MODIS, a major NASA's Earth Observing System (EOS) instrument, was launched aboard the Terra satellite on December 18, 1999 (10:30 am equator crossing time) for global monitoring of the atmosphere, the terrestrial ecosystems and oceans, to develop better understanding of the 'Total Earth System', and to study the effects of natural and human-induced changes on the global environment.

MODIS with its 2330 km viewing swath width provides almost daily global coverage. It acquires data in 36 high spectral resolution bands between 0.415 and 14.235 micron with spatial resolutions of 250 m (2 bands), 500 m (5 bands), and 1000 m (29 bands). This year a similar instrument will be flown on the EOS-Aqua satellite (1:30 pm equator crossing time). This will enable us to study diurnal variation of the rapidly varying systems.

The radiance data measured by MODIS at high spatial resolution with some new channels (never used before for remote sensing from space) provides improved and valuable information about the physical structure of the Earth system, such as vertical distribution of temperature and humidity, cloud and aerosol characteristics, sources and sinks of trace gases, surface emissivity, land and sea surface temperature, land cover and primary productivity, snow cover and sea ice concentration, glacier and polar ice sheets, ocean currents, ocean color, and phytoplankton.

Almost all key climate and environmental parameters are available as standard MODIS products and are derived from MODIS high spatial resolution radiances. However, these radiometrically corrected and geolocated high spatial resolution radiance data (referred as Level 1B product) are much in demand by the science user community. These radiances are needed to enhance existing algorithms, to test new algorithms for the retrieval of existing or new parameters, and for developing simulation datasets for characterization of new sensors. The multi-angle spectral radiance/reflectance data is also needed in developing a more realistic Bi-directional Reflectance Distribution Function (BRDF) for the accurate computation of surface albedo, an essential parameter used in the earth radiation budget and climate models.

MODIS radiance counts, calibrated radiance/reflectance, geolocation products, and all derived geophysical atmospheric and ocean products are archived at the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) Distributed Active Archive Center (DAAC). Detailed information pertaining to these data products is available from the Goddard DAAC Web site http://daac.gsfc.nasa.gov/. All land products are archived at Earth Resources Observation System (EROS) Data Center (EDC), and snow & ice products are archived at National Snow and Ice Data Center (NSIDC). MODIS products, ancillary and related data, related documents, and data analysis and visualization tools are freely made available to the public and science user community from these data archive centers.

This presentation will provide key characteristics of the MODIS radiance/reflectance products (Level-1B) with some examples of the applications of the MODIS radiances in detecting human impacts on the earth and its climate and how valuable this data is in improving the predictions and characterization of natural disasters such as wild fires, volcanoes, floods and drought.