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In 1998, two significant components of NASA's Mission to Planet Earth program, Landsat 7 and the first Earth Observing System, morning equator-crossing platform (EOS AM1), are each scheduled to be launched into 705 km, sun-synchronous orbits. Landsat 7 will carry the enhanced thematic mapper plus (ETM+) sensor, while the premier instrument on the EOS AM1 platform will be the moderate resolution imaging spectrometer (MODIS). In addition, NASA is currently assessing an option to fly a Landsat ocean color instrument (LOCI) on the Landsat 7 spacecraft along with the ETM+. The Landsat ETM+ will: (a) cover a ground swath of 185 km, (b) provide 30 m multispectral coverage over six bands in the visible (VIS), near infrared (NIR), and shortwave infrared (SWIR) regions, as well as a 15 m panchromatic (PAN) band and a 60 m thermal IR (TIR) band, and (c) yield global repeat coverage every 16 days. By contrast, the LOCI, would, if flown: (a) cover a usable ground swath of approximately equals 2000 km, (b) provide approximately equals 1.1 km spatial resolution at nadir in eight VNIR bands equivalent to those of the SeaWIFS instrument, (c) yield global coverage every two days at 12 bit quantization and with four available gain settings such that unsaturated radiance data could be collected over land surfaces, and (d) be tiltable +/- 20 degree(s) along-track to minimize sunglint effects over water bodies. The MODIS sensor on the EOS AM1 platform will: (a) cover a ground swath of 2048 km, (b) provide approximately equals 1 km spatial resolution at nadir in 29 bands covering the VNIR, SWIR, and TIR regions at 12 bit quantization, plus two VNIR bands at 250 m and five VNIR/SWIR bands at 500 m spatial resolution, and (c) yield complete global coverage every two days. Plans call for the two spacecraft to be placed in a same-day orbit, spaced 30 minutes apart, i.e., equatorial crossing times of 10:00 a.m. for Landsat 7 and 10:30 a.m. for EOS AM1. Thus, multispectral data having both high (30 m) and medium-to-coarse (250 m - 1000 m) spatial resolution will be acquired repetitively on a global basis under nearly identical atmospheric and plant physiological conditions. It is expected that significant benefits will be realized by utilizing these data in a multistage, multispectral sampling approach. In fact, NASA has recently endorsed the concept of jointly flying an advanced technology TM-class instrument with MODIS on the EOS AM2 platform scheduled for launch in 2004. Much of the following text was extracted from a white paper (Sellers and Williams, 1994) that was instrumental in leading NASA Headquarters to endorse this concept.
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