needs of the world population for millions of years. Several experimental thermonuclear fusion devices try to understand and control the nuclear fusion process. A very interesting diagnostic called Thomson scattering (TS) is performed in the Spanish fusion device TJ-II. This diagnostic takes images to measure the temperature and density profiles of the plasma, which is heated to very high temperatures to produce fusion plasma. Each image captures spectra of laser light scattered by the plasma under different conditions. Unfortunately, some images are corrupted by noise called stray light that affects the measurement of the profiles. In this work, we propose the use of deep learning models to reduce the stray light that appears in the diagnostic. The proposed approach utilizes a Pix2Pix neural network, which is an image-to-image translation based on a generative adversarial network (GAN). This network learns to translateimages affected by stray light to images without stray light. This allows for the effective removal of the noise that affects the measurements of the TS diagnostic, avoiding the need for manual image processing adjustments. The proposed method shows a better performance, reducing the noise up to 98 % inimages, which surpassesprevious works that obtained 85 % for the validation dataset. [ABSTRACT FROM AUTHOR]

Folded optical path designs have been widely applied in Virtual Reality (Pancake VR) displays in recent years. Compared with the traditional straight‐through and Fresnel optical path design, the Pancake design has obvious advantages in smaller size and clearer virtual image. However, the Pancake optical path uses polarization devices to fold the optical path and, light undergoes multiple refractions and reflections between lens groups, thus inevitably introducing stray light. This stray light greatly reduces the contrast ratio even if taking high‐contrasting Mini‐LED backlight LCD as panel, and seriously affects the user experience. In this paper, we first analyze the causes of stray light in the Pancake design and then propose an effective optical design method. In addition, an effective process scheme for improving image contrast is proposed by analyzing the impact of lens and tube reflectivity. Further, a prototype of the Pancake VR optical module is successfully implemented with low stray light and high contrast ratio. [ABSTRACT FROM AUTHOR]

Scattered light from the objective lens, directly exposed to the intense sunlight, is a dominant source of stray light in internally occulted coronagraphs. The variable stray light, such as the scatter from dust on the objective lens, can produce varying scattering backgrounds in coronal images, significantly impacting image quality and data analysis. Using data acquired by the Lijiang 10-cm Coronagraph, the quantitative relationship between the distribution of dust on the objective lens and the resulting scattering background is analyzed. Two empirical models for the scattering background are derived, and used to correct the raw coronal data. The second model, which depends on three parameters and performs better, shows that the scattering-background distribution varies with angle, weakens with increasing height, and enhances with increasing dust level on the objective lens. Moreover, we find that the dust on the center of the objective lens can contribute more significantly to the scattering background than on the edge. This study not only quantitatively confirms the significant impact of the stray light produced by dust on the objective lens of the coronagraph, but also corrects the coronal data with this stray light for the first time. Correcting for dust-scattered light is crucial for the high-precision calibration of ground-based coronagraph data, enabling a more accurate analysis of coronal structures. Furthermore, our model is envisioned to support the provision of reliable observational data for future routine coronal magnetic-field measurements using ground-based coronagraphs. [ABSTRACT FROM AUTHOR]

The miniaturization of integrated optical gyroscopes requires the effective suppression of stray light crosstalk, which arises from the cascade of passive functional devices and significantly affects system performance. This study focuses on a tightly confined silicon nitride platform, where the optical mode field is strongly confined within the SiN core, enabling a compact chip design with dimensions of just 2 mm × 3 mm. Guided by the principle of gyroscope reciprocity, we thoroughly investigate the stray light leakage mechanisms in waveguide splitters. To address the stray light radiation characteristics inherent to passive functional devices, we introduce a stray light suppression strategy incorporating a conical adiabatic waveguide structure and a rectangular deep-etched groove. This design effectively dissipates the asymmetric high-order mode leakage from splitters, preventing scattered light from coupling back into the main waveguide. Comparative analysis reveals that this approach optimizes the gyroscope system's zero-bias stability to within 0.2°/h. Experimental results validate the design's effectiveness in suppressing stray light, demonstrating its suitability for low-cost, high-performance optical gyroscope systems with high integration density. [ABSTRACT FROM AUTHOR]

Star trackers are currently the most accurate sensors for determining the attitude of a spacecraft. These sensors comprise not only highly capable optical detectors and processor units but also complicated software solvers. One of the main solvers employed in star trackers is image segmentation. In this study, the aim is to develop a hybrid image segmentation method which is a combination of both global thresholding and density-based spatial clustering of applications with noise (DBSCAN) method to increase detection probability of the stars in heavy noise. Secondly, a sorting algorithm is added to list the detected stars in terms of their brightness to increase the efficiency of the star tracking algorithm. Then, this new approach and two different conventional segmentation methods are applied to the Orion star constellation image polluted with Gaussian, salt and pepper, and uneven background noises. The resulting images of these segmentation methods are compared in terms of denoising capabilities. Although computationally more expensive, the proposed DBSCAN-based hybrid method displays a background pixel recovery performance of 99.5%, compared to Otsu global thresholding and adaptive thresholding methods' 73.5% and 79.9% recovery values, respectively. Additionally, it has been demonstrated that the sorting algorithm successfully listed the detected stars in accordance with their brightness. [ABSTRACT FROM AUTHOR]

Recently, we developed a simple theoretical model for the estimation of the irradiance distribution at the focal plane of commercial off-the-shelf (COTS) camera lenses in case of laser illumination. The purpose of such a model is to predict the incapacitation of imaging sensors when irradiated by laser light. The model is based on closed-form equations that comprise mainly standard parameters of the laser dazzle scenario and those of the main devices involved (laser source, camera lens and imaging sensor). However, the model also includes three non-standard parameters, which describe the scattering of light within the camera lens. In previous work, we have performed measurements to derive these typically unknown scatter parameters for a collection of camera lenses of the Double-Gauss type. In this publication, we compare calculations based on our theoretical model and the measured scatter parameters with the outcome of stray light simulations performed with the optical design software FRED in order to validate the reliability of our theoretical model and of the derived scatter parameters. [ABSTRACT FROM AUTHOR]

Most background suppression algorithms are weakly robust due to the complexity and fluctuation of the star image's background. In this paper, a background suppression algorithm for stray lights in star images is proposed, which is named BSC-Net (Background Suppression Convolutional Network) and consist of two parts: "Background Suppression Part" and "Foreground Retention Part". The former part achieves background suppression by extracting features from various receptive fields, while the latter part achieves foreground retention by merging multi-scale features. Through this two-part design, BSC-Net can compensate for blurring and distortion of the foreground caused by background suppression, which is not achievable in other methods. At the same time, a blended loss function of smooth_L1&Structure Similarity Index Measure (SSIM) is introduced to hasten the network convergence and avoid image distortion. Based on the BSC-Net and the loss function, a dataset consisting of real images will be used for training and testing. Finally, experiments show that BSC-Net achieves the best results and the largest Signal-to-Noise Ratio (SNR) improvement in different backgrounds, which is fast, practical and efficient, and can tackle the shortcomings of existing methods. [ABSTRACT FROM AUTHOR]

The Thermal Infrared Sensor 2 (TIRS-2) payload for the Landsat 9 mission closely follows the design of the TIRS instrument currently flying aboard Landsat 8. The TIRS-2 instrument, however, incorporates an important design change to mitigate the stray light issue that plagued the TIRS instrument. Shortly after the launch of Landsat 8 in 2013, calibration errors due to stray light artifacts were observed in Earth imagery from TIRS with magnitudes of 4% (10.8 $\mu \text{m}$ band) and 8% (12.0 $\mu \text{m}$ band). Out-of-field scans of the Moon were conducted to map the angles from which off-axis radiance was detected on the focal plane arrays. Optical modeling, constrained by reverse ray traces of the lunar data, identified the primary scattering sources within the TIRS telescope, and these results informed the locations and design of mitigating baffles for TIRS-2. The effect of the modifications to the TIRS-2 instrument was tested preflight through thermal vacuum (TVAC) characterization tests, and the optical models were updated to be consistent with the measured data. Preliminary assessments indicated at least an order of magnitude reduction of the total signal due to scattering in TIRS-2. On-orbit lunar scans provided the final confirmations and demonstrated that the new design changes to TIRS-2 have reduced the primary out-of-field scattering by over 40x from the original TIRS design bringing the total scattering to 1% or less. More importantly, Earth imagery produced by Landsat 9 TIRS-2 does not show any stray-light-related artifacts, as was prevalent in the Landsat 8 TIRS imagery. [ABSTRACT FROM AUTHOR]

Although it is beneficial to use an optical simulator to design a mid-air imaging system, the use of a simulator requires optical knowledge, and it cannot be handled by non-specialists. To create a design assistance system that can be used by non-specialists, we demonstrate three methods: a method for extracting mid-air images and images of stray light from computer graphics rendered images, a method for calculating the visible range of mid-air images, and an evaluation of design parameters. First, a mid-air image and an image of stray light are extracted by considering the differences of images rendered using different numbers of bounces at each camera position, after which the visible range of the mid-air image is calculated. In addition, other parameters, such as the distance between a micro-mirror array plate (MMAP) and the extracted mid-air image, are adjusted in detail and evaluated by considering the visible range of the obtained mid-air image. Moreover, to demonstrate the effectiveness of the proposed method, the design of the previous research was improved to eliminate images of stray light, and we reduced the size of the existing system. Unlike other conventional approaches, using the visible range of the extracted mid-air images and without the need for a visual check, our proposed method enables the extraction of mid-air images and unwanted light, and the evaluation of optical systems. This technique can be applied to improve the design of optical systems and in the examination of the related applications. [ABSTRACT FROM AUTHOR]

Stray light is a critical aspect for high performance optical instruments. When stray light control by design is insufficient to reach the performance requirement, correction by post-processing must be considered. This situation is encountered, for example, in the case of the Earth observation instrument 3MI, whose stray light properties are complex due to the presence of many ghosts distributed on the detector array. We implement an iterative correction method and discuss its convergence properties. Spatial and field binning can be employed to reduce the computation time but at the cost of a decreased performance. Interpolation of the stray light properties is required to achieve high performance correction. For that, two methods are proposed and tested. The first interpolate the stray light in the field domain while the second applies a scaling operation based on a local symmetry assumption. Ultimately, the scaling method is selected and a stray light reduction by a factor of 58 is obtained at 2σ (129 at 1σ) for an extended scene illumination. [ABSTRACT FROM AUTHOR]

• Ray tracing analysis was conducted to reduce stray light of OROCHI onboard the MMX. • OROCHI's optical system is simulated and its CCD reflectance was measured. • Our techniques are incorporated into the preliminary design of OROCHI. The Martian Moons eXploration (MMX) spacecraft is equipped with two cameras, i.e., the TElescopic Nadir imager for GeOmOrphology (TENGOO) and the Optical Radiometer composed Of CHromatic Imagers (OROCHI), for the scientific observation of the Martian moon Phobos. OROCHI is a wide-angle multiband camera system comprising seven cameras with different bandpass filters and one monochromatic camera in the visible and near-infrared range. Thus, OROCHI can simultaneously obtain multiband images. Previous space observations have revealed that the reflection spectra of Phobos exhibit regional differences, including a red unit and a blue unit with weak redness. Moreover, Phobos shows an absorption band near 650 nm, attributed to the red unit of Phobos. Global observations using OROCHI require the determination of such regional variations with high precision; therefore, we must reduce noise in the optical system design. In this study, to meet this requirement, we focus on stray light reduction. Stray light is a source of noise generated by reflections at surfaces of optical components (e.g., sensors, filters, lenses, and lens barrels). We design simulation models of the OROCHI optical system, measure the reflectance of its charge-coupled device (CCD) image sensor, and conduct stray light analysis via ray tracing. We estimate the ratio of the stray light intensity to the target signal intensity by deriving both the reflected (constituting stray light) and unreflected rays. We show that placing the filter away from the sensor and reducing the reflectances of the filter and lenses effectively reduce stray light. Such approaches are incorporated into the preliminary design of OROCHI. [ABSTRACT FROM AUTHOR]

• A LC system was constructed with a miniaturized photometric detector and a microfluidic chip. • The Z-shaped cell design increases the effective optical path length. • The Z-shaped cell and column are on the same chip without a pipeline connection. • The microchip can be filled with cation exchange resin and C18 particles. In recent years, miniaturized analytical instruments have been developing to meet the needs of portable and rapid analysis. The key of miniaturized analytical equipment is the miniaturization and integration of functional modules. This paper aims to develop a miniaturized photometric detector and separation microfluidic chip for a liquid chromatography (LC) system. The detector uses a light-emitting diode to emit ultraviolet light, which is collimated by an internal double lens. A Z-shaped flow cell with a long optical path is designed and fabricated in the separation microfluidic chip with a three-layer structure, which provides a tubing-free connection between the separation and detection unit. Detector performance is evaluated using hemoglobin (Hb) samples, with an upper limit of detection linearity (95 %) of 0.345 AU and stray light level as low as 0.08 %. Additionally, the microchip channel can be filled with cation exchange resin and C18 particles. Finally, an ion LC system and a reversed-phase LC system were constructed based on the miniaturized photometric detector and two microchips with different packed columns, respectively, and were successfully used in the separation and detection of two metabolic markers (glycated hemoglobin or bilirubin). The results of this study are expected to facilitate the development of a portable LC system and their application in community health services and family health management of chronic diseases. [ABSTRACT FROM AUTHOR]

• An analysis was conducted on the backward reflection of the telescope at the Tianqin Station. • A solution has been proposed for the secondary mirror backward reflection stray light of the Cassegrain telescope. • The effectiveness of the method was verified through ray tracing simulation and experiments with single photon detectors and cameras respectively. In the coaxial satellite laser ranging system or the other telescope-based measurement systems, the emitted beam produces backward reflection at the center of the secondary mirror, which affects the detector in the system. To reduce the impact of straylight, a new device for reduce the backward reflection of the secondary mirror has been proposed. The specific parameters of the device have been determined through numerical calculation and computer simulation. The device has been implemented in a 1.2 m laser ranging system and has been experimentally proven to reduce the laser straylight by 32.4 % with the single photon detector and there is an increase in the camera's contrast for target imaging, making it more effective to measuring the space target. [ABSTRACT FROM AUTHOR]

The Ozone Mapping and Profiler Suite (OMPS) Nadir Profilers (NPs) are advanced backscatter ultraviolet (BUV) hyperspectral instruments that measure ozone profiles in the Earth atmosphere. The first NP sensor onboard the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite began its science observations on January 26, 2012, after its aperture door opened. The second OMPS NP, flying on the NOAA-20 satellite, opened its aperture door on January 8, 2018, starting science its data collection. The two NP sensors acquire Earth spectral images along their satellite flight path with a 16.7° wide swath, enabling weekly coverage of vertical ozone distribution in the Earth atmosphere. A successful thorough sensor calibration enables the NP sensors’ data records (SDRs) to meet measurement accuracy requirements. The largest error term in the albedo calibration came from the spectral wavelength calibration. This article provides SDRs accuracy analysis for both NP sensors and discusses important aspects of the SDRs performance in relation to the sensors’ characterization and calibration. [ABSTRACT FROM AUTHOR]

We present a photometrically accurate restoration of the K- and F-coronae from white-light images obtained over 24 years [1996 – 2019] by the Large-Angle Spectrometric COronagraph (LASCO-C2) onboard the Solar and Heliospheric Observatory (SOHO). The procedure starts with the data set of unpolarized images of 512 × 512 pixels produced by the polarimetric analysis of the routine C2 polarization sequences (Lamy et al., Solar Phys. 295, 89, 2020) in which the F-corona, the instrumental stray light, and possible remnants of the K-corona due to the imperfect polarimetric separation are entangled. Disentangling these components requires a complex procedure organized in three stages, each composed of several steps. Stage 1 establishes the distinct variations of the radiance of these components with the Sun–SOHO distance, and generate a new data set of median images calculated for each Carrington rotation. Stage 2 achieves the restoration of a set of 36 stray-light images that account for the temporal variation of the stray-light pattern, in particular those associated with the periodic roll maneuvers of SOHO, which started in 2003. Stage 3 achieves the restoration of the F-corona, and a time series of daily images is generated. Combining these images with the set of stray-light images allowed us to process the whole set of routine LASCO-C2 images of 1024 × 1024 pixels (approximately 626,000 images) and to produce calibrated, high-resolution images of the K-corona. The two sets of images of the K-corona, that produced by polarimetric separation of 512 × 512 pixels images and that presently produced by subtraction, are in excellent photometric agreement. We extend our past conclusions that the temporal variation of the integrated radiance of the K-corona tracks the solar activity over Solar Cycles 23 and 24, and that it is highly correlated with the temporal variation of the total magnetic field. The behaviors of the integrated radiance during the last few years of the declining phases of Solar Cycles 23 and 24 are remarkably similar, reaching the same base level and leading to a duration of 11.0 years for the latter cycle, in agreement with that derived from sunspots. [ABSTRACT FROM AUTHOR]

• Four types of beam splitters in human eye wavefront sensing optical setup are compared from aspects of spot-field image quality and energy transfer efficiency. • Stray light is traced to the source and effectively eliminated according to the causes. • Polarizing beam splitters shows stray light suppression and increase the energy transfer efficiency to 64.9%, higher than 43.2% from the non-polarizing beam splitter plate. • Polarizing beam splitter plates are the optimal choice to merge the laser beam into the main path for human eye wavefront sensing. Beam splitters significantly affect the measurement accuracy of human eye wavefront sensing. To compare the beam splitters in human eye wavefront sensing optical path from aspects of spot-field image quality and energy transfer efficiency, the effect of polarizing beam splitter cubes, polarizing beam splitter plates, non-polarizing beam splitter cube and non-polarizing beam splitter plates on the sensing performance of the measurement path are studied. The stray light affecting spot-field image quality is traced to the source and effectively eliminated according to the causes respectively. The transfer efficiency of the measurement path built with polarizing optics is also studied. The application of polarizing beam splitters shows stray light suppression and increases the energy transfer efficiency to 64.9%, higher than 43.2% from the non-polarizing beam splitter plate. The experimental results show that a polarizing beam splitter plate is the optimal choice to merge the laser beam into the main path for human eye wavefront sensing. [ABSTRACT FROM AUTHOR]

Miniaturised photometric detection cell based on the 150 μm I. D. L-shaped fused silica capillary (L-cell) and silica optical fibre is discussed in this paper. Light enters the cell via right angle bend and transmitted light is collected by silica optical fibre inserted into the capillary outlet. Ray trace analysis reveals that L-cell geometry works as a waveguide and effectively eliminates parasitic light, which is guided by the wall of any fused silica capillary cell. Low total level of stray light is further documented by measurement of absorbance of acetone-water mixture at 266 nm with the observed upper limit of dynamic range 2.2 AU. 3-mm L-cell has a volume of 53 nL and exhibits effective optical path 2.7 mm. Cell variance determined in the flow rate range 1–10 μL min−1 indicates, that 3-mm L-cell is optimal for use with 200–300 μm I. D. capillary columns. Furthermore, isocratic separation of alkylbenzenes mixture at 0.5 μL min−1 demonstrates effective use of 0.5-mm L-cell (8.8 nL) and possible performance of longer L-cells with high efficiency 100 μm I. D. capillary column. Image 1 • L-cell exhibits low level of stray light and dynamic range upper limit 2.2 AU. • Effective optical path approaches 80–90% of the cell geometric length. • 3-mm L-cell has volume 53 nL and effective optical path 2.7 mm. • 3-mm L-cell is compatible with 200 and 300 μm I. D. column. • 0.5-mm and 1-mm L-cells are compatible with 100 μm I. D. column. [ABSTRACT FROM AUTHOR]

Following calibration, hyperspectral images remain affected by spatial dimension nonuniformity, i.e., stripe noise, due to stray light interference, slit contamination, and instrument instability. The full spectrum airborne hyperspectral imager (FAHI) is a Chinese next-generation pushbroom sensor with a spectral range covering the visible near-infrared, shortwave-infrared (SWIR), and thermal infrared regions with spectral sampling intervals of 2.34, 3, and 32 nm, respectively. However, the residual stripe noise remains in FAHI images after relative radiometric correction based on the laboratory calibration, especially in low signal-to-noise ratio bands. To solve this problem, a new technique combining image statistics and spatial filtering algorithms has been developed for FAHI image correction. In this method, image statistics are obtained to calculate the gain and offset of each pixel for image nonuniformity correction. Then, a spatial filter removes the residual stripes. This paper presents the principles of this method along with details of validation experiments and results. To validate the effectiveness of the proposed method, comparison with two destriping methods and quantitative analyses are carried out. Moreover, the method is applied to an SWIR hyperspectral image from the TianGong-1 spacecraft, yielding good results. The experimental results suggest that the proposed method is convenient and practical for improving the relative radiometric accuracy of airborne/spaceborne hyperspectral images. [ABSTRACT FROM AUTHOR]

The Bidirectional Reflectance Distribution Function (BRDF) of beryllium is important for a ray-tracing simulation to evaluate the effect of reflected light on optical diagnostics in the fusion device ITER. However, the BRDF for beryllium has not been investigated yet and is currently lacking. To fill this gap, this study measured BRDFs of beryllium specimens with different topographies using goniophotometers and optimized optical reflection models. Additionally, various surface topographic parameters were computed, and their correlation with parameters for the optical reflection models was explored. As a result, it was found that topographic parameters related to slope offer a certain correlation with the parameters of the reflection model. This can be useful for determining the optical reflection properties of materials for which direct BRDF measurements are not possible. • The Bidirectional Reflectance Distribution Functions (BRDFs) of beryllium are shown. • Topographic parameters have a certain correlation with a reflection model. • The maximum coefficient of determination for the correlation exceeds 0.91. • Improving the optical reflection model is the key to better correlations. [ABSTRACT FROM AUTHOR]

The stray light appearing in the low wavenumber region of Raman spectra has long been the intrinsic hindrance in Raman spectroscopy. In this work, we confirmed that the stray light mentioned above originates from the grating secondary maxima of Rayleigh scattering experimentally and theoretically. This result also gives a clear inspiration for the suppression of such kind of stray light. The stray light appearing in the low wavenumber region of Raman spectra has long been the intrinsic hindrance in Raman spectroscopy and the studying program. In this work, we confirmed that the stray light mentioned above originates from the grating secondary maxima of Rayleigh scattering experimentally and theoretically. This result also gives a clear inspiration for the suppression of such kind of stray light. [ABSTRACT FROM AUTHOR]

Abstract Stray light exists in optical lithography, and causes the CD (Critical Dimension) Variation. Therefore, it is important to obtain an appropriate description model of imaging with stray light. An improved optical lithography imaging model considering medium-range and long-range flare is proposed by using the PSF F (Point Spread Function of Flare) model and the Kirk flare model. The proposed simulation model is confirmed to have much better precision when compared to the experiment data. The effect of flare on CD is studied, in which the total flare is the same but the ratio of medium-range and long-rang flares are varied. The simulation results show that long-range flare has a bigger impact on CD than medium-range flare. The greater the proportion of long-rang flare, the smaller line-width of CD will be. Thus, long-range flare should be taken fully into account in optical lithography. [ABSTRACT FROM AUTHOR]

Operational retrievals of aerosol optical depth (AOD) from Multi-angle Imaging SpectroRadiometer (MISR) data have been shown to have a high bias in pristine oceanic areas. One line of evidence involves comparison with Maritime Aerosol Network (MAN) observations, including the areas of low aerosol loading close to Antarctica. In this paper, a principal reason for the AOD overestimation is identified, which is stray light measured by the MISR cameras in dark regions of high-contrast scenes. A small fraction of the light from surrounding bright areas, such as clouds or sea ice, is redistributed to dark areas, artificially increasing their brightness. Internal reflections and light scattering from optical elements in MISR's pushbroom cameras contribute to this veiling light effect. A simple correction model is developed that relies on the average scene brightness and an empirically determined set of veiling light coefficients for each MISR camera and wavelength. Several independent methods are employed to determine these coefficients. Three sets of coefficients are further implemented and tested in prototype MISR 4.4-km AOD retrievals. The results show dramatic improvements in retrieved AODs compared against MAN observations and the currently operational V22 MISR retrievals. For the best performing set of coefficients, the bias is reduced by 51%, from 0.039 to 0.019, the RMSE is lowered by 19%, from 0.062 to 0.050, and 84% of retrievals fall within the uncertainty envelope compared with 66% of retrievals in V22. The best performing set will be implemented operationally in the next V23 MISR AOD product release. [ABSTRACT FROM AUTHOR]

Diffractive telescope technology is an innovation solution in construction of large light-weight space telescope. However, the nondesign orders of diffractive optical elements (DOEs) may affect the imaging performance as stray light. To study the stray light characteristics of a diffractive telescope, a prototype was developed and its stray light analysis model was established. The stray light characteristics including ghost, point source transmittance, and veiling glare index (VGI) were analyzed. During the star imaging test of the prototype, the ghost images appeared around the star image as the exposure time of the charge-coupled device improving, consistent with the simulation results. The test result of VGI was 67.11%, slightly higher than the calculated value 57.88%. The study shows that the same order diffraction of the diffractive primary lens and correcting DOE is the main factor that causes ghost images. The stray light sources outside the field of view can illuminate the image plane through nondesign orders diffraction of the primary lens and contributes to more than 90% of the stray light flux on the image plane. In summary, it is expected that these works will provide some guidance for optimizing the imaging performance of diffractive telescopes. [ABSTRACT FROM AUTHOR]

The modeling of the scattering phenomena for the multielement telescope for imaging and spectroscopy (METIS) coronagraph on board the European Space Agency Solar Orbiter is reported. METIS is an inverted occultation coronagraph including two optical paths: the broadband imaging of the full corona in linearly polarized visible-light (580 to 640 nm) and the narrow-band imaging of the full corona in the ultraviolet Lyman-α (121.6 nm). METIS will have the unique opportunity of observing the solar outer atmosphere as close to the Sun as 0.28 AU and from up to 35 deg out-of-ecliptic. The stray-light simulations performed on the UV and VL channels of the METIS analyzing the contributors of surface microroughness, particulate contamination, cosmetic defects, and diffraction are reported. The results obtained with the nonsequential modality of Zemax OpticStudio are compared with two different approaches: the Monte Carlo ray trace with Advanced Systems Analysis Program (ASAP®) and a semianalytical model. The results obtained with the three independently developed approaches are in considerable agreement and show compliance to the requirement of stray-light level for both the UV and VL channels. [ABSTRACT FROM AUTHOR]

This paper provides a conceptual design of the laser transfer system to be installed for the JT-60SA Thomson scattering system. The optical design newly permits transferring two wavelength lasers, i.e., YAG (1064 nm) and ruby (694 nm) lasers, so that an in situ relative calibration for high-field edge measurements, where the scattering angle is close to 90°, is possible under severe radiation condition. Stray light generated from scattering at a vacuum window can be suppressed using multiple baffles. It is newly found that the baffles spaced at a geometric series, i.e., 40% of unit length, is an effective way and reduces the stray light. The amount of stray light can be reduced to ∼6% using only three baffles compared with the case of no-baffles. [ABSTRACT FROM AUTHOR]

This paper investigates very short duration (<1 ms) flashes caused by rapid discharge arcs from isolated, charged, insulating epoxy “glue dots” to an underlying grounded substrate while under electron bombardment. The possibility that a given arc might stimulate arcs in adjacent “glue dots” was investigated through coincidence correlation analysis, as was the dependence of such correlations with “glue dot” separation. Most arcs were found to be random localized events, which occurred only when accumulated charge produced an electric field large enough for electrostatic breakdown to occur. However, for 40-keV incident beams, significant temporal and spatial correlation were observed. It is hypothesised that at higher energies more samples are charged close to the breakdown field at any given time and that a discharge in one “glue dot” might cause a sudden electric field spike in neighboring “glue dots,” which could trigger premature arcing. Such stimulated arc rates might reasonably be expected to scale with electric field intensity. A power law fit to the arc data found a power of −1.06 ± 0.09, consistent with a field falling off inversely with separation distance for charges spreading out across a 2-D conducting surface. [ABSTRACT FROM PUBLISHER]

It has been known and documented that the Thermal Infrared Sensor (TIRS) on-board Landsat 8 suffers from a significant stray light problem (Reuter et al., 2015; Montanaro et al., 2014a). The issue appears both as a non-uniform banding artifact across Earth scenes and as a varying absolute radiometric calibration error. A correction algorithm proposed by Montanaro et al. (2015) demonstrated great potential towards removing most of the stray light effects from TIRS image data. It has since been refined and will be implemented operationally into the Landsat Product Generation System in early 2017. The algorithm is trained using near-coincident thermal data (i.e., Terra/MODIS) to develop per-detector functional relationships between incident out-of-field radiance and additional (stray light) signal on the TIRS detectors. Once trained, the functional relationships are used to estimate and remove the stray light signal on a per-detector basis from a scene of interest. The details of the operational stray light correction algorithm are presented here along with validation studies that demonstrate the effectiveness of the algorithm in removing the stray light artifacts over a stressing range of Landsat/TIRS scene conditions. Results show that the magnitude of the banding artifact is reduced by half on average over the current (uncorrected) product and that the absolute radiometric error is reduced to approximately 0.5% in both spectral bands on average (well below the 2% requirement). All studies presented here indicate that the implementation of the stray light algorithm will lead to greatly improved performance of the TIRS instrument, for both spectral bands. [ABSTRACT FROM AUTHOR]

A stray light compensated nonuniformity correction (SLCNUC) method is proposed for infrared (IR) cameras. The proposed approach formulates thermal stray light compensation functions according to the internal temperature changes of the IR camera. To derive the compensation functions, we analyze the variations of the NUC parameters over the entire range of internal temperatures and determine the function coefficients by using a least squares method. Compared with the existing NUC methods used in previous studies, the major advantage of the proposed method is its effective reduction of nonuniformity even in highly accumulated thermal stray light situations. Experiments and comparisons performed with real IR images show that the proposed method maintains lower spatial noise over a wide internal temperature range of the IR camera. It is shown that the proposed NUC achieves an 18 dB higher peak signal-to-noise ratio than that of the conventional reference-based NUC method. [ABSTRACT FROM AUTHOR]

Purpose To assess forward light scatter (stray light) before and after intrastromal corneal ring segment ( ICRS) implantation at different stages of keratoconus and to examine correlation between postoperative stray light and visual acuity ( VA). Methods In 27 eyes of 27 subjects with keratoconus, stray light was determined using the compensation comparison technique before and 6 months after ICRS implantation. Monocular corrected distance VA ( CDVA) was measured using a high-contrast log MAR letter chart. Corneal higher-order aberrations ( HOAs), contrast sensitivity ( CS) and minimum corneal thickness ( CT) were also measured. Results Mean CDVA was 0.42 ± 0.28 preoperatively and 0.24 ± 0.15 log MAR postoperatively (p < 0.01). Mean corneal coma-like aberration decreased postoperatively ( RMS 0.55 ± 1.18 μm, p < 0.01). Minimum CT increased 25.31 ± 18.59 μm (p < 0.01). Mean preoperative and postoperative stray light were 1.36 ± 0.31 and 1.48 ± 0.32 log units, respectively (p < 0.01). Mean changes produced in stray light (worsening) were 0.03 ± 0.21 (p > 0.05) for stage I, 0.13 ± 0.14 (p = 0.013) for stage II and 0.18 ± 0.21 (p = 0.023) for stage III. Significant positive correlation ( r = 0.47, p = 0.01) was detected between postoperative stray light and postoperative CDVA such that as stray light increased, CDVA worsened (higher log MAR values). Postoperative stray light was neither associated with HOAs, CS nor minimum CT. Conclusions Stray light values in these patients with keratoconus were higher than normal preoperatively. In eyes with stage II and III keratoconus, stray light increased 6 months after ICRS placement. Higher postoperative stray light was correlated with a worse visual acuity outcome. [ABSTRACT FROM AUTHOR]

Stray light formed by the reflection of photons on inner wall from a bright divertor region can be a serious issue in spectroscopic measurement systems in ITER. In this study, we propose a method to mitigate the influence of stray light using a ray tracing analysis. Usually, a ray tracing simulation requires a time consuming runs. We constructed transfer matrices based on the ray tracing simulation results and used them to demonstrate the influence of stray light. It is shown that the transfer matrix can be used to reconstruct the emission profile by considering the influence of the stray light without any additional ray tracing runs. Mitigation of the stray light in ITER divertor impurity monitor was demonstrated, and a method of prediction of the stray light level for the scrape off layer spectroscopy from divertor region was proposed. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The Geostationary Ocean Color Imager (GOCI) is the world's first ocean color sensor in geostationary orbit. Although the GOCI has shown excellent radiometric performance with little long-term radiometric degradation and a high signal-to-noise ratio, there are radiometric artefacts in GOCI Level 1 products caused by stray light detected within the GOCI optics. To correct the radiometric bias, we developed an image-based correction algorithm called the correction of the interslot discrepancy using the minimum noise fraction transform (CIDUM) in a previous study and evaluated its performance with respect to the physical radiometric quantity stored in Level 1 products, i.e., top-of-atmosphere radiance. This study evaluated the performance of the CIDUM algorithm in terms of remote sensing reflectance, which is one of the most important products in ocean color remote sensing. The resultant CIDUM-corrected remote sensing reflectance products were validated using both relative (within the image) and absolute references (in situ measurements). Image validation showed that CIDUM corrected the bias in remote sensing reflectance (up to 20%) and reduced the bias to ⩽5% in the tested image. In situ validation showed that relative uncertainty was reduced by around 10% within the visible bands and the correlation between the in situ and GOCI radiometric data was enhanced. [ABSTRACT FROM AUTHOR]

Inside the process of optical design, the diffusion phenomenon is usually set apart until the final stage: the study of tolerances. So, its influence is evaluated considering the whole of the system after having designed it taking into account all other parameters. The phenomenon of diffusion is relevant in many optical designs and its influence can determine the final design. So, this procedure, relegating diffusion to stage study, does not means that its influence over the system isn't heavy, but stems from the high computational cost of considering it on earlier stages. But there is a way to include it before the tolerances study stage by using a dual optimization process with an on/off mechanism. Thus the best system configuration is obtained considering the diffusion. In order to reduce the computation time we adjust dynamically the values of the diffuser model control parameters. The number of re-emitters is one of these strategic control parameters, inside this parameter are included two different values, the number of reemitting focus and the number of reemitting rays considered. Varying this value, different degrees of model accuracy can be obtained, allowing to adapt the model accuracy depending on the merit function instantaneous value. In this paper we analyse the use of a diffuser model, varying the parameter of the number of reemitters, and its influence on optical system computer aided design (CAD). We make so by employing a simple system consisting on a light source, a biconvex lens, on which the diffusion model is applied only on the second surface, and a detection display. [ABSTRACT FROM AUTHOR]

Baffle is a critical technique to suppress stray light. In order to reduce stray light of EAST Thomson scattering (TS) diagnostic system, a 60° cone angle double edged baffle array was installed for the system. Recently the 45° cone angle corrugation baffle was designed based on double edged baffle and simulation results indicate that the new design can reject 33.3% more stray light than the old one. Based on the mechanical structure and surface property of EAST TS diagnostic system, a stray light analysis model has been built, and using the model, stray light of the system was simulated with the two types of baffles added to the system respectively. Results show that the installation of 60° cone angle double edged baffle array in input tube can cut 92.1% of the stray light to the system, while using 45° cone angle corrugation baffle array in input tube and three 45° cone angle corrugation baffles in exit tube, additional 74.1% of the stray light will be removed. [ABSTRACT FROM AUTHOR]

Remote sensing of solar-induced chlorophyll fluorescence (SIF) advances our ability to monitor gross primary productivity. Because SIF is usually <5% of recorded canopy radiance, sources of measurement error must be reduced for accurate SIF retrieval. Here we quantify the impact of spectral stray light on SIF retrieval using a high-resolution imaging spectrometer. We first derived the FLD retrieval solution in the presence of stray light under the simplifying assumptions that SIF, reflectance, and stray light are constant across the region of the spectrum used in the retrieval. We show that stray light contributions from the canopy and reference spectra could cancel out if obtained from the same instrument. In practice however, the simplifying assumptions are unlikely to hold because SIF and reflectance vary across regions of the spectrum commonly exploited by the FLD retrieval, and stray light can also vary across the spectrum, as we demonstrate with an empirical example. To quantify the impact of spectral stray light on SIF retrievals in more realistic scenarios, we performed a sensitivity analysis. We used a stray light signal distribution function and measurements of spectral radiance and SIF to generate spectra with known quantities of SIF and stray light over four orders of magnitude of stray light. We then quantified the bias in retrieved SIF using four SIF retrieval approaches—standard FLD, 3FLD, a spectral fitting method (SFM), and a method based on singular value decomposition (SVD)—applied to the red and/or far-red spectral domains. We found that spectral stray light can cause either a positive or negative bias in SIF estimates. In the highest stray light scenario, with spectral stray light one order of magnitude smaller than the radiance signal, the stray light error ranged from < ± 1% of SIF (for O 2 -A band retrievals with FLD, 3FLD, and SFM methods, and for far-red retrievals in the 748 nm to 756 nm domain with SVD-based and 3FLD methods applied to Fraunhofer lines) to >30% of SIF (O 2 -B band retrieval with SFM, and 3FLD applied to Fraunhofer lines in the red domain). For context, a bias of 27% of SIF is a comparable magnitude to seasonal variation in SIF observed in the Amazon basin, and to SIF differences among plant functional types. However, when spectral stray light was three orders of magnitude smaller than the radiance signal, mean bias was < ± 2% for all retrieval methods. Our analysis informs when spectral stray light corrections must be performed for SIF remote sensing. • Spectral stray light— a ubiquitous source of error in spectroscopy— can bias SIF retrievals. • The spectral stray light bias could be negative or positive. • When spectral stray light was 3 orders of magnitude smaller than the radiance signal, bias was <1%. • Large spectral stray light, or different stray light properties for target / reference spectra, produced errors >10% of SIF. [ABSTRACT FROM AUTHOR]

We describe the process through which stray light analysis should be performed in optical systems involving image slicers. We detail how scattering models should be used depending on how the image slicer assembly will be fabricated. Our work describes how to determine all ray paths, compute cross-talk on the pupil mirrors due to scattering, quantify the ghost images' intensity, and determine baffle positions. In the example given, an ABg model is applied to all mirror arrays separately, before considering their contributions altogether. We also consider diffraction due to the image slicer's narrow slice apertures, which contribute to unwanted light in the system by causing cross-talk on the pupil mirrors. Using Fourier optics, this quantity is computed and compared with cross-talk caused by scattering. Our work represents a useful asset for optical engineers who work on image slicer-based systems and want to analyze stray light, by providing a clear and exhaustive procedure to follow to obtain accurate estimates. [ABSTRACT FROM AUTHOR]

We provide an analysis of the existing methods for calculating parasitic illumination, methods for its analysis, and visualization. To search for and analyze the sources of stray light in optical devices, a software model of the beam propagation criterion in an optical device is proposed, which makes it possible to select beams that satisfy a given criterion. We consider the possibility of using the method of bidirectional progressive stochastic ray tracing with inverse photon maps to calculate the stray illumination of an image and analyze the causes of its occurrence. To analyze the sources of stray illumination on the radiation detector, it was proposed to use progressive photon maps, which calculated the caustic and secondary components of the illumination and fixed the image illumination on a static regular mesh attached to the surfaces of the optical device. Special visualization tools allow the display of this illumination over the image of an optical device and determination of the elements of the device that have the greatest impact on the level of stray illumination of the image. We present examples of calculation, analysis, and visualization of parasitic illumination of a number of optical systems of lenses with real mechanical structures. [ABSTRACT FROM AUTHOR]

Efficient absorbance detection of a low-volume chromatography peak is a difficult task. In this work, an improved design of the fused silica capillary flow cell for absorbance detection in microcolumn liquid chromatography is described. The cell was fabricated from 0.15 mm I. D. fused silica capillary and silica optical fibres. Optical fibres were fully integrated into the cell design and enabled a convenient and effective connection of the cell with the light source and light detector (265 nm UV LED and photodiode in this work). Manufactured cells covered the range of physical lengths 3.1–9.9 mm (55–175 nL) and were used without any focusing optics and slits. Baseline noise was typically below 0.05 mAU and the effective optical path determined in the experiments was 83–97% of the cell's physical length. The level of stray (parasitic) light indicated by a 1% deviation from linearity at 1.7 AU was 0.08% only. The proposed cell design was found to be moderately susceptible to the refractive index change (20–35 mAU baseline change in 5–95% (v/v) gradient of acetonitrile or methanol in a mixture with water, G index up to 4 AU·s/RIU). Manufactured cells were finally applied for absorbance detection of components of test the mixture eluted off 0.3 mm I. D. microcolumn. 9.9 mm cell (175 nL) with an effective optical path of 8.9 mm exhibited contribution to the broadening of chromatography peak comparable with commercial 6 mm (80 nL) rectangular flow cell. [Display omitted] • Flow cell made from 0.15 mm I. D. silica capillary and silica optical fibres. • No focusing optics and slits used. • An effective optical path is 83–97% of the cell's physical length. • Level of stray light less than 0.1%. • Cell volume 175 nL, optical path 8.9 mm, effective use of 0.3 mm I.D. microcolumns. [ABSTRACT FROM AUTHOR]

Ocean color measurements taken near cloud boundaries suffer from cloud adjacency effects (AEs). As a result, ~ 50% of the cloud-free ocean data are flagged as low quality. Quantitative assessment of such effects, as well as the methodology required to minimize, or correct for them, is rarely available. The goal of this study is to quantify such effects on top-of-atmosphere (TOA) radiance and ocean color data products for MODIS/Terra, MODIS/Aqua, and SeaWiFS measurements. The AEs estimation was based on statistics and an objective method applied to carefully selected clear-water scenes (the number of cloud patches was > 100,000 for each instrument) where ocean properties are relatively homogeneous, over both the North Atlantic and South Pacific. The AEs were quantified as the relative difference between the near-cloud pixels and pixels at least 20 km away from any cloud. Results show that the AEs on TOA radiance share similar patterns among the three missions. Specifically, the AEs decrease sharply as distance increases from cloud edges, and the AEs increase monotonically with increasing wavelengths because they were evaluated in relative rather than absolute terms. However, while discernable memory effects (MEs) are observed on cloud-adjacency pixels of both MODIS missions, they are insignificant on the SeaWiFS mission, and are found in measurements along the scan direction downstream of the clouds, representing > 15% of the total AEs in TOA radiance. The AEs on the retrieved remote sensing reflectance (R rs ) data products are different among the three missions possibly due to their differences in vicarious calibration and uncertainties in atmospheric correction, leading to different patterns in the chlorophyll-a (Chl-a) and normalized Florescence Line Height (nFLH) data products. Large AEs (> 50%) are observed in nFLH of both MODIS/Terra and MODIS/Aqua, likely due to the opposite AEs on R rs between 667 and 678 nm. Finally, when the OCI Chl-a algorithm is used, the current MODIS stray-light masking window (7 × 5) used to mask the AE-contaminated pixels may be relaxed to 3 × 3 without sacrificing data quality, leading to > 40% of the previously masked low-quality data being recovered for clear waters. [ABSTRACT FROM AUTHOR]

The Soumi NPP VIIRS Day/Night Band (DNB) nighttime imagery quality is affected by stray light contamination. In this study, we examined the relationship between the Earth scene stray light and the signals in VIIRS's calibrators to better understand stray light characteristics and to improve upon the current correction method. Our analyses showed the calibrator signal to be highly predictive of Earth scene stray light and can provide additional stray light characteristics that are difficult to obtain from Earth scene data alone. In the current stray light correction regions (mid-to-high latitude), the stray light onset angles can be tracked by calibration view data to reduce correction biases. In the southern hemisphere, it is possible to identify the angular extent of the additional stray light feature in the calibration view data and develop a revised correction method to remove the additional stray light occurring during the southern hemisphere springtime. Outside of current stray light correction region, the analysis of calibration view data indicated occasional stray light contamination at low latitude and possible background biases caused by Moon illumination. As stray light affects a significant portion of nighttime scenes, further refinement in characterization and correction is important to ensure VIIRS DNB imagery quality for Soumi NPP and future missions. [ABSTRACT FROM AUTHOR]

To suppress the stray light caused by the diffraction and scattered light of a digital micromirror device (DMD) in a DMD-based spectrometer, a new concentrator system with a compound parabolic concentrator (CPC) is presented, which has the advantage that all stray light beyond the acceptance angle can be rejected with the most compact device available. The diffraction of DMD is explored to determine the acceptance angle, and the parameters of the concentrator system are analyzed to determine the geometric concentration ratio. The simulation results show that the spectrum concentration efficiency of the CPC is 98.7%, that the stray light concentration efficiency from the DMD is 36.3%, and that the stray light concentration efficiency beyond the acceptance angle is 0.00%. Finally, according to the discussion about tolerance on the CPC, a conclusion can be drawn that the new DMD-based spectrometer with CPC is feasible and significant in suppressing the stray light. [ABSTRACT FROM AUTHOR]

This paper investigates at the example of bathymetry how much an application can profit from comprehensive characterizations required for an improved calibration of data from a state-of-the-art commercial hyperspectral sensor. A NEO HySpex VNIR-1600 sensor is used for this paper, and the improvements are based on measurements of sensor properties not covered by the manufacturer, in particular, detector nonlinearity and stray light. This additional knowledge about the instrument is used to implement corrections for nonlinearity, stray light, spectral smile distortion and nonuniform spectral bandwidth and to base the radiometric calibration on a SI-traceable radiance standard. Bathymetry is retrieved from a data take from the lake Starnberg using WASI-2D. The results using the original and improved calibration procedures are compared with ground reference data, with an emphasis on the effect of stray-light correction. For our instrument, stray-light biases the detector response from 416–500 nm up to 8% and from 700–760 nm up to 5%. Stray-light-induced errors affect bathymetry mainly in water deeper than Secchi depth, whereas in shallower water, the dominant error source is the calibration accuracy of the light source used for radiometric calibration. Stray-light correction reduced the systematic error of water depth by 19% from Secchi depth to three times Secchi depth, whereas the relative standard deviation remained stable at 5%. [ABSTRACT FROM PUBLISHER]

The radiometric calibration of satellite data is critical in many environmental studies and applications that are based on remote sensing data. The Geostationary Ocean Color Imager (GOCI) has suffered from what is called an interslot radiometric discrepancy (ISRD), which creates clear inconsistency between the adjacent slots in GOCI Level 1B (L1B) radiometric products, the largest source of which is currently believed to be the stray light generated in the sensor instrument. Difficulties in removing the stray-light-driven anomalies are that the intensity and the spatial extent vary with time and location, depending on the reflectance of nearby bright targets, such as cloud and land. This paper proposes an image-based correction method that removes the stray-light-driven radiometric inflation without involving an independent reference so that the method can be used for GOCI operational data processing. First, the radiometric inflation pattern is characterized by independent sources, such as Moderate Resolution Imaging Spectrometer (MODIS) data, and the inflation pattern is modeled by the minimum noise fraction transform of the input data. The modeled inflation patterns in individual slots are then adjusted across the slots in such a way that the overall ISRD in all slot boundaries is minimized. The analysis shows that the stray-light-driven radiometric anomalies can be up to 20% of the normal signals in Bands 6 (680 nm) and 8 (865 nm) of the uncorrected L1B images, and the proposed correction method reduces it to less than 2% in most of the cases, recovering the spatial continuity of natural variability across the slots. [ABSTRACT FROM PUBLISHER]

The launch of VIIRS on-board the Suomi-National Polar-orbiting Partnership (S-NPP) on 28 October 2011, marked the beginning of the next chapter on nighttime lights observation started by the Defense Meteorological Satellite Program's (DMSP) OLS sensor more than two decades ago. The VIIRS observes the nighttime lights on Earth through its day-night band (DNB), a panchromatic channel covering the wavelengths from 500 nm to 900 nm. Compared to its predecessors, the VIIRS DNB has a much improved spatial/temporal resolution, radiometric sensitivity and, more importantly, continuous calibration using on-board calibrators (OBCs). In this paper, we describe the current state of the NASA calibration and characterization methodology used in supporting mission data quality assurance and producing consistent mission-wide sensor data records (SDRs) through NASA's Land Product Evaluation and Analysis Tool Element (Land PEATE). The NASA calibration method utilizes the OBCs to determine gains, offset drift and sign-to-noise ratio (SNR) over the entire mission. In gain determination, the time-dependent relative spectral response (RSR) is used to correct the optical throughput change over time. A deep space view acquired during an S-NPP pitch maneuver is used to compute the airglow free dark offset for DNB's high gain stage. The DNB stray light is estimated each month from new-moon dark Earth surface observations to remove the excessive stray light over the day-night terminators. As the VIIRS DNB on-orbit calibration is the first of its kind, the evolution of the calibration methodology is evident when the S-NPP VIIRS's official calibrations are compared with our latest mission-wide reprocessing. In the future, the DNB calibration methodology is likely to continue evolving, and the mission-wide reprocessing is a key to providing consistently calibrated DNB SDRs for the user community. In the meantime, the NASA Land PEATE provides an alternative source to obtain mission-wide DNB SDR products that are calibrated based on the latest NASA DNB calibration methodology. [ABSTRACT FROM AUTHOR]

The Suomi-NPP Visible Infrared Imager Radiometer Suite (VIIRS) instrument provides the next generation of visible/infrared imaging including the day/night band (DNB) with nominal bandwidth from 500 to 900 nm. Previous to VIIRS, the Defense Meteorological Satellite Program Operational Linescan System (OLS) measured radiances that spanned over seven orders of magnitude, using an onboard gain adjustment to provide the capability to image atmospheric features across the solar terminator, to observe nighttime light emissions over the globe, and to monitor the global distribution of clouds. The VIIRS DNB detects radiances that span over eight orders of magnitude, and because it has 13-14-b quantization (compared with 6 b for OLS) with three gain stages, the DNB has its full dynamic range at every part of the scan. One process that is applied to the VIIRS DNB radiances is a solar/lunar zenith angle dependent gain adjustment to create near-constant contrast (NCC) imagery. The at-launch NCC algorithm was designed to reproduce the OLS capability and, thus, was constrained to solar and lunar angles from 0° to 105°. This limitation has, in part, lead to suboptimal imagery due to the assumption that DNB radiances fall off exponentially beyond twilight. The VIIRS DNB ultrasensitivity in low-light conditions enables it to detect faint emissions from a phenomenon called airglow, thus invalidating the exponential fall-off assumption. Another complication to the NCC imagery algorithm is the stray light contamination that contaminates the DNB radiances in the astronomical twilight region. We address these issues and develop a solution that leads to high-quality imagery for all solar and lunar conditions. [ABSTRACT FROM PUBLISHER]

The Spectral Profiler (SP) is a visible-near infrared spectrometer onboard the Japanese Selenological and Engineering Explorer (SELENE), which was launched in 2007 and observed the Moon until June 2009. The SP consists of two gratings and three linear-array detectors: VIS (0.5-1.0 μm), NIR 1 (0.9- 1.7 μm), and NIR 2 (1.7-2.6 μm). In this paper, we propose a new method for radiometric calibration of NIR 2, specifically for the dark output (background) estimate, which is different from the previous method used for VIS and NIR 1. We show that the reflectance spectra of NIR 2 derived from the new radiometric calibration show less noise than those of the previous method. Based on an analysis of the reflectance spectra at exposure sites of the end-member minerals on the lunar surface, we demonstrated that the spectral features of the 2-μm band in the NIR 2 spectra are consistent with those expected from the minerals inferred from the features of the 1-μm band in the VIS and NIR 1 spectra. Finally, we examined the repeatability of the radiometric calibration of NIR 2 using the SP data near the Apollo 16 landing site observed at four different times. The typical difference in the reflectance at wavelengths <;~2.1 μm was a few percent, which is within the uncertainty due to the error in the background estimate, suggesting that there was no significant change in the sensitivity of NIR 2 over the mission period. [ABSTRACT FROM PUBLISHER]

The Thermal Infrared Sensor (TIRS) has been collecting imagery of the Earth since its launch aboard Landsat 8 in early 2013. In many respects, TIRS has been exceeding its performance requirements on orbit, particularly in terms of noise and stability. However, several artifacts have been observed in the TIRS data which include banding and absolute calibration discrepancies that violate requirements in some scenes. Banding is undesired structure that appears within and between the focal plane array assemblies. In addition, in situ measurements have shown an error in the TIRS absolute radiometric calibration that appears to vary with season and location within the image. The source of these artifacts has been determined to be out-of-field radiance that scatters onto the detectors thereby adding a non-uniform signal across the field-of-view. The magnitude of this extra signal can be approximately 8% or higher (band 11) and is generally twice as large in band 11 as it is in band 10. A series of lunar scans were obtained to gather information on the source of this out-of-field radiance. Analyses of these scans have produced a preliminary map of stray light, or ghost, source locations in the TIRS out-of-field area. This dataset has been used to produce a synthetic TIRS scene that closely reproduces the banding effects seen in actual TIRS imagery. Now that the cause of the banding has been determined, a stray light optics model is in development that will pin-point the cause of the stray light source. Several methods are also being explored to correct for the banding and the absolute calibration error in TIRS imagery. [ABSTRACT FROM AUTHOR]