Methods for Selected Sites (Collection 4 and 5)

Source for Selected Site Data: Full MODIS scenes (1200-km x 1200-km) are initially subset to 11-km x 31-km (Collection 4) or 25-km x 25-km (Collection 5) by the MODAPS; these initial subsets contain the field site or flux tower. Reformatting and additional subsetting to 7-km x 7-km containing the field site or flux tower are done by the ORNL DAAC.

Tools Used: The ORNL DAAC uses the MODIS Reprojection Tool (MRT) to reformat the MODIS data from HDF-EOS to binary format. A tool developed at ORNL is then used to convert the binary format to ASCII. The MRT is available from the Land Processes DAAC. Whereas the MRT can also be used to reproject data from its native projection to other projections, ORNL chose to forgo the resampling associated with reprojection to minimize data manipulation and distortion. The MOD12Q1 Land Cover Collection 3 data are in I-Sin projection, and the Collection 4 and Collection 5 data are in Sinusoidal projection.

File Format: Each data file represents one field site and one MODIS product. In the file name, the MODIS Product is first, followed by the site identifier. The site identifiers are tabulated in the links below

Collection 4
Collection 5

These ASCII data files contain a header row followed by comma-delimited rows of parameter values (image bands) for each pixel in a 7-km x 7-km area containing the flux tower or the field site. Each row contains data from an 8-day, 16-day, or annual period (depending on the temporal frequency of the data product represented). Quality information, represented as additional bands in MODIS imagery, are also included as rows in these data tables. Referring to the above example, the first four rows of the file MOD15A2_fn_uswipark_01.txt are associated with a single image compositing date and consist of one row containing FPAR values, one row containing LAI values, and two rows containing Quality information. The parameters/bands (number of rows) associated with each data product on a specific compositing date, are product specific. Please refer to the product documentation at the Land Processes DAAC for more information. These files will expand as new image dates are acquired (rows will be added for each subsequent MODIS compositing date). Check the MODIS Land Subsets Web site or ftp site periodically, for a complete time series of data. Time series analyses are also available at the MODIS Land Quality Assessment site.

Temporal Coverage: The Terra MODIS products are available with an acquisition date starting in February 2000. The Aqua MODIS products are available with an acquisition date starting in June 2002.

Collection 4 data are available for both instruments through the end of December 2006. Collection 5 data processing began in Fall 2006 and should be completed for both instruments in Fall 2008. Because of improvements in the product algorithms, the Collection 4 data will no longer be available after Fall 2008.

Each product represents a composite of an 8-, 16-day, quarterly, or annual period. In general, an 8-day composite represents the best value for that pixel considering all 8 days so that adjacent pixels with the same 8-day date may represent values from different overpasses.

Sites: Sites for the MODIS ASCII Subset activity include the EOS Core Validation sites, BigFoot Project sites, LAINet sites, the GTOS GTNET Net Primary Productivity sites, and the BSRN sites. The main requirements for inclusion in the MODIS ASCII subset collection are that sites have accurate coordinates (usually GPS- based with 4 significant decimal places) and there is a commitment to participate in data collection and analysis. The number of sites expanded to over 270 for Collection 4 and over 1,000 for Collection 5.

Methods for North America Tool (Collection 4)

The MODIS Land Products were initially downloaded from the Land Processes DAAC's data pool in HDF-EOS format. The ORNL DAAC uses the MODIS Reprojection Tool (HDF to Raw Binary Tool (v1.0 Beta November 2005)) to convert to binary, then custom software to convert from binary to ASCII.

The ASCII information is stored at ORNL in 1200 km tiles. When users request a site location, the tool mosaics ASCII tiles as needed and performs the subsetting.

The data are offered in several file formats.

Methods for the Global Tool (Collection 5)

The MODIS Land Products are pushed to ORNL DAAC from LPDAAC. These files are stored at the ORNL DAAC's data repository. When a subset data order is placed, customized HDF tools are used to create subsets of MODIS Land Products. Data are mosaiced as necessary. The "hdp" tool from 'The HDF Group' is used for creating the subsets. The "hdp" tool has been customized to meet the subsetting requirements of ORNL DAAC's subsetting tool. The subsets are then processed through customized Perl scripts to generate time series graphs, statistics and GIS files. More details of the data prepared could be found at the link below.

The data are offered in several file formats.