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Surface reflectance varies with changes in solar and viewing angles, exhibiting distinct anisotropic reflectance characteristics, which can be characterized using the bidirectional reflectance distribution function (BRDF). Normalizing reflectance from various directions to a common solar-viewing geometry can eliminate the effects of reflectance anisotropy, thereby enhancing the accuracy of surface parameter retrieval from reflectance data. In previous studies, the reflectance angular normalization typically relies on prior knowledge extracted from coarse-resolution BRDF products. In this study, we developed a universal BRDF archetype database and explored the applicability of each BRDF archetype across various solar and viewing angles. The results indicate that the following: 1) The 3 × 3 universal BRDF archetype database is sufficient to represent the surface anisotropy of different spectral bands. 2) The optimal BRDF archetype in the lookup table (LUT) undergoes notable variations under different solar and viewing geometries, and specific prior BRDF knowledge is applicable only to certain solar and viewing geometries. 3) Validations based on simulated MODerate resolution imaging spectroradiometer reflectance suggests that in the red and near-infrared (NIR) bands, when the observation zenith angle is 60°, the percentages of directions with the root mean square error (RMSE) values below 0.05 and 0.06 constitute 82.74% and 75.70% of the entire viewing hemisphere, respectively. And validations based on polarization and directionality of the Earth's reflectance observations indicate that after normalization with the BRDF archetype LUT, the RMSE decreases from 0.0291 to 0.0249. The BRDF archetype LUT is applicable to the vast majority of solar and viewing geometries, even for the large solar zenith angles. Additionally, the LUT demonstrates good noise resistance and high applicability in observations at different scales, particularly in the NIR band. This study provides a new approach for reflectance angular normalization, offering the potential to provide a more reliable data foundation for future scientific research and practical applications.

Reflectance anisotropy spectroscopy (RAS) is applied to investigate GaAsBi samples grown by molecular beam epitaxy on (001)‐oriented GaAs substrates with GaAs or InGaAs buffer layers, resulting in nearly lattice‐matched or compressive strain conditions, with Bi concentration in the alloy in the range 2–5%. These new samples allow to bridge the gap in the Bi concentration values of previous RAS experiments (C. Goletti et al., Appl. Phys. Lett. 2022, 120, 031902), confirming the [110]‐polarized Bi‐related anisotropy in optical spectra below 3 eV and the linear dependence of its amplitude on Bi concentration. The characterization of the grown GaAsBi samples by X‐Ray diffraction and transmission electron microscopy clearly demonstrates the presence of CuPt‐like ordering in the bulk. CuPt structure is the primary origin of the optical anisotropy measured by RAS and by polarized photoluminescence, due to the anisotropic strain produced in the bulk crystal lattice. The lineshape of the RAS spectra above 3 eV, with its overall and characteristic positive convexity, confirms this conclusion. [ABSTRACT FROM AUTHOR]

Reflectance anisotropy in remote sensing images can complicate the interpretation of spectral signature, and extracting precise structural information under these pixels is a promising approach. Low-altitude unmanned aerial vehicle (UAV) systems can capture high-resolution imagery even to centimeter-level detail, potentially simplifying the characterization of leaf anisotropic reflectance. We proposed a novel maize point cloud generation method that combines an advanced UAV cross-circling oblique (CCO) photography route with the Structure from the Motion-Multi-View Stereo (SfM-MVS) algorithm. A multi-spectral point cloud was then generated by fusing multi-spectral imagery with the point cloud using a DSM-based approach. The Rahman–Pinty–Verstraete (RPV) model was finally applied to establish maize leaf-level anisotropic reflectance models. Our results indicated a high degree of similarity between measured and estimated maize structural parameters (R2 = 0.89 for leaf length and 0.96 for plant height) based on accurate point cloud data obtained from the CCO route. Most data points clustered around the principal plane due to a constant angle between the sun and view vectors, resulting in a limited range of view azimuths. Leaf reflectance anisotropy was characterized by the RPV model with R2 ranging from 0.38 to 0.75 for five wavelength bands. These findings hold significant promise for promoting the decoupling of plant structural information and leaf optical characteristics within remote sensing data.

Over the last two decades, advancements in airborne imaging spectroscopy have prompted the exploitation of lightweight drones for detailed vegetation assessment at unprecedented resolutions. Yet, surface reflectance anisotropy and view-illumination effects may bias spectra extracted from push-broom scanners and derived spectral indices (SIs), particularly over aquatic vegetation, thus impacting the retrieval of biophysical and biochemical vegetation parameters. In this study, the impact of illumination conditions (overcast versus clear sky) and angular configurations (i.e., solar and viewing angles) on radiometric variability of centimetric resolution drone data was empirically investigated over four different aquatic plant species, representing different growth forms and canopy structures. Nadir-normalized reflectance spectra, broadband SIs, and the spectral angle distance to proximal leaf reflectance were used for characterizing and quantifying radiometric variability at canopy and leaf levels. Our findings demonstrated a decrement in reflectance under diffuse light conditions, especially in highly reflective domains within Green (520–580 nm) and Near-Infrared (700–850 nm) ranges, and a marked angular reflectance anisotropy in high absorption spectral regions (i.e., 450–500 nm and 630–700 nm) for aquatic vegetation. The normalized difference vegetation index (NDVI) showed overall lower sensitivity to incoming light variability and angular configurations compared to other tested SIs, whereas the water adjusted vegetation index (WAVI), suitably designed for aquatic vegetation, was less affected by angular anisotropy in floating plants. Indeed, radiometric variability exhibited a dependence on aquatic plant features, i.e., leaf orientation, canopy structure, and affinity with water (as canopy background).

Reflectance anisotropy spectroscopy (RAS) is applied to study the reconstructed GaAsBi(001) surfaces at room temperature. Arsenic‐capped GaAsBi samples with 7% Bi concentration are grown by molecular beam epitaxy (MBE) in nearly matched conditions on a proper buffer layer and annealed in ultra‐high vacuum (UHV). Low energy electron diffraction (LEED) shows that, following the As decapping, a 2 × 3/1 × 3 phase (Bi‐rich) is obtained after annealing the sample at 400 °C, while subsequent annealing at 450 °C yields a deterioration of the surface order. RAS spectra measured in situ allow to definitely confirm that the characteristic Bi‐dependent anisotropy measured below 2.5 eV has not a true surface origin, although being connected to the surface: it is related to the strain of the directional bonds between Bi atoms existing at the surface and below the surface. This result has a twofold significance: it recommends that previous attributions to the surface of RAS anisotropy features in III–V semiconductors should be in some cases revisited; for the future, it shows that RAS is suitable to characterize 2D‐layered materials, and to investigate the consequences of strain in the electronic properties of low‐dimensional systems. [ABSTRACT FROM AUTHOR]

The land surface albedo reflects the ability of the surface to reflect solar radiation and is a critical physical variable in the study of the Earth's energy budget and global climate change. Algorithms for the retrieval of albedo usually require multi-angle measurements due to surface anisotropy. However, most of the satellites cannot currently provide sufficient and well-distributed observations; therefore, the accuracy of remotely sensed albedo is constrained. Based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) and albedo product (MCD43A1), this study proposed a method to further subdivide reflectance anisotropy and build an updated database of BRDF archetype, using both the Anisotropic Flat Index (AFX) and Perpendicular Anisotropic Flat Index (PAFX). The BRDF archetypes were used to fit the corresponding MODIS BRDF, and the optimal number of BRDF archetype categories was determined according to the tendency of fitting error. The effect of surface anisotropy and observation noise on albedo retrieval were explored based on simulated MODIS reflectance. Finally, the BRDF archetype A2P2 was taken as prior knowledge to retrieve albedo from a different number of MODIS observations, and the result was validated by the high-quality MODIS albedo product. The results show that the fitting error between BRDF archetypes and MODIS BRDF shows a rapid decline when introducing the PAFX in the classification process. A 3-by-3 matrix of BRDF archetypes, which occupy 73.44% and 70.13% of the total decline in the red and NIR band, can be used to represent the characteristics of reflectance anisotropy. The archetype A2P2 may be used as prior knowledge to improve the albedo retrieval from insufficient observations. The validation results based on MODIS observations show that the archetype A2P2-based albedo can reach root-mean-square errors (RMSEs) of no more than 0.03. [ABSTRACT FROM AUTHOR]

Reflectance Anisotropy (RA) contains crucial information about the optical behavior and structure of ground objects and is typically described by the Bidirectional Reflectance Distribution Function (BRDF). However, traditional RA-retrieval methods from satellites or the ground are constrained due to the low spatial resolution, illumination conditions, and instrument-associated limitations. In this study, Unmanned Aerial Vehicle (UAV) based oblique photography technology is applied to RA retrieval, aiming to explore the feasibility of UAV to obtain spatially continuous RA data with high spatial resolution and high accuracy. The Monte Carlo method is used to select and optimize the combination of multi-angle observation data of a variety of ground objects obtained by UAV-based oblique photogrammetry. The accuracy and applicability of two BRDF inversion models, namely the linear semi-empirical kernel-driven (LSEKD) model and the non-linear Rahman-Pinty-Verstraete (RPV) model, are analyzed, and the effects of different sampling window sizes on the BRDF results of various ground objects are compared. The main conclusions are: 1) Oblique photogrammetry is a highly efficient method for RA measurement at the centimeter-level resolution for spatially continuous regions, because it enables cameras with a narrow field of view (FOV) to obtain observation data with a wider viewing angle and more directions, ensuring the robustness and accuracy of the BRDF inversion model, with RMSE in the visible and near-infrared bands are about 0.003 and 0.019 (8–14%); 2) Both the LSEKD and the RPV model are suitable for the inversion of the BRDF with comparable accuracy, but the kernel functions for the LSEKD need to be carefully chosen in advance according to the characteristics of the ground object, while the RPV is adaptive for most objects; 3) The Monte Carlo method can ensure that the multi-angle observation data is distributed evenly in the hemisphere, thus providing the optimal dataset for a high-accuracy BRDF inversion; and 4) The RA of ground objects may change with the change of spatial resolution; the extremely high-resolution RA provides the ability to study ground objects at a finer scale. This study expands the methods for obtaining high-spatial resolution, high-accuracy, and spatially continuous RA. It has significant application potential in areas such as quantitative remote sensing, calibration of high-accurate remote-sensing products, and bridging the scale gap between satellite and ground-collected RA data.

Background/Aim. Medicines based on nucleic acid derivatives, primarily nucleotides (N), are effective, nontoxic and widely used in medical practice. However, the currently known drugs based on N are used only in indeprotonated (D) forms. We studied the mechanism of action, antiviral, antitumor and cardioprotective properties of protonated (P)N, which still remain outside the attention of researchers. Methods. We used spectrometry methods, such as circular dichroism and reflectance anisotropy, determination of antiviral and antitumor activity in tissue culture, and cardioprotective action in rats. Results. It was shown that both forms of N interact with proteins in the medium affinity zone of 10–5 – 10–8 M. This interaction is based on proton-ion exchange, which significantly changes the conformation of proteins. However, the action of PN and DN on proteins is multidirectional in nature. PNs reduce protein stiffness, changing its conformation, thus increasing its surface area. DNs, on the contrary, make the protein molecule more rigid, reducing its surface area. The specified properties of PNs and DNs are often accompanied by opposite biological properties. PNs are especially valuable in the creation of active pharmaceutical ingredients (APIs) with increased efficiency and therapeutic effect, increased biological activity, and prevention of an unwanted immune response. Such APIs allow to reduce and optimize the treatment time, as well as reduce the total cost of treatment. A positive result is provided by the use of purine and pyrimidine PNs to boost the interaction between the protein-ligand and the protein-receptor, with an optimal ratio between PN and target proteins of 0.1 μM/10 mM. The recombinant proteins of cytokine and hormonal nature are used to create PN compositions. PNs themselves exhibit properties of antiviral APIs. In the cell culture of DNA-containing herpes virus, PNs have an efficiency index (IS) equal to 1082. When using PN in experiments with RNA-containing influenza virus, the IS is equal to 400. It is believed that antiviral APIs with IS=15 are already promising for further research. PNs demonstrate antitumor activity in tumor cell cultures in concentration from 1 μM to 10 mM with no toxic effects. At the same time, in concentrations from 1 μM to 1 mM, PNs stimulate the division of normal cells. The studies on rats revealed cardioprotective effect of purine PNs in concentrations from 1 to 10 mg/kg of animal weight, reducing the accumulation of uric acid by 10 times, which is characteristic of the known medicinal preparation based on inosine. Conclusions. The ability of protonated forms of nucleotides to bind to proteins has been established, changing their conformation in the direction of reducing their rigidity, which ultimately provide the antiviral, antitumor, and cardioprotective effects. [ABSTRACT FROM AUTHOR]

The canopy bidirectional reflectance distribution function (BRDF) plays a pivotal role in estimating the biophysical parameters of plants, whereas soil background anisotropy creates challenges for their retrieval. Soil optical properties affect canopy anisotropic characteristics, especially in open-canopy areas. However, the remote sensing of background anisotropy is challenging due to the difficulties of information extraction in complex forest ecosystems and varying illumination conditions. This study develops an efficient photogrammetric technique to extract the background soil bidirectional reflectance factor (BRF) from unmanned aerial vehicle (UAV)-based multiangular images and to verify the need for accurate soil anisotropy information in canopy radiative transfer modeling. Soil BRF profiles were measured over three open-canopy sample plots from multiangular remotely sensed multispectral images collected with a hexacopter. As validation, reference soil BRF profiles were synchronously acquired by a ground-based multiangular imaging system. A high level of consistency between the ground- and UAV-measured soil BRF was observed with an RMSE of less than 0.012. Uncertainty analysis of the measured soil BRF showed that multiple scattering between sunlit soil in large sunflecks and foliage elements contributed less than 5%. Both results demonstrated that soil anisotropy can be accurately extracted from UAV multiangular measurements. To explicitly demonstrate that the use of soil anisotropy can reduce uncertainties in canopy radiative transfer simulations, we simulated the canopy BRF with Lambertian soil and with anisotropic soil using a three-dimensional (3D) radiative transfer model under different soil moisture content (SMC) levels, canopy cover (CC) levels and solar zenith angles (SZAs) with simulated realistic forest scenes. We found that less CC, lower SZAs and less SMC lead to a more significant influence of soil anisotropy on canopy reflectance; e.g., the reflectance bias reaches up to 0.3 in the hotspot direction. This illustrates that neglecting soil anisotropy can cause considerable errors in the modeling of the canopy BRF of open forests (i.e., CC levels of less than 0.5). The proposed technique facilitates the characterization of anisotropic forest background soil, which is important for advancing canopy radiative transfer modeling and validation and for the retrieval of vegetation parameters. [ABSTRACT FROM AUTHOR]

The land surface albedo reflects the ability of the surface to reflect solar radiation and is a critical physical variable in the study of the Earth’s energy budget and global climate change. Algorithms for the retrieval of albedo usually require multi-angle measurements due to surface anisotropy. However, most of the satellites cannot currently provide sufficient and well-distributed observations; therefore, the accuracy of remotely sensed albedo is constrained. Based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) and albedo product (MCD43A1), this study proposed a method to further subdivide reflectance anisotropy and build an updated database of BRDF archetype, using both the Anisotropic Flat Index (AFX) and Perpendicular Anisotropic Flat Index (PAFX). The BRDF archetypes were used to fit the corresponding MODIS BRDF, and the optimal number of BRDF archetype categories was determined according to the tendency of fitting error. The effect of surface anisotropy and observation noise on albedo retrieval were explored based on simulated MODIS reflectance. Finally, the BRDF archetype A2P2 was taken as prior knowledge to retrieve albedo from a different number of MODIS observations, and the result was validated by the high-quality MODIS albedo product. The results show that the fitting error between BRDF archetypes and MODIS BRDF shows a rapid decline when introducing the PAFX in the classification process. A 3-by-3 matrix of BRDF archetypes, which occupy 73.44% and 70.13% of the total decline in the red and NIR band, can be used to represent the characteristics of reflectance anisotropy. The archetype A2P2 may be used as prior knowledge to improve the albedo retrieval from insufficient observations. The validation results based on MODIS observations show that the archetype A2P2-based albedo can reach root-mean-square errors (RMSEs) of no more than 0.03.

The electronic properties and optical response of Si(111)–Ag reconstructions, with distinct interface structures, are studied with scanning tunneling microscopy (STM), reflectance anisotropy spectroscopy (RAS), and infrared spectroscopic ellipsometry (IRSE). The results are compared to previous studies on the Si(111)‐(3 × 1)–Ag surface. Depending on the preparation conditions, STM shows hybrid surfaces comprising (√3 × √3) areas with semiconducting (3 × 1)–Ag regions or metallic Ag islands. RAS of the (√3 × √3)–Ag reconstruction mostly shows a flat response, confirming the isotropic nature of the surface while Ag islands on this surface produce a steep increase in the infrared as well as a strong optical anisotropy at 3.5 eV. Scanning tunneling spectroscopy (STS) of the islands shows a high density of states with almost no structure. STS of Ag nanodots on the (3 × 1)–Ag surface shows distinct Coulomb resonances within the Si bandgap while the Si(111)‐(3 × 1)–Ag surface reveals an expected semiconducting behavior with a band gap and no sign of resonances. Ag islands on the (3 × 1)–Ag surface also show weak Coulombic oscillations indicating that local transport depends on the electronic properties of the interface. [ABSTRACT FROM AUTHOR]

In addition to single-angle reflectance data, multi-angular observations can be used as an additional information source for the retrieval of properties of an observed target surface. In this paper, we studied the potential of multi-angular reflectance data for the improvement of leaf area index (LAI) and leaf chlorophyll content (LCC) estimation by numerical inversion of the PROSAIL model. The potential for improvement of LAI and LCC was evaluated for both measured data and simulated data. The measured data was collected on 19 July 2016 by a frame-camera mounted on an unmanned aerial vehicle (UAV) over a potato field, where eight experimental plots of 30 × 30 m were designed with different fertilization levels. Dozens of viewing angles, covering the hemisphere up to around 30° from nadir, were obtained by a large forward and sideways overlap of collected images. Simultaneously to the UAV flight, in situ measurements of LAI and LCC were performed. Inversion of the PROSAIL model was done based on nadir data and based on multi-angular data collected by the UAV. Inversion based on the multi-angular data performed slightly better than inversion based on nadir data, indicated by the decrease in RMSE from 0.70 to 0.65 m 2 /m 2 for the estimation of LAI, and from 17.35 to 17.29 μg/cm 2 for the estimation of LCC, when nadir data were used and when multi-angular data were used, respectively. In addition to inversions based on measured data, we simulated several datasets at different multi-angular configurations and compared the accuracy of the inversions of these datasets with the inversion based on data simulated at nadir position. In general, the results based on simulated (synthetic) data indicated that when more viewing angles, more well distributed viewing angles, and viewing angles up to larger zenith angles were available for inversion, the most accurate estimations were obtained. Interestingly, when using spectra simulated at multi-angular sampling configurations as were captured by the UAV platform (view zenith angles up to 30°), already a huge improvement could be obtained when compared to solely using spectra simulated at nadir position. The results of this study show that the estimation of LAI and LCC by numerical inversion of the PROSAIL model can be improved when multi-angular observations are introduced. However, for the potato crop, PROSAIL inversion for measured data only showed moderate accuracy and slight improvements. [ABSTRACT FROM AUTHOR]

We introduce a new method to determine the anisotropy of reflectance of sea ice and snow at spatial scales from 1 m2 to 80 m2 using a multispectral circular fish‐eye radiance camera (CE600). The CE600 allows measuring radiance simultaneously in all directions of a hemisphere at a 1° angular resolution. The spectral characteristics of the reflectance and its dependency on illumination conditions obtained from the camera are compared to those obtained with a hyperspectral field spectroradiometer manufactured by Analytical Spectral Device, Inc. (ASD). Results confirm the potential of the CE600, with the suggested measurement setup and data processing, to measure commensurable sea ice and snow hemispherical‐directional reflectance factor, HDRF, values. Compared to the ASD, the reflectance anisotropy measured with the CE600 provides much higher resolution in terms of directional reflectance (N = 16,020). The hyperangular resolution allows detecting features that were overlooked using the ASD due to its limited number of measurement angles (N = 25). This data set of HDRF further documents variations in the anisotropy of the reflectance of snow and ice with the geometry of observation and illumination conditions and its spectral and spatial scale dependency. Finally, in order to reproduce the hyperangular CE600 reflectance measurements over the entire 400–900 nm spectral range, a regression‐based method is proposed to combine the ASD and CE600 measurements. Results confirm that both instruments may be used in synergy to construct a hyperangular and hyperspectral snow and ice reflectance anisotropy data set. [ABSTRACT FROM AUTHOR]

Viewing and illumination geometry has a strong influence on optical measurements of natural surfaces due to their anisotropic reflectance properties. Typically, cameras on-board unmanned aerial vehicles (UAVs) are affected by this because of their relatively large field of view (FOV) and thus large range of viewing angles. In this study, we investigated the magnitude of reflectance anisotropy effects in the 500–900 nm range, captured by a frame camera mounted on a UAV during a standard mapping flight. After orthorectification and georeferencing of the images collected by the camera, we calculated the viewing geometry of all observations of each georeferenced ground pixel, forming a dataset with multi-angular observations. We performed UAV flights on two days during the summer of 2016 over an experimental potato field where different zones in the field received different nitrogen fertilization treatments. These fertilization levels caused variation in potato plant growth and thereby differences in structural properties such as leaf area index (LAI) and canopy cover. We fitted the Rahman–Pinty–Verstraete (RPV) model through the multi-angular observations of each ground pixel to quantify, interpret, and visualize the anisotropy patterns in our study area. The Q parameter of the RPV model, which controls the proportion of forward and backward scattering, showed strong correlation with canopy cover, where in general an increase in canopy cover resulted in a reduction of backward scattering intensity, indicating that reflectance anisotropy contains information on canopy structure. In this paper, we demonstrated that anisotropy data can be extracted from measurements using a frame camera, collected during a typical UAV mapping flight. Future research will focus on how to use the anisotropy signal as a source of information for estimation of physical vegetation properties. [ABSTRACT FROM AUTHOR]

Despite the arguments in favour of oblique photographs acquired during observer-directed reconnaissance sorties, many aerial archaeologists have extracted much valuable information from verticals generated during total coverage mapping surveys. This paper looks at one of these arguments: the issue of anisotropic surface reflectance, which is responsible for the allegedly superior rendering of (mainly) vegetation and shadow marks when observed from certain oblique viewpoints. However, after a theoretical and practical assessment of the Bidirectional Reflectance Distribution Function (BRDF) of vegetation, it becomes clear that nadir views provide a more than satisfying alternative to the extremes of an oblique approach. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The canopy structure of wheat changes significantly with growth stages and leads to changes in reflectance anisotropy. Bidirectional reflectance distribution function characterises the reflectance anisotropy of the targets, which can be approximated. Spectrodirectional reflectance measurements on wheat crop were acquired using a field goniometer system. The bidirectional reflectance spectra were acquired at 54 view angles to cover the hemispheric span up to 60° view zenith. The observations were made during early growth stages till maturity of the crop. The anisotropy was not constant for all wavelengths and anisotropic factors clearly revealed spectral dependence, which was more pronounced in near principal plane. In near infrared, wheat canopy expressed less reflectance anisotropy because of higher multiple scattering. The broad hotspot signature was noticeable in reflectance of canopy whenever view and solar angles were close. Distinct changes in bidirectional reflectance distribution function were observed during booting to flowering stages as the canopy achieves more uniformity, height and head emergence. The function clearly reveals bowl shape during heading to early milking growth stages of the crop. Late growth stages show less prominent gap and shadow effects. Anisotropy index revealed that wheat exhibits changes in reflectance anisotropy with phenological development and with spectral bands. [ABSTRACT FROM AUTHOR]

This article presents and technically describes a new field spectro-goniometer system for the ground-based characterization of the surface reflectance anisotropy under natural illumination conditions developed at the Alfred Wegener Institute (AWI). The spectro-goniometer consists of a Manual Transportable Instrument platform for ground-based Spectro-directional observations (ManTIS), and a hyperspectral sensor system. The presented measurement strategy shows that the AWI ManTIS field spectro-goniometer can deliver high quality hemispherical conical reflectance factor (HCRF) measurements with a pointing accuracy of ±6 cm within the constant observation center. The sampling of a ManTIS hemisphere (up to 30° viewing zenith, 360° viewing azimuth) needs approx. 18 min. The developed data processing chain in combination with the software used for the semi-automatic control provides a reliable method to reduce temporal effects during the measurements. The presented visualization and analysis approaches of the HCRF data of an Arctic low growing vegetation showcase prove the high quality of spectro-goniometer measurements. The patented low-cost and lightweight ManTIS instrument platform can be customized for various research needs and is available for purchase.

In this paper, a laboratory goniometer system for performing multi-angular measurements under controlled illumination conditions is described. A commercially available robotic arm enables the acquisition of a large number of measurements over the full hemisphere within a short time span making it much faster than other goniometers. In addition, the presented set-up enables assessment of anisotropic reflectance and emittance behaviour of soils, leaves and small canopies. Mounting a spectrometer enables acquisition of either hemispherical measurements or measurements in the horizontal plane. Mounting a thermal camera allows directional observations of the thermal emittance. This paper also presents three showcases of these different measurement set-ups in order to illustrate its possibilities. Finally, suggestions for applying this instrument and for future research directions are given, including linking the measured reflectance anisotropy with physically-based anisotropy models on the one hand and combining them with field goniometry measurements for joint analysis with remote sensing data on the other hand. The speed and flexibility of the system offer a large added value to the existing pool of laboratory goniometers.

Many previous studies have attempted to extract prior reflectance anisotropy knowledge from the historical MODIS Bidirectional Reflectance Distribution Function (BRDF) product based on land cover or Normalized Difference Vegetation Index (NDVI) data. In this study, the feasibility of the method is discussed based on MODIS data and archetypal BRDFs. The BRDF is simplified into six archetypal BRDFs that represent different reflectance anisotropies. Five-year time series of MODIS BRDF data over three tiles are classified into six BRDF archetype classes according to the Anisotropy Flat indeX (AFX). The percentage of each BRDF archetype class in different land cover classes or every 0.1-NDVI interval is determined. Nadir BRDF-Adjusted Reflectances (NBARs) and NDVIs simulated from different archetypal BRDFs and the same multi-angular observations are compared to MODIS results to study the effectiveness of the method. The results show that one land cover type, or every 0.1-NDVI interval, contains all the potential BRDF shapes and that one BRDF archetypal class makes up no more than 40% of all data. Moreover, the differences between the NBARs and NDVIs simulated from different archetypal BRDFs are insignificant. In terms of the archetypal BRDF method and MODIS BRDF product, this study indicates that the land cover or NDVI is not necessarily related to surface reflectance anisotropy. [ABSTRACT FROM AUTHOR]

Reflectance anisotropy is a signal that contains information on the optical and structural properties of a surface and can be studied by performing multi-angular reflectance measurements that are often done using cumbersome goniometric measurements. In this paper we describe an innovative and fast method where we use a hyperspectral pushbroom spectrometer mounted on a multirotor unmanned aerial vehicle (UAV) to perform such multi-angular measurements. By hovering the UAV above a surface while rotating it around its vertical axis, we were able to sample the reflectance anisotropy within the field of view of the spectrometer, covering all view azimuth directions up to a 30° view zenith angle. We used this method to study the reflectance anisotropy of barley, potato, and winter wheat at different growth stages. The reflectance anisotropy patterns of the crops were interpreted by analysis of the parameters obtained by fitting of the Rahman-Pinty-Verstraete (RPV) model at a 5-nm interval in the 450-915 nm range. To demonstrate the results of our method, we firstly present measurements of barley and winter wheat at two different growth stages. On the first measuring day, barley and winter wheat had structurally comparable canopies and displayed similar anisotropic reflectance patterns. On the second measuring day the anisotropy of crops differed significantly due to the crop-specific development of grain heads in the top layer of their canopies. Secondly, we show how the anisotropy is reduced for a potato canopy when it grows from an open row structure to a closed canopy. In this case, especially the backward scattering intensity was strongly diminished due to the decrease in shadowing effects that were caused by the potato rows that were still present on the first measuring day. The results of this study indicate that the presented method is capable of retrieving anisotropic reflectance characteristics of vegetation canopies and that it is a feasible alternative for field goniometer measurements. [ABSTRACT FROM AUTHOR]

Viewing and illumination geometry has a strong influence on optical measurements of natural surfaces due to their anisotropic reflectance properties. Typically, cameras on-board unmanned aerial vehicles (UAVs) are affected by this because of their relatively large field of view (FOV) and thus large range of viewing angles. In this study, we investigated the magnitude of reflectance anisotropy effects in the 500–900 nm range, captured by a frame camera mounted on a UAV during a standard mapping flight. After orthorectification and georeferencing of the images collected by the camera, we calculated the viewing geometry of all observations of each georeferenced ground pixel, forming a dataset with multi-angular observations. We performed UAV flights on two days during the summer of 2016 over an experimental potato field where different zones in the field received different nitrogen fertilization treatments. These fertilization levels caused variation in potato plant growth and thereby differences in structural properties such as leaf area index (LAI) and canopy cover. We fitted the Rahman–Pinty–Verstraete (RPV) model through the multi-angular observations of each ground pixel to quantify, interpret, and visualize the anisotropy patterns in our study area. The Θ parameter of the RPV model, which controls the proportion of forward and backward scattering, showed strong correlation with canopy cover, where in general an increase in canopy cover resulted in a reduction of backward scattering intensity, indicating that reflectance anisotropy contains information on canopy structure. In this paper, we demonstrated that anisotropy data can be extracted from measurements using a frame camera, collected during a typical UAV mapping flight. Future research will focus on how to use the anisotropy signal as a source of information for estimation of physical vegetation properties.

Optical methods to study soil moisture content (SMC) are often based on empirically or physically based models that relate changes in reflectance intensity to SMC. The effects of SMC on the reflectance anisotropy, however, have not received much attention. In this paper the effects of SMC on the anisotropic reflectance behaviour of soils were studied. Biconical reflectance factors (BCRFs) of five different soil samples were acquired at 60 positions covering the full hemisphere in the optical domain at different SMC levels using Wageningen University's laboratory goniometer facility. In addition, we inverted the Rahman–Pinty–Verstraete (RPV) model against the measured BCRFs in the principal plane. The results show that the anisotropic reflectance behaviour of soils is strongly influenced by the SMC. Dry soils displayed strong backward scattering behaviour, with a maximum reflectance close to the hotspot position. An increase of the SMC level up to the soil's saturation point caused the soils to scatter more in the forward direction and induced a weakening of the hotspot effect. Oversaturated soils displayed a strong sun-glint-like reflectance peak in the anti-solar direction. The RPV model fitted the measured BCRFs in the principal plane up to saturated SMC levels in general with an R 2 > 0.9. It was not possible to fit the model through observations of oversaturated soils, since the RPV model is not capable of simulating specular reflectance. The asymmetry parameter ( Θ ) of the RPV model, which controls the proportion of forward and backward scattering, showed a strong correlation to SMC for individual samples. This correlation remained significant when we considered all samples together with a maximum R 2 of 0.797 at 2123 nm, indicating that reflectance anisotropy contained information on the water content of soils. The amplitude parameter ( ρ 0 ), which is closely related to the reflectance intensity, only had a maximum R 2 of 0.622 at 1921 nm. This indicated that reflectance anisotropy contained more information on SMC than the level of spectral reflectance as such. [ABSTRACT FROM AUTHOR]

The spectral and radiometric quality of airborne imaging spectrometer data is affected by the anisotropic reflectance behavior of the imaged surface. Illumination and observation angle-dependent patterns of surface reflected radiation propagate into products, hinder quantitative assessment of biophysical/biochemical parameters, and decrease the comparability of data from multiple flight lines. The Ross–Li model, originally developed for multiangular observations, can be inverted to estimate and correct for surface anisotropy effects. This requires land cover be stratified into distinct types of scattering behavior. When the observations subsumed in these classes cover a range of view angles, a pseudo multiangular view on the surface can be employed to invert the Ross–Li model. A discrete land cover classification, however, bears the risk of inappropriate scattering correction resulting in spatial artifacts in the corrected data, predominantly in transition regions of two land cover types (e.g., soil and sparse vegetation with varying fractions). We invert the Ross–Li model on continuous land cover fraction layers. We decompose land cover in dominating structural types using linear spectral unmixing. Ross–Li kernel weights and formulations are estimated for each type independently; the correction is then applied pixel-wise according to the fractional distribution. The corrected Airborne Prism EXperiment imaging spectrometer data show significant reduction of anisotropic reflectance effects of up to 90% (average 60% to 75%, $p=0.05$), measured in the overlapping regions of adjacent flight lines. No spatial artifacts or spectral irregularities are observed after correction. [ABSTRACT FROM PUBLISHER]

Reflectance anisotropy (RA) spectra of clean, dimerized Si and Ge (001) surfaces with (2 [ABSTRACT FROM AUTHOR]

Imaging spectroscopy (IS) provides an efficient tool to assess vegetation status and functioning at ecologically relevant scales. Reliable extraction of vegetation information from spatial and spectral high resolution spectroscopy data requires accurate retrieval schemes to account for the complex radiative transfer in the coupled vegetation-atmosphere system. Particularly the coupling of the atmosphere and vegetation considering combined effects of anisotropy, absorption and scattering typically relies on many assumptions, rendering estimates of direct ( E dir ) and diffuse ( E dif ) surface irradiance error prone. This impacts the reliability of retrieved vegetation properties. In this study we discuss and quantify the retrieval sensitivity of vegetation information using high resolution IS data to inaccurate assumptions of direct and diffuse surface irradiance. We use observations and simulations and focus on the two vegetation indices normalized difference vegetation index (NDVI) and the photochemical reflectance index (PRI), and on sun-induced chlorophyll fluorescence (Fs). Our results indicate that, even if the irradiance field ( E ) is exactly known, reflectance based vegetation indices show an inherent variation of 9% (NDVI) and 12% (PRI) respectively. These variations are caused by complex interactions of surface irradiance and reflectance anisotropy. The emitted Fs signal was found to be almost unaffected by those variations, if the retrieval considers surface anisotropy. Further, estimation of vegetation properties is subject to large uncertainties if instantaneous E fields are unknown. In that case, they range up to 13% for the NDVI, up to 32% for the PRI, and up to 58% for Fs. We conclude that retrieval sensitivities of vegetation indices and Fs to illumination effects must be carefully considered in data interpretation and suggest using coupled surface-atmosphere models to exploit the full information content of IS data. [ABSTRACT FROM AUTHOR]

Reflectance anisotropy is a signal that contains information on the optical and structural properties of a surface and can be studied by performing multi-angular reflectance measurements that are often done using cumbersome goniometric measurements. In this paper we describe an innovative and fast method where we use a hyperspectral pushbroom spectrometer mounted on a multirotor unmanned aerial vehicle (UAV) to perform such multi-angular measurements. By hovering the UAV above a surface while rotating it around its vertical axis, we were able to sample the reflectance anisotropy within the field of view of the spectrometer, covering all view azimuth directions up to a 30° view zenith angle. We used this method to study the reflectance anisotropy of barley, potato, and winter wheat at different growth stages. The reflectance anisotropy patterns of the crops were interpreted by analysis of the parameters obtained by fitting of the Rahman-Pinty-Verstraete (RPV) model at a 5-nm interval in the 450–915 nm range. To demonstrate the results of our method, we firstly present measurements of barley and winter wheat at two different growth stages. On the first measuring day, barley and winter wheat had structurally comparable canopies and displayed similar anisotropic reflectance patterns. On the second measuring day the anisotropy of crops differed significantly due to the crop-specific development of grain heads in the top layer of their canopies. Secondly, we show how the anisotropy is reduced for a potato canopy when it grows from an open row structure to a closed canopy. In this case, especially the backward scattering intensity was strongly diminished due to the decrease in shadowing effects that were caused by the potato rows that were still present on the first measuring day. The results of this study indicate that the presented method is capable of retrieving anisotropic reflectance characteristics of vegetation canopies and that it is a feasible alternative for field goniometer measurements.

Directional effects in airborne imaging spectrometer (IS) data are mainly caused by anisotropic reflectance behavior of surfaces, commonly described by bi-directional reflectance distribution functions (BRDF). The radiometric and spectral accuracy of IS data is known to be highly influenced by such effects, which prevents consistent comparison of products. Several models were developed to approximate surface reflectance anisotropy for multi-angular observations. Few studies were carried out using such models for airborne flight lines where only a single observation is available for each ground location. In the present work, we quantified and corrected reflectance anisotropy on a single airborne HyMap flight line using a Ross-Li model. We stratified the surface in two vegetation structural types (different in vertical structuring) using spectral angle mapping, to generate a structure dependent set of angular observations. We then derived a suite of products [indices (structure insensitive pigment index, normalized difference vegetation index, simple ratio index, and anthocyanin reflectance index) and inversion-based (SAIL/PROSPECT-leaf area index, Cw, Cdm, Cab)] from corrected and uncorrected images. Non-parametric analysis of variance (Kruskal-Wallis test) showed throughout significant improvements in products from corrected images. Data correction resulting in airborne nadir BRDF adjusted reflectance (aNBAR) showed uncertainty reductions from 60 to 100% (p-value = 0.05) as compared to uncorrected and nadir observations. Using sparse IS data acquisitions, the use of fully parametrized BRDF models is limited. Our normalization scheme is straightforward and can be applied with illumination and observation geometry being the only a priori information. We recommend aNBAR generation to precede any higher level airborne IS product generation based on reflectance data. [ABSTRACT FROM AUTHOR]

This article presents and technically describes a new field spectro-goniometer system for the ground-based characterization of the surface reflectance anisotropy under natural illumination conditions developed at the Alfred Wegener Institute (AWI). The spectro-goniometer consists of a Manual Transportable Instrument platform for ground-based Spectro-directional observations (ManTIS), and a hyperspectral sensor system. The presented measurement strategy shows that the AWI ManTIS field spectro-goniometer can deliver high quality hemispherical conical reflectance factor (HCRF) measurements with a pointing accuracy of ± 6 cm within the constant observation center. The sampling of a ManTIS hemisphere (up to 30° viewing zenith, 360° viewing azimuth) needs approx. 18 min. The developed data processing chain in combination with the software used for the semi-automatic control provides a reliable method to reduce temporal effects during the measurements. The presented visualization and analysis approaches of the HCRF data of an Arctic low growing vegetation showcase prove the high quality of spectro-goniometer measurements. The patented low-cost and lightweight ManTIS instrument platform can be customized for various research needs and is available for purchase. [ABSTRACT FROM AUTHOR]

In this paper, a laboratory goniometer system for performing multi-angular measurements under controlled illumination conditions is described. A commercially available robotic arm enables the acquisition of a large number of measurements over the full hemisphere within a short time span making it much faster than other goniometers. In addition, the presented set-up enables assessment of anisotropic reflectance and emittance behaviour of soils, leaves and small canopies. Mounting a spectrometer enables acquisition of either hemispherical measurements or measurements in the horizontal plane. Mounting a thermal camera allows directional observations of the thermal emittance. This paper also presents three showcases of these different measurement set-ups in order to illustrate its possibilities. Finally, suggestions for applying this instrument and for future research directions are given, including linking the measured reflectance anisotropy with physically-based anisotropy models on the one hand and combining them with field goniometry measurements for joint analysis with remote sensing data on the other hand. The speed and flexibility of the system offer a large added value to the existing pool of laboratory goniometers. [ABSTRACT FROM AUTHOR]

The Compact High Resolution Imaging Spectrometer (CHRIS) mounted onboard the Project for Onboard Autonomy (PROBA) spacecraft is capable of sampling reflected radiation at five viewing angles over the visible and near-infrared regions of the solar spectrum with high spatial resolution. We combined the spectral domain with the angular domain of CHRIS data in order to map the surface heterogeneity of an Alpine coniferous forest during winter. In the spectral domain, linear spectral unmixing of the nadir image resulted in a canopy cover map. In the angular domain, pixelwise inversion of the Rahman-Pinty-Verstraete (RPV) model at a single wavelength at the red edge (722 nm) yielded a map of the Minnaert-k parameter that provided information on surface heterogeneity at a subpixel scale. However, the interpretation of the Minnaert- k parameter is not always straightforward because fully vegetated targets typically produce the same type of reflectance anisotropy as non-vegetated targets. Merging both maps resulted in a forest cover heterogeneity map, which contains more detailed information on canopy heterogeneity at the CHRIS subpixel scale than is possible to realize from a single-source optical data set. [ABSTRACT FROM AUTHOR]

Abstract: View angle effects present in spectral vegetation indices can either be regarded as an added source of uncertainty for variable retrieval or as a source of additional information, enhancing the variable retrieval; however, the magnitude of these angular effects remains for most indices unknown or unquantified. We use the ESA-mission CHRIS-PROBA (Compact High Resolution Imaging Spectrometer onboard the Project for On-board Autonomy) providing spaceborne imaging spectrometer and multiangular data to assess the reflectance anisotropy of broadband as well as recently developed narrowband indices. Multiangular variability of Hemispherical Directional Reflectance Factor (HDRF) is a prime factor determining the indices´ angular response. Two contrasting structural vegetation types, pine forest and meadow, were selected to study the effect of reflectance anisotropy on the angular response. Calculated indices were standardized and statistically evaluated for their varying HDRF. Additionally we employ a coupled radiative transfer model (PROSPECT/FLIGHT) to quantify and substantiate the findings beyond an incidental case study. Nearly all tested indices manifested a prominent anisotropic behaviour. Apart from the conventional broadband greenness indices [e.g. Simple Ratio Index (SRI), Normalized Difference Vegetation Index (NDVI)], light use efficiency and leaf pigment indices [e.g. Structure Insensitive Pigment Index (SIPI), Photochemical Reflectance Index (PRI) and Anthocyanin Reflectance Index (ARI)] did express significant different angular responses depending on the vegetation type. Following the quantification of the impact, we conclude that the angular-dependent fraction of non-photosynthetic material is of critical importance shaping the angular signature of these VIs. This work highlights the influence of viewing geometry and surface reflectance anisotropy, particularly when using light use efficiency and leaf pigment indices. [Copyright &y& Elsevier]

We report on in situ RD measurements of In0.3Ga0.7As/GaAs epitaxial layers, 0–75 A˚ thick, grown by Molecular Beam Epitaxy (MBE) on GaAs (0 0 1). A plot of the amplitude of the RD spectrum at 2.5 eV versus epilayer thickness shows that it rises sharply when a film thickness of about 38 A˚ is reached. Comparison with RHEED measurements shows that such rise correlates well to the onset of 3D growth. RD line shape calculations show that the experimental RD line shapes can be described on the basis of InGaAs islands under an anisotropic strain. Results presented here show the high potential of RD spectroscopy as an in situ probe to the study of In0.3Ga0.7As/GaAs growth processes. [Copyright &y& Elsevier]

While it has long been recognized that the anisotropic reflectance properties of a natural surface affect the intensity and spectral distribution of radiance received by a remote sensing instrument, the effects of canopy reflectance geometry on the observed spatial structure of canopy reflectance have not adequately been evaluated. In this paper, near-surface spectrometers were used as part of two experiments to evaluate the systematic variations in the sun-target-sensor geometry on semivariogram metrics (range, silI+nugget variance) summarizing the spatial structure observed in a tallgrass prairie canopy. In the first experiment, reflectance measurements and normalized difference vegetation index (NDVI) values were collected at five sensor viewing angles (-50°, -25°, 0°, 25°, and 50°) from six measurement grids representing three burn treatments and two slope/aspect situations. In the second experiment, data were collected at 2-h intervals, beginning at ≈0800 LST from the same grids with the radiometer at nadir, allowing the spatial structure of reflectance and NDVI to be observed under naturally changing illumination. Results of the geostatistical analysis show that both the range and sill+nugget variance values change with viewing angle. These effects were consistent across all treatments and slope/aspect combinations. However, when viewed from nadir, the sill+nugget variance values of the canopy changed with solar illumination angle and the range values remained nearly constant. These relationships were also observed across all treatments and slope/aspect combinations. The results suggest that sill+nugget values for the same surface may not be directly comparable if not acquired under very similar view angle and illumination conditions. Range values are comparable if the nadir view is used, but not under off-nadir viewing conditions. [ABSTRACT FROM AUTHOR]

The aim of the study was to determine optical properties of vitrinite, subjected to temperatures within the range of 400–1200 °C for durations of 1–7 h, in an argon atmosphere. The samples of vitrinite concentrate (Vt content 90%, Rr=1.17%) were inserted in the furnace at room temperature and subjected to a heating rate of 60 °C/min.To assess the effects of the experiment, random reflectance as well as apparent maximum and minimum reflectances of vitrinite were measured on the raw and thermally treated concentrates. Employing the method and computer programme of W.E. Kilby, the true maximum, intermediate and minimum reflectances of vitrinite as well as reflectance anisotropy and Reflectance-Indicating Surface (RIS) shapes were evaluated.Transformation of vitrinite subjected to heating is influenced more by the increase of temperature than the time applied. During the plastic stage (400–500 °C), vitrinite is subjected to substantial chemical and physical alteration. It is manifested by chemical decomposition, significant mass loss and mesophase appearance. Porosity, relief, reflectance and bireflectance of the vitrinite grains increase with heating. At the temperature of 1200 °C, random vitrinite reflectance reaches 6.62% with bireflectance of 3.46%. Mesophase at 1200 °C was characterised by mean reflectance equal to 9.25% and a bireflectance of 13.35%.The reflectance character of vitrinite changes from biaxial negative into biaxial positive–negative. However, the original RIS shape, resulting from the tectonic regime during the main phase of coalification, is not fully transformed until heated to 1200 °C. Reflectance character of mesophase is consistently biaxial negative. The internal structure of mesophase is thought to be better organised than the internal structure of vitrinite. [Copyright &y& Elsevier]

We present a study of the growth of strained ultrathin GaSb quantum well (QW) layers in a GaAs host crystal by organometallic vapor phase epitaxy (OMVPE). We report surface anisotropy features observed by reflectance difference spectroscopy (RDS) during exposure of the GaAs (001) surface to trimethylantimony (TMSb) and during subsequent growth interruption. We demonstrate the formation of a floating layer of Sb during growth of GaAs over GaSb quantum well layers. The periodic nature of the RDS signal during growth of multiple quantum well (MQW) structures allows us to construct time-resolved RDS spectra, detailing the evolution of the surface anisotropy. We show how x-ray diffraction (XRD) data may be used to determine the graded compositional profile resulting from Sb segregation at the GaAs/GaSb interface. Photoluminescence (PL) spectra at 2 K from MQW structures exhibit two peaks below the GaAs bandgap. The lower-energy peak, which we attribute to a type-II transition at the GaSb/GaAs interface, shifts logarithmically with excitation power density. The higher energy peak shows no shift with excitation power, and is attributed to a transition occurring within the graded barrier layers. [ABSTRACT FROM AUTHOR]

The procedure of fitting an ellipsoid to vitrinite reflectance anisotropy is described. Several authors on this subject use incorrect fitting formulae. The correct formulae are given and a least- squares procedure is developed to give confidence regions for the principal reflectances and their orientations. A FORTRAN program is offered that computes the principal reflectances using the correct formulae. A test is constructed for whether the principal reflectance orientations are the same at two locations. Because of the ellipsoid shape, the reflectance anisotropy can be compared to the strain ellipsoid. As an example, the methods are used to compare two coal blocks from an openpit mine in Alberta, Canada. The test shows that the principal reflectances of the two blocks have different orientations, indicating that the orientation of the principal strain axes is different at the two sites. [ABSTRACT FROM AUTHOR]

We present reflectance measurements collected from virgin and ocean-harvested plastics. Virgin plastics included high and low density polyethylene (HDPE, LDPE), polypropylene (PP) as well as polystyrene (PS). Ocean-harvested plastics were ropes, sheets, foam, pellets and fragmented items previously trawled from the North Pacific Garbage Patch. Nadir viewing angles and plastic pixel coverage were varied to advance our understanding of how reflectance shape and magnitude can be influenced by these parameters. We also investigated the effect of apparent colour of plastics on the measured reflectance from the ultraviolet (UV - 350 nm), visible, near to shortwave infrared (NIR, SWIR - 2500 nm). Statistical analyses indicated that the spectral reflectance of the plastics was significantly correlated to the percentage pixel coverage. There was no clear relationship between the reflectance observed and the viewing nadir angle but dampened materials seemed to be more isotropic (near-Lambertian) than their dry counterparts. A loss in reflectance was also determined between dry and wet plastics. Location of absorption features was not affected by the apparent colour of objects. In general, ocean-harvested plastics shared more identical absorption features (~960, 1215, 1440, 1732, 1920 nm) and had lower reflectance intensity compared to the virgin plastics (~980 nm). Prospects for satellite retrieval of plastic type and pixel plastic coverage are discussed based on Top-of-Atmosphere (TOA) signal simulated through radiative transfer computation using the documented plastic reflectances. Non-linear relationships between TOA reflectance and plastic coverage were observed depending on wavelength and plastic type. Most of the plastics analysed impact significantly the TOA signal but two plastic types did not produce strong signal at TOA (hard fragments, LDPE). Nevertheless, all plastic types produced detectable signals when observations were simulated within the sunglint direction. The measurements collected in this study are an extension to available high quality spectral reference libraries and can support further research in developing remote sensing algorithms for marine litter. ga1 • Showcase remote sensing as complementary plastic litter monitoring strategy. • Present hyperspectral measurements of virgin and ocean plastics from UV to SWIR. • Explore anisotropic reflectance properties of plastics at varying pixel coverages. • Show the apparent colour of plastics affects UV to SWIR spectral shape and magnitude. • Assess satellite remote sensing of plastics using radiative transfer solutions. [ABSTRACT FROM AUTHOR]