Monday, 14 January 2002
MODIS Level 1B data from GES DAAC - advantages and challenges
As part of Earth Observing System (EOS) mission, the Moderate-Resolution Imaging Spectroradiometer (MODIS) on board of Terra satellite began data acquisition in February, 2000. With its unique characteristics, MODIS improves far upon the heritage of similar sensors. It scans the Earth with a 2330 km wide swath in 36 optical bands. Data from all bands are processed and distributed by Goddard Earth Sciences Distributed Active Archive Center (GES DAAC) as calibrated radiances, known as Level 1B product (L1B). The latter received broad popularity and demand, which can be attributed to a number of reasons. MODIS is always on, thus allowing L1B data to completely cover the Earth every two days. Two of the reflective bands (RB) provide this coverage at 250 m resolution, five RB's provide 500 m, and the rest of the reflective and all emissive bands are at 1 km resolution. The data is stored in HDF-EOS format, and is available to users all over the world free of charge. Interested users have the opportunity to invest in a receiving station of their own, thus acquiring L1B within hours of Terra overpass.
At the same time L1B with its shear volume poses challenges never seen before, to the data production and distribution systems, and to the users. The daily volume of processed and archived L1B is order of 200 GB, while the daily distribution limit of GES DAAC is order of 500 GB. From users perspective, even though the data is broken into 5-min granules, their size is still too big (order of 300 MB per granule). L1B data is georeferenced, but not mapped, and hence require special tools and detailed understanding in order to properly map the data on an appropriate projection.
Hence, in this poster we present the essence of the MODIS L1B data, and suggest links and references for reading to better understand the data. Ways to search and order the data are discussed, together with the upcoming subsetting services from GES DAAC. Tools to visualize and map L1B data are presented. Samples of images of L1B data are given in the light of possible applications.