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We have measured and characterized the thermal crosstalk in two different arrays of transition-edge sensor (TES) X-ray micro-calorimeters with frequency-domain multiplexing (FDM) readout. The TES arrays are fabricated at SRON and are a 8$\times$8 and a 32$\times$32 "kilo-pixel" uniform array. The amount of crosstalk is evaluated as the ratio between the averaged crosstalk signal and the X-ray pulse amplitudes. The crosstalk ratios (CR) for our detectors are compliant with the requirements for future X-ray space missions, such as Athena X-IFU (CR$< 10^{-3}$ for first-neighbour pixels): we measured a nearest-neighbour thermal crosstalk ratio at a level of $10^{-4}$, with a highest crosstalk ratio of $4\times 10^{-4}$ for the kilo-pixel array (worst case, center of array) and $1\times 10^{-4}$ for the 8$\times$8 array, with a margin of improvement achievable by optimizing the Cu metallization and the width of the Si supporting structures (muntins) in the backside of the TES array chip. Based on the measured crosstalk ratios, we have estimated the impact on the spectral resolution by means of noise equivalent power (NEP) considerations and a Monte Carlo simulation, finding an average degradation in quadrature of less than 40~meV, compliant with the < 0.2~eV requirement for Athena X-IFU.

We report on the development and demonstration of a MHz frequency domain multiplexing (FDM) technology to read out arrays of cryogenic transition edge sensor (TES) X-ray microcalorimeters. In our FDM scheme, TESs are AC-biased at different resonant frequencies in the low MHz range through an array of high-$Q$ LC resonators. The current signals of all TESs are summed at superconducting quantum interference devices (SQUIDs). We have demonstrated multiplexing for a readout of 31 pixels using room temperature electronics, high-$Q$ LC filters and TES arrays developed at SRON, and SQUID arrays from VTT. We repeated this on a second setup with 37 pixels. The summed X-ray spectral resolutions $@$ 5.9 keV are $\Delta E_{\rm 31 pix ~MUX}=2.14\pm0.03$ eV and $\Delta E_{\rm 37 pix ~MUX}=2.23\pm0.03$ eV. The demonstrated results are comparable with other multiplexing approaches. There is potential to further improve the spectral resolution and to increase the number of multiplexed TESs, and to open up applications for TES X-ray microcalorimeters., Comment: 6 pages, 3 figures, accepted for publication on Applied physics letters

Southeast Australia experienced intensive and geographically extensive wildfires during the 2019–2020 summer season1,2. The fires released substantial amounts of carbon dioxide into the atmosphere3. However, existing emission estimates based on fire inventories are uncertain4, and vary by up to a factor of four for this event. Here we constrain emission estimates with the help of satellite observations of carbon monoxide5, an analytical Bayesian inversion6 and observed ratios between emitted carbon dioxide and carbon monoxide7. We estimate emissions of carbon dioxide to be 715 teragrams (range 517–867) from November 2019 to January 2020. This is more than twice the estimate derived by five different fire inventories8–12, and broadly consistent with estimates based on a bottom-up bootstrap analysis of this fire episode13. Although fires occur regularly in the savannas in northern Australia, the recent episodes were extremely large in scale and intensity, burning unusually large areas of eucalyptus forest in the southeast13. The fires were driven partly by climate change14,15, making better-constrained emission estimates particularly important. This is because the build-up of atmospheric carbon dioxide may become increasingly dependent on fire-driven climate–carbon feedbacks, as highlighted by this event16. The amount of carbon dioxide released by the Australian wildfires of 2019–2020 is uncertain, but is estimated here using satellite observations of carbon monoxide to be more than twice the amount suggested by fire inventories.

During its first year in operation the short-wave infrared (SWIR) Tropospheric Monitoring Instrument (TROPOMI) was calibrated in-flight and its performance was monitored. In this paper we present the results of the in-flight calibration and the ongoing instrument monitoring. This includes the determination of the background signals, noise performance, instrument spectral response function (ISRF) stability, and stray-light stability. From these results, the number of incurred dead and bad pixels due to cosmic-ray impacts is determined. The light-path transmission is checked by monitoring internal lamp and diffuser stabilities. Due to its high sensitivity to Earth radiation on the eclipse side, the calibration strategy for the background (i.e. dark current and offset) monitoring was adjusted. Trends over the first full year of nominal operations reveal a very stable SWIR module. The number of newly incurred dead and bad pixels is less than 0.1 % over nearly a full year since the start of operations. Assuming linear degradation of various components, the SWIR module is expected to keep performing within expected parameters for the full operational lifetime.

Transition Edge Sensors (TESs) are the selected technology for future spaceborne X-ray observatories, such as Athena, Lynx, and HUBS. These missions demand thousands of pixels to be operated simultaneously with high energy-resolving power. To reach these demanding requirements, every aspect of the TES design has to be optimized. Here we present the experimental results of tests on different devices where the coupling between the x-ray absorber and the TES sensor is varied. In particular, we look at the effects of the diameter of the coupling stems and the distance between the stems and the TES bilayer. Based on measurements of the AC complex impedance and noise, we observe a reduction in the excess noise as the spacing between the absorber stem and the bilayer is decreased. We identify the origin of this excess noise to be internal thermal fluctuation noise between the absorber stem and the bilayer. Additionally, we see an impact of the coupling on the superconducting transition in the appearance of kinks. Our observations show that these unwanted structures in the transition shape can be avoided with careful design of the coupling geometry. Also the stem diameter appears to have a significant impact on the smoothness of the TES transition. This observation is still poorly understood, but is of great importance for both AC and DC biased TESs., Comment: 9 pages, 8 figures

Large format arrays of transition edge sensor (TES) are crucial for the next generation of X-ray space observatories. Such arrays are required to achieve an energy resolution of $\mathrm{\Delta }E 3 eV full-width-half-maximum (FWHM) in the soft X-ray energy range. We are currently developing X-ray microcalorimeter arrays as a backup option for the X-IFU instrument on board of ATHENA space telescope, led by ESA and foreseen to be launched in 2031. In this contribution, we report on the development and the characterization of a uniform 32 × 32 pixel array with (length × width) 140 × 30 $\mu$ m $^2$ TiAu TESs, which have a 2.3 $\mu$ m thick Au absorber for X-ray photons. The pixels have a typical normal resistance $R_{\mathrm{n}}$ = 121 m $\Omega$ and a critical temperature $T_{\mathrm{c}}\sim$ 90 mK. We performed extensive measurements on 60 pixels out of the array in order to show the uniformity of the array. We obtained an energy resolutions between 2.4 and 2.6 eV (FWHM) at 5.9 keV, measured in a single-pixel mode at AC bias frequencies ranging from 1 to 5 MHz, with a frequency domain multiplexing (FDM) readout system, which is developed at SRON/VTT. We also present the detector energy resolution at X-ray with different photon energies generated by a modulated external X-ray source from 1.45 keV up to 8.9 keV. Multiplexing readout across several pixels has also been performed to evaluate the impact of the thermal crosstalk to the instrument's energy resolution budget requirement. This value results in a derived requirement, for the first neighbour, that is less than 1 $\;\times\; 10^{-3}$ when considering the ratio between the amplitude of the crosstalk signal to an X-ray pulse (for example at 5.9 keV).

We are developing a kilo-pixels Ti/Au TES array as a backup option for Athena X-IFU. Here we report on single-pixel performance of a 32$\times$32 array operated in a Frequency Division Multiplexing (FDM) readout system, with bias frequencies in the range 1-5 MHz. We have tested the pixels response at several photon energies, by means of a $^{55}$Fe radioactive source (emitting Mn-K$\alpha$ at 5.9 keV) and a Modulated X-ray Source (MXS, providing Cr-K$\alpha$ at 5.4 keV and Cu-K$\alpha$ at 8.0 keV). First, we report the procedure used to perform the detector energy scale calibration, usually achieving a calibration accuracy better than $\sim$ 0.5 eV in the 5.4 - 8.9 keV energy range. Then, we present the measured energy resolution at the different energies (best single pixel performance: $\Delta$E$_{FWHM}$ = 2.40 $\pm$ 0.09 eV @ 5.4 keV; 2.53 $\pm$ 0.10 eV @ 5.9 keV; 2.78 $\pm$ 0.16 eV @ 8.0 keV), investigating also the performance dependency from the pixel bias frequency and the count rate. Thanks to long background measurements ($\sim$ 1 day), we finally detected also the Al-K$\alpha$ line at 1.5 keV, generated by fluorescence inside the experimental setup. We analyzed this line to obtain a first assessment of the single-pixel performance also at low energy ($\Delta$E$_{FWHM}$ = 1.91 eV $\pm$ 0.21 eV @ 1.5 keV), and to evaluate the linearity of the detector response in a large energy band (1.5 - 8.9 keV)., Comment: Accepted for publication in IEEE Transactions on Applied Superconductivity for ASC2020 special issue

CNES (French Space Agency) is in charge of the development of the X-IFU instrument for Athena. The main sensor array detection chain sub-system of the X-IFU instrument is one of the major sub-subsystem of the instrument, as the main contributor to the performance. This sub-system involves major partners of the X-IFU instrument, e.g GFSC, SRON, VTT, APC, and IRAP. The purpose of this paper is to present the baseline of the definition of the X-IFU detection chain in the frame at end of phase A/beginning of phase B. The readout is based on Time Domain Multiplexing (TDM). There are strong design issues which couple the different sub-components of the detection chain (the main sensor array, the cold electronics stages, and the warm electronics). The detection chain environment (thermal, mechanical and EMI/EMC environment) also requires a transverse analysis. This paper focuses on those aspects while providing design description of the sub-components of the detection chain.

We are developing Frequency Domain Multiplexing (FDM) read-out of Transition-Edge Sensors (TESs) for the X-ray Integral Field Unit (X-IFU) on board of the future European X-Ray observatory Athena. The X-IFU Focal-Plane Assembly consists of a $sim$ 3000-pixel array, read out by SQUID-based FDM. The multiplexing readout scheme is a critical technology for the X-IFU instrument because of the cooling and electronic power limits for the satellite. In this contribution, we report on the development of FDM readout technology and on the performance of TESs array under an AC bias at MHz frequencies.

Methane emissions due to accidents in the oil and natural gas sector are very challenging tomonitor, and hence are seldomconsidered in emission inventories and reporting. One of the main reasons is the lack of measurements during such events. Here we report the detection of large methane emissions from a gas well blowout in Ohio during February to March 2018 in the total column methane measurements from the spaceborne Tropospheric Monitoring Instrument (TROPOMI). From these data, we derive a methane emission rate of 120 ± 32 metric tons per hour. This hourly emission rate is twice that of the widely reported Aliso Canyon event in California in 2015. Assuming the detected emission represents the average rate for the 20-d blowout period, we find the total methane emission from the well blowout is comparable to one-quarter of the entire state of Ohio's reported annual oil and natural gas methane emission, or, alternatively, a substantial fraction of the annual anthropogenic methane emissions from several European countries. Our work demonstrates the strength and effectiveness of routine satellite measurements in detecting and quantifying greenhouse gas emission from unpredictable events. In this specific case, the magnitude of a relatively unknown yet extremely large accidental leakage was revealed using measurements of TROPOMI in its routine global survey, providing quantitative assessment of associated methane emissions. © 2019 National Academy of Sciences. All rights reserved.

During its first year in operation the SWIR module of the TROPOMI instrument was calibrated in-flight and its performance was monitored. In this paper we present the results of the in-flight calibration and the ongoing instrument monitoring. This includes the determination of the background signals, noise performance, ISRF stability and stray-light stability. From these results, the number of incurred dead and bad pixels due to cosmic-ray impacts is determined. The light-path transmission is checked by monitoring internal lamp and diffuser stabilities. Due to its high sensitivity for Earth radiation on the eclips side, the calibration strategy for the background (i.e. dark flux and offset) monitoring was adjusted. Trends over the first full year of nominal operations reveal a very stable SWIR module with little to no degradation. The number of newly incurred dead and bad pixels is negligible since the start of operations. Assuming linear degradation of various component, the SWIR module is expected to keep performing within expected parameters for the full operational lifetime.

TROPOMI (the TROPOspheric Monitoring Instrument) is the single instrument aboard the ESA’s Copernicus Sentinel-5 Precursor (S-5P) satellite launched on October 13, 2017 . S-5P is dedicated to monitoring our atmosphere over a period of at least 7 years. Through spectral absorption features within reflected sunlight, TROPOMI measures total column densities of a large number of gases relevant for air quality and climate. This is done at unprecedented spatial resolution of approximately 3.5-7x7 km2. At this resolution, air pollution at scales of midsized cities can be distinguished from its surroundings. In addition, it can be used to estimate other air pollutant quantities such as aerosols. Each gas has a unique spectral fingerprint across the TROPOMI channels, which range from the UV to the infrared. The Short Wavelength Infrared channel, or SWIR, measures reflected sunlight between wavelengths of 2305 to 2385 nanometers. This channel has been designed to accurately determine methane (CH4) and carbon monoxide (CO) columns To obtain scientifically useful values for both gas species, measured spectra require the SWIR channel to be calibrated to a very high precision and accuracy. The requirements are particularly important for the CH4 product to achieve the ambitious S-5P mission goals. A reliable CH4 product will prove invaluable to the atmospheric scientific community in the next decade. The first six months after the launch of S5-P were used a.o. to execute an in-flight calibration campaign. This campaign was performed as a complement to the on-ground calibration campaign. It was designed to (a) take calibration measurements that were unable to be done on-ground, (b) validate on-ground calibration and (c) prepare for the instrument calibration monitoring during regular operations. Here, we report the calibration results obtained by the SRON Level 1 team for the TROPOMI-SWIR channel. This includes the correct method and settings for background corrections (both dark flux and offset), determination of the initial pixel quality map, the evolution of the background correction and quality map during the first 10 months of flight, validation of the on-ground calibration of the instrumental spectral response function (ISRF) and stray light correction.

The X-ray Integral Field Unit (X-IFU) is an imaging microcalorimeter being developed for ESA's Athena X-ray observatory to providing high spectral resolution imaging between 0.2-12 keV, with moderate count-rate capability and a large field-of-view. The X-IFU focal plane assembly (FPA) will contain the instrument's large-format transition edge sensor (TES) microcalorimeter array and its superconducting readout electronics, plus a second TES detector, located behind the main sensor array, is used to detect high-energy cosmic rays and secondary particles passing through the sensor array and enable the rejection of false events that they generate in the sensor array's event list. A Kevlar thermal suspension is used to isolate the detectors at 55 mK from the 2 K environment of the X-IFU instrument cryostat's cold stage, while three layers of shielding are used to allow the detector's to achieve their low-noise performance in the expected on-ground and in-flight electromagnetic and microvibration environment. This paper will describe the preliminary design concept of the X-IFU focal plane assembly and its critical technology building blocks.

The Tropospheric Monitoring Instrument (TROPOMI) is the single instrument on board of the ESA Copernicus Sentinel-5 Precursor satellite. TROPOMI is a nadir-viewing imaging spectrometer with bands in the ultraviolet and visible, the near infrared and the short-wave infrared (SWIR). An accurate instrument spectral response function (ISRF) is required in the SWIR band where absorption lines of CO, methane and water vapor overlap. Therefore a novel method for ISRF determination for an imaging spectrometer was developed and applied to the TROPOMI-SWIR band. The ISRF of all detector pixels of the SWIR spectrometer has been measured during an on-ground calibration campaign. The accuracy of the derived ISRF is well within the requirement for accurate trace-gas retrievals. Long-term in-flight monitoring of the ISRF is guaranteed by the presence of five SWIR diode lasers.

SPEX (Spectropolarimeter for Planetary EXploration) is an innovative, compact remotesensing instrument for measuring and characterizing aerosols in the atmosphere. The shoebox size instrument is capable of accurate full linear spectropolarimetry without moving parts or liquid crystals. High precision polarimetry is performed through encoding the degree and angle of linear polarization of the incoming light in a sinusoidal modulation of the spectrum. Measuring this intensity spectrum thus provides the spectral dependence of the degree and angle of linear polarization. Polarimetry has proven to be an excellent tool to study microphysical properties of atmospheric particles. Such information is essential to better understand the weather and climate of a planet. Although SPEX can be used to study any planetary atmosphere, including the Earth's, the current design of SPEX is tailored to study Martian dust and clouds from an orbiting platform. SPEX’ 9 entrance pupils can simultaneously measure intensity spectra from 0.4 to 0.8 microns, in different directions along the flight direction (including two limb viewing directions). This way, the scattering phase functions of dust and cloud particles within a ground pixel are sampled while flying over it. SPEX can provide synergy with instruments on rovers and landers, as it provides an overview of spatial and temporal variations of the Martian atmosphere.

We present the status of our immersed diffraction grating technology, as developed at SRON and of their multilayer optical coatings as developed at CILAS. Immersion means that diffraction takes place inside the medium, in our case silicon. The high refractive index of the silicon medium boosts the resolution and the dispersion. Ultimate control over the groove geometry yields high efficiency and polarization control. Together, these aspects lead to a huge reduction in spectrometer volume. This has opened new avenues for the design of spectrometers operating in the short-wave-infrared wavelength band. Immersed grating technology for space application was initially developed by SRON and TNO for the short-wave-infrared channel of TROPOMI, built under the responsibility of SSTL. This space spectrometer will be launched on ESA's Sentinel 5 Precursor mission in 2015 to monitor pollution and climate gases in the Earth atmosphere. The TROPOMI immersed grating flight model has technology readiness level 8. In this program CILAS has qualified and implemented two optical coatings: first, an anti-reflection coating on the entrance and exit facet of the immersed grating prism, which reaches a very low value of reflectivity for a wide angular range of incidence of the transmitted light; second, a metal-dielectric absorbing coating for the passive facet of the prism to eliminate stray light inside the silicon prism. Dual Ion Beam Sputtering technology with in-situ visible and infrared optical monitoring guarantees the production of coatings which are nearly insensitive to temperature and atmospheric conditions. Spectral measurements taken at extreme temperature and humidity conditions show the reliability of these multi-dielectric and metal-dielectric functions for space environment. As part of our continuous improvement program we are presently developing new grating technology for future missions, hereby expanding the spectral range, the blaze angles and grating size, while optimizing performance parameters like stray light and wavefront error. The program aims to reach a technology readiness level of 5 for the newly developed technologies by the end of 2012. An outlook will be presented.

The Tropospheric Monitoring Instrument TROPOMI is ready for system level verification. All sub-units have been integrated and tested and final integration at Dutch Space in Leiden has been completed. The instrument will be subjected to a testing and calibration program and is expected to be ready for delivery to the spacecraft early 2015. Using TROPOMI measurements, scientists will be able to improve and continue the study of the Earth’s atmosphere and to monitor air quality, on both global and local scale. TROPOMI is a passive UV-VIS-NIR-SWIR imaging spectrograph and as such is the next step in a series of successful instruments like SCIAMACHY, GOME and OMI. TROPOMI is the only instrument on the Sentinel 5 Precursor satellite (S5P), indicating also its function as a forerunner for the Sentinel 5 instrument. Compared with its predecessors, TROPOMI will be a major improvement in terms of spatial resolution and data quality. In previous papers on TROPOMI, emphasis has been on the performance specifications and on some novel technologies applied in TROPOMI. This paper provides a short recapitulation of TROPOMI’s main features, presents some test results obtained and provides an overview of the verification steps still to come. Subsystem test results are very promising and we anticipate that TROPOMI will fully meet the user’s expectations.

The TROPospheric Monitoring Instrument (TROPOMI) is a sun-backscatter imaging spectrometer. It is the single instrument on board ESA’s Copernicus Sentinel-5P satellite, which is now planned for launched in early 2017.

The OMI instrument is an ultraviolet-visible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction with a 115° wide swath, which enables global daily ground coverage with high spatial resolution. This paper presents a selection of in-flight radiometric and CCD detector calibration and performance monitoring results since the launch in July 2004. From these examples it will be shown that OMI is performing very well after more than four years in orbit. It is shown how the OMI irradiance measurement data have been used to derive a high resolution solar reference spectrum with good radiometric calibration, good wavelength calibration and high spectral sampling. The surface reflectance climatology derived from three years of in-orbit OMI measurement data is presented and discussed. The OMI mission may possibly be extended in 2009 for another two or four years, depending on the performance of the instrument. By 2013-2014 OMI on EOS-Aura and SCIAMACHY on ENVISAT will have reached more that twice their anticipated lifetimes. In order to guarantee continuity of Earth atmosphere tropospheric and climate measurement data new instrumentation shall be available around that time. A successor of OMI and SCIAMACHY, named TROPOspheric Monitoring Instrument (TROPOMI), scheduled for launch by the end of 2013, is discussed in this paper.

The Tropospheric Monitoring Instrument (TROPOMI) on-board the Sentinel-5 Precursor satellite is an Earth-observing spectrometer with bands in the ultraviolet, visible, near infrared and short-wave infrared (SWIR). It provides daily global coverage of atmospheric trace gases relevant for tropospheric air quality and climate research. Three new techniques will be presented that are unique for the TROPOMI-SWIR spectrometer. The retrieval of methane and CO columns from the data of the SWIR band requires for each detector pixel an accurate instrument spectral response function (ISRF), i.e. the normalized signal as a function of wavelength. A new determination method for Earth-observing instruments has been used in the on-ground calibration, based on measurements with a SWIR optical parametric oscillator (OPO) that was scanned over the whole TROPOMI-SWIR spectral range. The calibration algorithm derives the ISRF without needing the absolute wavelength during the measurement. The same OPO has also been used to determine the two-dimensional stray-light distribution for each SWIR pixel with a dynamic range of 7 orders. This was achieved by combining measurements at several exposure times and taking saturation into account. The correction algorithm and data are designed to remove the mean stray-light distribution and a reflection that moves relative to the direct image, within the strict constraints of the available time for the L01b processing. A third new technique is an alternative calibration of the SWIR absolute radiance and irradiance using a black body at the temperature of melting silver. Unlike a standard FEL lamp, this source does not have to be calibrated itself, because the temperature is very stable and well known. Measurement methods, data analyses, correction algorithms and limitations of the new techniques will be presented.

TROPOMI is the single instrument on ESA’s Sentinel 5 precursor satellite to be launched in October 2016. TROPOMI will measure the atmospheric constituents absorbing in the UV-SWIR wavelength range, being O3, NO2, SO2, CH4, CO, CH2O, and aerosol properties. TROPOMI is a sun back-scatter instrument in the line of SCIAMACHY and OMI with 4 spectrometer bands and a spectral resolution of 0.25 – 0.5 nm. Following the earlier sensors, firstly the spatial resolution is improved by a factor 6 (OMI) to 7 x 7 km2 and at the same time the sensitivity by an order of magnitude. The paper discusses the instrument performances as acquired from on-ground performance / calibration measurements. For the calibration an extremely condensed measurement campaign of 4 months 24/7 measurements was performed with virtually no slack and still gathering all of the data necessary from on-ground measurements. Given the fact that the trace gas signals and their variation in the measured spectra can be quite small, calibration is crucial to get accurate results and this illustrates that TROPOMI is a highly success driven and efficient programme. TROPOMI / Sentinel-5p bridges the data streams from on one hand OMI and SCIAMACHY and on the other hand the future Sentinel-5. It is the first of a series of satellites from the Copernicus programme devoted to air quality and will soon be ready for use.

Immersed gratings offer several advantages over conventional gratings: more compact spectrograph designs, and by using standard semiconductor industry techniques, higher diffraction-efficiency and lower stray-light can be achieved. We present the optical tests of the silicon immersed grating demonstrator for the Mid-infrared E-ELT Imager and Spectrograph, METIS. We detail the interferometric tests that were done to measure the wavefront-error and present the results of the throughput and stray-light measurements. We also elaborate on the challenges encountered and lessons learnt during the immersed grating demonstrator test campaign that helped us to improve the fabrication processes of the grating patterning on the wafer.

The ESA (European Space Agency) Sentinel-5 Precursor (S-5 P) is a low Earth orbit polar satellite to provide information and services on air quality, climate and the ozone layer in the timeframe 2015-2022. The S-5 P mission is part of the Global Monitoring of the Environment and Security (GMES) Space Component Programme. The payload of the mission is the TROPOspheric Monitoring Instrument (TROPOMI) that will measure key atmospheric constituents including ozone, NO2, SO2, CO, CH4, CH2O and aerosol properties. TROPOMI has heritage to both the Ozone Monitoring Instrument (OMI) as well as to the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY). The S-5 P will extend the data records of these missions as well as be a preparatory mission for the Sentinel-5 mission planned for 2020 onward. The mission is pre-operational and is the link between the current scientific and the operational Sentinel-4/-5 missions. This contribution describes the science and mission objectives, the mission and the instrument, and the data products. While building on a solid foundation of the heritage instruments, the S-5P/TROPOMI mission is an exciting step forward with a strong focus on the troposphere. This is achieved by a combination of a high spatial resolution and improved signal-to-noise, as well as dedicated data product development. It is anticipated that the S-5 P mission will make a large contribution to the monitoring of the global atmospheric composition, as well as to the scientific knowledge of relevant atmospheric processes. © 2012 Elsevier Inc.

A Superconducting Integrated Receiver (SIR) was proposed more than 10 years ago and has since then been developed up to the point of practical applications. We have demonstrated for the first time the capabilities of the SIR technology for heterodyne spectroscopy both in the laboratory and at remote operation under harsh environmental conditions for atmospheric research. Within a SIR the main components needed for a superconducting heterodyne receiver such as an SIS-mixer with quasi-optical antenna, a Flux-Flow oscillator (FFO) as the local oscillator, and a harmonic mixer to phase-lock the FFO are integrated on a single chip. Light weight and low power consumption combined with broadband operation and nearly quantum limited sensitivity make the SIR a perfect candidate for future airborne and space-borne missions. The noise temperature of the SIR was measured to be as low as 85 K, with an intermediate frequency band of 4-8 GHz in double sideband operation; the spectral resolution is well below 1 MHz. The SIR was implemented in the three-channel balloon-borne instrument TELIS (TErahertz and submillimeter LImb Sounder) that detects spectral emission lines of stratospheric trace gases (like ClO and BrO). These gases even in small quantities can have a significant impact on the atmosphere because they speed up certain chemical processes, such as ozone depletion.

The performance of the SCIAMACHY detectors has been monitored since launch. Only minor degradation of the silicon-based UV–Vis detectors and the lattice-matched InGaAs NIR detector is observed. The degradation of the NIR extended-wavelength InGaAs detector arrays, however, which are used for the first time in a space-based remote sensing application, is unexpectedly large. The degradation of individual detector pixels is abrupt and mostly leads to excessively high (spread in) dark current. Evidence is presented that non-ionizing radiation due to trapped-protons leads to displacement damage to the InGaAs detector material. The current degradation rate leads to a loss of approximately 50 out of 1024 pixels per channel per year.

In this report we present design and first experimental results for development of the submm superconducting integrated receiver spectrometer for Terahertz Limb Sounder (TELIS). TELIS is a collaborative European project to build up a three-channel heterodyne balloon-based spectrometer for measuring a variety of atmospheric constituents of the stratosphere. The 550 - 650 GHz channel of TELIS is based on a phase-locked Superconducting Integrated Receiver (SIR). SIR is an on-chip combination of a low-noise Superconductor-Insulator-Superconductor (SIS) mixer with quasioptical antenna, a superconducting Flux Flow Oscillator (FFO) acting as Local Oscillator (LO), and SIS harmonic mixer (HM) for FFO phase locking. A number of new solutions were implemented in the new generation of SIR chips. To achieve the wide-band performance of the spectrometer, a side-feed twin-SIS mixer and balanced SIS mixer with 0.8 µm2 junctions integrated with a double-dipole (or double-slot) antenna is used. An improved design of the FFO for TELIS has been developed and optimized providing a free-running linewidth between 10 and 2 MHz in the frequency range 500 - 700 GHz. It is important to ensure that tuning of a phase-locked (PL) SIR can be performed remotely by telecommand. For this purpose a number of approaches for the PL SIR automatic computer control have been developed. All receiver components (including input optical elements and Martin-Puplett polarization rotating interferometer for single side band operation) will be mounted on a single 4.2 K plate inside a 40 × 180 × 80 mm3 box. First measurements give an uncorrected double side band (DSB) noise temperature below 250 K measured with the phase-locked FFO; more detailed results are presented at the conference.

TELIS (Terahertz and submm Limb Sounder) is a cooperative European project to develop a three-channel heterodyne balloon-based spectrometer for measuring a variety of atmospheric constituents within the lower stratosphere. The 600-650GHz channel is based on a phase-locked Superconducting Integrated Receiver (SIR). SIR is the on-chip combination of a low-noise SIS mixer with quasioptical antenna, a superconducting Flux Flow Oscillator (FFO) acting as Local Oscillator (LO) and an SIS harmonic mixer (HM) for FFO phase locking. A number of new solutions was implemented in the new generation of SIR chips. To achieve the wide-band performance of the spectrometer, a side-feed twin-SIS mixer with 0.8 /spl mu/m/sup 2/ junctions integrated with a double-dipole (or double-slot) antenna is used. A Fourier transform spectrometer (FTS) test demonstrated a possibility to obtain the required instantaneous bandwidth for the SIS mixer. To ensure the autonomous operation of the phase-locked SIR on the balloon a number of approaches for the PLL SIR automatic control have been developed.

ESA's new Earth observation satellite ENVISAT was launched successfully on 2002-02-28. Among nine other instruments it is carrying the new imaging spectrometer SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography). This paper covers part of the calibration and validation efforts during the first seven months of SCIAMACHY in orbit with special emphasis on the application of the internal white light source for radiometric calibration. The solar irradiance spectrum measured by SCIAMACHY is presented and compared with a solar spectrum derived by R. L. Kurucz as well as with solar irradiances measured by the UARS instruments SOLSTICE and SUSIM.

The atmospheric chemistry instrument SCIAMACHY is a joint German-Dutch-Belgian contribution to the European Space Agency environmental satellite ENVISAT scheduled for launch in mid 2001. Instrument performance and calibration measurements recently carried out under thermal vacuum conditions have confirmed predicted performance. Algorithm development at SRON using the UV and visible part of the solar spectrum for ozone profile retrieval and the near infrared for carbon monoxide and methane retrieval has shown good progress. In particular, new avenues have been explored for the development of a fast operational algorithm for the retrieval of ozone profiles, including a new forward model based on perturbation theory that is faster than the current operational algorithm, coupled to a new inversion scheme with no use of a-priori ozone profile information. The near-infrared retrieval of CO and CH 4 is expected to yield higher accuracy data products based on the optimization of retrieval using micro-windows. New and advanced SCIAMACHY data products will be piloted in the Netherlands SCIAMACHY Data Centre that complements the operational ENVISAT payload data segment.

We present results of our integrated approach to the development of novel diffraction gratings. At SRON we manufacture prism-shaped silicon immersed gratings. Diffraction takes place inside the high-refractive index medium, boosting the resolving power and the angular dispersion. This enables highly compact spectrometer designs. We are continuously improving the cycle of design, simulation and test to create custom gratings for space and ground-based spectroscopic applications in the short-wave infrared wavelength range. Applications are space-based monitoring of greenhouse and pollution gases in the Earth atmosphere and ground-based SWIR spectroscopy for, a.o., characterization of exo-planet atmospheres [1]. We make gratings by etching V-shaped grooves in mono-crystalline silicon. The groove facets are aligned with the crystal lattice yielding a smooth and highly deterministic groove shape. This enables us to predict the polarized efficiency performance accurately by simulation. Feeding back manufacturing tolerances from our production process, we can also determine reliable error bars for the predicted performance. Combining the simulated values for polarized efficiency with ray-tracing, we can optimize the shape of the grating prism to eliminate unwanted internal reflections. In this contribution we present the architecture of our design and simulation platform as well as a description of test setups and typical results.

The TROPOMI Earth-observing instrument is the single payload on board ESA's Sentinel-5 Precursor mission. It is the successor of the Sciamachy instrument (ESA ENVISAT) and the OMI instrument (NASA EOS/Aura), and combines and improves the best of both instruments. TROPOMI copies the push broom observation geometry of OMI allowing for daily global coverage due to its instantaneous field of view of 108 degrees, or 2600 km swath on ground. From Sciamachy the 2305 - 2385 nm Short-Wave Infra-Red (SWIR) observational band is copied with which methane and carbon monoxide are observed. This paper reports on the development of the SWIR detector module and the detailed characterization of the 1000x256 SWIR Saturn detector array produced by Sofradir (F) as measured with the SRON-developed Front-End Electronics. The detailed characterization comprises not only the regular properties such as dark current, noise and photo-response, but also more complex characteristics including non-linearity and memory. Characterization of the detection module was performed for all operational parameters: detector temperature (135 - 145 K), bias voltage and integration time. Thanks to the detector-characterization program, the operational clocking of the detector could be optimized, resulting in significantly improved performance.

The Tropospheric Monitoring Instrument, TROPOMI, is a passive UV-VIS-NIR-SWIR spectrograph, which uses sun backscattered radiation to study the Earth's atmosphere and to monitor air quality, on both global and local scale. It follows in the line of SCIAMACHY (2002) and OMI (2004), both of which have been very successful. OMI is still operational. TROPOMI is scheduled for launch in 2015. Compared with its predecessors, TROPOMI will take a major step forward in spatial resolution and sensitivity. The nominal observations are at 7 x 7 km2 at nadir and the signal-tonoises are sufficient for trace gas retrieval even at very low albedos (2 to 5%). This allows observations of air quality at sub-city level. TROPOMI has reached CDR status and production of flight model units has started. Flight detectors have been produced and detector electronics is expected to be finished by mid-2013. The instrument control unit is undergoing extensive tests, to ensure full instrument functionality. Early results are promising and this paper discusses these H/W results, as well as some challenges encountered during the development of the instrument. © 2013 SPIE.

We have developed the technology to manufacture an immersed grating in silicon for the Mid-infrared E-ELT Imager and Spectrograph, METIS. We show that we can meet the required diffraction-limited performance at a resolution of 100000 for the L and M spectral bands. Compared to a conventional grating, the immersed grating drastically reduces the beam diameter and thereby the size of the spectrometer optics. As diffraction takes place inside the high-index medium, the optical path difference and angular dispersion are boosted proportionally, thereby allowing a smaller grating area and a smaller spectrometer size. The METIS immersed grating is produced on a 150 mm industry standard for wafers and replaces a classical 400 mm echelle. Our approach provides both a feasible path for the production of a grating with high efficiency and low stray light and improves the feasibility of the surrounding spectrometer optics. In this contribution we describe and compare the classical-grating solution for the spectrometer with our novel immersed-grating based design. Furthermore, we discuss the production route for the immersed grating that is based on our long-standing experience for space-based immersed gratings. We use standard techniques from the semiconductor industry to define grating grooves with nanometer accuracy and sub-nanometer roughness. We then use optical manufacturing techniques to combine the wafer and a prism into the final immersed grating. Results of development of the critical technology steps will be discussed.

TROPOMI is the sun backscatter trace gas instrument on ESA's Sentinel-5 precursor satellite. TROPOMI builds upon a rich heritage from similar instruments, the main ones being SCIAMACHY on ESA's ENVISAT and OMI on NASA's AURA satellite. This paper explains how the technology from the heritage instruments evolved, considering high level design aspects such as geometry for Earth and sun viewing, polarization treatment, spectral calibration and whisk- or push-broom concept and leading to the TROPOMI concept. Netherlands parties have played and continue to play an important role in the relevant instruments. TROPOMI is the single payload on the Sentinel-5 precursor mission. The launch in 2015 is meant to bridge the data gap between OMI and SCIAMACHY and the upcoming Sentinel 5 mission. The instrument is funded jointly by the Netherlands Space Office and by ESA1. Dutch Space acts as overall instrument prime.

A superconducting integrated receiver (SIR) comprises in a single chip a planar antenna combined with a superconductor-insulator-superconductor (SIS) mixer, a superconducting Flux Flow Oscillator (FFO) acting as a Local Oscillator (LO) and a second SIS harmonic mixer (HM) for the FFO phase locking. In this report, an overview of the SIR and FFO developments and optimizations is presented. Improving on the fully Nb-based SIR we have developed and studied Nb–AlN–NbN circuits, which exhibit an extended operation frequency range. Continuous tuning of the phase locked frequency has been experimentally demonstrated at any frequency in the range 350–750 GHz. The FFO free-running linewidth has been measured between 1 and 5 MHz, which allows to phase lock up to 97% of the emitted FFO power. The output power of the FFO is sufficient to pump the matched SIS mixer. Therefore, it is concluded that the Nb–AlN–NbN FFOs are mature enough for practical applications.These achievements enabled the development of a 480–650 GHz integrated receiver for the atmospheric-research instrument TErahertz and submillimeter LImb Sounder (TELIS). This balloon-borne instrument is a three-channel superconducting heterodyne spectrometer for the detection of spectral emission lines of stratospheric trace gases that have their rotational transitions at THz frequencies. One of the channels is based on the SIR technology. We demonstrate for the first time the capabilities of the SIR technology for heterodyne spectroscopy in general, and atmospheric limb sounding in particular. We also show that the application of SIR technology is not limited to laboratory environments, but that it is well suited for remote operation under harsh environmental conditions. Light weight and low power consumption combined with broadband operation and nearly quantum limited sensitivity make the SIR a perfect candidate for future airborne and space-borne missions. The noise temperature of the SIR was measured to be as low as 120 K in double sideband operation, with an intermediate frequency band of 4–8 GHz. The spectral resolution is well below 1 MHz, confirmed by our measurements. Remote control of the SIR under flight conditions has been demonstrated in a successful balloon flight in Kiruna, Sweden.Capability of the SIR for high-resolution spectroscopy has been successfully proven also in a laboratory environment by gas cell measurements. The possibility to use SIR devices for the medical analysis of exhaled air will be discussed. Many medically relevant gases have spectral lines in the sub-terahertz range and can be detected by an SIR-based spectrometer. The SIR can be considered as an operational device, ready for many applications.

We have developed a novel diffraction grating based on lithographical techniques and anisotropic etching in silicon. The grating is designed for the short-wave-infrared channel of the TROPOMI imaging spectrometer that will be launched on ESA's Sentinel 5 Precursor mission to monitor trace gases in the earth atmosphere. Stringent requirements on both the imaging properties and the quality of the spectra translate to a high-tech grating. In our design the dispersion and resolution is increased with a factor 3.4 with respect to conventional gratings by using the grating in immersion, such that diffraction takes place inside the silicon grating material. By lithographic patterning and anisotropic etching of the mono-crystalline silicon we precisely control line spacing and blaze angle. The grating has a line spacing of 2.5 μm and is operated in sixth order. We show that an efficiency of 60% is reached on a 50 x 60 mm2 grating surface. We compare our test results with numerical calculations for grating efficiency for both polarizations and find good agreement. © 2010 Copyright SPIE - The International Society for Optical Engineering.

The balloon-borne instrument TELIS (TErahertz and submillimetre LImb Sounder) is a three-channel superconducting heterodyne spectrometer for atmospheric research use. It detects spectral emission lines of stratospheric trace gases that have their rotational transitions at THz frequencies. One of the channels is based on the superconducting integrated receiver (SIR) technology. We demonstrate for the first time the capabilities of the SIR technology for heterodyne spectroscopy in general, and atmospheric limb sounding in particular. We also show that the application of SIR technology is not limited to laboratory environments, but that it is well suited for remote operation under harsh environmental conditions. Within a SIR the main components needed for a superconducting heterodyne receiver such as a superconductor–insulator–superconductor (SIS) mixer with a quasi-optical antenna, a flux-flow oscillator (FFO) as the local oscillator, and a harmonic mixer to phase lock the FFO are integrated on a single chip. Light weight and low power consumption combined with broadband operation and nearly quantum limited sensitivity make the SIR a perfect candidate for use in future airborne and space-borne missions. The noise temperature of the SIR was measured to be as low as 120 K, with an intermediate frequency band of 4–8 GHz in double-sideband operation. The spectral resolution is well below 1 MHz, confirmed by our measurements. Remote control of the SIR under flight conditions has been demonstrated in a successful balloon flight in Kiruna, Sweden. The sensor and instrument design are presented, as well as the preliminary science results from the first flight. (Some figures in this article are in colour only in the electronic version)

Around 490 GHz relatively strong HDO and H218O emission lines can be found in the submillimeter thermal-emission spectrum of the Earth's atmosphere, along with lines of the principal isotopologue of water vapour. These can be used for remote sensing of the rare/principal isotope ratio in the stratosphere. A sensitivity study has been performed for retrieval simulations of water isotopologues from balloon-borne measurements by the limb sounder TELIS (TErahertz and submillimeter LImb Sounder). The study demonstrates the capability of TELIS to determine, from a single limb scan, the profiles for H218O and HDO between 20 km and 37 km with a retrieval error of ≈3 and a spatial resolution of 1.5 km, as determined by the width of the averaging kernel. In addition HDO can be retrieved in the range of 10–20 km, albeit with a strongly deteriorated retrieval error. Expected uncertainties in instrumental parameters have only limited impact on the retrieval results.

We present the flight configuration and performance of the superconducting integrated receiver (SIR) channel on the TELIS instrument (terahertz and submm limb sounder). The SIR is an on-chip combination of a low-noise SIS mixer with a quasioptical antenna, a superconducting Flux Flow Oscillator (FFO) acting as Local Oscillator (LO) and an SIS harmonic mixer (HM) for FFO phase locking. The SIR has been assembled, fully integrated into the system and thoroughly tested in preparation for the flight campaign in May 2008 (Teresina, Brazil).

SPEX (Spectropolarimeter for Planetary EXploration) is an innovative, compact remote-sensing instrument for detecting and characterizing aerosols. With its 1-liter volume it is capable of full linear spectropolarimetry, without moving parts. High precision polarimetry is performed through encoding the degree and angle of linear polarization of the incoming light in a sinusoidal modulation of the intensity spectrum. This is achieved by using an achromatic quarter-wave retarder, an athermal multiple-order retarder and a polarizing beamsplitter behind each entrance pupil. Measuring a single intensity spectrum thus provides the spectral dependence of the degree and angle of linear polarization. Polarimetry has proven to be an excellent tool to study microphysical properties (size, shape, composition) of atmospheric particles. Such information is essential to better understand the weather and climate of a planet. Although SPEX can be used to study any planetary atmosphere, including the Earth's, the current design of SPEX is tailored to study Martian dust and ice clouds from an orbiting platform: a compact module with 9 entrance pupils to simultaneously measure intensity spectra from 350 to 800 nm, in different directions along the flight direction (including two limb viewing directions). This way, both the intensity and polarization scattering phase functions of dust and cloud particles within a ground pixel are sampled while flying over it. In the absence of significant amounts of dust and clouds, the surface properties can be studied. SPEX provides synergy with instruments on rovers and landers, as it provides a global view of spatial and temporal variations of the planet.

TELIS (TErahertz and submm LImb Sounder) is a three-channel balloon-borne heterodyne spectrometer for atmospheric research. The observational techniques of TELIS can be compared to the presently flying MLS instrument on board NASA's EOS-Aura satellite, but TELIS is built with a new generation of cryogenic heterodyne detectors and novel compact systems suitable for integration into the confined space of a balloon borne cryostat. TELIS will fly on the MIPAS-B2 gondola. The two instruments together will yield the most complete set of stratospheric constituents, measured so far. TELIS is a cooperation between the European institutes DLR (PI-institute), RAL and SRON. First flight foreseen in the spring of 2008 from Teresina, Brasil. The three TELIS receivers provide simultaneous vertical profile measurement of a range of molecules. The 500 GHz channel is developed by RAL and will produce vertical profiles of BrO, ClO, O 3 and N 2 O. The 1.8 THz channel is developed by DLR and will mainly target the OH radical, and will also measure HO 2 , HCl, NO, NO 2 , O 3 , H 2 O, O 2 and HOCl. Finally the 480 - 650 GHz channel is developed by SRON and IREE and will measure profiles of ClO, BrO, O 3 , HCl, HOCl, H 2 O and its 3 isotopomers, H 2 O 2 , NO, N 2 O, HNO 3 , CH 3 Cl and HCN. In this paper, the science and technology of TELIS will be discussed with emphasis on the channel developed by SRON. It contains a Superconducting Integrated Receiver (SIR), which combines on a 4x4 mm 2 chip the low-noise SIS mixer and its quasioptical antenna, a superconducting phase-locked Flux Flow Oscillator (FFO) acting as Local Oscillator (LO) and a SIS harmonic mixer (HM) for FFO phase locking. The latest results from the pre-flight test and integration campaigns will be presented.

We present the flight configuration and performance of the superconducting integrated receiver (SIR) channel on the TELIS instrument (terahertz and submm limb sounder). The SIR is an on-chip combination of a low-noise SIS mixer with a quasioptical antenna, a superconducting flux flow oscillator (FFO) acting as local oscillator (LO) and an SIS harmonic mixer (HM) for FFO phase locking. The SIR has been assembled, fully integrated into the system and is currently being thoroughly tested in preparation for the flight campaign in October 2007 (Teresina, Brazil).

In this report an overview of the results on the development of a single-chip superconducting integrated receiver for the Terahertz Limb Sounder (TELIS) balloon project intended to measure a variety of stratosphere trace gases is presented. The Superconducting Integrated Receiver (SIR) comprises in one chip a planar antenna integrated with a superconductor-insulator-superconductor (SIS) mixer, a superconducting Flux Flow Oscillator (FFO) acting as Local Oscillator (LO) and a second SIS harmonic mixer (HM) for FFO phase locking. As a result of the FFO design optimization a free-running linewidth between 9 and 1.5 MHz has been measured in the frequency range 500-710 GHz resulting in phase-locking of 35 to 95% of the FFO power correspondingly. A new generation of the SIR devices with improved FFO performance and optimized interface between FFO and SIS/HM has been developed and comprehensively tested. As a result all required TELIS parameters were demonstrated., Phase-locked FFO operation over entire SIR channel frequency range has been realized, spectral resolution below 1 MHz has been confirmed by gas cell and CW signal measurements. An uncorrected double side band (DSB) noise temperature below 250 K has been measured with the phase-locked FFO. The intermediate frequency bandwidth 4-8 GHz; has been realized. To ensure remote operation of the phase-locked SIR several procedures for its automatic computer control have been developed and tested.

In preparation for future atmospheric space missions a consortium of Dutch organizations is performing design studies on a nadir viewing grating-based imaging spectrometer using OMI and SCIAMACHY heritage. The spectrometer measures selected species (O3, NO2, HCHO, H2O, SO 2, aerosols (optical depth, type and absorption index), CO and CH4) with sensitivity down to the Earth's surface, thus addressing science issues on air quality and climate. It includes 3 UV-VIS channels continuously covering the 270-490 nm range, a NIR-channel covering the 710-775 nm range, and a SWIR-channel covering the 2305-2385 nm range. This instrument concept is, named TROPOMI, part of the TRAQ-mission proposal to ESA in response to the Call for Earth Explorer Ideas 2005, and, named TROPI, part of the CAMEO-proposal prepared for the US NRC decadal study-call on Earth science and applications from space. The SWIR-channel is optional in the TROPOMI/TRAQ instrument and included as baseline in the TROPI/CAMEO instrument. This paper focuses on derivation of the instrument requirements of the SWIR-channel by presenting the results of retrieval studies. Synthetic detector spectra are generated by the combination of a forward model and an instrument simulator that includes the properties of state-of-the-art detector technology. The synthetic spectra are input to the CO and CH4 IMLM retrieval algorithm originally developed for SCIAMACHY. The required accuracy of the Level-2 SWIR data products defines the main instrument parameters like spectral resolution and sampling, telescope aperture, detector temperature, and optical bench temperature. The impact of selected calibration and retrieval errors on the Level-2 products has been characterized. The current status of the SWIR-channel optical design with its demanding requirements on ground-pixel size, spectral resolution, and signal-to-noise ratio will be presented.

We present a design concept for a new state-of-the-art balloon borne atmospheric monitor that will allow enhanced limb sounding of the Earth's atmosphere within the submillimeter and far-infrared wavelength spectral range: TELIS, TErahertz and submm LImb Sounder. The instrument is being developed by a consortium of major European institutes that includes the Space Research Organization of the Netherlands (SRON), the Rutherford Appleton Laboratory (RAL) will utilize state-of-the-art superconducting heterodyne technology and is designed to be a compact, lightweight instrument cpaable of providing broad spectral coverage, high spectral resolution and long flight duration (~24 hours duration during a single flight campaign). The combination of high sensitivity and extensive flight duration will allow evaluation of the diurnal variation of key atmospheric constitutenets sucyh as OH, HO2, ClO, BrO togehter will onger lived constituents such as O3, HCL and N2O. Furthermore, TELIS will share a common balloon platform to that of the MIPAS-B Fourier Transform Spectrometer, developed by the Institute of Meteorology and Climate research of the over an extended spectral range. The combination of the TELIS and MIPAS instruments will provide atmospheric scientists with a very powerful observational tool. TELIS will serve as a testbed for new cryogenic heterodyne detection techniques, and as such it will act as a prelude to future spaceborne instruments planned by the European Space Agency (ESA).

SCIAMACHY is a UV-vis-near IR spectrograph for atmospheric trace gas monitoring, due to be launched on the ESA ENVISAT in 2000. The SCIAMACHY Instrument Simulation Software was used to aid in the design of the instrument, support on- ground performance and calibration measurements, develop the level 1 algorithms and establish in-flight operational scenarios. The instrument simulator is based on a traveling spectrum approach from entrance aperture to detector electronics. Relevant optical properties of the individual components are used to model the spectrum and polarization state of the light at each component in the instrument. Subsequently, noise properties and electronic effects are added. The resulting simulated signal is directly comparable with recently performed measurements on the assembled instrument under flight representative conditions. In this paper the measured SCIAMACHY instrument performance is discussed on the basis of these simulations, in aid of better instrument knowledge required during space operation.

SFINX (SRON's Fabry-perot INterferometer eXperiment) consists of a 65 - 90 micrometer wavelength spectrometer based on a Fabry-Perot interferometer, and is equipped with both a conventional Ge:Ga photon detector operating at 4 K, and a novel high-temperature superconductor (HTS) bolometer detector operating at 87 K. The spectral resolution is about 8000, or 0.015 cm-1, comparable with the width of the thermal emission lines of the stratospheric species under study. Target molecules are OH, HCl, HO2, and possibly more. The SFINX instrument now under development will fly as a piggy-back instrument on a stratospheric balloon together with the MIPAS-B2 instrument of IMK/FZK (Karlsruhe, Germany), and can be regarded as a proof of concept for a satellite application. Because of its low satellite resource demands, for a satellite application a SFINX like instrument has great advantages with respect to Fourier transform spectrometers or heterodyne receivers. In particular, the HTS bolometer detector can be cooled by mechanical coolers which are presently available in space- qualified versions, thereby avoiding the use of liquid cryogen.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

SCIAMACHY has been selected for the ESA environmental satellite ENVISAT with the objective to carry out atmospheric research in the UV, VIS, and IR spectral range. The most innovative parts of the instrument are the low- noise InGaAs semiconductor focal plane arrays covering the 1.0-2.4 micrometers wavelength range. For the first time InGaAs focal plane arrays with an extended wavelength range have become space qualified. In this paper theory and measurement of the dark current and noise behavior of these detectors is presented. Each InGaAs focal plane array consists of a 1024 pixel linear photo-detecting sliver and two 512 pixel multiplexing read-out chips. Each multiplexer contains 512 individual charge transimpedance amplifier and correlated double sampling circuits. A cylindrical lens, integrated in the detector housing, focuses the light on detector in the cross-dispersion direction. The InGaAs composition of the detectors is tuned to match the required wavelength range. Measurements have been performed of the dark current and noise as function of temperature and bias voltage in order to relate their performance to theory presented in this paper. InGaAs detectors sensitive to 2400 nm wavelength achieve dark current levels as low as 20-100 fA per detector pixel area of 1.25 (DOT) 10 -4 cm 2 at an operating temperature of 150 K and a bias voltage of 2 mV. Lower temperatures further reduce the dark current but also decrease the quantum efficiency at long wavelengths, yielding no net gain in performance. The development programme of these SCIAMACHY detectors has been carried out by Epitaxx Inc., for and in cooperation with the Space Research Organization Netherlands.