NASA's innovative data analysis and visualization system Giovanni has recently received a new version of the atmospheric data set from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite. The new version, Collection 5.1, supersedes Collection 5.0. According to the MODIS atmospheric data processing team, most of the changes in the data set relate to the "Deep Blue" aerosol product, which provides atmospheric aerosol data over bright land surfaces, particularly desert regions. The regular MODIS aerosol data products are provided globally over the oceans and continental land masses.
The MODIS atmospheric data science team reports there are significant improvements in the science of the Collection 5.1 Deep Blue algorithm, which include new parameterization of the surface bidirectional reflectance distribution function (BRDF) effect, cloud screening, and changes to the quality analysis/quality control (QA/QC) flag selection criteria.
Additional changes in the Collection 5.1 data included improvements to cloud optical properties, reducing the effect of "striping" related to observations of thin cirrus clouds, and a fix for the Cloud Optical Thickness Retrieval over Land, which affected the computation of several other cloud properties.
Note: Deep Blue Aerosol data is not available for the entire Terra mission period at this time. The following is from the MODIS Atmosphere Products: Processing and Availability Calendar:
"Aerosol data users should note that for Terra, the Deep Blue algorithm required polarization corrections to the L1B data; however this effort has only progressed for data through 2007. Therefore, the Aerosol Deep Blue SDS's are not populated for Terra after Dec 2007, however the Terra Aerosol Dark Target SDS's are still available. (Aqua requires no polarization correction, which means Aerosol Deep Blue SDS's are available for the entire Aqua record.)"
Also note: The Terra data record has a few short periods early in the mission where data is missing; attempts to plot data for these periods in Giovanni could result in an error message. Please consult the calendar to determine when these periods of missing data occur.
The first image below shows MODIS-Terra Aerosol Optical Depth at 555 nm data for the period June-August 2007, showing the transport of Saharan dust over the tropical Atlantic Ocean off the coast of Africa. The bright reflective areas of the Sahara Desert are not processed by the regular MODIS aerosol algorithm. The second image is the Deep Blue aerosol data product which provides aerosol data over bright land areas. In the Deep Blue aerosol image, the large red area in central Africa (near the midline of the country of Chad) corresponds to the location of the Bodele Depression, source of much of the Saharan dust that crosses the Atlantic Ocean and falls on the Amazon Basin. (Koren et al. 2006, The Bodélé depression: a single spot in the Sahara that provides most of the mineral dust to the Amazon forest, Environmental Research Letters, 1 (1), doi:10.1088/1748-9326/1/1/014005)