The HyperSpectral Imager for Climate Science (HySICS) is the sole instrument of the CLARREO Pathfinder (CPF) mission, which was previously planned for launch to the International Space Station (ISS) in 2026. It is an Offner-Chrisp imaging spectrometer designed to achieve an exceptional radiometric uncertainty of 0.3%-0.6% (k=1) for Earth reflectance measurements across a spectral range of 350-2260 nm. This represents a significant improvement over existing spaceborne spectrometers, which typically achieve uncertainties greater than 2%. To validate this performance, an Independent Calibration (IndCal) strategy has been developed, relying on a pre-launch, detector-based absolute radiometric calibration (RadCal) approach using the Goddard Laser for Absolute Measurement of Radiance (GLAMR), a tunable laser source developed at NASA's Goddard Space Flight Center. The RadCal test, conducted in September 2023, systematically characterized the radiometric and spectral performances of HySICS through full-field, full-aperture, and full-spectrum evaluations. The test measured the absolute spectral responses (ASRs), band-integrated responsivities and other radiometric parameters of HySICS' detector at the pixel level, focusing on minimizing uncertainties at every stage of the measurement process. This paper details the methodology, configuration and key results of the test, which notably marks the first application of detector-based absolute RadCal to an operational imaging spectrometer. The demonstrated performance is expected to establish a new benchmark for high-accuracy absolute RadCal of remote sensing instruments in Earth observation.

Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Terra and Aqua spacecraft have been successfully operating for nearly two decades and providing complementary observations of the Earth's land, ocean, and atmosphere. Although the two MODIS instruments view the entire Earth's surface once every 2-3 days, simultaneous views between them are limited due to their varying orbits. Therefore, the intercomparison between these two instruments has been previously performed using a transfer instrument [such as Advanced Very-high-resolution Radiometer (AVHRR)] or using lunar measurements normalized using a common model, such as the USGS Robotic Lunar Observatory (ROLO). In recent years RadCalNet, a Committee on Earth Observation Satellites (CEOS) initiative, has provided SI-traceable Top-of-Atmosphere (TOA) reflectances from a coordinated network of instrumented land-based sites. RadCalNet facilitates a unique mechanism to perform cross-calibration of instruments by minimizing the uncertainties associated with overpass time differences. In this letter, the near-simultaneous TOA reflectance measurements from the Railroad Valley (RRV), US (RVUS) are used as a transfer to compare the on-orbit observations for the Terra and Aqua MODIS reflective solar bands (RSBs). Near-nadir overpasses from January 2013 to January 2019 are processed and matched up with near-simultaneous RadCalNet measurements. Results show that the visible (VIS)/near-infrared response (NIR) bands agree to within 2%, and the short-wave infrared (SWIR) bands agree to within 5%. Also discussed in this letter are the future efforts that will be undertaken to expand this comparison to include other instruments, other sites, and both nadir- and off-nadir views after compensation for bidirectional reflectance distribution function (BRDF) effects.

Remote sensing instruments, both aircraft and on-orbit platforms, undergo extensive laboratory calibrations to determine their geometric, spectral, and radiometric responses. Additional in-flight radiometric calibrations can be performed using well-characterized earth targets. The Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign provided such an opportunity when the ER-2 aircraft overflew Railroad Valley on August 13 and 15, 2019. Surface reflectances were available from the August 4, 2019 field team and from the Radiometric Calibration Network (RadCalNet) portal, and spectral aerosol optical depths from an on-site AERosol RObotic NETwork (AERONET) sunphotometer. The Enhanced MODIS Airborne Simulator (eMAS), the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI), and the “Classic” Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-C) sensors individually performed a vicarious calibration using their respective methodologies and selection of input parameters. A comparison of the at-sensor radiances predicted from these independent analyses highlights some of the uncertainties in the inputs, including choice of solar irradiance model. Although good agreement, within 5%, is found at visible wavelengths, difference can be as large as 15% in the shortwave infrared (SWIR). This highlights the need for the remote sensing community to agree upon a standard solar model, to remove sensor-to-sensor biases derived from in-flight calibrations.

The Thermal Infrared Sensor-2 (TIRS-2) that will be onboard Landsat 9 has undergone a prelaunch testing campaign to characterize its radiometric, spectral, and spatial performances and demonstrate compliance to its requirements. This work reviews the key elements of the instrument-level radiometric testing using an SI-traceable source to derive its uncertainties. Those arising from on-orbit calibration using the TIRS-2 onboard blackbody are also discussed. We use a Monte Carlo approach to propagate the uncertainties through a nonlinear calibration equation and address both random and systematic uncertainty terms. Achieving the required performance demonstrates the instrument's potential for enhancing our understanding of the Earth's environment.

The Radiometric Calibration Network (RadCalNet) is a coordinated multinational effort to provide in situ data that are suitable for the radiometric calibration and validation of Earth observation sensors that operate in the visible to shortwave infrared solar reflective spectral region (400 nm to 1000 nm). The main goals of RadCalNet are to provide top-of-atmosphere reflectance data to the scientific community, standardize data collection protocols for automated test sites, and to document the SI-traceable uncertainty budgets for each automated test site, of which there are currently four. The data available from RadCalNet are suitable for the calibration and validation of spaceborne imaging spectrometers. The work presented here provides a description of RadCalNet as well as a sample of the current results from the Radiometric Calibration Test Site (RadCaTS), which is located at Railroad Valley, Nevada, USA. Selected sensors for comparison include Terra and Aqua MODIS, SNPP and NOAA-20 VIIRS, and Sentinel-3A and -3B OLCI.

Landsat 9 is currently under development as a joint effort between NASA and the United States Geological Survey (USGS). Landsat 9 is largely a rebuild of Landsat 8 and has the same two sensors, an Operational Land Imager (OLI) and a Thermal InfraRed Sensor (TIRS). The OLI-2 on Landsat 9, being built by Ball Aerospace, has completed its pre-launch characterization and calibration and is scheduled to be delivered in the summer of 2019. The TIRS-2, with improved stray light performance and increased redundancy for improved reliability, is being built by Goddard Space Flight Center. TIRS-2 is undergoing testing through Spring 2019 and is also scheduled for summer 2019 delivery. Several improvements to the characterization of both instruments have been incorporated into the testing plan, including improved spectral and radiometric characterization. The instruments will then be integrated onto the spacecraft being built by Northrop Grumman Innovation Systems (NGIS). The mission is targeted to launch as early as December 2020 on an Atlas V.

The Thermal Infrared Sensor 2 (TIRS-2) will fly aboard the Landsat 9 spacecraft and leverages the Thermal Infrared Sensor (TIRS) design currently flying on Landsat 8. TIRS-2 will provide similar science data as TIRS, but is not a build-to-print rebuild due to changes in requirements and improvements in absolute accuracy. The heritage TIRS design has been modified to reduce the influence of stray light and to add redundancy for higher reliability over a longer mission life. The TIRS-2 development context differs from the TIRS scenario, adding to the changes. The TIRS-2 team has also learned some lessons along the way.

Ground reflectance was acquired at the Railroad Valley Playa calibration site in Nevada USA using different methods of collection. The data was collected near the time and date of Landsat 8 OLI and Sentinel-2 satellite overpasses so an inter-comparison could be made with the reflectance products to determine which method was more suitable for vicarious calibration. The field spectrometers and reference panels were characterized before the field campaign. A continuous acquisition method was compared to stop and measure collections. Both acquisition methods were collected along an 80 m east-west transect as well as for a series of north-south transects over an 80 × 320 m area, with the stop and measure method being performed at random sampling locations. The measurements were performed using two field spectrometers by three teams of two people to compare the repeatability. The aim of the field campaign was to determine the variability due to the operator and the method of collection.

Landsat 9 will continue the Landsat data record into its fifth decade with a near-copy build of Landsat 8 with launch scheduled for December 2020. The two instruments on Landsat 9 are Thermal Infrared Sensor-2 (TIRS-2) and Operational Land Imager-2 (OLI-2). TIRS-2 is a two-channel pushbroom imager with a 15-degree field of view that will have a 16-day measurement cadence from its nominal 705-km orbit altitude. Its carefully developed instrument performance requirements and associated characterization plan will result in stable and well-understood science-quality imagery that will be used for environmental, economic and legal applications. This paper will present a summary of the plan for TIRS-2 prelaunch characterization at the component, subsystem, and instrument level.

Century, flying on-board the Terra (T) and Aqua (A) spacecrafts. Both instruments far exceeded their 6 year design life and continue to operate satisfactorily for more than 15 and 13 years, respectively. The MODIS instrument is designed to make observations at nearly a 100% duty cycle covering the entire Earth in less than 2 days. The MODIS sensor characteristics include a spectral coverage from 0.41 μm - 14.4 μm, of which those wavelengths ranging from 3.7 μm - 14. 4 μm cover the thermal infrared region which is interspaced in 16 Thermal Emissive Bands (TEB). Each of the TEB contains 10 detectors which record samples at a spatial resolution of 1 km. In order to ensure a high level of accuracy for the TEB measured Top Of Atmosphere (TOA) radiances, an onboard BlackBody (BB) is used as the calibration source. This paper reports the noise characterization and performance of the TEB on various counts. First, the stability of the onboard BB is evaluated to understand the effectiveness of the calibration source. Next, key noise metrics such as the Noise Equivalent Temperature difference (NEdT) and the Noise Equivalent dn difference (NEdN) for the various TEB are determined from multiple temperature sources. These sources include the nominally controlled BB temperature of 290 K for T-MODIS and 285 K for A-MODIS, as well as a BB Warm Up - Cool Down (WUCD) cycle that is performed over a temperature range from roughly 270 K - 315 K. The Space View (SV) port that measures the background signal serves as a viable cold temperature source for measuring noise. In addition, a well characterized Earth View (EV) Target, the Dome C site located in the Antarctic plateau, is used for characterizing the stability of the sensor, indirectly providing a measure of the NEdN. Based on this rigorous characterization, a list of the noisy and inoperable detectors for the TEB for both instruments is reported to provide the science user communities quality control of the MODIS Level 1B calibrated product.

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission was recommended by the National Research Council in 2007 to conduct highly accurate and International System of Unit-traceable decadal change observations and provide an on-orbit intercalibration standard with high accuracy for relevant Earth observing sensors. The goal of reference intercalibration is to enable rigorous observations of critical climate change variables, including reflected broadband radiation, cloud properties, and changes in surface albedo, including snow and ice albedo feedback, to be made consistently among different sensors. This requires the CLARREO Reflected Solar Spectrometer (RSS) to provide highly accurate spectral reflectance measurements to establish an on-orbit reference with a radiometric accuracy requirement better than 0.3%$(\mathrm{k} =2) $for existing sensors. In this paper, MODTRAN-simulated top-of-atmosphere spectral data and spectral measurements from the SCIAMACHY instrument on Envisat are used to determine sensitivity of intercalibration uncertainty on key design parameters of the CLARREO spectrometer: spectral range, sampling and resolution. Their impact on intercalibration uncertainty for MODIS and VIIRS imagers is estimated for various surface types (ocean, vegetation, desert, snow, deep convective clouds, clouds and all-sky) . Results indicate that for the visible to near-infrared spectral region (465–856 nm) , the RSS instrument under current design concept produces uncertainties of 0.16% for the spectral range and 0.3% for the sampling and resolution. However, for the water vapor absorption bands in the short wavelength infrared region (1242–1629 nm) , the same requirement is not met for sampling and resolution due to their high sensitivity to the influence of atmospheric water vapor.

Since launch, the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua spacecraft have operated successfully for more than 14 and 12 years, respectively. A key instrument for National Aeronautics and Space Administration Earth Observing System missions, MODIS was designed to make continuous observations for studies of Earth's land, ocean, and atmospheric properties and to extend existing data records from heritage Earth observing sensors. The 16 thermal emissive bands (TEBs) (3.75-14.24 μm) are calibrated on orbit using a temperature controlled blackbody (BB). Both Terra and Aqua MODIS BBs have displayed minimal drift over the mission lifetime, and the seasonal variations of the BB temperature are extremely small in Aqua MODIS. The long-term gain and noise equivalent difference in temperature performance of the 160 TEB detectors on both MODIS instruments have been well behaved and generally very stable. Small but noticeable variations of Aqua MODIS bands 33-36 (13.34-14.24 μm) response in recent years are primarily due to loss of temperature control margin of its passive cryoradiative cooler. As a result, fixed calibration coefficients, previously used by bands when the BB temperature is above their saturation temperatures, are replaced by the focal-plane-temperature-dependent calibration coefficients. This paper presents an overview of the MODIS TEB calibration, the on-orbit performance, and the challenging issues likely to impact the instruments as they continue operating well past their designed lifetime of six years.

Terra and Aqua MODIS have successfully operated for over 14 and 12 years since their respective launches in 1999 and 2002. The MODIS on-orbit calibration is performed using a set of on-board calibrators, which include a solar diffuser for calibrating the reflective solar bands (RSB) and a blackbody for the thermal emissive bands (TEB). On-orbit changes in the sensor responses as well as key performance parameters are monitored using the measurements of these on-board calibrators. This paper provides an overview of MODIS on-orbit operation and calibration activities, and instrument long-term performance. It presents a brief summary of the calibration enhancements made in the latest MODIS data collection 6 (C6). Future improvements in the MODIS calibration and their potential applications to the S-NPP VIIRS are also discussed.

The MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands, covering a wavelength range from 0.4 to 14.4 μm. Terra MODIS band 27 (6.72 μm), a water vapor band, was found to have electronic crosstalk from other bands located on the same focal plane assembly, which causes surface feature contamination and pronounced detector level striping in the images. In a previous study, an algorithm using a linear approximation derived from on-orbit lunar observations was developed to correct the crosstalk effect. Results demonstrated that the correction substantially reduces the striping and removes the contaminated surface features. However, it was also demonstrated that the crosstalk effect might bring about a long-term increase in the brightness temperatures (BTs) in Terra band 27. In this paper, it is shown that there is a long-term drift (or decrease), which is strongly detector dependent, in the BT for the band induced by the crosstalk effect. It is also shown that the crosstalk correction with the linear algorithm substantially removes the detector-dependent long-term drift and greatly improves the radiometric accuracy of the band. The comparison between the BT of Terra band 27 in the most recent MODIS Level 1B (L1B) collection [Collection 6 (C6)] and those from the Infrared Atmospheric Sounding Interferometer using simultaneous-nadir-overpass observations shows that the detector-averaged long-term drift in the BT in Terra band 27 varies from approximately 1 K to 3 K. The detector difference can be as large as 9 K for a few detectors during the last five years in the northern and southern polar areas. With crosstalk correction applied, the long-term drift is reduced to be less than 0.5 K, and the detector difference is within 1 K. The crosstalk effect-induced detector-dependent long-term drift in Terra band 27 and the capability of the crosstalk correction algorithm to remove the drift are also assessed at three well-characterized sites with different radiance levels, namely, Dome Concordia (Dome C), Libya 1, and the Pacific Ocean at various radiometric levels. The long-term drift and the strong detector dependence of the drift are clearly observed at the three sites with the BT in the Terra band 27 C6 L1B products. The band-averaged BT drifts are about 0.8 K, 5 K, and 5.5 K, and the detector differences can be as large as 4 K, 12 K, and 15 K, respectively, for the three sites. With the crosstalk correction applied, the long-term drifts in the BT over the three sites are substantially removed, and the observed detector differences of Terra band 27 at the three sites are also significantly reduced. The crosstalk correction greatly improves the radiometric accuracy of the band as well as the image quality.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the National Aeronautics and Space Administration Earth observing system. The first MODIS instrument was launched in December, 1999 onboard the Terra spacecraft. MODIS has 36 bands, covering a wavelength range 0.4-14.4 μm. MODIS band 27 (6.72 μm) is a water vapor band, which is designed to be insensitive to Earth surface features. In recent Earth view images of Terra band 27, surface feature contamination is clearly seen with pronounced striping. In this paper, it is shown that these band-27 issues are caused by electronic crosstalk from bands 28-30. An algorithm using a linear approximation is developed to correct the crosstalk effect. The crosstalk coefficients are derived from Terra MODIS lunar observations. They show that the crosstalk is strongly detector-dependent and the crosstalk pattern has changed in a noticeable fashion since launch. The crosstalk contributions were positive to the instrument response of band 27 early in the mission but became negative and much larger in magnitude at later stages of the mission for most detectors of the band. The algorithms are applied to both the black body (BB) calibration and the MODIS L1B calibrated products. With the crosstalk effect significantly removed, the calibration coefficients of Terra MODIS band 27 derived from the BB show that the detector differences become smaller. With the algorithms applied to MODIS L1B products, the Earth surface features are significantly removed, thereby restoring the radiometric balance of the band and substantially reducing the striping features in the image.

Since launch, Terra and Aqua MODIS have successfully operated for more than 13 and 11 years, respectively. MODIS observations, made in 36 spectral bands covering wavelengths from visible to long-wave infrared, have enabled a broad range of science and research activities and made significant contributions to the earth remote sensing applications. MODIS on-orbit calibration is performed by a set of on-board calibrators (OBC). In addition, lunar observations are made regularly to monitor sensor radiometric calibration stability. This paper provides an overview of the Terra and Aqua MODIS instrument operation and calibration activities, and summarizes their radiometric calibration performance. Also discussed in this paper are the latest changes made in MODIS L1B collection 6 (C6), remaining challenging issues, and future calibration effort.

As a key instrument for NASA's Earth Observing System (EOS), the Moderate Resolution Imaging Spectroradiometer (MODIS) has made significant contributions to the remote sensing community with its unprecedented amount of data products continuously generated from its observations and freely distributed to users worldwide. MODIS observations, covering spectral regions from visible (VIS) to long-wave infrared (LWIR), have enabled a broad range of research activities and applications for studies of the earth's interactive system of land, oceans, and atmosphere. In addition to extensive pre-launch measurements, developed to characterize sensor performance, MODIS carries a set of on-board calibrators (OBC) that can be used to track on-orbit changes of various sensor characteristics. Most importantly, dedicated and continuous calibration efforts have been made to maintain sensor data quality. This paper provides an overview of the MODIS calibration program, on-orbit calibration activities, methods, and performance. Key calibration results and lessons learned from the MODIS calibration effort are also presented in this paper.

The Landsat series of satellites provides the longest running continuous data set of moderate-spatial-resolution imagery beginning with the launch of Landsat 1 in 1972 and continuing with the 1999 launch of Landsat 7 and current operation of Landsats 5 and 7[1]. The Landsat Data Continuity Mission (LDCM) will continue this program into a fourth decade providing data that are keys to understanding changes in land-use changes and resource management. LDCM consists of a two-sensor platform comprised of the Operational Land Imager (OLI) and Thermal Infrared Sensors (TIRS). A description of the applications and design of the TIRS instrument is given as well as the plans for calibration and characterization. Included are early results from preflight calibration and a description of the inflight validation.

Since launch in December 1999, the MODIS ProtoFlight Model (PFM) onboard the Terra spacecraft has successfully operated for more than 11 years. Its Flight Model (FM) onboard the Aqua spacecraft, launched in May 2002, has also successfully operated for over 9 years. MODIS observations are made in 36 spectral bands at three nadir spatial resolutions and are calibrated and characterized regularly by a set of on-board calibrators (OBC). Nearly 40 science products, supporting a variety of land, ocean, and atmospheric applications, are continuously derived from the calibrated reflectances and radiances of each MODIS instrument and widely distributed to the world-wide user community. Following an overview of MODIS instrument operation and calibration activities, this paper provides a summary of both Terra and Aqua MODIS long-term performance. Special considerations that are critical to maintaining MODIS data quality and beneficial for future missions are also discussed.

Since launch, Terra and Aqua MODIS have successfully operated for more than 10 years and 8 years, respectively. Data products derived from MODIS observations have been widely distributed to the science and user community, enabling a broad range of applications. MODIS collects data in 36 spectral bands, covering wavelengths from visible (VIS) to long-wave infrared (LWIR). They are calibrated on-orbit by a set of on-board calibrators (OBC). This paper provides an overview of instrument operation, calibration, and performance, including lessons learned. Though having exceeded their design lifetime of 6 years, both Terra and Aqua MODIS continue to perform well, collect useful data, and support Earth remote sensing applications.

Terra and Aqua MODIS have flown for more than 9 years and 7 years, respectively. Data products derived from MODIS observations have been publically distributed and widely used by the science community and users worldwide. MODIS observations are made in 36 spectral bands covering wavelengths from visible (VIS) to longwave infrared (LWIR). Its on-orbit calibration and characterization are regularly performed using a set of onboard calibrators. This paper provides an overview of sensor calibration and characterization activities, performance, and lessons learned. Though having been operated beyond their design lifetime (6 years), both instruments continue to function well and make major contributions to remote sensing applications. Lessons from both MODIS missions have provided and will continue to provide valuable information for future missions and sensor development.

Two Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are currently in orbit, making continuous global observations in visible to long-wave infrared wavelengths. Compared to heritage sensors, MODIS was built with an advanced set of onboard calibrators, providing sensor radiometric, spectral, and spatial calibration and characterization during on-orbit operation. For the thermal emissive bands (TEB) with wavelengths from 3.7 to 14.4 mum, a v-grooved blackbody (BB) is used as the primary calibration source. The BB temperature is accurately measured each scan (1.47 s) using a set of 12 temperature sensors traceable to the National Institute of Standards and Technology (NIST) temperature standards. The onboard BB is nominally operated at a fixed temperature, 290 K for Terra MODIS and 285 K for Aqua MODIS, to compute the TEB linear calibration coefficients. Periodically, its temperature is varied from 270 K (instrument ambient) to 315 K in order to evaluate and update the nonlinear calibration coefficients. This paper describes MODIS onboard BB functions with emphasis on on-orbit operation and performance. It examines the BB temperature uncertainties under different operational conditions and their impact on TEB calibration and data product quality. The temperature uniformity of the BB is also evaluated using TEB detector responses at different operating temperatures. On-orbit results demonstrate excellent short-term and long-term stability for both the Terra and Aqua MODIS onboard BB. The on-orbit BB temperature uncertainty is estimated to be 10 mK for Terra MODIS at 290 K and 5 mK for Aqua MODIS at 285 K, thus meeting the TEB design specifications. In addition, there has been no measurable BB temperature drift over the entire mission of both Terra and Aqua MODIS.

The NASA's Earth Observing System Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) has continued to operate with satisfactory performance since its launch in May 2002, exceeding its nominal six-year design lifetime. Its continuous Earth observations have been used to generate many science data products for studies of the Earth's system. MODIS has 36 spectral bands: 20 reflective solar bands and 16 thermal emissive bands (TEBs). All TEB observations are made at 1-km nadir spatial resolution with spectral wavelengths from 3.7 to 14.4 mum. Primary applications of MODIS TEB include surface, cloud, and atmospheric temperatures, water vapor, and cloud top altitude. MODIS TEB on-orbit calibration uses a quadratic algorithm with its calibration coefficients derived using an onboard blackbody (BB). This paper will present Aqua MODIS TEB on-orbit calibration, characterization, and performance over its six-year mission. Examples of instrument thermal behavior, BB temperature stability, detector short-term stability, and changes in long-term response (or system gain) will be presented. Comparisons will also be made with Terra MODIS, launched in December 1999. On-orbit results show that Aqua MODIS and its focal plane temperatures have behaved normally. BB temperature has remained extremely stable with typical scan-to-scan variations of less than plusmn0.15 mK. Most TEB detectors continue to exceed their specified signal-to-noise ratio requirements, exhibiting excellent short-term stability and calibration accuracy. Excluding a few noisy detectors, either identified prelaunch or occurring postlaunch, on-orbit changes in TEB responses have been less than 0.5% on an annual basis. By comparison, the overall Aqua TEB performance has been better than that of Terra MODIS.

The Moderate Resolution Imaging Spectroradiometer (MODIS) has successfully provided Earth image products for instruments on the Terra and Aqua satellites since 2000 and 2002, respectively. Maintaining accurate radiometric calibration and calibration consistency between two sensors is an important issue for continued quality of long-term data records, especially as the instruments operate beyond their original projected mission lifetime. A strategy to use frequent MODIS measurements of the brightness temperature of the land surface in the area surrounding Dome Concordia, Antarctica (75.1, 123.4 ) to track the long-term stability of MODIS Band 31 is presented. Dome Concordia, located on the Antarctic plateau, is one of the most homogeneous land surfaces on Earth in terms of surface temperature and emissivity, with a seasonal temperature range of 190-250 K. The extremely dry, cold, and rarefied atmosphere of the site makes it ideal to track and detect any long-term changes in the MODIS thermal band response through trend analyses of near-nadir MODIS overpass data in conjunction with surface temperature measurements. Application of this approach shows an average relative bias between Terra and Aqua MODIS Band 31 (11 ) measurements of 0.08 K, which is well within the calibration uncertainty.

Since launch the NASA EOS Terra MODIS has been in operation for more than seven years and the Aqua MODIS for nearly five years. Each MODIS has 20 reflective solar bands and 16 thermal emissive bands. It makes observations at three nadir spatial resolutions: 0.25km, 0.5km, and Ikm and is calibrated on orbit by a set of on-board calibrators (OBC) that include a solar diffuser, a solar diffuser stability monitor, a blackbody, and a spectro-radiometric calibration assembly. This paper provides an overview of Terra and Aqua MODIS on-orbit calibration and characterization activities and results.