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 and it acquires data at three spatial resolutions: 250-m, 500-m, and 1,000-m.
MODIS filenames (i.e., the local granule ID) follow a naming convention which gives useful information regarding the specific product. For example, the filename MOD09A1.A2006001.h08v05.005.2006012234657.hdf indicates:
The MODIS Long Name (i.e., Collection-Level) convention also provides useful information. For example, all products belonging to the MODIS/Terra Surface Reflectance 8-Day L3 Global 500m SIN Grid V005 collection have the following characteristics:
The high level MODIS Land products distributed from LP DAAC are produced at various temporal resolutions, based on the instruments' orbital cycle. These time steps are possible in the generation of MODIS Land products:
The MODIS instruments acquire data in three native spatial resolutions:
The high level MODIS Land Products distributed from LP DAAC are produced at four nominal spatial resolutions: 250-meter, 500-meter, 1000-meter, and 5600-meter (0.05 degrees).
Most standard MODIS Land products use this Sinusoidal grid tiling system. Tiles are 10 degrees by 10 degrees at the equator. The tile coordinate system starts at (0,0) (horizontal tile number, vertical tile number) in the upper left corner and proceeds right (horizontal) and downward (vertical). The tile in the bottom right corner is (35,17).
LP DAAC distributes MODIS Land data processed to level-2 or higher:
|BAND #||RANGE nm||RANGE um||KEY USE|
|1||620–670||Absolute Land Cover Transformation, Vegetation Chlorophyll|
|2||841–876||Cloud Amount, Vegetation Land Cover Transformation|
|7||2105–2155||Cloud Properties, Land Properties|
|16||862–877||Aerosol Properties, Atmospheric Properties|
|17||890–920||Atmospheric Properties, Cloud Properties|
|18||931–941||Atmospheric Properties, Cloud Properties|
|19||915–965||Atmospheric Properties, Cloud Properties|
|20||3.660–3.840||Sea Surface Temperature|
|21||3.929–3.989||Forest Fires & Volcanoes|
|22||3.929–3.989||Cloud Temperature, Surface Temperature|
|23||4.020–4.080||Cloud Temperature, Surface Temperature|
|24||4.433–4.498||Cloud Fraction, Troposphere Temperature|
|25||4.482–4.549||Cloud Fraction, Troposphere Temperature|
|26||1360–1390||Cloud Fraction (Thin Cirrus), Troposphere Temperature|
|27||6.535–6.895||Mid Troposphere Humidity|
|28||7.175–7.475||Upper Troposphere Humidity|
|31||10.780–11.280||Cloud Temperature, Forest Fires & Volcanoes, Surface Temp.|
|32||11.770–12.270||Cloud Height, Forest Fires & Volcanoes, Surface Temperature|
|33||13.185–13.485||Cloud Fraction, Cloud Height|
|34||13.485–13.785||Cloud Fraction, Cloud Height|
|35||13.785–14.085||Cloud Fraction, Cloud Height|
|36||14.085–14.385||Cloud Fraction, Cloud Height|
MODIS products have two sources of metadata: the embedded HDF metadata, and the external ECS metadata. The HDF metadata contains valuable information including global attributes and data set-specific attributes pertaining to the granule. The structure of this metadata is broadly similar to that of an ASTER HDF file. The ECS (generated by the EOSDIS Core System) .met file is the external metadata file in XML format, which is delivered to the user along with the MODIS product. It provides a subset of the HDF metadata. Some key features of certain MODIS metadata attributes include the following:
• The Xdim and Ydim represent the rows and columns of the data, respectively
• The Projection and ProjParams identify the projection and its corresponding projection parameters
• The Sinusoidal Projection is used for most of the gridded MODIS land products, and has a unique sphere measuring 6371007.181 meters.
• The UpperLeftPointMtrs is in projection coordinates, and identifies the very upper left corner of the upper left pixel of the image data
• The LowerRightMtrs identifies the very lower right corner of the lower right pixel of the image data. These projection coordinates are the only metadata that accurately reflect the extreme corners of the gridded image
• There are additional BOUNDINGRECTANGLE and GRINGPOINT fields within the metadata, which represent the latitude and longitude coordinates of the geographic tile corresponding to the data
The Data Set attributes contain specific SDS information such as the data range and applicable scaling factors for the data. The LP DAAC data products page provides these details within a concise document for each of the products. An HDF-EOS file also contains EOS core metadata essential for EOS search services. Any tool that processes standard HDF files can read an HDF-EOS file. However, it is difficult for a standard HDF call to interpret HDF-EOS geolocation or temporal information without further knowledge of the file structure.
Along with all the data from other instruments on board the Terra and Aqua platforms, 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. After Level-0 processing at EDOS, the Goddard Space Flight Center Earth Sciences Distributed Active Archive Center (GES DAAC) produces the Level 1A, Level 1B, geolocation and cloud mask products.
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||L1 and Atmosphere Archive and Distribution System (LAADS)|
|Land products||Land Processes Distributed Active Archive Center (LP DAAC)|
|Cryosphere data products||National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC)|
|Ocean color and sea surface temperature products||Ocean Color Web|
Users with an appropriate x-band receiving system may capture regional data directly from the spacecraft using the MODIS Direct Broadcast signal.