Virginia G. Ford

A multiangle imaging spectroradiometer for terrestrial remote sensing from the earth observing system

The Multiangle Imaging SpectroRadiometer (MISR) instrument for the Earth Observing System (EOS) will provide a unique opportunity for studying the ecology and climate of the Earth through the acquisition of systematic, global multiangle imagery in reflected sunlight. MISR employs nine discrete cameras pointed at fixed angles, viewing the nadir direction and forward and aftward along the spacecraft ground track. Each camera is a charge‐coupled‐device –based pushbroom imager. Within a 7‐minute period, every point in a 204‐km‐wide swath is imaged at the nine viewing angles, ensuring observations acquired under virtually identical illumination and atmospheric conditions. The cameras will image the Earth in the nadir direction and at 30.7°, 45.6°, 60.0°, and 72.5° forward and aftward of the local vertical at the Earths surface. Images at each angle will be obtained in four spectral bands centered at 440, 550, 670, and 860 nm. MISR is capable of taking image data in two different spatial resolution modes: Local Mode, in which selected targets are observed with 240‐m spatial sampling, and Global Mode, where the entire sunlit Earth is observed continuously with 1.92‐km sampling. Absolute radiometric calibration of the MISR instrument will be performed in‐flight using special on‐board hardware. The data produced by MISR will be valuable in a number of scientific discipline areas, and MISR images and geophysical products will be archived at the EOS Data and Information System to make them available to the broad scientific community.

Terrestrial Planet Finder Coronagraph Observatory summary

Creating an optical space telescope observatory capable of detecting and characterizing light from extra-solar terrestrial planets poses technical challenges related to extreme wavefront stability. The Terrestrial Planet Finder Coronagraph design team has been developing an observatory based on trade studies, modeling and analysis that has guided us towards design choices to enable this challenging mission. This paper will describe the current flight baseline design of the observatory and the trade studies that have been performed. The modeling and analysis of this design will be described including predicted performance and the tasks yet to be done.

Design of new photodiode standards for use in the MISR in-flight calibrator

The Multi-Angle Imaging SpectroRadiometer (MISR) is to be launched in 1998 as part of NASAs Earth Observing System. The 3% (1/spl sigma/) absolute radiometric calibration requirement for this instrument is considered challenging, particularly since it must be maintained through the five-year mission life. To meet this specification MISR will rely on detector-based calibration techniques, which are primarily founded on High Quantum Efficiency (HQE) detector technology. Filtered HQE photodiodes will be used to characterize solar-reflected light from a diffuse calibration target during the mission. In addition, radiation-hard photodiodes, which have an extended lifetime over the HQE detectors, will be utilized as part of the on-board calibrator. To date, flight photodiodes and filters have been fabricated, along with components of the photodiode flight package, and the photodiodes have undergone performance and stability testing. This paper gives a status report on these new in-flight photodiode standards, with primary emphasis on the photodiode performance measurements taken to date.<<ETX>>

State of the art radiometer standards for NASA's Earth Observing System

The multi-angle imaging spectro-radiometer (MISR), to be launched in 1998, is one of five instruments on NASAs first Earth Observing System (EOS) platform. The 3% (1/spl sigma/) absolute radiometric calibration requirement is considered challenging, particularly since it must be maintained through the five-year mission life. The instrument requirements have led to the development of an on-board calibrator (OBC) consisting of diffuse panels and photodiode-based radiometric standards. Although used extensively in national standard laboratories, MISR will be the first in-orbit instrument to utilize Spectralon calibration targets, and the first instrument to establish a radiometric scale in orbit using detector-based standards. The team has adopted the nomenclature high quantum efficiency (HQE) technology to refer to the implementation of 100% internal quantum efficient photodiodes in a trapped configuration. Filtered HQE radiometers are being utilized in the preflight calibration phase to calibrate the flat-field source, they will also be used to characterize solar-reflected light from the diffuse calibration targets during the mission. In addition, radiation-resistant photodiodes will be utilized as part of the OBC.<<ETX>>