MODIS (or Moderate Resolution Imaging Spectroradiometer) is a key instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites. Terra's orbit around the Earth is timed so that it passes from north to south across the equator in the morning, while Aqua passes south to north over the equator in the afternoon. Terra MODIS and Aqua MODIS are viewing the entire Earth's surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths (see MODIS Technical Specifications). These data will improve our understanding of global dynamics and processes occurring on the land, in the oceans, and in the lower atmosphere. MODIS is playing a vital role in the development of validated, global, interactive Earth system models able to predict global change accurately enough to assist policy makers in making sound decisions concerning the protection of our environment.
Terra
Terra is a multi-national, multi-disciplinary mission involving partnerships with the aerospace agencies of Canada and Japan. Managed by NASA’s Goddard Space Flight Center, the mission also receives key contributions from the Jet Propulsion Laboratory and Langley Research Center. Terra is an important part of NASA’s Science Mission, helping us better understand and protect our home planet.
Aqua, Latin for water, is a NASA Earth Science satellite mission named for the large amount of information that the mission will be collecting about the Earth's water cycle, including evaporation from the oceans, water vapor in the atmosphere, clouds, precipitation, soil moisture, sea ice, land ice, and snow cover on the land and ice. Additional variables also being measured by Aqua include radiative energy fluxes, aerosols, vegetation cover on the land, phytoplankton and dissolved organic matter in the oceans, and air, land, and water temperatures.
The Aqua mission is a part of the NASA-centered international Earth Observing System (EOS). Aqua was formerly named EOS PM, signifying its afternoon equatorial crossing time. A timeline of Aqua on-orbit progress through the initial 120 day check-out period can be found here.
Aqua was launched on May 4, 2002, and has six Earth-observing instruments on board, collecting a variety of global data sets. Aqua was the first member launched of a group of satellites termed the Afternoon Constellation, or sometimes the A-Train. The second member to be launched was Aura, in July 2004, the third member was PARASOL, in December 2004, and the fourth and fifth members are CloudSat and CALIPSO, in May 2006. Expected upcoming missions are OCO and Glory, with the placement of Glory not yet determined. Once completed, the A-Train will be led by OCO, followed by Aqua, then CloudSat, CALIPSO, PARASOL, and, in the rear, Aura.
The MODIS instrument is operating on both the Terra and Aqua spacecraft. It has a viewing swath width of 2,330 km and views the entire surface of the Earth every one to two days. Its detectors measure 36 spectral bands between 0.405 and 14.385 µm, and it acquires data at three spatial resolutions -- 250m, 500m, and 1,000m.
Along with all the data from other instruments on board the Terra spacecraft and Aqua Spacecraft, MODIS data are transferred to ground stations in White Sands, New Mexico, via the Tracking and Data Relay Satellite System (TDRSS). The data are then sent to the EOS Data and Operations System (EDOS) at the Goddard Space Flight Center. The Level 1A, Level 1B, geolocation and cloud mask products and the Higher-level MODIS land and atmosphere products are produced by the MODIS Adaptive Processing System (MODAPS), and then are parceled out among three DAACs for distribution. Ocean color products are produced by the Ocean Color Data Processing System (OCDPS) and distributed to the science and applications community.
The many data products derived from MODIS observations describe features of the land, oceans and the atmosphere that can be used for studies of processes and trends on local to global scales. As just noted, MODIS products are available from several sources. MODIS Level 1 and atmosphere products are available through the the LAADS web. Land Products are available through the Land Processes DAAC at the U. S. Geological Survey EROS Data Center (EDC). Cryosphere data products (snow and sea ice cover) are available from the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado. Ocean color products and sea surface temperature products along with information about these products are obtainable at the OCDPS at GSFC. Users with an appropriate x-band receiving system may capture regional data directly from the spacecraft using the MODIS Direct Broadcast signal.
MODIS data in HDF-EOS format (Hierarchical Data Format - Earth Observing System). Hierarchical Data Format (HDF) is the standard data format for all NASA Earth Observing System (EOS) data products. HDF is a multi-object file format developed by The HDF Group.
MODIS Tools is helping us to read, extract or subset, convert HDF-EOS data.
1. MODIS Reprojection Tool (MRT)- http://edcdaac.usgs.gov/landdaac/tools/modis/index.asp
a software tool for reading data files in HDF-EOS format, specify a geographic subset or band subset as input to processing, perform geographic transformation to a different coordinate system/cartographic projection, write the output to file formats other than HDF-EOS
Platforms : Unix (Sun, SGI), Windows (9x, 2000, NT, XP), and Linux
2. QA Tools - http://edcdaac.usgs.gov/landdaac/tools/ldope/index.asp
provides links to QA tools developed for science team and user community
Platforms : Unix
3. HDF Tools (http://hdf.ncsa.uiuc.edu/)
The NCSA HDF Home Page - contains links to an array of HDF support tools and information
Platforms : specific to tool selected
4. HDF-EOS Web-Based Subsetter (HEW) - http://subset.itsc.uah.edu/hew2k/hew.html
can extract a subset of any grid or swath data file that is in HDF-EOS format Platforms : independent
5. MODIS Swath-to-Grid Toolbox - http://nsidc.org/data/modis/ms2gt/
a set of software tools that reads HDF-EOS files containing MODIS swath data and produces flat binary files containing gridded data in a variety of map projections Platforms : Unix, with a standard C compiler, also requires Perl 5.0 or higher and IDL 5.0 or higher
6. HDF-EOS to GeoTIFF converter (HEG) - http://edcdaac.usgs.gov/landdaac/tools/heg/heg_announce.asp
converts many EOS products written in HDF-EOS to GeoTIFF, native binary or HDF-EOS Grid, also has re-projection, resampling, subsetting, stitching (mosaicing), and metadata creation capabilities
Platforms : Linux , Macintosh , SGI , Sun, Windows
7. MODIS Land Tile Calculator - http://landweb.nascom.nasa.gov/cgi-bin/developer/tilemap.cgi
converts latitude/longitude decimal degrees to MODIS Tile grid and Line/Sample coordinates and vice-versa
Platforms: online tool
source informations :
- http://modis.gsfc.nasa.gov/
- http://modis-land.gsfc.nasa.gov/tools.htm
- http://nsidc.org/data/hdfeos/
