This PDF file contains the front matter associated with SPIE Proceedings Volume 11858, including the Title Page, Copyright information, and Table of Contents.

In recent years the Earth observation (EO) programmes of the European Space Agency (ESA) have been dramatically extended. They now include activities that cover the entire spectrum of the wide EO domain, encompassing both upstream and downstream developments, i.e. related to flight elements (e.g. sensors, satellites, supporting technologies) and to ground elements (e.g. operations, data exploitation, scientific applications and services for institutions, businesses and citizens). In the field of EO research missions, ESA continues the successful series of Earth Explorer (EE) missions. The last additions to this series include missions under definition, namely Harmony (the tenth EE) and four candidates for the 11th EE: CAIRT (Changing Atmosphere InfraRed Tomography Explorer), Nitrosat (reactive nitrogen at the landscape scale), SEASTAR (ocean submesoscale dynamics and atmosphere-ocean processes), WIVERN (Wind Velocity Radar Nephoscope). On the smaller programmatic scale of the Scout missions, ESA is also developing two new missions: ESP-MACCS (Earth System Processes Monitored in the Atmosphere by a Constellation of CubeSats) and HydroGNSS (hydrological climate variables from GNSS reflectometry). Another cubesat-scale mission of technological flavor is also being developed, Φ-sat-2. Furthermore, in collaboration with NASA, ESA is defining a Mass change and Geosciences International Constellation (MAGIC) for monitoring gravity variations on a spatio-temporal scale that enables applications at regional level, continuing - with vast enhancements - the successful series of gravity mapping missions flown in the last two decades. The key features of all these missions will be outlined, with emphasis on those relying on optical payloads. ESA is also developing a panoply of new missions for other European institutions, namely Eumetsat and the European Union, which will be briefly reviewed too. These operational-type missions rely on established EO techniques. Nonetheless some new technologies are applied to expand functional and performance envelopes. A brief resume’ of their main features will be provided, with emphasis on the new Sentinel missions for the EU Copernicus programme.

Today, space is experiencing a revolution: from large space agencies, multimillion dollar budgets, and big satellite missions to spin-off companies, moderate budgets, and fleets of small satellites. Some have called this the “democratization” of space, in the sense that it is now more accessible than it was just a few years ago. To a large extent, this revolution has been fostered on one side by the standardization of the platforms’ mechanical interfaces, and on the other side by the technology developments coming from mobile communications. Standard platform’s mechanical interfaces have led to standard orbital deployers, and new launching capabilities. The technology developed for cell phones has brought more computing resources, with less power consumption and volume. Small satellites are used as pure technology demonstrators, for targeted scientific missions, mostly Earth Observation, some for Astronomy, and they are starting to enter in the field of communications, as huge satellite constellations are now becoming more possible. In this lecture, the most widely used nano/microsats form factors, and its main applications will be presented. Then, the main Scientific Earth Observation and Astronomy missions suitable to be boarded in SmallSats will be discussed, also in the context of the rising Constellations of SmallSats for Communication. Finally, the nanosat program at the Universitat Politècnica de Catalunya (UPC) will be introduced, and the results of the FSSCAT mission will be presented.

Currently, Japan Aerospace Exploration Agency (JAXA), Japan Meteorological Agency (JMA) and Japan Space Systems (JSS) are operating major Earth Observation Satellites. Ibuki (GOSAT) carrying TANSO-CAI and -FTS, GOSAT-2 carrying TANSO-CAI2 and -FTS2, Shizuku (GCOM-W) carrying AMSR2, Daichi-2 (ALOS-2) carrying PALSAR-2 + CIRC, DPR on GPM-core satellite of NASA, and Shikisai (GCOM-C) carrying SGLI, are being operated by JAXA under cooperation with some domestic agencies, such as Ministry of Environment (MoE), National Institute of Information and Communications Technology (NICT). JMA is operating weather satellite Himawari-8 and -9 on geostationary orbit. JSS are operating ASTER on EOS-Terra satellite of NASA and HISUI on ISS. For coming satellites or instruments, JAXA is going to operate CPR on EarthCARE satellite of ESA, ALOS-3 carrying the “wide-swath and high-resolution optical imager”, ALOS-4 carrying PALSAR-3 and GOSAT-GW carrying TANSO-3 + AMSR-3 as follow-on mission for GOSAT-2. In addition to follow-on mission studies, several new studies are underway for near future missions, such as Lidar altimeter mission, Wind Lidar mission and new geostationary missions for land observation and GHG observation.

Global Change Observation Mission-Climate (GCOM-C) was developed as a satellite following Global Change Observation Mission-Water (GCOM-W), and successfully launched on December 23, 2017. We learned from GCOM series satellites that our rigorous analysis of the components on both the satellites allowed us to develop them efficiently and to operate stably. GCOM-C has been operating stably even now, over three years after its launch. The Second-Generation Global Imager (SGLI) initial calibration and validation activities were completed and GCOM-C/SGLI products were publicly released in December 2018, currently we are preparing to release Ver.3. We ware plan twice updates (Ver.2 was updated on June 29, 2020. Ver.3 is preparing) to improve our products accuracy during 5-years mission period. In this report, we present about the status of GCOM-C operation after the launch including sensor calibration, SGLI products and data processing and providing.

Hyperspectral Imager Suite (HISUI) is a hyperspectral sensor for a remote sensing on the International Space Station (ISS). HISUI is composed of one radiometer that obtains spectral images of 185 bands from the visible to shortwave-infrared region with the ground sampling distance (GSD) of 20 meters for the cross track and 31 meters for the along track. The sensor system is the follow-on mission of the Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) in the visible to shortwave infrared region. The observation data of the hyperspectral sensor is expected to an important role in the future spatial-spectral data for the resource exploration, disaster monitoring, environmental observation, agriculture, forestry and fisheries, etc. The tests of a flight model of HISUI have been carried out successfully in 2019 and HISUI is operating on the ISS. This paper describes the design and the performances of the flight model of HISUI and also presents radiometric performances in orbit.

This paper describes the current status of Advanced Land Observing Satellite-4 (ALOS-4) and its two instruments: Phased Array-type L-band Synthetic Aperture Radar-3 (PALSAR-3) and SPace based Automatic Identification System for ships Experiment (SPAISE3). PALSAR-3 is the successor of PALSAR-2 which is boarded on ALOS-2(Advanced Land Observing Satellite-2) and has 3m resolution and 200km observation swath by using Digital Beam Forming (DBF) technology. Its antenna consists of 5 panels and is about 20% larger than PALSAR-2, to get the same NESZ (Noise Equivalent Sigma Zero) performance for a wide observation swath. PALSAR-3 will be in the same orbit and observation geometry as PALSAR-2 to enable InSAR time series analysis over 10 years using both of PALSAR-2 and PALSAR-3 data. PALSAR-3 has several observation modes with different spatial resolutions to fulfill the mission requirements. In order to achieve temporally and spatially consistent data, systematic observation, a Basic Observation Scenario (BOS) will be defined. SPAISE3 is a high-performance satellite AIS receiver and the successor of SPAISE2 boarded on ALOS2. SPAISE3 has eight antennas and adopts ground-based DBF method as one of effective countermeasures against radio wave interference regions. Using this technology, the detection success rate of ships in heavy marine traffic area will be improved compared to SPAISE2.

This paper presents the results of a conceptual study of an Earth observation system. The new system represents a technical breakthrough in larger telescope aperture, which is necessary to improve spatial resolution. The system makes it possible to improve temporal resolution while maintaining a practical spatial resolution. The observation system was designed to have a latency of 30 minutes from the observation request until data delivery. The mission study emphasized the system's need to immediately assess the situation when a natural disaster occurs and thus reduce human suffering. Due to the required spatial resolution, the optical system needed to have a 3.6 m aperture. A synthetic aperture optical sensor with a segmented primary mirror was investigated and adopted. The segmented-mirror optical system was the most technically challenging and was investigated using a full-scale one-segment prototype to evaluate the feasibility and identify technical risks. This paper presents the tentative design of the sensor and satellite system and reports on the technical demonstration and the proposed geostationary observation system.

The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing as part of the EC’s Copernicus programme, a space-borne observing system for quantification of anthropogenic carbon dioxide (CO2) emissions. The anthropogenic CO2 monitoring (CO2M) mission will be implemented as a constellation of identical LEO satellites, to be operated over a period > 7 years and measuring CO2 concentration in terms of column-averaged dry air mole fraction (denoted as XCO2). Industrial activities for the phase B2CD have been kicked-off Mid 2020. The demanding requirements necessitate a payload composed of a suite of instruments, which simultaneously perform co-located measurements. A push-broom imaging spectrometer will perform co-located measurements of top-of-atmosphere radiances in the Near Infrared (NIR) and Short-Wave Infrared (SWIR) at high to moderate spectral resolution (NIR: 747- 773nm @0.1nm, SWIR-1: 1595-1675nm @0.3nm, SWIR-2: 1990-2095nm @0.35nm) for retrieving XCO2. These observations are complemented in the same spectrometer by measurements in the visible spectral range (405-490 nm @0.6nm), providing vertical column measurements of nitrogen dioxide (NO2) that serve as a tracer to high temperature combustion of fossil-fuel and related emission plumes (e.g. from coal-fired power plants and cities). High quality retrievals of XCO2 will be ensured even in situations of large aerosol loading, thanks to co-located measurements of aerosol resulting from a Multiple- Angle Polarimeter (MAP). Polarimetric measurements are performed over 40 angular views and in six spectral channels between 410 and 865 nm. Finally, due to the strong sensitivity of the XCO2 retrieval to cloud contamination, a three-band Cloud Imager (CLIM) will provide the required capacity to detect small tropospheric clouds and cirrus cover with an accuracy of 1% to 5% and a sampling better than 400 m.

This paper will describe the current status of instrument pre-development activities that are being performed in the frame of a potential Aeolus Follow-On mission (Aeolus-2). The main inputs for a future Doppler Wind Lidar (DWL) instrument that have been used are: lessons learned from the Aeolus development phases and the in-orbit operations and performance; initial inputs from EUMETSAT including a total mission lifetime of 10-15 years utilizing 2-3 spacecraft with a launch of the first satellite in 2029, increased robustness and operability of the instrument, and an emphasis on reduction of recurrent costs; the maximum utilization of the demonstrated design heritage; and a number of recommendations for the requirements of a future DWL mission from the Aeolus Scientific Advisory Group. These inputs have been collated and combined into a set of preliminary requirements which have been used as the basis for a dedicated Instrument Consolidation Study. The aim of the study is to adapt the design (taking account of the heritage retention principle), in order to improve the performance of the instrument for the Aeolus follow-on mission. In addition, three instrument subsystem pre-development activities have been kicked-off: two laser transmitter engineering model pre-developments aiming at increasing the output energy level up to 150mJ in UV and the robustness of the laser transmitter and the pre-development of an improved detector with better vertical sampling. These developments have the aim to demonstrate that issues identified from the above are resolved and that the technology levels are sufficiently mature for the follow-on DWL mission.

The cheapest method for an instrument to perform radiometric monitoring in orbit is to compare its radiometric response from a scene to the known radiance of that same scene. This is known as vicarious calibration. The known radiance of this scene comes mostly from other space instruments. The limiting factors of this vicarious calibration approach arise from differences in the acquisition time and illumination/viewing geometry between the two measurements. Earth scenes may change over time, which limits vicarious calibration to quasi stable scenes. The level of stability of these scenes limits the level of accuracy that can be achieved. Likewise, the bi-directional scattering distribution function (BSDF) of the observed scene is likely to cause differences in observed radiance if the illumination and/or viewing geometry changes. If the observation of the scene is at the same time, stability of the scene is no longer an issue, and if the observation is at the same geometry then BSDF effects will cancel, and direct comparison is possible. This is rarely the case unless the instrument is on the same satellite. In this paper we present the design and measurement concept of such a small, on-board calibration instrument; the Absolute Radiometric Reference Instrument (ARRI). We believe this concept will revolutionize the approach to in-orbit absolute reflectance calibration.

The HYPerspectral Stereo Observing System (HYPSOS) is a novel remote sensing pushbroom instrument able to give simultaneously both 3D spatial and spectral information of the observed features. HYPSOS is a very compact instrument, which makes it attractive for both possible planetary observation and for its use on a nanosat, e.g. for civilian applications. This instrument collects light from two different perspectives, as a classical pushbroom stereocamera, which allows to realize the tridimensional model of the observed surface, and then to extract the spectral information from each resolved element, thus obtaining a full 4-dimensional hypercube dataset. To demonstrate the actual performance of this novel type of instrument, we are presently realizing a HYPSOS prototype, that is an instrument breadboard to be tested in a laboratory environment. For checking its performance, we setup an optical facility representative of a possible flight configuration. In this paper we provide a description of HYPSOS concept, of its optomechanical design and of the ground support equipment used to characterize the instrument. An update on the present status of the experiment is finally given.

The compositions of asteroids are of interest for the planetary sciences, mining, and planetary defense. The main method for evaluating these compositions is reflectance spectroscopy. Spectroscopic measurements performed from Earth can not resolve how different materials are distributed on the asteroids, making flyby-- and rendezvous missions necessary for obtaining detailed information. Using the CubeSat platform could reduce the costs of these missions, but it also sets constraints on the payload mass and volume. One small and light instrument capable of producing spatially resolved spectral data is a hyperspectral imager based on the Fabry-Perot interferometer. We propose a method of calculating reflectance data from hyperspectral radiance images of an asteroid and a computationally evaluated incident spectral radiance. The proposed method was tested in laboratory conditions with inconclusive results. The obtained reflectances differed from reference measurements, but we believe this was caused by improper calibration of the used imager rather than errors in the method itself.

NASA’s Multi-Angle Imager for Aerosols (MAIA) mission, under development at the Jet Propulsion Laboratory, is designed to study the adverse health effects of different types of particulate air pollution. Planned for launch in late 2022 for a 3-year mission, the MAIA satellite instrument will focus on a selected set of metropolitan target areas, where air quality monitors and health data are available. Aerosol concentration and speciation are inferred from multi-angle measurements of backscattered sunlight in 14 spectral bands from 350-2200 nm, with bands near 442, 645 and 1040 nm measuring the degree (DoLP) and angle of linear polarization (AoLP) in addition to radiance. The pushbroom camera has a ~240-km cross-track field of view with a nadir resolution of ~200 m, and is mounted onto a biaxial gimbal to provide along-track view angles within ±60°, to extend the field of regard to ±48°, and to view the instrument’s onboard calibrator (OBC) and dark target. The OBC consists of a sunlit transmissive diffuser, followed by 12 polarizers at different orientations. MAIA’s polarimetry is implemented using miniature wiregrid polarizers on the focal plane array, and dual photoelastic modulators (PEMs) and achromatic quarter-wave plates to rapidly rotate the polarization. The resulting ~26-Hz intensity modulation encodes the linearly polarized and total radiance in each pixel, leaving the DoLP and AoLP insensitive to gain calibration. We report on the polarimetric calibration of the MAIA camera using a vacuum-compatible polarization state generator, consisting of a 1600W Xenon lamp, 12-inch integrating sphere, and rotating high-extinction polarizer. Mueller-matrix-based calibration coefficients for each detector pixel are derived from measurements at multiple polarizer angles, and are used to correct the measurements for instrumental polarization aberrations. Prior to flight, the calibrated MAIA camera is panned across the OBC to characterize its output, using uniform illumination with an irradiance similar to the Sun.

The Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission was selected by NASA as part of the Earth Venture--Instrument (EVI-3) program. The TROPICS Engineering Qualification Unit has been refurbished for flight, and a launch is planned for July 2021 on a SpaceX Falcon 9 to a 550-km sun synchronous orbit. This Pathfinder mission will provide risk reduction for the subsequent TROPICS constellation mission, which comprises six CubeSats in three low-Earth low-inclination orbital planes, with launches provided by Astra in early 2022. Each of these identical CubeSats will host a high performance radiometer to provide temperature profiles using seven channels near the 118.75 GHz oxygen absorption line, water vapor profiles using three channels near the 183 GHz water vapor absorption line, imagery in a single channel near 90 GHz for precipitation measurements (when combined with higher resolution water vapor channels), and a single channel at 205 GHz that is more sensitive to precipitation-sized ice particles. The TROPICS mission highlights a number of aspirations of future earth observing sysems, including high revisit rate, system resilience, rapid technology infusion, and low cost. This paper presents these elements with an eye toward future operational architectures for weather and climate monitoring.

Synthetic Aperture Radar (SAR) imaging systems operate by emitting radar signals from a moving object, such as a satellite, towards the target of interest. Reflected radar echoes are received and later used by image formation algorithms to form a SAR image. There is great interest in using SAR images in computer vision tasks such as classification or automatic target recognition. Today, however, SAR applications consist of multiple operations: image formation followed by image processing. In this work, we train a deep neural network that performs both the image formation and image processing tasks, integrating the SAR processing pipeline. Results show that our integrated pipeline can output accurately classified SAR imagery with image quality comparable to those formed using a traditional algorithm, showing that fully neural network based SAR processing pipeline is feasible.

Optical remote sensing satellites, utilized for Earth observation applications, provide the essential information for space, scientific, and technological aspects. The design of a remote sensing satellite camera is the outcome of a huge effort performed by the satellite camera designers and several trade-off studies, to fulfil the requirements. The capability of estimating the quality of the images acquired by the satellite camera is a basic part of the design analysis procedure. This paper proposes a model for estimating the image quality based on a detailed simulation of the imaging chain within the entire space system. Two different types of imaging sensors are involved in the simulation; the TDI-CCD and the new concept of the TDI-CMOS. Numerous issues are considered in the simulation involving the radiometry, atmosphere, optics, imaging sensor, satellite attitude, and smear perspectives. The modeling and simulation processes start with a ground original image as an input to the model. The input radiance is computed using MODTRAN software to simulate the main atmospheric effects. The image radiance is calculated and converted into photons producing digital numbers, representing the simulated image. The assessment of the simulated images is performed through different quality metrics; the modulation transfer function (MTF), signal-to-noise ratio (SNR), and minimum resolvable contrast (MRC). Finally, it may conclude that, for a definite case study, the performance of the TDI CCD is slightly better than that of TDI CMOS in the case of image MTF. On the other hand, the TDI CMOS has better SNR and MRC than TDI CCD.

In October 2024, European Space Agency’s Hera mission will be launched, targeting the binary asteroid Didymos. Hera will host the Juventas and Milani CubeSats, the first CubeSats to orbit close to a small celestial body performing scientific and technological operations. The primary scientific payload of the Milani CubeSat is the SWIR, NIR, and VIS imaging spectrometer ASPECT. The Milani mission objectives include mapping the global composition and the characterization of the binary asteroid surface. Onboard data processing and evaluation steps will be applied due to the limited data budget for the downlink to Earth and to perform the technological demonstration of a novel semi-autonomous hyperspectral imaging mission. Before downloading, the image data is evaluated in terms of sharpness and coverage and processed by compression. The challenges and their proposed solutions for the data processing part of the mission are investigated through studies. Since most noise contributors are unknown until Milani is activated, different noises are studied based on previous missions and derived from hyperspectral images taken in a laboratory environment mimicking the real-life situation. The hyperspectral camera technology in the laboratory is similar to the one used in the ASPECT imager payload. Both ASPECT and the imagers utilized in our measurements are based on employing a Fabry-Pérot interferometer as an adjustable transmission filter. The imagers are also designed and built by the same party, the Technical Research Centre of Finland (VTT). Best performing denoising techniques for each noise type are discussed on the one hand for the entire datacubes and on the other hand for the spatial domain only since the mission includes images taken only at specific wavebands. The advantage of applying denoising for the whole datacube comes from the internal dependencies between the wavebands, allowing efficient processing. A trade-off study for several noise reduction algorithms is presented. The goal is to implement efficient image processing algorithms with low computational complexity, securing the successful execution of the mission.

The VIIRS has a unique spectral band that can sense reflected light from space during both day and nighttime, thus referred to as the day-night band (DNB). This band operates in three different gain stages: low, mid, and high gain (LG, MG, and HG) that cover a remarkable dynamic range with its HG stage being extremely sensitive to low-light scenes. Similar to its reflective solar bands, the VIIRS uses an on-board solar diffuser for its DNB LG stage calibration, whereas the DNB MG and HG calibrations are performed using relative or ratioing approaches. In this paper, we provide an assessment of VIIRS DNB HG calibrations using stars that appear in the field-of-view of its space view (SV), focusing on the computation of the gain trending and associated tool development. We also describe various strategies and procedures developed for DNB HG calibration stability monitoring and inter-comparisons among different VIIRS instruments and discuss some of the complications and limits to this approach, including under-sampling of the stellar image, saturation, and crowding. For S-NPP VIIRS, it includes the use of the modulated relative spectral response (RSR) resulting from wavelength-dependent degradation of the sensor optics. Results show that the star-based response trending for the DNB HG is consistent with that derived from on-board solar diffuser and that the calibration difference between S-NPP and N-20 VIIRS DNB requires additional effort to address, especially for research studies and applications using data from both sensors.

The MODIS thermal emissive bands (TEB) radiometric calibration uses a quadratic function for the instrument response, and the calibration coefficients look-up tables (LUTs) are updated using the response of an on-board blackbody (BB). After more than 21 and 19 years on-orbit, the TEB performances for Terra and Aqua MODIS have been generally stable. However, contamination from electronic crosstalk, a known issue since prelaunch, has affected the L1B image quality and measurement accuracy. In addition to the photovoltaic (PV) longwave infrared (LWIR) bands crosstalk correction included in Terra MODIS Collection 6.1 (C6.1), a crosstalk correction for select detectors in the Terra and Aqua mid-wave infrared (MWIR) and Aqua PV LWIR bands are applied in C7. The mission-long crosstalk coefficients for the selected detectors are derived and populated in the form of LUTs. The crosstalk correction is applied to both on-orbit calibration and the algorithm used to generate Earth-view L1B products. Among these detectors, the Aqua MODIS band 24 detector 1 crosstalk has the largest impact on image quality, with striping observed over cold scenes for both Terra and Aqua MODIS. The images of C7 L1B and C6.1 are compared to assess the impact of the correction. Additional assessments using Earthview measurements and inter-comparison also revealed the need for improvement of calibration stability and consistence for select bands. Additional improvements for long-term stability and mirror side consistence were developed using quasideep convective clouds (qDCC), Dome-C, ocean, desert, and inter-comparison with other instruments.

Calibration of Terra and Aqua MODIS reflective solar bands (RSB) has evolved significantly since the launch of the first MODIS instrument on the Terra satellite more than 21 years ago. In NASA’s current Collection 6 and 6.1 Level 1B products (C6/C6.1 L1B), the RSB calibration algorithm continues to rely primarily on the onboard solar diffuser to calibrate the instrument gain. Lunar observations are used to track on-orbit changes in the response versus scan angle (RVS), and data from pseudo-invariant desert sites are used to apply adjustments to the gain and RVS calibration for select bands. The resulting reflectance products have in general shown a very stable performance. In recent years, some performance degradation has been noted for a few bands and algorithm changes have been tested to further improve the calibration accuracy for the upcoming Collection 7 (C7) L1B reprocess. In this paper, we present the MODIS RSB calibration improvements that will be included in C7. Major improvements include: applying polarization correction to the desert data before using it to generate RVS for Terra bands 8, 9, 3, and 10; using ocean scene data and an interband calibration approach to correct for long-term drift of Terra bands 11 and 12; applying an updated crosstalk correction to Terra SWIR bands over the entire mission; and using data from deep convective clouds in Terra SWIR band calibration, including the addition of time-dependent RVS for bands 5 and 26. All other minor calibration changes are also covered. Overall, the reflectance differences at nadir between C6.1 and C7 are within a few percent, though the differences increase in some cases at large scan angles. The Terra visible (3, 8-12) and SWIR bands (5-7, 26) have the most significant improvements. For all other Terra bands and all Aqua bands, the C7-C6.1 differences are mostly within 1%.

The MODIS instruments aboard the Terra and Aqua satellites and the VIIRS instruments aboard the SNPP and NOAA-20 satellites each contain several arrays of Si detectors that measure Earth-reflected radiance in the visible and near-infrared spectral range. Even in the absence of incident light, the Si detectors are occasionally excited by high energy charged particles that pass through the spacecraft. These particle radiation events are, fortunately, infrequent enough that they do not lead to significant degradation of the detectors and they do not have a significant impact on the Earth scene radiance images. On the other hand, they are frequent enough that the cumulative data from many years on orbit may provide valuable diagnostic information about the sensors. In this paper, we provide some basic statistics on the frequency and magnitude of the particle excitation events for MODIS and VIIRS and explore the usefulness of this data as a measure of electronic crosstalk. Large amounts of crosstalk can degrade the quality of the Earth images, so it is crucial to have methods to characterize and correct for it on-orbit, which has previously been done for MODIS using lunar image analysis. The particle excitations can manifest as single-pixel spikes in the otherwise dark space view background, which may be an ideal source for evaluating crosstalk. We derive crosstalk coefficients between the NIR band detectors of Terra MODIS, and compare them to coefficients previously derived from lunar observations. The same approach is applied to SNPP VIIRS, which does not show any significant electronic crosstalk. While the HgCdTe detectors used in the MODIS and VIIRS infrared bands can also be excited by particle radiation, the magnitudes of the excitations are much smaller compared to the Si detectors and in general are not large enough to be useful for examining crosstalk.

The Multi-View, Multi-Channel, Multi-Polarisation Imaging (3MI) instrument is a passive scanning radiometer dedicated to aerosol characterisation, air quality and numerical weather prediction, as well as climate monitoring and more generally characterisation of the microphysical properties of the atmosphere, including clouds. The 3MI mission has heritage from the POLarization and Directionality of the Earth's Reflectances (POLDER) on-board the ADEOS and PARASOL satellites. Compared to POLDER, 3MI has improved spatial coverage, higher spatial resolution, and an expanded spectral range with more spectral bands in the reflective part of the spectrum, all bands being polarised (except absorption bands). It is scheduled for launch on the EPS-SG platform in 2024. 3MI’s mission is to provide images of the Earth Top-Of-Atmosphere outgoing radiance for 12 different spectral bands (from 410nm to 2130nm), with 3 different polarisers (-60°, 0° and +60°), and 14 angles. The design consists of two optical heads (SWIR and VNIR) composed by a detector along with a filter and polariser rotating wheel and a wide field-of-view optics. The multi-view is achieved by several successive overlapping acquisitions of the same Earth-Atmosphere target under different angles thanks to the instrument large field of view. Using the experience acquired for the POLDER missions, CNES is cooperating with EUMETSAT and is providing the necessary analysis and expertise for the in-flight calibration and/or validation of several key parameters, both for geometric and radiometric aspects. Here we present the different methodologies that will be used to achieve that goal.

The Sentinel-2 (S-2) mission is part of the Copernicus Space Component (CSC) – the European Commission’s Earth Observation program. It is designed to provide systematic global acquisitions of land and coastal areas at high-spectral resolution and with high revisit frequency, generating products feeding a large range of operational applications in domains such as agriculture, ecosystems management, natural disaster monitoring or water quality monitoring. The mission is currently in its operational phase with a constellation of two satellites (Sentinel-2A and Sentinel-2B) launched in 2015 and 2017 respectively, each designed for a minimum lifetime of 7.25 years with consumables sized for 12 years. In order to provide a long-term service (up to 20-year of overall mission duration), two additional satellites Sentinel-2C and Sentinel-2D were funded by the European Commission and are presently under development. The main S-2 payload, the Multi Spectral Instrument (MSI), is a push broom instrument with 13 spectral bands covering from the visible and the near infrared (VNIR) to the short wave infrared (SWIR). Operational experience from S-2 A&B, with new applications raising up, demonstrates how crucial and valuable accurate instrument spectral characterization is becoming. In the frame of S-2 C&D development, an enhanced spectral characterization method was implemented in order to address all the pixels of the Field Of View (FOV) on all the bands of the instrument with high precision, accuracy and sampling. This paper describes this novel approach as well as the test setup used to characterize both VNIR channels operated at ambient pressure and SWIR channels operated at low temperature in vacuum conditions. The results of the spectral response of the thirteen bands obtained during the MSI-C test campaign executed between 2019 and 2020 and their associated accuracy are presented. Finally, the impact of spectral response variation on typical targets and the added value for the users from the accurate knowledge of the spectral response is addressed.

The Sentinel 2 (S2) orthorectification process converts the Level-1B (L1B) radiance data generated at sensor geometry into orthorectified top-of-atmosphere (TOA) reflectance data, which is the Level-1C (L1C) product distributed to users. However, the spatial resampling operations involved by the orthorectification also transform the radiometric quality of the data. In this work, we evaluate the impact of the S2 orthorectification process on the radiometric quality of the data, with focus on the radiometric uncertainty budget. In particular, the study reports the variation of the S2 noise model attached to the S2 L1C metadata and the effects on the L1C uncertainty products produced by an offline processor named Radiometric Uncertainty Tool (RUT). This assessment is divided into three steps, namely noise propagation, interpolation uncertainty, and covariance impact. For the first of them, the results show that noise is reduced by a factor of 0.65 from L1B to L1C data, both by simulations and an empirical approach that estimates noise variance from real L1B and L1C acquisitions at different sites. Regarding the evaluation of the interpolation uncertainty, aerial orthoimages are convolved by the S2 Point Spread Function (PSF) and upsampled into the S2 spatial resolution. The study shows that, from this S2-like image, a distribution of interpolation errors (i.e. uncertainty) can be associated to the standard deviation of the neighbouring pixels. Finally, the covariance change due to the spatial resampling has been simulated with a propagation of the L1B radiance errors in order to understand the increase of correlation between neighbouring pixels

In this paper, we will report our recent efforts in achieving high performance in Antimonides type-II superlattice (T2SL) based infrared photodetectors using the barrier infrared detector (BIRD) architecture. The high operating temperature (HOT) BIRD focal plane arrays (FPAs) offer the same high performance, uniformity, operability, manufacturability, and affordability advantages as InSb. However, mid-wavelength infrared (MWIR) HOT-BIRD FPAs can operate at significantly higher temperatures (<150K) than InSb FPAs (typically 80K). Moreover, while InSb has a fixed cutoff wavelength (~5.4 μm), the HOT-BIRD offers a continuous adjustable cutoff wavelength, ranging from ~4 μm to <15 μm, and is therefore also suitable for long wavelength infrared (LWIR) as well. The LWIR detectors based on the BIRD architecture has also demonstrated significant operating temperature advantages over those based on traditional p-n junction designs. Two 6U SmalSat missions CIRAS (Cubesat Infrared Atmospheric Sounder) and HyTI (Hyperspectral Thermal Imager) are based on JPL’s T2SL BIRD focal plane arrays (FPAs). Based on III-V compound semiconductors, the BIRD FPAs offer a breakthrough solution for the realization of low cost (high yield), high-performance FPAs with excellent uniformity and pixel-to-pixel operability. Furthermore, we will discuss the advantages of the utilization of all digital read out integrated circuits with HOT-BIRDs.

In 2019, IRnova launched a full-scale production of a reduced size, weight and power integrated detector dewar cooler assemblies (Oden MW; VGA format with 15 μm pixel pitch) covering the full mid-wavelength infrared spectral domain (3.7 μm – 5.1 μm). Oden MW exhibits excellent performance with operating temperatures up to 110 K at F/5.5 with typical values of temporal and spatial noise equivalent temperature of 22 mK and 7 mK, respectively, and an operability higher than 99.85%. More recently, IRnova developed a new detector design with a cut-off wavelength of 5.3 μm which can potentially allow an operating temperature of the detector up to 150K with excellent performance demonstrated on single pixels with a quantum efficiency as high as 46% at 4 µm without antireflection coating, a turn on bias lower than -100 mV and a dark current density as low as 8 × 10^-6 A/cm², which is a factor of < 5 higher than Rule07. The dark current was also found independent of the device size ranging from 10 μm to 223 μm indicating that surface leakage currents are not limiting the dark current. The achievable operating temperature of an FPA made of this new detector design has been estimated to be <150 K with F/5.5 optics. These outstanding results demonstrate that this new generation of detector design is an excellent candidate for future high operating temperature and high-definition focal plane array.

The Large Format Array-Controller (aLFA-C) development is sponsored by the ESA Cosmic Vision Program, resulting in an interfacing ASIC matched to the larger, clearer, lower-temperature focal plane arrays (FPA’s) demanded for future astronomical science missions [1]. The goal of this ASIC is to control and readout detector arrays and address the stringent operation requirements detector in a cryogenic infrared (IR) spacecraft environment [2]. Destined for use in space, the device is designed “radiation hard” throughout, and uses the imec DARE technology in the digital core and Caeleste’s “RH” in the analog part. The ASIC is capable of driving power supplies and bias lines, of delivering timing sequences, of acquiring the output signals of a wide range of FPA technologies, at temperatures even below 30K, with high accuracy; and of interfacing with the warm front-end electronics via a SpaceWire interface. For external use, the chip contains 12 regulators (LDO or normal regulator), 32 accurate voltage sources (VDAC), 8 programmable current sources (IDAC), 36 analog to digital converters(ADC) running at 100 kHz sampling rate, of which 32 can be interleaved to allow higher conversion rates on fewer channels, each input signal can be amplified and conditioned by a low noise programmable gain amplifier, and then digitized by a 16-bit successive approximation analog-to-digital converter (SAR-ADC). The programmable sequencer allows for 8 signal loops with a maximum word depth of 512, capable to work together with the embedded S8 microprocessor for more elaborate schemes. The specified operating range is 35 – 400K, yet the ASIC is found to be fully functional from 25K to room temperature (elevated temperature not yet tested). This paper presents an overview of the aLFA-C ASIC design with descriptions of its analog, mixed-signal and digital circuit blocks, test environment and preliminary test results.

Broadband antireflection (AR) optical coatings covering the ultraviolet (UV) to infrared (IR) spectral bands have many potential applications for various NASA systems. The performance of these systems is significantly limited by signal loss due to reflection off substrates and optical components. Tunable nanoengineered optical layers offer omnidirectional suppression of light reflection/scattering with increased optical transmission to enhance detector and system performance particularly over IR band wavelengths. Nanostructured AR coatings enable the realization of optimal AR coatings with high laser damage thresholds and reliability in extreme low temperature environments and under launch conditions for various NASA applications. We are developing and advancing high-performance AR coatings on GaSb and various other substrate types for spectral bands ranging from UV to LWIR. The nanostructured AR coatings enhance transmission of light through optical components and detector devices by greatly minimizing reflection losses over range of incidence angles, providing substantial improvements over more conventional thin film AR coating technologies. In this paper, we review our latest developments in high performance nanostructurebased AR coatings, focusing primarily on recent efforts in designing and fabricating AR coatings for the LWIR spectral band for performance improvements in airborne and space detector applications.

With the advent of “New Space” and the explosion of nanosatellite missions, an extended latitude is offered for the emergence of innovative technological devices such as novel compact solid state UVC sensors. In this context, β-Ga₂O₃-based photodetectors are emerging as very promising candidates to overcome current technological limits for UVC detection in Space. Indeed, monitoring UVC solar radiation, and more specifically the Herzberg continuum (200-242nm), is fundamental to understand its’ impact on the earth’s climate and build better chemistry-climate models [1]. It is also, however, extremely challenging to achieve due to the harsh operating environment including large thermal variations, high energy particles, ionizing radiation and filter contamination due to satellite outgassing. The Ultra Wide Band Gap semiconductor, β-Ga₂O₃ (Eg ~ 4.9eV at 253nm), is intrinsically solar blind, radiation-hard and thermally-robust. Furthermore, the authors have recently shown that the bandgap can be engineered upwards through Al alloying so as to obtain optical transitions from 253 down to 200nm [2,3]. This allows the realization of β-Ga₂O₃-based photodetectors with peak operating wavelengths which capture the Herzberg continuum selectively and thus, dispenses with the need for short pass filters. Therefore, these β-Ga₂O₃-based photodetectors are excellent candidates to monitor the Herzberg continuum from Space. Hence, they have been selected to be integrated on the INSPIRE-Sat 7 (International Satellite Program in Research and Education) nanosatellite (“2U” CubeSat) which will monitor the Herzberg continuum on a low Earth orbit, following a prototype mission UVSQ-Sat (INSPIRE-Sat 5) successfully launched in January 2021 [4]. This work presents the realization of β-Ga₂O₃-based photodetectors going from the wafer to the final packaged sensors including device architecture development, photolithography, contacting, probing, singulation, packaging, stringent robustness testing (in a simulated environment) and performance binning, so as to obtain the final flight model photodetectors.

The mission of the Earth Observation Programme (EOP) Directorate in ESA is to keep observation techniques at the most updated technological state, creating cutting-edge products and expanding Earth science knowledge. In recent years, in the spirit of its own mission, the EOP Directorate investigated the capabilities offered by small satellites establishing three different lines of mission implementation activities depending on the overall objective i.e., novel Earth Observation techniques in Earth science (Scout class), industrial innovation to support European industry competitiveness (InCubed class) or In Orbit Demonstration (IOD) of innovative EO techniques enabled by disruptive technologies such as artificial intelligence (Φ-Sat class). [ “Overview of ESA’s Earth Observation upcoming small satellites missions” M. Pastena et Al. 34th Small Satellite Conference] Although these mission lines are all relatively new, they have produced a consistent number of studies, ideas and developments and in particular many CubeSat based mission developments. This paper will present an overview of all the missions under development in the ESA Earth Observation Programmes which are based on CubeSats, starting with preliminary in-flight results of the Φ-Sat-1 mission launched in Q3 2019 representing the first ESA Earth Observation CubeSat mission. Within the Φ-Sat class a follow-on mission, namely Φ-Sat-2, has just started its preparation phase and it is planned to be launched by the end of 2022. Concerning the Scout programme, for the CubeSat-based missions the focus will be on the ESP-MACCS mission, based on a small constellation of three 12U CubeSats, that has been selected for implementation as the first Scout mission. In parallel to the ESP-MACCS mission implementation, as part of the follow-up of the Scout consolidation phase, risk retirement activities will be initiated for the NanoMagSat and TANGO missions. Finally, the paper will present the InCubed missions based on CubeSat currently under preparation, i.e. MANTIS and Hyperfield.

Passive microwave temperature and water vapor sounding of the Earth’s atmosphere provides one of the most valuable quantitative contributions to weather prediction and is a key factor in initializing and validating climate models. Recent advances in the capabilities and robustness of small satellite components and systems provide an opportunity for NOAA, EUMETSAT and other operational agencies to explore the value of launching passive microwave sounder/imagers and complementary instruments on small spacecraft, including CubeSats, for relatively small investments. This provides the potential for deployment of microwave sounder constellations in low-Earth orbit (LEO) to substantially shorten revisit times. In this context, the first CubeSat-based multi-frequency microwave sounder to provide global data over a substantial period is the Temporal Experiment for Storms and Tropical Systems Demonstration (TEMPEST-D) mission. This mission was designed to demonstrate on-orbit capabilities of a five-frequency millimeter-wave radiometer to enable a future constellations of 6U CubeSats with low-mass, low-power millimeter-wave sensors to observe changes in convection and water vapor vertical profiles with revisit times on the order of minutes instead of hours. TEMPEST millimeter-wave radiometers provide observations at five frequencies from 87-181 GHz, with spatial resolution ranging from 12.5-25 km. To demonstrate technology necessary for deployment and operation of a CubeSat constellation of microwave sounders, the TEMPEST-D satellite was launched on May 21, 2018 from NASA Wallops to the ISS and successfully deployed into a 404-km orbit at 51.6° inclination on July 13, 2018. Now more than two years and nine months into its mission, the TEMPEST-D radiometer continues to provide science-quality data. The TEMPEST-D mission met all of its Level-1 requirements within the first 90 days of operations and achieved TRL 9 for both instrument and spacecraft systems. Validation of the TEMPEST-D brightness temperatures was performed over 50 days during a 13-month period through comparisons with GPM/GMI and MHS on NOAA-19, MetOp-A, MetOp-B and MetOp-C satellites. Results demonstrated calibration accuracy of TEMPEST-D within 1 K and stability within 0.6 K, as well as no evidence of any significant changes over time or with instrument temperature. TEMPEST-D brightness temperatures have been used to demonstrate data assimilation into NOAA numerical weather prediction models as well as atmospheric science parameter retrievals. In summary, on-orbit results show that TEMPEST-D is a very well-calibrated, highly stable radiometer, indistinguishable in performance from larger, more expensive operational sensors. Over its mission lifetime of nearly three years, TEMPEST-D has demonstrated the feasibility of deployment of a constellation of microwave sounders on CubeSats for relatively low cost and short timeline for implementation. A recently-completed CSU study, funded by NOAA, showed the potential for a CubeSat constellation of TEMPEST-based microwave sounders to perform temperature and moisture profiling with shorter refresh times. The InP HEMT low-noise amplifier technology developed for TEMPEST-D receivers for moisture profiling using 87-181 GHz frequencies can be enhanced by adding receivers with temperature profiling frequencies from 114-118 GHz range. The NOAA study demonstrated that a TEMPEST-based constellation of less than 12 CubeSats has the potential to greatly improve revisit times of current polar-orbiting operational microwave sensors.

Adverse air quality impacts human health and climate and has implications for environmental equity. The Compact Hyperspectral Air Pollution Sensor (CHAPS) is a newly designed small imaging spectrometer for remote sensing of nitrogen dioxide (NO2) and other air pollutants from space. It incorporates two emerging technologies, to achieve the miniaturization necessary to fit within a 6U CubeSat. The first is freeform optics, which can be used to reduce the size of an imaging spectrometer without compromising optical performance. We report the science requirements; preliminary, fully freeform and fully reflective optical design of the CHAPS demonstrator, CHAPS-D; and model its performance. The second technology is additive manufacturing, coupled with topology optimization, which has a number of potential advantages over traditional subtractive manufacturing. The instrument mechanical structure, including optical mounts and integral light baffles, and two of the optical elements will be additively manufactured using a high-strength nextgeneration aluminum alloy. We show preliminary results of additive manufacturing tests. CHAPS-D is currently being developed for ground-based and airborne testing.

The Hyper-Angular Rainbow Polarimeter (HARP) Cubesat started data collection in April 2020 from the ISS orbit and is the first Hyper-Angular imaging polarimeter in space. The HARP payload produces pushbroom images at four wavelengths (440, 550, 670 and 870nm) with up to 60 viewing angles at 670 nm and up to 20 along track angles for the other three wavelengths. HARP swath consists of 94 degs in the cross track direction, allowing for a very wide coverage around the globe, and +/-57 degs in the along track direction, providing wide scattering angle sampling for aerosol and cloud particle retrieval. The HARP satellite is still active on orbit and so far have produce a large collection of scenes providing an unprecedented demonstration of the hyperangular retrieval of cloud and aerosol properties from space. This presentation will discuss the performance of the HARP sensor in space, as well as its first results for aerosol and cloud measurements. HARP is preceded by its airborne version, the AirHARP instrument, which has flown in two NASA aircrafts to demonstrate the capabilities of the HARP payload. The HARP payload is also a precursor to the HARP-2 polarimeter that will fly on the NASA PACE mission to collect global data on aerosol and cloud particles.

Nanosatellite and CubeSat remote sensing platforms for Earth observation missions are steadily growing in number due to their great potential for cost effectiveness. For this reason, there is a significant interest in developing small hyperspectral and multispectral cameras for earth observation compatible with the constraints of these satellite platforms. These cameras offer the advantage of operating at different spectral bands simultaneously, overcoming limitations of single-wavelength cameras, and facilitating tasks such as object classification and material identification. In this context, the use of hyperspectral cameras based on liquid crystal variable retarders (LCVRs) enables the realization of more compact devices, as they can replace dispersive elements, mirrors, and rotating polarization optics, as well as reducing costs, all of which are essential for the emerging small satellite sector. We have recently implemented LCVR technology onboard the Solar Orbiter mission to perform polarization measurements of the incoming light from the Sun. This is the first time to our knowledge this technology has been implemented for space instrumentation. Based on our implementation of LCVR technology for space, we are developing new instrumentation for hyperspectral imaging based on the principles of Fourier transform infrared spectroscopy (FTIR). We will demonstrate several hardware configurations of the hyperspectral camera using LCVRs of different thicknesses. We will discuss the hardware specifications, driving schemes and trade-offs associated with the use of LCVRs in a FTIR configuration.

For evaluation of system design validity of earth observation sensors in the early development phase, recently many endto-end performance simulators to predict final product accuracy based on sensor hardware design as well as data analysis algorithm were developed. Nevertheless, these performance simulators are very complicated because of most earth observation satellite projects have become too huge, as a result, it is hard to grasp the whole picture of the simulator. We are planning to develop generic end-to-end performance simulator. Its basic strategy is to make the simulator to be simple and to be able to explain the whole system including the relation between instrumental design and the final product, and not to introduce outside complicated black-box model. We started with fundamental mathematics which describe sensor performance and retrieval algorithm. A performance simulator of a Fourier Transform Spectrometer (FTS) applied for green house observation like Greenhouse Gases Observing SATellite (GOSAT) was constructed as a model case. Key performance of the sensor for determination of CO₂ column averaged mole fractions (XCO₂) during retrieval process are determination accuracy of the instrumental line shape (ILS) and Signal to Noise Ratio (SNR). The ILS was calculated based on mathematical models with instrumental design parameters of GOSAT, and then expected synthetic atmospheric absorption spectrum obtained by the sensor was simulated based on the ILS and an atmospheric forward model. The atmospheric forward model was based on Lambert-Beer law together with the solar irradiance and CO₂ absorption cross section database with assumed XCO₂, as well as vertical profile of background atmospheric temperature and pressure from meteorological model. Retrieved XCO₂ was simulated with its accuracy based on various ILS determination accuracy and SNR. We also applied this simulator to on-orbit data of GOSAT and retrieved XCO2 from Level-1B spectra during period of April 1-30, 2021. As a result, the mean XCO₂ during the period of interest agreed with the mean XCO₂ of Level-2 products provided by the National Institute for Environmental Studies (NIES) by a difference of 0.5 ppm. In this way, we not only constructed the end-to-end simulator from scratch, but also evaluated the validity of the output products by the actual on-orbit data.

The LSA-SAF produces and disseminates variables for the characterization of terrestrial ecosystems and their role in the energy balance of Earth, such as land surface fluxes and vegetation parameters, taking full advantage of remotely sensed data from EUMETSAT satellites and sensors. All LSA SAF products are distributed according with EUMETSAT data policy and have been classified as essential and are distributed free of charge. This work provides an overview of the SEVIRI/MSG and AVHRR/MetOp LSA-SAF vegetation products. The LSA-SAF vegetation products provide consistent long-term data records with well-characterized uncertainty, which are required by the scientific community to model terrestrial ecosystems and energy cycles at regional and global scales. Three vegetation products (FVC, LAI, FAPAR) are provided from SEVIRI/MSG and AVHRR/MetOp observations. The vegetation products are routinely validated and provide pixel-wise uncertainty estimates and quality flag information to identify unreliable observations. The entire archive with the latest version of the several retrieval algorithms has been reprocessed in recent years in order to generate a homogeneous Climate Data Records (CDRs) of these vegetation variables. LSA-SAF has also developed recently two new products, SEVIRI/MSG GPP and EPS/AVHRR CWC. The future generation of new LSA-SAF products derived from the future MTG and EPS-SG satellites, with higher spatial and spectral resolution, will guarantee the continuity of the service.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on-board the Aqua and Terra spacecraft have collected valuable Earth data for the last 19 and 21 years, respectively. MODIS is equipped with various on-orbit calibrators, including a solar diffuser (SD) and solar diffuser stability monitor (SDSM), that are used to monitor changes in the instrument’s gain over time. Nominally, SD calibrations alternate between two configurations: screen open and screen closed. Terra MODIS, however, experienced an anomaly in 2003, which has left the SD door and screen in a permanent open-closed configuration. This resulted in accelerated degradation of the SD on Terra MODIS due to the direct solar radiation exposure every orbit. It also led to an unexpected divergence between the calibration coefficients, m1, or the inverse of the gain, generated using SD data and those generated using lunar observations at the time of the 2003 anomaly. This paper examines the effect of the screen configuration on the Terra SD degradation by analyzing Terra SDSM data and comparing to Aqua. We generate “pseudo-open” Terra SDSM data by modeling the ratio of Aqua screen open and screen closed SDSM data and calculate the Terra SD degradation using this new screen open data. We then examine the effects on our m1 values calculated using this new pseudo-open SD degradation for Terra. Implementing this new degradation results in a smaller discrepancy between the lunar and SD m1 values after the door anomaly, indicating that there may be a systematic error in the SD degradation calculated with screen closed data.