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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2018

Assessing the Calibration Differences in the Reflective Solar Bands of Terra MODIS and Landsat-7 Enhanced Thematic Mapper Plus

Long-term data records obtained from Earth observing sensors depend not only onthe calibration accuracy of individual sensors but also on the consistency across instruments andplatforms. Hence, sensor calibration intercomparison plays a vital role for a better understandingof various science products. The Moderate Resolution Imaging Spectroradiometer (MODIS)and enhanced thematic mapper plus (ETM+) on the Terra and Landsat 7 platforms have operatedsuccessfully since their launch, collecting measurements in the reflective solar and infrared partsof the spectrum. Terra MODIS has employed a reflectance-based calibration since beginning itsmission. In the case of ETM+, a radiance-based calibration was employed until recent years,when a reflectance-based calibration was introduced. Being in the AM constellation with lessthan 30 min difference in overpass times, near-simultaneous Earth scene measurements can beeffectively used to assess the calibration differences between the spectrally matching bands ofthese two instruments. The pseudoinvariant calibration sites (PICS) in the North African desertare widely used for on-orbit calibration and validation of satellite sensors. Four PICS from thisregion have been employed to assess the multitemporal reflectance differences. Correction forbidirectional reflectance, spectral response function mismatch, and impacts of atmosphericwater-vapor have been incorporated to provide an assessment of the long-term stability ofeach spectral band and reflectance differences amongst them. Results indicate that the spectralbands of both instruments show a long-term stability to within 2% from 2000 to 2017. Thetop-of-atmosphere reflectances between the two instruments postcorrection agree to within 4%.Also included in this paper is a detailed discussion of various parameters contributing to theuncertainties of this cross-calibration. The techniques presented in this paper can be furtherextended to perform similar intercomparison between Landsat 8 Operational Land Imager, AquaMODIS, and Suomi-NPP VIIRS.

Angal, Amit↗
NASA NTRSDate not supplied

Inverse Solution to the Electronic Crosstalk Correction of Bands 27-30 in Terra MODIS

In the Terra MODIS Collection 6.1 (C6.1) Level-1B (L1B) product, an electronic crosstalk correction is implemented for bands 27 30 using a linear algorithm. In this algorithm, the measured (contaminated) signal from the detectors in the bands was used as a reference signal for deriving the correction coefficients from lunar images and for applying the correction to the calibration and L1B data. As the mission progressed, the level of contamination steadily increased in each detector, with an additional large increase associated with the Terra MODIS safe-mode anomaly in February of 2016. In this work, we developed a modified algorithm for deriving the crosstalk coefficients and applying the correction which uses the inverse crosstalk coefficient matrix in order to remove the contamination from the reference signal. We apply the coefficients using this modified algorithm to calibration and Earth-view data in order to assess the difference with the data in C6.1. We also perform calculations using simulated contamination to show the difference in the recovery of the corrected signal between the C6.1 algorithm and the modified algorithm. We will show, that although the current levels of contamination are much higher than early in the mission, the overall impact of having contamination on the reference signal for the correction is small. However, this impact is non-linear as a function of the magnitude of the contamination level, so it should be monitored as the mission continues.

Truman Wilson↗
NASA NTRS2020

Cross-Calibration of Terra and Aqua MODIS Using RadCalNet

The twin 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 AVHRR) or using lunar measurements normalized using a common model such as the USGS ROLO. In recent years RadCalNet, a 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 work, the near-simultaneous TOA reflectance measurements from the Railroad Valley, US (RVUS) are used as a transfer to compare the on-orbit observations for the Terra and Aqua MODIS RSB. Near-nadir overpasses from January 2013 to January 2019 are processed and matched up with near-simultaneous RadCalNet measurements. Results show that the VIS/NIR bands agree to within 2% and the SWIR bands agree to within 5%. Also, discussed in this work 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 BRDF effects.

Amit Angal↗
NASA NTRS2021

Cryovolcanic flooding in Viking Terra on Pluto

A prominent fossa trough (Uncama Fossa) and adjacent 28-km diameter impact crater (Hardie) in Pluto's Viking Terra, as seen in the high-resolution images from the New Horizons spacecraft, show morphological evidence of in-filling with a material of uniform texture and red-brown color. A linear fissure parallel to the trough may be the source of a fountaining event yielding a cryoclastic deposit having the same composition and color properties as is found in the trough and crater. Spectral maps of this region with the New Horizons LEISA instrument reveal the spectral signature of H2O ice in these structures and in distributed patches in the adjacent terrain in Viking Terra. A detailed statistical analysis of the spectral maps shows that the colored H2O ice filling material also carries the 2.2-μm signature of an ammoniated component that may be an ammonia hydrate (NH3·nH2O) or an ammoniated salt. This paper advances the view that the crater and fossa trough have been flooded by a cryolava debouched from Pluto's interior along fault lines in the trough and in the floor of the impact crater. The now frozen cryolava consisted of liquid H2O infused with the red-brown pigment presumed to be a tholin, and one or more ammoniated compounds. Although the abundances of the pigment and ammoniated compounds entrained in, or possibly covering, the H2O ice are unknown, the strong spectral bands of the H2O ice are clearly visible. In consideration of the factors in Pluto's space environment that are known to destroy ammonia and ammonia-water mixtures, the age of the exposure is of order ≤109 years. Ammoniated salts may be more robust, and laboratory investigations of these compounds are needed.

Pluto↗
NASA NTRS2022

Preface, special issue of “20th Anniversary of Terra Science”

The Terra satellite, launched in December 1999 as the flagship mission of the Earth Observing System, is an international mission carrying instruments developed by the United States, Japan, and Canada. These instruments, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Clouds and Earth’s Radiant Energy System (CERES), Multi-angle Imaging SpectroRadiometer (MISR), Moderate-resolution Imaging Spectroradiometer (MODIS), and Measurements of Pollution in the Troposphere (MOPITT), provide valuable observations to investigate the interconnections between Earth's land, atmosphere, ocean, snow and ice, and energy balance, and have yielded the first global and seasonal measurements of the Earth system for long-term monitoring of climate and environmental change. Over the past 20 years and with more than 100,000 orbits, Terra’s observations have greatly enhanced our understanding of the Earth's climate and the effects of human activity and natural disasters on communities and ecosystems.

Lahouari Bounoua↗
NASA NTRSDate not supplied

Using Scattered Light From Nadir Port to Aid the Terra and Aqua MODIS Reflective Solar Band Calibration

The MODIS instruments on the Terra and Aqua spacecraft employ a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) system to calibrate their reflective solar bands (RSBs), covering a spectral range from 0.4 to 2.1 µm. The UV exposure of the SD, from its sun-view port as well as the scattered light (sunlight reflected from top-of-atmosphere), has led to a wavelength dependent degradation of the SD, with larger degradation observed at shorter wavelengths. The scatter off the diffuser onto the scan mirror is in the forward direction, whereas the scatter off the diffuser onto the SDSM fold mirror is in the backward direction. Since the outgoing angles (viewed by MODIS detectors) are the same as the scheduled SD calibration, the gain derived from scattering light facilitates monitoring the dependence of the SD’s degradation on incident angles. In this paper, we present a method that uses multiple orbits over each mission to obtain a SD response to the nadir port illumination. The SD degradation estimated from the nadir port illumination is compared with the degradation derived from the sun-illuminated SD. As both Terra and Aqua spacecraft continue to drift from their nominal orbits, the SD calibration mechanism has been adapted to these drifts, especially in terms of characterizing the transmission screen function. This paper also presents the utility of this scattering light data to support the RSB calibration in the post-nominal orbit drift era of operations.

MODIS↗
NASA NTRSDate not supplied

Terra Orbit Drift and its Impacts on MODIS Geometric Performance

NASA Terra satellite has provided earth observations from its 5 onboard instruments for 25 years since its launch in December 1999. All these instruments are still mostly healthy, and observations are expected to extend 2 more years of life into late 2026. The onboard fuel is preserved by ceasing inclination adjust maneuvers (IAMs, stopped 2020) and drag make-up maneuvers (DMUs, stopped 2022). Without IAMs, the orbital plane is drifting, changing the sunlight conditions by late 2026 from nominal 10:30 AM to 8:30 AM local time at descending node (LTDN). The ceasing of DMUs combined with a constellation exit maneuver in October 2022 result in orbit altitude drifting down. Altitude will drift from a nominal mean of 715 km to 702 km by late 2026. A companion earth observing satellite, Aqua, is going through a similar orbit drift process. This presentation shows the details of the drifts, that have potentials to impact data products, especially those products from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on Terra and Aqua satellites.

Guoqing (Gary) Lin↗
NASA NTRS2016

EOS Terra: Mission Status Constellation MOWG

This EOS Terra Mission Status Constellation MOWG will discuss mission summary; spacecraft subsystems summary, recent and planned activities; inclination adjust maneuvers, conjunction history, propellant usage and lifetime estimate; and end of mission plan.

constellation MOWG↗
NASA NTRS2015

Terra Constellation Exit (Part 2)

The Terra Constellation Exit power point presentation will discuss the baseline and proposed constellation exit plan and debris concerns.

Exit Plan↗
NASA NTRS2016

Marine Boundary Layer Cloud Property Retrievals from High-Resolution ASTER Observations: Case Studies and Comparison with Terra MODIS

A research-level retrieval algorithm for cloud optical and microphysical properties is developed for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard the Terra satellite. It is based on the operational MODIS algorithm. This paper documents the technical details of this algorithm and evaluates the retrievals for selected marine boundary layer cloud scenes through comparisons with the operational MODIS Data Collection 6 (C6) cloud product. The newly developed, ASTERspecific cloud masking algorithm is evaluated through comparison with an independent algorithm reported in Zhao and Di Girolamo (2006). To validate and evaluate the cloud optical thickness (tau) and cloud effective radius (r(sub eff)) from ASTER, the high-spatial-resolution ASTER observations are first aggregated to the same 1000m resolution as MODIS. Subsequently, tau(sub aA) and r(sub eff, aA) retrieved from the aggregated ASTER radiances are compared with the collocated MODIS retrievals. For overcast pixels, the two data sets agree very well with Pearson's product-moment correlation coefficients of R greater than 0.970. However, for partially cloudy pixels there are significant differences between r(sub eff, aA) and the MODIS results which can exceed 10 micrometers. Moreover, it is shown that the numerous delicate cloud structures in the example marine boundary layer scenes, resolved by the high-resolution ASTER retrievals, are smoothed by the MODIS observations. The overall good agreement between the research-level ASTER results and the operational MODIS C6 products proves the feasibility of MODIS-like retrievals from ASTER reflectance measurements and provides the basis for future studies concerning the scale dependency of satellite observations and three-dimensional radiative effects.

marine boundary layer↗
NASA NTRS2018

EOS Terra Mission Status Constellation MOWG

This package presents the current health of the Terra mission, along with recent activities, status on documentation and plans for the recent future.

Terra spacecraft status↗
NASA NTRS2018

Sensor Performance Assessment for Terra and Aqua MODIS Using Unscheduled Lunar Observations

The Moderate Resolution Imaging Spectroradiometer (MODIS) has been in operation for over 18 and 16 years on the Terra and Aqua spacecrafts, respectively. In order to maintain long-term calibration stability over the life of each mission, MODIS uses a set of on-board calibrators as well as observations of the Moon and selected Earth-view targets. The lunar observations nominally occur in a narrow phase angle range, 55 degrees - 56 degrees, and use scheduled spacecraft maneuvers in order to bring the Moon into alignment with the MODIS space-view port. These observations are used to help characterize the MODIS scan-mirror response versus scan-angle. In addition to these scheduled lunar observations, MODIS also views the Moon through the space-view port without a spacecraft maneuver when the geometry is appropriately aligned. This occurs over a wider phase angle range, between 51 degrees - 82 degrees, than those of the scheduled moon observations. While the phase angle restriction of our scheduled observations provides consistency between the calibration events, the unscheduled Moon data can provide a valuable assessment of many calibration related investigations that use the Moon. In this paper, we compare the results of unscheduled versus scheduled lunar observations for several sensor calibration and performance assessments. These include the lunar calibration trending used to characterize the scan-mirror response versus scan angle and the electronic crosstalk correction of bands 27-30, which are currently used in the MODIS Level-1B data products, as well as sensor performance assessments such as band-to-band and detector-to-detector spatial registration.

Aqua↗
NASA NTRS2018

Subsample Difference Correction for Terra MODIS SWIR Bands 5-7 Using Lunar Observations

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the key instruments on board the Terra (EOS (Earth Observing Satellite) AM-1) spacecraft. MODIS has 36 spectral bands ranging in wavelength between 0.4 and 14.2 microns, at three spatial resolutions of 250 meters (bands 1-2), 500 meters (bands 3-7), and 1 kilometer (bands 8-36). For each 1-km sample, the 250-m and 500-m bands use 4 and 2 detectors with each acquiring 4 and 2 subsamples respectively in order to maintain consistent along-scan and along-track resolutions at nadir. The SWIR (Short-Wave Infrared) bands, 57 and 26, share the same focal-plane array as the 1-km thermal emissive bands, 20-25. During one of the two 500-m subsamples for bands 57, sampling of the 1-km bands introduces increased electronic crosstalk contamination, resulting in a subsample difference for both Earth-view and on-board calibrator observations. For this work, we use data from lunar and on-board blackbody observations, which occur at different signal levels for bands 20-25, to derive a correction to the contamination. This correction can be applied to reduce the subsample differences in the MODIS Earth-view data over a wide range of scenes. The impact of this correction on the sensor calibration and Earth-view data will be assessed.

SWIR↗
NASA NTRS2018

EOS Terra: Mission Status Constellation MOWG

General information regarding the current health and status of the EOS (Earth Observing System) Terra Spacecraft. Updates to activities accomplished since the last MOWG (Mission Operations Working Group) and future maneuver plans are included as well.

Terra Spacecraft Status↗
NASA NTRS2019

EOS Terra Mission Status Constellation MOWG

Slide presentation regarding the current state of health of the Terra mission, subsystem status, fuel remaining, recent activities and upcoming plans.

Terra Spacecraft Status↗
NASA NTRSDate not supplied

EOS Terra Mission Status Constellation MOWG

This package presents the current health of the Terra mission, along with recent activities, status on documentation and plans for the recent future.

Terra Spacecraft Status↗