Harry E. Montgomery

Prelaunch algorithm and data format for the Level 1 calibration products for the EOS-AM1 Moderate Resolution Imaging Spectroradiometer (MODIS)

The Moderate Resolution Imaging Spectroradiometer (MODIS) radiometric calibration product (Level 1B) is described for the thermal emissive and reflective solar bands. A band-integrated radiance is produced for all measurements. A reflectance factor product is also produced for the reflected solar band measurements. Specific sensor design characteristics are identified to assist in understanding how the calibration algorithm software product is designed. The product file format is summarized, and the location for the current file format is provided.

Determination of spatial characteristics by using the spectro-radiometric calibration assembly (SRCA) of MODIS: I. Along-scan

The Spectro-Radiometric Calibration Assembly (SRCA) is briefly described. This paper discusses one of the SRCA functions -- spatial calibration to determine the channel position shift along-scan. The band centroid shift along- track will be discussed in Part II. Discussion in this part mainly focuses on the algorithm, the methodology, and the stability of the calibration signals. The algorithm and the methodology includes: a model of the image motion as a function of data sample and the centroid calculation to determine the detector/band positions. The SRCA stability is examined by checking the data inconsistencies between redundant samples, sub-samples, and the two mirror sides. Also described is the handling of the dark-reading for the thermal bands, which is affected by background energy for the opaque part of the reticle. A series of results are presented, which compare the relative position shift and co- registration between channels, bands, and Focal Plane Assemblies. Test results are illustrated for calibration under different environments and by different instruments. These results indicate that the SRCA is a stable an sensitive calibrator which provides consistent results. The overall uncertainty analysis will be presented in Part II.

Determination of MODIS band-to-band co-registration on-orbit using the SRCA

This paper presents the measurement results of how well the thirty-six MODIS bands are registered with respect to each other on the Earth at nadir. Test data show that the SRCA provides consistent results. Excluding FPA shifts, the repeatability on-orbit for four tests is within /spl plusmn/0.01 km. Results indicate that the worst band-to-band registration is /spl plusmn/0.11 km in along-scan direction (perpendicular to the satellite ground track) and /spl plusmn/0.17 km along-track.

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.

SRCA radiometric calibration tracking from pre-launch to on-orbit

The launch-related spectral band radiance change of the Spectro-Radiometric Calibration Assembly (SRCA) of MODurate Resolution Imaging Spectrometer (MODIS) is mainly attributable to its lamp temperature variations. Comparison of the spectral profiles, measured by the SRCA at different times, provides a way of tracking change in the band radiance while the integrated SRCA radiance remains constant. Prelaunch the SRCA was calibrated against a ground Spherical Integration Source (SIS100). Meanwhile the SRCA calibrations were run in spectral and radiometric modes. Comparison of the on-orbit data from the SRCA spectral and radiometric modes to prelaunch data will transfer SIS100 ground calibration to orbit. For validation, data form TV at nominal temperature plateau will define the radiometric transfer; this transfer will be applied to SRCA data measured at other temperature plateaus and compared with the measured SIS100 radiance values.

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.

Determination of spectral characteristics of MODIS on-orbit using SRCA

This paper describes the results of on-orbit center wavelength calibration of twenty MODIS Solar Reflective Bands (SRB) by the SRCA. The calibration signal problems and the uncertainty estimates are described. The calibration results show that (1) SRCA monochromator parameters are stable; (2) MODIS band center wavelengths measured have less than 0.4 nm change from prelaunch to on-orbit; and (3) MODIS band response profile changes slightly for band 8 and remains unchanged for the other measured SRBs.

Tracking MODIS gain change on-orbit by relating it to SRCA lamp parameters

This paper addresses the methodology and algorithm for using the Spectro-Radiometric Calibration Assembly (SRCA) lamp electrical parameters to track its output band radiance change. This allows the use of the SRCA to track MODurate resolution Imaging Spectroradiometer (MODIS) detector gain variation at different orbit positions because the MODIS dn change is attributed to its gain change after subtracting the SRCA output radiance change itself. Pre-launch test data show that using lamp current as a parameter is valid. Orbit data prove that the approach is valid for longer periods of time for all Solar Reflective Bands (SRBs). Data indicate that the MODIS has undetectable gain change at different orbit positions.