Summary:

The Moderate Resolution Imaging Spectroradiometer (MODIS) precipitable water product consists of vertical column water vapor amounts in centimeters (cm) at 1-km spatial resolution. The SAFARI 2000 product, provided in flat binary data files, is a subset of the official MODIS Level 2 MOD05 product in EOS Hierarchical Data Format (HDF). Specifically, the SAFARI product contains data from daytime-only MODIS granules over southern Africa for the period August 21, 2000, through September 20, 2000. A granule is the data collected over the full MODIS swath in a five-minute period. Further, the SAFARI product contains values generated by the MODIS near-infrared algorithm applied over clear land areas only (determined via the QA bit field). All values were derived from MODIS on the morning-pass Terra satellite. The product is very sensitive to boundary-layer water vapor since it is derived from attenuation of reflected solar light from the surface. This data product is essential to understanding the hydrological cycle, aerosol properties, aerosol-cloud interactions, energy budget, and climate.

The MOD05 water vapor data files were converted from their original HDF format to flat binary files for this SAFARI 2000 data set. The conversion was performed using code developed in the Interactive Data Language (IDL) Version 5.5. The following Scientific Data Sets (SDS) are provided in this data set: Latitude; Longitude; Sensor_Zenith; and Water_Vapor_Near_Infrared.

Data Citation:

Cite this data set as follows:

Gao, B. C., Y. J. Kaufman, and D. Tanré. 2005. SAFARI 2000 MODIS MOD05_L2 Water Vapor Data, Binary Format, for Southern Africa. Data set. Available on-line [http://daac.ornl.gov/] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/812.

References:

Gao B. C. and Y. J. Kaufman. 1998. The MODIS Near-IR Water Vapor Algorithm. Products: MOD05_L2, MOD08_D3, MOD08_E3, MOD08_M3. ATBD Reference Number: ATBD-MOD-03.

Data Format:

The MOD05 water vapor data files were converted from their original HDF to flat binary files for this SAFARI 2000 data set. The following Scientific Data Sets (SDS) are provided in this data set:

• Latitude (bilinearly interpolated to 1 km from the original 5 km resolution)
  
• Longitude (bilinearly interpolated to 1 km from the original 5 km resolution)
  
• Sensor_Zenith (bilinearly interpolated to 1 km from the original 5 km resolution)
  
• Water_Vapor_Near_Infrared (1 km original)

The image file names were derived from the standardized EOS Data Gateway (EDG) HDF file name. The names have been shortened to accommodate the 31-character file name limits of the Macintosh computer. The files names have had the HDF processing date and time removed, and the extension .xxx replacing .hdf. In this format, xxx is replaced with .dat for Water Vapor, .lat for Latitude, .lon for Longitude, or .senz for Sensor Zenith Angle.

Example: MOD05_L2.AYYYYDDD.HHMM.VVV.dat

The flat binary format consists of unique files corresponding to individual SDSs extracted from the HDF format file of the MODIS product.

The parameters for the SAFARI MODIS precipitable water product are defined as:

Data scaling factors: All data are stored in binary files as 2 or 4 byte signed integers:

2 byte integers: file .dat; Scaling factor=1000
4 byte integers: all other files

Scaling factors: 10000 for files .lat and .lon
Scaling factors: 1000 for file .senz

To retrieve the true value, the stored value must be divided by the scaling factor. See the companion file for information about data flags.

Additional information about the MODIS water vapor product, parameters measured, and data format is found in the companion file: http://daac.ornl.gov/daacdata/safari2k/remote_sensing/modis_MOD05_watervapor/comp/modis_MOD05_watervapor_readme.pdf.

Document Information:

2005/8/18

Document Review Date:

2005/8/18

Document Curator:

webmaster@www.daac.ornl.gov

Document URL: