1. Goddard Earth Sciences Data and Information Services Center, NASA/GSFC, Code 902, Greenbelt, Maryland 20771, USA INTRODUCTION  NASA Goddard Earth Sciences Distributed Active Archive Center (GES DAAC) archives and distributes the following MODIS products: Radiometric and Geolocations, Level 1A and 1B Sea Surface Temperature (SST), Level 2 and Level 3 Historical records of Ocean Color and Primary productivity, Level 2, 3 and 4 Atmosphere, Level 2 and 3  File format of most of MODIS data from GES DAAC is HDF-EOS  Ocean Primary productivity, Binned products, and Ocean Level 2 parameter subset are native HDF Ocean Color, Sea Surface Temperature (SST), and Primary Productivity (OPP) Important notes:  As of February 1, 2004 the production of MODIS/Terra Ocean Color and all Ocean Primary Productivity has been ceased.  MODIS/Aqua Ocean Color is produced, archived, and distributed by the Ocean Color Data Processing Group: http://oceancolor.gsfc.nasa.gov/  The historical records of MODIS Ocean Color and Primary Productivity from Terra and Aqua from before February 1, 2004, are still available and are supported by the GES DAAC.  All MODIS SST are continued to be archived and supported by the GES DAAC (but see Figure 1).  The file formats from OCDPG and GES DAAC are drastically different (Figure 1, Figure3). Highlighted here are the GES DAAC products that are under the standard ESDIS model. Standard ESDIS MODIS Ocean products from GES DAAC (using Terra notation)  At Level 2, MODIS Ocean products are grouped in three Ocean Color types, and one SST, all at 1-km swath: MODOCL2, normalized water leaving radiances, clear water epsilon. MODOCL2A, chlorophyll and pigment concentration, fluorescence. MODOCL2B, chlorophyll concentrations: SeaWiFS analog for case-1, and semianalytic for case-2 waters. MOD28L2, Sea Surface Temperatures.  The GES DAAC provides On-Demand Ocean Parameter Subset. It conveniently packs user-requested parameters, and seamlessly adds quality arrays and 1-km geolocations, into one HDF file.  At Level 3 and Level 4 (OPP), there exist a big variety of standard ESDIS products: Grid products, in Cylindrical Equidistant Projection: 4.89 and 39 KM, and 1 Deg. Aggregations available: Daily, 8-days, Monthly, and Yearly. Binned, Integerized Sinusoidal Projection, 4.63 KM.  The GES DAAC provides On-Demand Ocean Spatial Subset to all Grid products. The spatial subset from the Data Pool is executed on-the-fly, as Users download files on-line. MODIS Ocean products details:  All variety of Ocean products is not possible to list here. Please, visit: http://daac.gsfc.nasa.gov/MODIS/Terra/product_descriptions_modis.shtml http://daac.gsfc.nasa.gov/MODIS/Aqua/product_descriptions_modis.shtml  Processing status, science quality, quality flags descriptions: http://modis-ocean.gsfc.nasa.gov/processingstatus.html http://modis-ocean.gsfc.nasa.gov/qual.html/ http://modis-ocean.gsfc.nasa.gov/qualfilter.html Radiometric and Geolocation  Three major types: Level 1A Geolocation swath: 1 KM Level 1A raw counts: 0.250, 0.5, and 1 KM, depending on the band Level 1B Calibrated Radiances swath: 0.250, 0. 5, and 1 KM, depending on the product and channels  GES DAAC provides On-Demand Channel Subset of the 1-KM data types, MOD021KM/MYD021KM  GES DAAC runs full production of 5-km subset from MOD021KM/MYD021KM.  The 5-km subset is distributed in both, HDF-EOS and Binary formats.  GES DAAC provides on-line access to full collection of the 5-km subset from the Data Pool.  GES DAAC provides on line access to full collection of Attitude and Ephemeris from the Data Pool  Code versions, file specs, and User’s Guide: http://www.mcst.ssai.biz/mcstweb/L1B/product.html  MODIS specifications: http://modis.gsfc.nasa.gov/ Atmosphere (Using Terra notation)  At Level 2, MODIS atmosphere products are grouped as follows: MODATML2, Joint swath product. Contains most popular Level 2 parameters. One data day fits on one CD. MOD04_L2, Aerosols over Ocean and Land, 10-km at nadir. MOD05_L2, Water Vapor Amounts, total column precipitable water, 5-km NIR, 1-km IR retrieval. MOD06_L2, Clouds, top radiative properties at 5-km, physical properties and cirrus detection at 1-km. MOD07_L2, Atmospheric Profiles at 20 levels, ozone burden, stability, temperature and moisture, at 5-km. MOD35_L2, Cloud Mask, thin cirrus, high clouds, snow/ice, land/water, etc., at 1-km, cloud flags at 250-m.  At Level 3, all parameters from above are consolidated in a file of: Daily (MOD08_D3), 8-days (MOD08_E3), and Monthly (MOD08_M3) average (Figure 2). The grid is always 1 deg, cylindrical equidistant Files are fairly big, can approach 800 MB Data Pool offers on-line access to all Atmosphere grid data.  File specifications, tools, sample images can be found at: http://modis-atmos.gsfc.nasa.gov/  Product status and availability: http://modis-atmos.gsfc.nasa.gov/products_calendar.html Data Access, Tools, Documentation: http://daac.gsfc.nasa.gov/MODIS/ Help: help@daac.gsfc.nasa.gov Figure 1. The difference between the OCDP-produced and the standard, (MYD28L2) 11-  m, sst is well within 0.5 deg o C. However, the OCDP masks the sun glint, which is unnecessary in the 11-  m sst. Furthermore, it is available during Day- time only. Figure 3. SeaWiFS and MODIS formats are quite different, Level-3 Grids including, which is of inconvenience for a number of users. Nevertheless, both instruments can complement each other as shown. SeaWiFS didn’t cover the Gulf of Tehuantepec, (a), as MODIS did on 12/5/2000, (b). However, MODIS was impacted by clouds, lower right corner of the image, (b). Combining (a) and (b) can result in improved coverage, (c). Used here are the 9-km SeaWiFS and the 4.89-km MODIS Global Grid data. (a) (b) (c) Figure 2. The MODIS/Aqua monthly mean global snapshot of aerosol for May 2003, is created from the MYD08_M3 product. This time-averaged and gridded product is derived from the MYD04_L2 product. High tropospheric aerosol loading is seen over parts of Africa ( biomass burning ) and over Asia (Pollution). (Source:http://modis-atmos.gsfc.nasa.gov)