V.V. Salomonson

Development, characterization, and performance of the EOS MODIS sensors

The MODerate-resolution Imaging Spectroradiometer (MODIS) is the keystone instrument for the NASA’s Earth Observing System (EOS). Currently two nearly identical MODIS instruments are operating on-board the EOS Terra spacecraft (launched in December 1999) and the EOS Aqua spacecraft (launched in May 2002), providing global coverage of the Earth’s land, oceans, and atmosphere with both morning and afternoon observations. This paper reviews the EOS MODIS development history, its design concepts, system implementation and calibration, current status and the follow-on Visible/Infrared Imaging Radiometer Suite (VIIRS) under development for the National Polar Orbiting Environmental Satellite System (NPOESS).

Five years of Terra MODIS on-orbit spectral characterization

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the five Earth-observing instruments onboard the NASA EOS Terra spacecraft launched in December 1999. It makes frequent global observations over a broad spectral range (0.41 to 14.4μ) and at three spatial resolutions (0.25km, 0.5km, and 1km at nadir). The MODIS was designed with a set of on-board calibrators (OBCs) that include a solar diffuser (SD), a blackbody (BB), and spectro-radiometric calibration assembly (SRCA). One SRCA function is to provide on-orbit spectral characterization of the MODIS reflective solar bands (RSB) with wavelengths from 0.41 to 2.2μ. This paper provides an overview of the MODIS SRCA on-orbit spectral characterization approach and summarizes the results derived from five years of Terra MODIS on-orbit observations. In general, the on-orbit characterization of the Terra MODIS RSB relative spectral responses (RSR) has been satisfactory. The measured center wavelength (CW) shifts are less than 0.6nm for the 412nm spectral band, 0.5nm for the 443nm band, and 0.4nm for the remaining reflective solar bands (short-wave infrared bands excluded). The bandwidth (BW) changes are typically less than 1nm. Excluding the differences between pre-launch and initial on-orbit results, the CW shifts and BW changes are very stable. For a given band, the detector-to-detector spectral characterization differences are typically less than 0.2nm.

Moderate Resolution Imaging Spectrometer-Nadir (MODIS-N): Progress 1988

The Moderate Resolution Imaging Spectrometer-Nadir (MODIS-N) is one of two MODIS sensors being planned as a facility for the Earth Observing System (Eos). The Eos is scheduled for operation in the late 1990s as a major observing facility to study the Earth as a system. The MODIS-N is a 40-band scanning system designed, principally, to provide observations that would facilitate studies of the interactions between the land and ocean surfaces of the Earth with the atmosphere. At the planned orbital altitude of Eos near 824 kilometers, the swath width of the instrument is presently 1790 kilometers thereby providing nearly complete two-day coverage of the Earth. The spatial resolution of the instrument is 250 and 500 meters for bands designed primarily for land surface processes studies and 1000 meters for bands applied to oceans and atmosphere studies. Thirty-one of the bands are baseline and nine are optional. The inclusion of the optional bands will depend upon the strength of scientific proposals submitted to the Eos Program to make use of the bands for Earth science studies. At present a Request for Proposals (RFP) to perform Phase-B, detailed design studies has been released. Two contractors from private industry will be selected for one-year studies. A single Phase C/D contract will be awarded following the completion of Phase-B studies.

Four years of Aqua MODIS on-orbit radiometric calibration

MODIS is currently onboard NASAs EOS Terra and Aqua spacecraft launched in December 1999 and May 2002, respectively. Together, Terra and Aqua MODIS have generated over 10 years of global observations for the study of changes in the Earths land, oceans, and atmosphere. Each sensor produces more than 40 science data products using measurements from 36 spectral bands with wavelengths ranging from 0.41 to 14.4μm. MODIS on-orbit radiometric calibration is performed using a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the reflective solar bands (RSB) and a blackbody (BB) for the thermal emissive bands (TEB). In addition, regularly scheduled lunar observations are used to track RSB radiometric calibration stability. This paper discusses Aqua MODIS radiometric calibration performance using four-years of on-orbit calibration data. Results include detector noise characterization (SNR for the RSB and NEdT for the TEB), short- and long-term radiometric stability, and optics (scan mirror and solar diffuser) degradation.

Five-years of Terra MODIS on-orbit spatial characterization

The Moderate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands that are distributed, according to their wavelengths, on four focal plane assemblies (FPAs): visible (VIS), near infrared (NIR), short- and mid-wave infrared (SMIR), and long-wave infrared (LWIR). One of the MODIS on-board calibrators, the spectro-radiometric calibration assembly (SRCA), is used to track the sensors on-orbit spatial characterization. It is also capable of performing instrument radiometric stability monitoring and spectral characterization (measurements of the center wavelengths and bandwidths). This paper focuses on the SRCAs spatial characterization function and presents the results (on-orbit performance) derived from the observations made by the Terra MODIS since its launch in December 1999. The SRCA spectral characterization results of Terra MODIS over the same five-year period are covered in another paper in these proceedings (Xiong et. al.). The MODIS on-orbit spatial characterization discussed in this paper includes measurements of the detector-to-detector registration (DDR) in the along-scan direction, the band-to-band registration (BBR) in both along-scan and along track directions, and the focal plane-to-focal plane registration (FFR) in both directions. These measurements are typically performed bi-monthly. The results will show that the overall along-scan BBR performance of the Terra MODIS has been satisfactory (less than 0.16km), meeting the specification of 0.20km. Except for a few bands of slightly over 0.20km, the along-track BBR values are also within the specification.

An overview of MODIS on-orbit calibration and instrument performance

The MODIS ProtoFlight Model on-board the EOS Terra spacecraft was launched on December 18, 1999 and the Flight Model 1 on-board the EOS Aqua spacecraft was launched on May 04, 2002. Together they have produced over 5 years of calibrated data sets from which many land, oceans, and atmosphere products have been developed and provided to the science community and public users for better understanding of both long- and short-term changes in the global environment. Overall, both Terra and Aqua MODIS have been performing well with constant on-orbit calibration and characterization efforts. The Level 1B algorithms and the corresponding production code used to generate the calibrated data sets are mature and stable.

Moderate Resolution Imaging Spectrometer A Progress Report (april 1989)

The Moderate Resolution Imaging Spectrometer (MODIS) is a facility instrument to be flown on the first Earth Observing System (scheduled launch in the late 1990s). The MODIS has two components. One component is a 110-deg-scan-angle instrument called MODIS-N (nadir). This instrument has 40 selected bands supporting observations of the land surface, the oceans, and atmosphere in the visible, NIR, short-wave IR (1.0-3.0 microns), and thermal IR (3.0-15.0 microns). The other component is a 90-deg-scan-angle scanning instrument that can tilt fore and aft along the satellite track, called MODIS-T (tilt). Both MODIS-N and MODIS-T are nearing the end of detailed design studies. The driving scientific requirements include absolute calibration accuracy 2 percent, instrument-induced polarization less than 2 percent, SNR reaching 800:1 for observing ocean color at large solar zenith angles, and dynamic range allowing observations of cloud characteristics and snow-covered areas.

An Overview of Aqua MODIS after Five-year On-orbit Operation and Calibration

Launched in May 2002, the Aqua MODIS has successfully operated on-orbit for more than five years and continuously produced many high quality data products that have significantly contributed to studies of the Earths climate and environmental changes. The MODIS collects data in 36 spectral bands ranging from the visible (VIS) to the long-wave infrared (LWIR) spectral region and at three (nadir) spatial resolutions: 250m (2 bands), 500m (5 bands), and 1km (29 bands). Bands 1-19 and 26 are the reflective solar bands (RSB) with wavelengths from 0.41 to 2.2μm and bands 20-25 and 27-36 are the thermal emissive bands (TEB) with wavelengths from 3.7 to 14.4μm. The MODIS on-board calibrators, noticeably improved over those of its heritage sensors, include a solar diffuser (SD), a solar diffuser stability monitor (SDSM), a blackbody (BB), a spectro-radiometric calibration assembly (SRCA), and a space view (SV) port. This paper provides an overview of Aqua MODIS on-orbit operation and calibration activities with emphasis on the performance of its on-board calibrators. Results discussed in this paper include TEB and RSB detector noise characterization, short-term stability and long-term response change. The sensors overall spectral (RSB) and spatial (RSB and TEB) parameters are also presented in this paper.