With the launch of the Geostationary Environment Monitor Spectrometer (GEMS) in 2020, the Tropospheric Emissions: Monitoring of Pollution (TEMPO) in 2023, and the near-term launch of Sentinel 4, the Atmospheric Composition Virtual Constellation, as envisioned by the Committee on Earth Observation Satellites (CEOS), is on its way to being realized. The established atmospheric composition sensor designs, associated retrieval algorithms and the science around the data’s use offers an opportunity to extend the CEOS constellation to the Southern Hemisphere. BAE Systems, Inc. is in a unique position to offer build-to-print geostationary sensors for the Southern Hemisphere based on GEMS and TEMPO. An overview of the GEMS and TEMPO instrument capabilities and the extension of these instruments to the Southern Hemisphere will be presented.

The Earth’s coupled ionosphere and thermosphere play a critical role in the Earth’s Heliospheric system, providing a pathway for energy from the solar wind and magnetosphere to enter the Earth’s upper atmosphere. Ionospheric disturbances and variability caused by this energy occur on timescales from seconds to years and play a crucial role in space weather, with impacts on the performance and reliability of space-borne and ground-based technological systems used for communication, navigation, and surveillance. The Multichannel Thermosphere-Ionosphere Photometer Scanner (MTIPS) instrument is a CubeSat scale instrument for narrowband photometric measurements of excited atomic oxygen and molecular nitrogen species. MTIPS will provide simultaneous high-sensitivity Vacuum Ultra-Violet (VUV) photometer measurements of key atomic oxygen (135.6 nm) and molecular nitrogen Lyman-Birge-Hopfield (LBH) band emissions for targeted (135.6 nm, LBH, and background) nightside, dayside, and auroral zone investigations of the thermosphere and ionosphere.

The 3MI instrument is a multi-directional spectro-polarimeter to fly on-board the Metop-SG platform with a launch scheduled end 2025, as part of EUMETSAT’s EPS-SG system space segment. The performance of the Level-1 products is an important pre-requisite for the quality of the Level-2 products devoted to aerosol and cloud characterisation. Like for all polarimeters, this performance is the result of a system implying many contributors, radiometric as well as geometric. The instrument sensitivity to the polarisation is obviously a crucial part in this budget while it is used in the Level-1 processing to convert the measured radiometry through different polarisers into the physical Stokes vector characterising the observed polarisation. If direct measurements of the polarisation sensitivity, called the Mueller Matrix, can be made through a dedicated on-ground characterisation, a physical understanding of this behaviour is a clear asset. It is indeed important to distinguish in the Mueller Matrix, all the physical contributors which are supposed to play a significant role according the theoretical ray-tracing calculation. These terms are the polariser itself obviously, but also the contribution of the lenses and their polarisation signatures in term of small linear polarisation and retardance. In this paper, the 3MI Proto-Flight Model behaviour measured during the ground campaign, is analysed and a modelling is proposed trying to provide a complete interpretation of the instrumental behaviour. Moreover, this model will be very useful for interpretation of the in-flight vicarious calibration results which will check and monitor this instrumental behaviour.

The most important difficulty encountered in obtaining high-resolution and quality images from earth observation satellites is the image motion that occurs in the focal plane of the optical system due to the orbital movement of the satellite. The orbital motion of satellites requires optical systems to perform their tasks on a fast-moving platform. As a result of this, smear occur in the obtained ground images, this reduces the image quality and is resulting in blurred images. By keeping the exposure time short so that images of the desired region can be captured in a short time to reduce blur, however, in this case, the signal-to-noise ratio of the image and its contrast are reduced, resulting in noisy and poor-quality images. Forward Motion Compensation (FMC) methods make it possible to obtain high quality images by limiting the focal plane image motion caused by the forward motion of satellites. In this research, it has been extensively analyzed why the secondary mirror of RC telescope has been chosen to apply tilt motion for the purpose of FMC, and the best location of the pivot point has been analyzed by using Zemax OpticStudio program. When tilting the secondary mirror, it is important to avoid causing de-focus. In addition, the pivot point must be located in the optical axis directly behind the secondary mirror, and results have shown that a pivot point distance of 24 mm is also sufficient for the mechanical design of the piezo tilt stage. Approximately 52 pixels can be shifted by moving the secondary mirror by 0.015 degrees. This movement allows for an increase in the image exposure time by 52 times. TSM to compensate for forward motion allows high-resolution images to be obtained without degrading image quality by limiting focal plane image motion and still maintaining the diffraction-limited performance of the optical system. This research has been proposed to develop new method to increase the exposure time without need of additional optical element to apply tilt motion, such as scanning mirrors or high cost TDI sensors.

Labsphere, Inc. in conjunction with NASA GSFC and Genesis Engineering Solutions Inc., has developed an innovative, vacuum compatible, calibration spectro-radiometric illumination source with a highly uniform large-area rectangular flat panel active area. This device features a uniquely shaped diffuse integration geometry to achieve high uniformity over a large active output area while maintaining a smaller and more robust overall form-factor when compared to previous designs or integrating spheres. A new liquid-cooled hybrid quartz-tungsten (QT) and light emitting diode (LED) source module has been engineered to provide direct-in-vacuum reference illumination over the full dynamic range and spectrum of the VIIRS instrument’s optical bands during pre-launch testing. The first unit has been demonstrated to meet its requirements using ambient technology and a fully-vacuum-compatible second unit is planned to allow testing in thermal vacuum (TVAC) campaigns. This technology is flexible and capable of meeting the needs of many other instruments/missions requiring this type of test/calibration capability.

A new solid-state source has been developed to emulate the solar spectrum for absolute radiometric calibration of advanced multispectral and hyperspectral imagers. The source is used in conjunction with quartz tungsten-halogen lamps (QTH) on an integrating sphere to provide a solar spectrum matching the AM1.5 spectrum from 385nm to 2500nm. The performance criteria required a source with “smooth” spectral shape to minimize spectral mismatch errors in the calibration as well as minimizing the differences between power in different bands to allow sensor arrays to be calibrated with equivalent integration times. A method has also been developed to quantify the “smoothness” of the calibration spectra and the expected error in the resulting spectral response calibration for measurement of various source spectra.

Recently, NASA Goddard Space Flight Center Biospheric Science Laboratory (Code 618) Field Calibration Lab acquired a new laboratory spectrometer system. With the intention of becoming a standard transfer spectrometer for the lab, the system is comprised of 4 separate units covering the spectral range of 185-2500nm. The Field Calibration Lab has been serving the Earth Sciences Division and specializing in spectral radiometric measurements with Field spectrometers and radiometers. This new system was acquired as a complimentary lab standard to the fieldwork and other transfer work performed by the laboratory’s field spectrometer working standard. This work details the initial lab characterizations of two of the four units that cover the spectral range of 185-740nm and 655-1100nm respectively, with a narrow-band LED-driven light source and a standalone silicon reference detector. The results will be discussed, with some comparisons to a widely used commercially available field spectrometer system. We have found that the new laboratory system can be comparable to the historically used field spectrometer in most circumstances, but with key differences in spectral resolution and sensitivity. As a result, the new system has potential use as an absolute transfer standard, in characterization of fine spectral features and exploration of low-level light sources and environments.

Within the NASA GSFC Code 618 Calibration Laboratory, the Radiometric Calibration Lab (RCL) is focused on maintaining National Institute of Standards and Technology (NIST) traceable calibrated sources and detectors to calibrate, characterize, and monitor remote sensing instrumentation throughout NASA and the larger scientific community.

Among these RCL sources, the Grande broadband source, a 9-lamp 1m diameter integrating sphere with a 25.4cm aperture and PTFE coating housed in a Class 10,000 cleanroom environment, is the workhorse for providing regular NIST traceable calibration services to ground, flight, and remote sensing missions on a consistent basis.

As part of an initiative to improve the Grande calibration uncertainty budget, monitoring spectrometers were recently installed on Grande to provide continuous spectral radiance measurements of the integrating sphere source whenever Grande is in use. This monitoring data is used to characterize Grande’s ramp up stabilization and nominal operation process. Over multiple calibration sessions with Grande, we can observe long term source behavioral changes as the lamps age.

Having continuous monitoring allows us to validate Grande’s stability during remote sensing calibration sessions. As stability data is accumulated and analyzed it results in updated and improved uncertainty budget for calibrations using Grande.

The Joint Polar Satellite System 4 (JPSS-4) Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is the fifth in a series (S-NPP VIIRS, JPSS-1,2,3 VIIRS) of highly advanced polar-orbiting environmental satellites. JPSS-4 VIIRS underwent a comprehensive sensor-level Thermal Vacuum (TVAC) testing at the Raytheon Technologies El Segundo facility in the fall of 2023. While the test program provided characterization for many spatial, spectral, and radiometric aspects of the VIIRS sensor performance, this paper focuses on the radiometric performance of the 14 reflective solar bands (RSB) that cover the wavelength range from 0.41 to 2.3 μm. Key calibration parameters, such as the instrument gain, signal-to-noise ratio (SNR), dynamic range and radiometric uniformity, were derived in a TVAC environment for both the primary and redundant electronics at three instrument temperature plateaus: cold, nominal, and hot. This paper shows that all the JPSS-4 VIIRS RSB detectors have been well characterized, with the key performance metrics being comparable to those of the previous VIIRS instruments. Comparison of radiometric performance to sensor requirements, as well as a summary of key sensor testing and performance issues, will also be presented.

The Visible-Infrared Imaging Radiometer Suite (VIIRS) is a primary sensor on-board both the Suomi-National Polar-orbiting Partnership (SNPP) and Joint Polar Satellite System spacecrafts. SNPP, JPSS-1, and JPSS-2 VIIRS are currently on-orbit, JPSS-3 VIIRS is in spacecraft integration, and JPSS-4 VIIRS completed sensor level thermal vacuum (TVAC) testing in late 2023. TVAC testing covered the spatial, spectral, and radiometric performance of the sensor at three temperature plateaus on both the primary and redundant electronic sides. This paper will focus on the radiometric performance of the 7 thermal emissive bands (TEBs) that cover a spectral range of 3.7 to 12 μm. This includes key instrument performance parameters such as the gain, dynamic range, noise equivalent delta temperature, and absolute radiometric difference. It also includes the performance of the on-board calibrator blackbody (OBCBB). Finally, a comparison of the JPSS-4 VIIRS TEB radiometric performance with previous builds will be discussed. The results of the JPSS-4 VIIRS TVAC testing show that the TEB radiometric performance is consistent with the previous builds. The Sensor Data Record (SDR) quality from JPSS-4 VIIRS is expected to be similar to SNPP, JPSS-1 and -2 VIIRS.

The Joint Polar-Orbiting Satellite System’s (JPSS) flagship instrument is the Visible Infrared Imaging Radiometer Suite (VIIRS) which features a panchromatic band with high dynamic range known as the Day Night Band (DNB). The DNB excels over a wide range of lighting conditions and as such is particularly important for nighttime imagery. In this capacity it has been serving the science community since October 2011 as part of the Suomi NPP, NOAA-20, and NOAA-21 satellites. Two more VIIRS instruments have been produced by Raytheon Corporation and are planned to go into service in 2027 and 2032 extending the current generation of polar orbiting environmental satellites into the next decade.

The last VIIRS instrument, JPSS-4 VIIRS, has been produced and recently underwent extensive environmental testing at Raytheon’s El Segundo test facility in late 2023. Measurements were made in a Thermal Vacuum (TV) chamber at three different instrument temperatures to simulate expected conditions encountered on-orbit. A comprehensive set of calibration coefficients and performance parameters have been generated from these data for both primary and redundant set of electronics. Detailed here is the radiometric calibration of the JPSS-4 VIIRS DNB with its performance in key parameters detailed including Signal-to-Noise Ratio (SNR), dynamic range, and uniformity comparted with the sensor requirement and previous builds.

The NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS) is a key instrument in the JPSS missions (SNPP, JPSS-1-4). Being part of the calibration and validation process, JPSS-4 VIIRS prelaunch geometric performance assessment focuses on the sensor’s spatial response, band-to-band co-registration (BBR), and pointing knowledge. In general, JPSS-4 VIIRS’ prelaunch geometric performance is very good, and consistent with SNPP and JPSS-1-2-3 VIIRS. This paper highlights some specific key findings from the JPSS-4 VIIRS’ prelaunch tests. We first show that with timing adjustments, JPSS-4 VIIRS scan BBR error between VisNIR and SMWIR and LWIR bands has been reduced from 0.11/0.04 M-band sampling intervals to around 0.01 M-band sampling intervals, respectively. Focal Plane Assembly (FPA) rotations are about 0.03 degree in VisVIR, 0.08 degree in SMWIR and LWIR. Another finding from the prelaunch test is that JPSS-4 VIIRS track direction band-to-band co-registration errors between VisNIR and SMWIR and LWIR bands have been improved when compared to JPSS-3. This BBR mis-registration increases when aft‐optics assembly (AOA) temperature decreases. During TVAC cold performance test (AOA temperature is 253K), the track BBR mis-registration is about 0.04 M-band sampling intervals between VisNIR and SMWIR bands, and 0.03 M-band sampling intervals between VisNIR and LWIR bands. By comparison, the track BBR mis-registration in JPSS-3 is 0.10/0.08 M sampling intervals between VisNIR and SMWIR/LWIR bands, respectively. The unsymmetrical Day Night Band (DNB) scan-direction Line Spread Function (LSF) of JPSS-2 VIIRS at different gain stages and aggregation modes have been corrected in J4 VIIRS. Lastly, to correct the scan-to-scan underlaps in J1/J2, the scan rate of J4 VIIRS is increased to 3.546 rad/sec, compared to 3.510 rad/sec of J2. As a result, NOAA IDPS will reduce from 85.35 sec to 85.00 secs in each 48-scan granule, and NASA LSIPS will increase the number of scans from 202 scans in J2 to 204 scans in J4 in each 6-minute granule.

The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is a key component of the Joint Polar Satellite System (JPSS). VIIRS are currently operating on-board the JPSS-1/NOAA-20 and JPSS-2/NOAA-21 spacecraft in addition to the Suomi-National Polar-orbiting Partnership (SNPP) satellite. Two additional VIIRS instruments, designated for JPSS-3 and JPSS-4 have completed their instrument-level pre-launch testing campaigns. Within the pre-launch characterization program, multiple tests are performed to assess the impact of electronic and optical crosstalk between bands and detectors in both ambient and simulated space environment (thermal vacuum) environments. Though the specific crosstalk behavior of each instrument is unique, the overall crosstalk performance has remained steady or improved with each successive unit. Additionally, performance specifications and test procedures have evolved over the JPSS test program, which has spanned over a decade. We present a comprehensive review of VIIRS crosstalk measured during pre-launch testing along with analysis and direct comparisons between VIIRS sensor builds.

Quantifying uncertainties in Atmospheric Infrared Sounder (AIRS) spatial response functions (SpatialRFs) is critical for enhancing the quality of climate data records. Previously, AIRS in-flight SpatialRF calibrations have utilized an incomplete set of pre-flight data obtained during instrument assembly. In our current work, we combined various pre-flight data sets to interpolate a complete set of pre-flight SpatialRFs. Concurrently, we employed two consecutive days of AIRS and Moderate Resolution Imaging Spectroradiometer (MODIS) data to independently retrieve in-flight SpatialRFs for multiple channels and scan angles. Our methodology, based on our previous work, aligns AIRS and MODIS radiances to derive spatially corrected SpatialRFs. This paper compares in-flight SpatialRFs obtained from consecutive days and examines the discrepancies between pre-flight SpatialRFs from a completed set and in-flight SpatialRFs. Employing the total variation distance metric with two days of consecutive data revealed that the average uncertainties in in-flight SpatialRFs are approximately 5%, attributed mainly to noise, which establishes a baseline. In contrast, pre-flight SpatialRFs displayed an average uncertainty of about 16% when compared to the values derived in-flight. Our findings underscore the value of reconstruction techniques to derive in-flight SpatialRFs to validate pre-flight measurements, which is vital for ensuring the long-term reliability and precision of climate data records obtained from AIRS.

The Atmospheric Infrared Sounder (AIRS) was launched on May 4, 2002 on the NASA Earth Observing System (EOS) Aqua spacecraft. AIRS measures the hyperspectral upwelling spectral radiance of the Earth in the infrared from 3.7- 15.4μm in 2378 channels. Instrument raw digital counts are converted to radiances using a hybrid physical, empirical approach that maintains high measurement accuracy with SI traceability. Before launch, a comprehensive On-board Calibration Plan was developed that configures the AIRS instrument into certain modes that enable characterization and/or validation of various performance parameters. Ten of the eleven on-board tests have been performed on-orbit with varying frequencies. This paper addresses three of the tests that focus on the radiometric performance of the instrument including instrumental gain and noise, non-linearity, non-Gaussian noise and stray light effects on the On-Board Calibrator (OBC) Blackbody and Space View (SV), respectively. The Guard Test, C1, uploads A only and B only detector redundancy gain tables that allow characterization of the noise and gain in normal operational mode. The Space View Noise Test, C8, stops the scan mirror while AIRS views space, providing a long, continuous, measurement of a cold target for characterization of instrumental noise and drift. The OBC Float Test, C5, turns off the OBC blackbody to provide a range of observational temperatures to the instrument for calibration of the nonlinearity. All tests show excellent stability of the instrument response, albeit regular non-automated adjustments to the detector redundancy has been required throughout the mission due to normal instrumental aging and radiation hits. Despite the changes, the AIRS Calibration Team has managed to maintain the number of active channels to the values experienced shortly after launch for the life of the mission.

A key parameter of the AIRS spectral calibration is the position of the detector arrays in the focal plane, Yo. Given Yo, the centroid of the spectral response function for each AIRS channel is give by the grating model. A 1µm shift of Yo corresponds to a 1% shift of the centroid of the spectral response functions. Spectral shift at the 0.02µm level are readily detectable. The amplitude of seasonal and diurnal shifts in Yo is about 0.5 µm. Between 2002 and 2024 Yo stayed within 1 µm of −13 µm. This is a tribute to the fact that the AIRS spectrometer and the focal plane are actively temperature controlled. Real-time users are not likely to notice the radiometric effect of a 1 µm variation of the spectral calibration in the presence of other noise and natural variability. However, if left uncorrected changes as small as 1 µm can create false trends in a time series analysis which may interfere with the detection of true climate change signals. Given the spectral calibration, the AIRS data can be presented on a fixed spectral sampling grid. This data is available as the AIRS L1c v6.7 product. An L1c V8 product with consistent processing for 20 years is under development.

Orbital Sidekick's GHOSt (Global Hyperspectral Observation Satellite) constellation had launches in April and June 2023 and in March 2024. These sensors are among the first ever commercial space-based hyperspectral sensors that span the VIS-SWIR range. Post launch, a calibration campaign began to characterize each sensor's optical and radiometric quality. One of the areas of interest that were trended over time are the dark offsets, which are images taken with a closed shutter in front of the entrance slit of the spectrometer. Especially for SWIR-sensitive cryo-cooled detectors, a significant sensitivity in dark offsets is thought to be observed based on season, albedo, and spacecraft orientation. As a result, unlike a CMOS sensor, a "dark" must be collected at least before image collection and subtracted before imaging tasks. This paper discusses the difference in darks between space-based and ground based sensors and impacts on spatial/spectral noise and bad pixel computation.

The NASA Clouds and the Earth's Radiant Energy System (CERES) project provides the scientific community with observed top-of-atmosphere (TOA) shortwave and longwave fluxes for climate monitoring and climate model validation. To achieve this goal, CERES relies on TOA broadband fluxes derived from geostationary satellite (GEO) imagery to account for the diurnal flux variations between the CERES observation intervals. Consistent global flux derivation depends on accurate and consistent cloud retrievals. Scene-dependent spectral measurement inconsistency of the instruments that make up the contiguous ring of GEO observations (GEO-Ring), as well as limb darkening effects, can cause discontinuities in derived cloud properties and radiative fluxes at the boundaries of adjacent imager domains. Although the algorithms utilize radiative transfer models to account for instrument-band-dependent atmospheric correction and viewing zenith angle (VZA) dependency, small discontinuities may persist due to uncertainties inherent to the multiple imager-specific algorithms. Furthermore, while hyperspectral-instrument-based spectral band adjustment factors may effectively account for spectrally induced bias, they are less effective at reducing variance owed to the specific composition of the viewed scene, which is challenging to robustly characterize. As such, this article highlights the use of a deep neural network (DNN) to resolve spectral- and VZA-induced biases between GEO-Ring imagers. The DNN uses available infrared (IR) channels from the GEO instruments, along with viewing and solar illumination geometry, to estimate homogenized, VIIRS-like IR radiances for use in the GEO cloud algorithm. This approach is effective at mitigating scene-dependent spectral variance and VZA dependency, resulting in consistent radiance measurements across the GEO-Ring, thereby leading toward a more seamless global cloud assessment.

The Meteosat Third Generation (MTG) Programme is a EUMETSAT geostationary satellite mission developed by the European Space Agency (ESA). It will ensure the future continuity with, and enhancement of, operational meteorological and climate data from Geostationary Orbit as currently provided by the Meteosat Second Generation (MSG) system. The MTG satellites series is composed of 4 MTG-I and 2 MTG-S to bring to the meteorological community a continuous Imagery and Sounding capabilities with high spatial, spectral, and temporal resolution observations including geophysical parameters of the Earth based on new state-of-the-art sensors. The first satellite (MTG-I1) was launched on 13th December 2022 by an Ariane 5 rocket. It features the Flexible Combined Imager (FCI) and the Lightning Imager (LI). MTG-S series of satellites, whose first launch is planned in 2025, embarks the Infra-Red Sounder (IRS) and the Sentinel-4/ Ultra-violet/Visible/Near-Infrared (UVN) sounder instruments on geostationary orbit. This presentation will summarise the outcomes of the Cal/Val of the MTG-I1 FCI and LI Level-1 and Level-2 operational products, and will provide the status of the MTG-S1 mission.

We analyzed the radiance differences between GOES-East and GOES-West at ten-minute interval for a year and found some subtle fluctuation patterns around satellite midnight, which also varies seasonally. One occurs annually around the winter solstice, when the Internal Calibration Target (ICT) can be heated rapidly and unevenly after midnight. This fluctuation has the longest duration in late February and late October, lasting about two hours. The other occurs semiannually during eclipse seasons, when the Sun is close to the Earth before and after being occluded. This fluctuation is most pronounced near the times of occlusion and disappears as the Sun moves behind the Earth. The magnitudes of these two fluctuations are instrument-dependent and within only a few tenth of a degree at 300 K. Detecting and characterizing these fluctuations, while compliant with the calibration requirement, demonstrates the utility of comparing two nearby geostationary sensors (“GEO-GEO”) on a fine temporal scale. This complements the comparison of GEO with well-calibrated hyperspectral sensors on Low Earth Orbit (GEO-LEO).

The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, recently launched on February 8, 2024, has a payload of two polarimeters and the Ocean Color Instrument (OCI). OCI is the next generation sensor for ocean color science from low Earth orbit, drawing heritage from sensors such as MODIS and SeaWiFs, but with increased spectral coverage and improved accuracy. OCI is a grating spectrometer with hyperspectral coverage from the ultraviolet (about 315 nm) to near-infrared (about 895 nm), with additional filtered channels in the short-wave infrared (940 nm – 2260 nm). In order to maintain the high levels of accuracy demanded by the science community, the sensor calibration is monitored on-orbit through daily observations of the Sun. These solar observations are made via one of two quasi-volume diffusers, whose BRDF was measured prior to launch, during a dedicated spacecraft maneuver. One diffuser is used on a daily basis, while the other is used on a monthly basis to track any changes in the daily diffuser performance. These solar observations are used to monitor variations in the instrument gain over time for all spectral bands, and update the gain in the calibration algorithm. The methodology used to estimate the gain variation and the results of this variation since launch are presented in this work.

Launched in February 2024, the Ocean Color Instrument (OCI) onboard NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission has started performing its monthly lunar calibrations at ±7 degrees lunar phase angle in March 2024. In this paper, we will describe the OCI lunar calibration methodology and show the results of lunar calibration events during the initial months of PACE/OCI operation. A key difference of OCI lunar calibration from heritage sensors is that the lunar disk integrated irradiance is computed from lunar pixel radiance and sampling distance instead of the instrument’s IFOV. PACE provided a near constant sweep rate during lunar calibration allowing accurate determination of OCI pixel sampling extent. OCI performs lunar calibration in baseline science mode with 282 hyperspectral bands from 315 – 895 nm and 7 shortwave infrared bands (940 - 2260 nm). For each OCI band, we compute the integrated lunar disk irradiance, and compare the result with a lunar irradiance model (ROLO) prediction. The early results presented here clearly show that OCI’s lunar image acquisition is working as intended and will provide accurate data for OCI’s on-orbit radiometric characterization. The hyperspectral lunar irradiances provided by OCI are expected to become a valuable dataset for the evaluation of lunar irradiance models.

The NASA Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission Project Science Team has used Ocean Color Instrument (OCI) measurements of Fraunhofer lines in spectra of sunlight reflected by the solar diffuser and measurements of atmospheric absorption bands in cloudtop and ocean spectra to characterize the spectral calibration of OCI on orbit. Multiple lines have been analyzed for both the ultraviolet to visible (UVVIS, 340−607 nm) and visible to near-infrared (VISNIR, 597−897 nm) grating spectrographs. The spectrographs yield hyperspectral observations with 5 nm bandwidths and 0.625 nm sampling intervals. The on-orbit observations have been compared with the prelaunch spectral calibration of OCI performed by the Goddard Laser for Absolute Measurement of Radiance (GLAMR) during thermal vacuum testing to track any changes in the calibration since launch. The calibration analyzed the line positions and strengths for the Fraunhofer lines for each spectrograph by comparing the solar spectra measured by OCI with predicted solar spectra derived from the solar reference spectrum and the BRDF of the solar diffuser, convolved with the OCI relative spectral responses. The calibration also compared the line positions of the atmospheric absorption bands with the model transmissions used by the PACE Project. The line position comparisons show that the root mean square (RMS) spectral difference between the measured and predicted spectra is 0.15 nm, the average spectral shift is 0.062 nm, and the residual spectral dispersion over the wavelength range of the Fraunhofer lines is 0.17 nm. All three estimates of the spectral accuracy of OCI meet the instrument functional requirement of a spectral accuracy of 0.5 nm and are well within the 0.625 nm sampling interval of the data. The line strength comparisons between measured and predicted spectra are essentially the same. These results show that the spectral calibration of OCI on orbit has not drifted since the prelaunch calibration of OCI by GLAMR and that the on-orbit spectral calibration of OCI is stable over time. These results also provide a baseline for monitoring the future spectral performance of OCI on orbit.

The third Earth observing Visible Infrared Imaging Radiometer Suite (VIIRS) is on the recently launched NOAA-21 satellite. Like its predecessors on the SNPP and NOAA-20 satellites, the VIIRS provides daily global geometrically and radiometrically calibrated observations via its 22 spectral bands from 0.41 to 12 mm. VIIRS has 14 reflective solar bands (RSBs), covering wavelengths from 0.41 to 2.25 m. On orbit, the RSBs are radiometrically calibrated through a sunlit solar diffuser (SD). The on-orbit change of the SD’s bidirectional reflectance distribution function (BRDF) is determined by using the onboard solar diffuser stability monitor (SDSM). An SDSM screen and an SD screen, both with holes to let sunlight pass through, are involved in the calibration. The SDSM screen relative transmittance and the products of the SD screen transmittance and the SD BRDF for the SDSM and the telescope SD views were measured prelaunch. But large errors are associated with the prelaunch SDSM screen function. As a result, the SDSM measured SD BRDF onorbit change factor versus time data points have large unrealistic undulations. To improve the screen functions, satellite yaw maneuvers were performed and the calibration data from the yaw maneuver orbits were used to rederive the screen functions. Here, we apply a previously developed methodology with a slight improvement to further refine the screen functions, using the calibration data not only from the yaw maneuver orbits but also from a small portion of the regular orbits. With the updated screen functions, the SDSM determined SD BRDF on-orbit change factors, as well as the retrieved NOAA-21 VIIRS RSB radiometric gains, are much smoother functions of time.

The Visible Infrared Imaging Radiometer Suite (VIIRS) instruments aboard the Suomi NPP (SNPP), NOAA-20 (N20), and NOAA-21 (N21) spacecraft have successfully provided Earth image products since 2011, 2017, and 2022, respectively. VIIRS has 22 bands with resolutions of 375 m and 750 m for the imaging and moderate resolution bands, respectively, covering a spectral range of 400-12,490 nm. Among them, moderate bands (M-band) 1 to 11 and imaging bands (I-band) 1 to 3 are reflective solar bands (RSBs), and M12 to M16 and I4 and I5 are thermal emissive bands (TEB). Each M-band has 16 detectors, and each I-band has 32 detectors. M-bands (1-5, 7, and 13) have dual-gain stages to enhance the measurement dynamic range. The nonlinear responses of RSB and TEB detectors were characterized during pre-launch testing. An on-board solar diffuser tracks any linear response degradation for RSB detectors. For TEB detectors, an on-board blackbody (BB) tracks linear response change, and a scheduled BB warmup and cooldown event is used to monitor the non-linearity change. Unknown biases or uncertainty in the linear or nonlinear calibration coefficients between different detectors can cause unwanted striping in the image product. In this work, the striping is assessed for all RSB and TEB of the three VIIRS instruments on SNPP, N20, and N21. The assessment is performed using the NASA Level 1B reflectance and radiance products over the entire globe to analyze the aggregate striping and any changes over time. For each band of the three instruments, the striping assessment is performed at different signal levels to analyze their nonlinearity. The striping assessment is also performed separately for both gain stages of the dual-gain bands. The motivation of this work is to have a comprehensive understanding of VIIRS striping and its signal dependency to support calibration improvements and to reduce the striping over a broad radiance range.

The Advanced Baseline Imagers (ABI) on NOAA’s GOES-R series satellites perform sequential scans to collect swaths of image data that are assembled on the ground to produce Full Disk images of the Earth. The alignment of each swath relative to adjacent swaths is essential for accurate Image Navigation and Registration (INR) of the ABI images. Assessment of Swath-to-Swath Registration (SSR) errors is performed using the INR Performance Assessment Tool Set (IPATS), but the process currently depends on 24-hour special collections of Mesoscale data that typically occur only during the post launch testing phase. Through analysis and modification of an offline copy of the software that generates the fixed grid Level 1b product from the Level 1𝛽 swath data, it is possible to perform SSR performance assessment using Full Disk images during normal operations. The modifications preserve all Level 1b data in the swath overlap regions, whereas the operational ground system necessarily trims the overlap to yield a seamless image. In this paper we present the tool that generates the swath overlap Level 1b data for use with SSR analysis. This tool can be used as an add-on to the current GOES-R ABI Trending and Data Analysis Toolkit (GRATDAT). Additionally, we present the initial IPATS results of this SSR analysis, as well as comparison with previous Mesoscale image based SSR measurements.

Uvsq-SatNG is a Six-Unit GHG CubeSat dedicated to the simultaneous measurements of the Earth Radiation Budget and greenhouse gases. This space mission aims to evaluate the potential of using a compact spectrometer mounted on a CubeSat for determining atmospheric GHG concentrations (CO₂, CH₄). This spectrometer operates in the Near-Infrared (NIR) range, typically between 1200 to 2000 nm, which is an ideal wavelength range for detecting and measuring the spectral signatures of the most significant greenhouse gases. The inclusion of such a spectrometer on Uvsq-SatNG represents an important step forward in climate research. It not only provides essential data for environmental science but also demonstrates the growing capability of satellite technology to support crucial observations of our planet’s changing climate. The aim of this article is to present an optical configuration for this instrument. The performance achieved with this design will be presented. We will see if the proposed instrument design is capable of measuring greenhouse gas concentrations with good accuracy (absolute measurements of ±4.0 ppm with an annual stability of ±1.0 ppm for CO₂, absolute measurements of ±25.0 ppb with an annual stability of ±10.0 ppb for CH₄).

Two recent projects at Spectral Sciences Inc. share the goal of improving the calibration of overhead optical sensors. In the first, we have developed a vicarious calibration method that utilizes our MODTRAN software, a recognized standard for atmospheric radiative transport modeling along with contemporaneous satellite measurements from known sensors, to retrieve top-of-atmosphere radiance and subsequent band integrations provide calibration constants. In the second, we are developing a new thermally controlled array of spectrally characterized panels to support accurate calibration of imagers in the visible through long wavelength infrared (LWIR). Progress and results of both efforts will be described.

In December 2024, Terra will have been on orbit for 25 years with all five instruments operational. The high quality instruments allow calibration and scientists the opportunity to evaluate the sensors as well as methods for on-orbit calibration. The role Terra played in development and improvement of relative and absolute radiometric calibration is described including vicarious methods implemented as part of the Earth Observing System Project. Cross-calibration techniques and relative trending approaches are described with an emphasis on the three imagers on Terra as are impacts that Terra has had on follow-on sensor designs, on-ground testing approaches, and validation methods.

PRISMA is the hyperspectral mission from the Italian Space Agency (ASI) launched in 2019. It samples the solar irradiance reflected and diffused by the earth-atmosphere system between 400 nm and 2500 nm with a spectral distance better than 11nm and a 30m Ground Sampling Distance. To answer the demanding need of hyperspectral applications, a high absolute radiometric accuracy is required and reached through the combination of on board and natural targets based calibration.
This paper describes PRISMA mission and focuses on the natural targets based calibration methods used to assess the instrument sensitivity. Two methods are used:
- PICS (Pseudo Invariant Calibration Sites) allow to cross-calibrate PRISMA with SENTINEL-2 and 3 ESA missions.
- Gobabeb and La Crau Instrumented sites known as RadCalNet sites which provide a BOA spectral BRDF through a dedicated acquisition protocol and processing as well as atmospheric parameters simultaneously to the satellite pass.
The adaptation of these methods to hyperspectral sensors calibration is presented. The calibrations results which show the very good temporal stability of PRISMA instrument are discussed as well as the methods and in situ instrumentation evolutions planned to improve the calibration of hyperspectral sensors using natural targets.

Accurate satellite measurements depend on rigorous radiometric performance monitoring for reliability and precision in data collection. EUMETSAT achieves this through ongoing monitoring of operational missions using vicarious calibration and inter-calibration systems.

Vicarious calibration and inter-calibration techniques employ natural targets, such as warm deserts, the Moon, Deep Convective Clouds (DCC), and dark oceans, to transfer calibration from a radiometric reference to the monitored mission. These methods are indispensable for instruments like MSG/SEVIRI, lacking an on-board calibration device for solar channels, yet widely used for monitoring and validating the radiometric performance of on-board calibration systems.

This paper presents the routine radiometric calibration monitoring of MTG-I1/FCI, MSG/SEVIRI and Sentinel-3 OLCI and SLSTR Level-1 products using our multi-mission tool, Mission Integrated Calibration Monitoring and Inter-Calibration System (MICMICS). The monitoring process encompasses diverse calibration targets, such as desert sites, DCC, lunar observations, and inter-comparisons with other reference instruments, enhancing the overall assessment.

Data from Earth-observing imaging spectrometers installed on the International Space Station (ISS) platform provide opportunities to use fine spectral information about the Earth with various imaging angles and conditions. The results here are based on hyperspectral scenes captured by the Earth Surface Mineral Dust Source Investigation (EMIT) and the DLR Earth Sensing Imaging Spectrometer (DESIS). Intercomparison of EMIT and DESIS from the same platform provides many opportunities for coincident views of various surface types and atmospheric conditions. Here, we focus on observations of the radiometric calibration sites with automated SI-tractable surface-characterization instruments of the Radiometric Calibration Network (RadCalNet) and conduct comparative analyses of EMIT and DESIS. We validate the data by comparing them to measurements from RadCalNet sites as a quantitative inter-calibration approach. The results of this study show the utility of RadCalNet for the harmonization of hyperspectral instruments. In addition, the approach here makes use of the precessing orbit of the ISS enables observations under similar sensor/sun angles for varying sun/sensor angles over short time periods, limiting the effect of sensor or site changes and highlighting directionality dependencies of the surface reflectance and corresponding atmospheric conditions. The intercomparison methodology discussed here can eventually be used for calibration and validation of hyperspectral instruments of the Surface Biology and Geology (SBG) and Copernicus Hyperspectral Imaging Mission for the Environment (CHIME).

The CEOS recommended Pseudo Invariant Calibration Site (PICS) have been extensively used for post-launch radiometric calibration and stability assessment of high, medium, and low-resolution satellite imagers, including MODIS and VIIRS. The NASA CERES Imager and Geostationary Calibration Group (IGCG) utilizes Libya-4 to perform an independent assessment of the radiometric stability of the MODIS and VIIRS L1B products, as well as to radiometrically scale between MODIS, VIIRS, and geostationary imagers to ensure consistent cloud and radiative flux retrievals. The IGCG has recently enhanced their PICS stability assessment by improving their clear-sky identification, BRDF, and atmospheric corrections. The Libya-4 PICS trend stability was similar across all scan angles, spectral bands, Aqua-MODIS and VIIRS imagers. Using the same Libya-4 PICS methodology, the study evaluated the stability of 15 Saharan and Arabian PICS. The optimal PICS would have the least surface natural variability with no long term discernable trends, the most spectrally consistent after atmospheric correction, and have the greatest clear-sky probability.

Nine of the 100 km PICS had clear-sky probabilities between 45% to 55%, however the clear-sky probability for Mali, Mauritania-1, and Mauritania-2 was less than 30%. The 1.61μm, 0.65μm, 2.15μm, 0.48μm, and 0.55μm band atmospheric corrections improved the temporal stability by 5-19%, 12-24%, 47-68%, 22-68%, and 14-54%, respectively. The PW atmospheric correction was the most effective across all PICS, whereas the AOD and ozone atmospheric corrections were less effective. Surprisingly, Libya-2 and Libya-4 had 0.48μm and 0.55μm band atmospheric correction reductions less than 22%, whereas Libya-1 had 0.48μm and 0.55μm band atmospheric corrections greater than 46%. However, the AOD and ozone variability was very similar for the Libya PICS. Libya-1 and Libya-2 are the most optimal PICS having temporal fluctuations within 0.5%. Algeria-1, Algeria-2, Algeria-3, Egypt-1, Libya-4, Niger-1, and Sudan-1 are favorable sites where the temporal variability was within 1.0%. Future work will include combining PICS stabilities as well as finding the most optimal 20 km region contained within the 100 km PICS to attain PICS temporal stabilities less than 0.5%.

The NASA Clouds and the Earth's Radiant Energy System (CERES) project provides the scientific community with regional broadband fluxes designed for long-term climate monitoring. The CERES climate quality dataset requires that the CERES instrument, as well as the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) imager records to be radiometrically stable over time. Deep Convective Clouds (DCCs) are spectrally uniform, near-Lambertian natural diffusers offering high signal-to-noise ratio and stable radiometric response in the VIS-NIR spectrum. For shortwave infrared (SWIR) wavelengths greater than 1 μm, the DCC is significantly influenced by cloud particle size and atmospheric absorption. Previous studies improved the characterization of the SWIR band DCC radiance, by using channel specific monthly empirical Bidirectional Reflectance Distribution Functions (BRDFs) as well as using the probability density function mean statistic to track the SWIR band stability. Also, that the DCC radiance is greater over land than over ocean and that the TWP DCC radiance has the lowest tropical DCC radiance. This study confirms and improves upon the previous studies. The study stratified the tropics regionally into land and ocean domains and applied their respective ocean-only and land-only empirical monthly BRDFs and adjusted both the land and ocean BRDF corrected radiances to the same ocean-only BRDF reference radiance. This approach provided the most stable DCC response. The DCC BRDF corrected radiance monthly trend standard error was 0.24%, 0.62%, 0.59%, and 0.43% for the 1.24μm, 1.37μm, 1.61μm, and 2.25μm SWIR bands, which reduced the trend standard error 20%, 13%, 24%, and 26%, respectively when compared with the all-surface approach. The same approach was attempted over the Tropical Western Pacific and found not to be an improvement over the tropical domain. Further stratification of the tropical domain will need to balance sufficient sampling while accounting for regional DCC radiance differences. Keywords: Deep Convective Clouds, inter-calibration, VIIRS, SWIR, BRDF, characterization.

The NASA CERES SYN1deg product provides the scientific community regional hourly TOA and surface broadband fluxes and clouds. For consistent geostationary (GEO) derived fluxes and clouds the GEO imagers are radiometrically scaled to the Aqua-MODIS calibration reference. The CERES project utilizes GEO and MODIS or VIIRS analogous channel coincident, collocated, and co-angled radiance pairs as the primary method to inter-calibrate the GEO imagers. Tropical deep convective clouds (DCC) are bright, near Lambertian, top of atmosphere pseudo invariant Earth targets that do not rely on coincident ray-matched radiance pairs to radiometrically scale sensors to a common calibration reference. The DCC invariant target (DCC-IT) methodology collectively analyzes all tropical DCC identified pixel radiances by way of probability density function (PDF) distributions. Perfectly inter-calibrated sensor pairs should reveal nearly identical PDF distributions given the same DCC identification criterion. The PDF median, mean, mode, and inflection point statistics were tested as a function of DCC identification criterion using SNPP-VIIRS and Himawari-8 AHI 0.65μm channel radiances during January 2019. It was found that the PDF inflection point provided inter-calibration factors within 0.25% that were nearly independent of DCC identification criterion. The PDF median provided inter-calibration factors within 0.25% for the coldest BT and most stringent homogeneity factors The PDF mean and mode statistics were inadequate under any DCC conditions. It is critical for the DCC pixel radiances to be anisotropically corrected. The DCC-IT methodology will also be tested for other visible and SWIR bands.

This study evaluates the inter-sensor consistency of the Visible Infrared Imaging Radiometer Suite (VIIRS) moderate-resolution Thermal Emissive Bands (M TEBs; M12–M16) across three satellites−Suomi National Polar-orbiting Partnership (S-NPP), NOAA-20, and NOAA-21, covering a period from March 18, 2023, to June 30, 2024. The field of interest is limited to the ocean surface between 60°S and 60°N, specifically under clear-sky conditions. Taking radiative transfer modeling (RTM) as the transfer reference, we employed the Community Radiative Transfer Model (CRTM) to simulate VIIRS TEB brightness temperatures (BTs) using collocated European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis data as inputs.

Excellent inter-sensor consistency among these three VIIRS instruments is confirmed through the double-difference analysis method (O-O) using CRTM simulation as a radiance transfer. This method relies on the observation minus background BT differences (O-B ΔBTs), between VIIRS measurements obtained from daily operational data (O) and CRTM simulations (B). The mean inter-VIIRS O-O BT differences remain within 0.08 K for all M-band TEBs, except for M13. Even in the case of M13, the O-O BT differences between NOAA-21 and NOAA-20/S-NPP have values of 0.312 K and 0.236 K, respectively, which are comparable to the 0.2 K difference observed in overlapping TEBs between VIIRS and MODIS at simultaneous nadir overpasses (SNOs). These disparities are primarily attributed to the significant differences in the Spectral Response Function (SRF) of NOAA-21 compared to NOAA-20 and S-NPP.

Our study confirms the effectiveness of the RTM-based TEB quality evaluation method in assessing inter-sensor consistency. The double-difference approach effectively mitigates uncertainties and biases inherent to CRTM simulations, establishing a robust mechanism for assessing inter-sensor consistency. Moreover, it has been noticed that for M12, both the time-series of O-O and O-B BT differences possess the greatest vibrations (i.e., largest standard deviations) compared to other bands, alongside the distinct seasonal variations of O-B BT differences. These observations can be attributed to the fact that M12 radiance is affected by reflected solar radiation during daytime, as M12 operates as a shortwave infrared channel. Furthermore, in this study, we’ve also characterized the spatial distributions of inter-VIIRS BT differences, identifying variations among VIIRS M TEBs.

With the rapid development of maritime transportation, marine environmental pollution has become more and more serious. In particular, oil leakage from ships is regarded as a major threat to marine environmental pollution. Synthetic Aperture Radar (SAR) imagery has become an important technology for marine environment monitoring because of its high resolution, wide coverage, and less influence by light and weather conditions. However, SAR images cannot provide realtime information about ships. The Automatic Identification System (AIS) can provide dynamic information about ships, such as real-time position, heading, speed, etc., helping to identify ships in the sea area. This study combined SAR imagery and AIS data to detect oil spills at sea and identify suspicious oil-discharging vessels. First, an improved U-Net model was adopted to detect oil spills and ships in SAR imagery. To achieve high detection performance, the U-Net was modified by using a lightweight MobileNetv3 backbone architecture, convolutional block attention module (CBAM), atrous spatial pyramid pooling (ASPP), and full-scale feature aggregation. Experimental results showed that the proposed U-Net model improved the detection accuracy of oil spills and reduced the misclassification between oil spills and look-alikes. Then, the AIS data corresponding to the SAR image was collected and the trajectories of ships passing near the SAR acquisition time can be screened out. The study compared AIS data with SAR detection results to look for the ship that was closest to the oil spill and whose navigation trajectory was almost parallel to the direction of the oil spill extension. Thus, it can be inferred that the ship was suspected of discharging oil pollution. Through experiments on oil pollution incidents, the effectiveness of combining SAR and AIS in tracking oil-discharging ships was verified.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is an Earth-observing satellite sensor. VIIRS data are used to generate about 30 products (see Ref. 3) for Earth studies and weather forecasting. Out of the 22 VIIRS spectral bands, 14 are the reflective solar bands (RSBs). Earth views from some of these RSBs onboard the NOAA-20 (N20) satellite show unexpected striping. Our investigation shows that the striping for the N20 VIIRS visible and near-infrared (VisNIR) bands comes from three sources: first, for bands M1 (412 nm) and M2 (445 nm), an obvious dependence on the sides of the half-angle-mirror (HAM), a result of a likely error in the HAM’s reflectivity extrapolated to the telescope solar diffuser (SD) view angle; second, a gradual increase in the striping over time for band M1, resulting from not accounting for the positional dependence of the SD reflectance; and finally, a small (~0.3%) but universal amount of time invariant striping for all the VisNIR bands, possibly coming from a small amount of positional dependence in the prelaunch measured SD reflectance. Here, we apply appropriate methods to resolve the unwanted striping for the N20 VIIRS VisNIR bands. The de-striping algorithms have been applied in the NASA N20 VIIRS Collection 2.1 L1B products, with the first delivery of the forward L1B F-factor LUTs (version v3.1.1.7) in November 2023.

The JPSS-4 VIIRS sensor, the last in a JPSS program that will eventually span some 25+ years of on-orbit data collection, has completed its pre-launch test program. The test program included measurements for characterizing the VIIRS relative spectral response (RSR) in support of the Sensor and Environmental Data Records that will be generated from JPSS-4 VIIRS on-orbit observations after launch. Subject matter experts of the Government Team’s VIIRS DAWG have analyzed the VIIRS spectral measurements and produced the VIIRS spectral characterization, in the form of band averaged and supporting detector level RSR for each VIIRS band. The characterization is based upon the analysis of independent SpMA dual monochromator (all bands) and GSFC GLAMR laser system (reflectance bands only) spectral measurements. The SpMA and GLAMR measurements for reflectance bands (DNBLGS and DNBMGS, I1-I3, M1-M11) were combined to produce a “fused” RSR. For emissive bands (I4, I5, M12-M16), the SpMA measurements provide the entire characterization. The effort has led to the VIIRS Version 2 RSR product, the official at-launch RSR characterization for the JPSS-4 VIIRS mission, which is currently slated to be the next launch (expected Fall 2027) of the JPSS program. As expected, the JPSS-4 RSR are a close match to those of JPSS-3 and JPSS-2 (NOAA-21) VIIRS, while showing some spectral position and shape differences with SNPP and JPSS-1 (NOAA-20) VIIRS. An assessment on compliance with spectral performance metrics finds that VIIRS band-average RSR are compliant on nearly all metrics, with only a single minor exception. The Version 2 RSR will be available under EAR99 restrictions to the science community on the restricted access NASA Sharepoint.

To complement the successful manufacture and deployment of two custom ultra-portable field-capable visible and nearinfrared (VNIR) transfer radiometers developed by the Remote Sensing Group (RSG) at the University of Arizona, RSG has been testing custom short-wave infrared (SWIR) detectors towards a new radiometer system design. Similar to the Silicon-based Calibration Test Site SI-Traceable Transfer Radiometer (CaTSSITTR), these thermoelectrically (TE) cooled InGaAs-based SWIR instruments are designed for stable and SI-traceable transfer radiometry in support of various field and laboratory calibrations around the world, much in support of the Radiometric Calibration Network, or RadCalNet, an initiative of the Working Group on Calibration and Validation of the Committee on Earth Observation Satellites (CEOS). To accomplish widespread transfer radiometry in various field and laboratory environments, design goals include singleoperator portability and data collection, standalone battery power for field collection, and system operation at a wide ambient temperature range (-10–35°C). These goals were recently realized into complete prototype system design and manufacture. This work presents updated details of this final design but focuses mostly on the initial radiometric performance of these custom instruments as an evaluation of their suitability for high accuracy transfer radiometry in the 800 – 2500 nm spectral region.

The MODIS instruments onboard the Terra and Aqua satellites have provided continuous global observations for science research and applications for more than 24 and 22 years, respectively. The sensors’ calibration accuracy and product quality have been maintained. Electronic crosstalk in the photovoltaic (PV) longwave infrared (LWIR) bands is a known issue. The crosstalk coefficients are derived using scheduled monthly lunar observations. Crosstalk corrections for the Terra MODIS PV LWIR bands have been applied in both Collection 6.1 (C6.1) and the upcoming Collection 7 (C7) Level 1B products. The correction for the Aqua PV LWIR bands crosstalk has also been applied to C7 for the entire mission and C6.1 after the March 2022 safe mode. The lunar phase of the scheduled lunar events is around -55 for Aqua and 55 for Terra over the mission until the Aqua orbit started drifting in December 2021 and the Terra Constellation Exit Maneuvers (CEM) were performed in October 2022. To meet the constraint of the 0-20° spacecraft roll maneuvers, the phase angle range for the scheduled moon events is lower after the de-orbiting and CEM. Since unscheduled lunar observations cover a larger range of phase angles, the coefficients derived from those lunar observations can be used to assess the phase angle impact on the crosstalk coefficients calculation. A comparison between the crosstalk coefficients from scheduled and unscheduled lunar observations is also performed. The dependency on the phase angle is small except for the cases when Terra band 30 is the sending band. This analysis is performed over a wide range of phase angles covered by the unscheduled lunar observations. The assessment is useful for future PV LWIR bands crosstalk corrections and to maintain the L1B product quality for both Terra and Aqua MODIS.

In the paper, we proposed a compact Korsch-type CubeSat telescope for optical remote sensing validation. The optical payload will be mounted on a 6U CubeSat named ONGLISAT. This telescope has an aperture of 92 mm and an effective focal length of 725 mm, providing a field of view of 2.2 degrees. The optical payload is equipped with a linear TDI CMOS image sensor, capable of capturing high-resolution panchromatic images with a ground sampling distance (GSD) of 2.8 meters in a low-Earth orbit at an altitude of 406 kilometers. The Korsch telescope consists of three aspheric mirrors (primary, secondary, and tertiary mirrors) as well as a roof mirror. This paper presents details of the optical design, assembly, integration, and performance test for the compact Korsch telescope. The image quality of the Korsch telescope is evaluated by the contrast transfer function (CTF). Finally, after thermal vacuum cycling testing and vibration testing, the telescope still maintains a CTF of 0.12 at 50 lp/mm line pairs. The Korsch telescope has the characteristics of a low obstruction ratio and high stray light blocking. The design of the telescope has higher resolution, a smaller size, and lower launch costs, which are beneficial for future applications in science, agriculture, commerce, and disaster relief. Furthermore, its optical quality can be quickly validated, serving as a preliminary study for larger telescopes.

As Earth observation satellite data grows, the need for higher temporal and spatial resolutions becomes crucial for accurate monitoring and decision-making. Achieving both of high temporal and spatial resolutions is challenging due to trade-offs in sensor design; for instance, Sentinel-2 and Landsat offer higher temporal but lower spatial resolution, while high-resolution sensors like NEONSAT with small coverages. This study introduces a deep learning-based spatiotemporal image fusion method that integrates multi-sensor data, combining low and high spatial resolution images from different sensors over time. The method estimates adjustment features from temporal and spatial differences, using fusion and convolutional blocks to enhance resolution. Trained on Sentinel-2 and Planet images, the method effectively maintains spectral integrity and enhances spatial details under varying conditions. By leveraging multi-sensor data, this approach addresses sensor quality and stability issues, expanding NEONSAT’s potential applications. Future research will refine the method by incorporating more datasets, including NEONSAT imagery, to advance spatiotemporal fusion techniques.