SAFARI 2000 SeaWiFS Images -------------------------- Abstract -------- The purpose of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project is to provide quantitative data on global ocean bio-optical properties to the Earth science community. Subtle changes in ocean color signify various types and quantities of marine phytoplankton (microscopic marine plants), the knowledge of which has both scientific and practical applications. The SeaWiFS Project develops and operates a research data system that processes, calibrates, validates, archives, and distributes data received from the Earth-orbiting ocean color sensor. The SeaWiFS Web site is http://seawifs.gsfc.nasa.gov/SEAWIFS.html ========================================================================= Background Information ---------------------- Project: SAFARI 2000 Data Set Title: SeaWiFS Images Site: Southern Africa Data Set Link: http://seawifs.gsfc.nasa.gov/SEAWIFS.html ========================================================================= SeaWiFS Data File Information ----------------------------- Level-1A Data Products ---------------------- Level-1A products contain all the Level-0 data (raw radiance counts from all bands as well as spacecraft and instrument telemetry), appended calibration and navigation data, and instrument and selected spacecraft telemetry that are reformatted and also appended. Each Level-1A product is stored as one physical HDF file. There are Level-1A products for each of the following data types: global-area coverage (GAC), local-area coverage (LAC), lunar calibration, solar calibration, TDI check, and HRPT for direct- readout data. (The generic term LAC is also used to refer to all full-resolution, recorded data, including lunar, solar, and TDI data.) HRPT data are collected at the NASA/GSFC HRPT station or NOAA HRPT stations, whereas all other data types are from recording dumps to the Wallops Flight Facility. GAC data are subsampled from full-resolution data with every fourth pixel of a scan line (from LAC pixels 147 to 1135) and every fourth scan line being recorded for each swath (the Earth data collection portion of an orbit). Thus, GAC data are comprised of 248 pixels per scan line, whereas all other types are comprised of 1,285 pixels per scan line. A GAC scene will also represent an entire swath, whereas LAC scenes are defined by the number of continuously recorded scans, and HRPT scenes are defined by the number of continuously received scans from one satellite pass. Level-1A Browse Products ------------------------ Each Level-1A browse product is generated from a corresponding Level-1A GAC or HRPT product. The main data contents of the product are a subsampled version of the band-8 raw radiance counts image stored as one byte per pixel. Each Level-1A browse product corresponds exactly in geographical coverage (scan-line and pixel extent) to that of its parent Level-1A product and is stored in one physical HDF file. Level-2 GAC Data Products ------------------------- Each Level-2 GAC product is generated from a corresponding Level-1A GAC product. The main data contents of the product are the geophysical values for each pixel, derived from the Level-1A raw radiance counts by applying the sensor calibration, atmospheric corrections, and bio-optical algorithms. Each Level-2 GAC product corresponds exactly in geographical coverage (scan-line and pixel extent) to that of its parent Level-1A product and is stored in one physical HDF file. The 12 geophysical values derived for each pixel are five water-leaving radiances for bands 1 to 5, two aerosol radiances for bands 6 and 8, the pigment concentration using a CZCS- type algorithm, the chlorophyll a concentration, the diffuse attenuation coefficient at band 3, the epsilon value for the aerosol correction of bands 6 and 8, and the aerosol optical thickness at band 8. In addition, 16 flags are associated with each pixel indicating if any of the following conditions existed for that pixel: atmospheric correction algorithm failure, land, missing ancillary data, Sun glint, total radiance greater than the knee value, large spacecraft zenith angle, shallow water, negative water-leaving radiance, stray light, cloud or ice, coccolithophores, Case 2 water, large solar zenith angle, high aerosol concentration, low water -- leaving radiance at band 5, and a chlorophyll algorithm failure. Level-2 Browse Products ----------------------- Each Level-2 browse product is generated from a corresponding Level-2 GAC product. The main data contents of the product are a subsampled version of the chlorophyll a image stored as one byte per pixel. Each Level-2 browse product corresponds exactly in geographical coverage (scan-line and pixel extent) to that of its parent Level-2 product and is stored in one physical HDF file. SeaWiFS Level-2 Product Parameters ---------------------------------- See the GIF file "seawifs_l2_params.gif" in the "0_figures" directory. ========================================================================= Hierarchical Data Format (HDF) Information ------------------------------------------ The National Center for Supercomputing Applications (NCSA) http://hdf.ncsa.uiuc.edu/ at the University of Illinois developed HDF as a multi-object file format. It was created to help scientists reduce the time they were spending trying to convert data sets to familiar formats and instead have more time available for actually analyzing data. HDF is a physical file format that allows storage of many different types of scientific data including images, multidimensional data arrays, record oriented data, and point data. It also provides command utilities to analyze the structures of existing HDF files and display their contents on the user's screen. With a standard format like HDF, once scientists become acquainted with the necessary libraries, they can quickly begin work with the data themselves. A few advantages of HDF include: * portability to multiple machines (i.e. platform independent) * self documented files. * efficient storage of and access to large data sets. * capability of storing multiple data structures or types within the same file. * extensibility for future enhancements. HDF File Viewing Options ------------------------ WebWinds HDF Viewer ------------------- WebWinds is a free interactive tool to aid in the visualization and exploration of scientific data, developed by NASA/JPL. It is the successor to LinkWinds. WebWinds is written in Java and is currently running on most major computer platforms. Copies of WebWinds are stored on SAFARI 2000 CD-ROM #1 for your convenience (for Macintosh, Windows95 and above, UNIX). Within your operating system (not in Netscape), go to the "software/image_viewing/web_winds/" directory and activate the installer appropriate to your operating system. Newer versions and additional information can be found at the JPL's WebWinds Web Site (http://webwinds.jpl.nasa.gov/). Commercial HDF-viewing Products ------------------------------- * IDL (Interactive Data Language) & Noesys -- http://www.rsinc.com/ * PCI (EASI, PACE) -- http://www.pci.on.ca/ * HDF Explorer -- http://www.space-research.pt/ File Compression Information ---------------------------- For this archive, the data files have been compressed with the MS Windows-standard Zip compression scheme. These files were compressed using Aladdin's DropZip on a Macintosh. DropZip uses the Lempel-Ziv algorithm, also used in Zip and PKZIP programs. The compressed files may be uncompressed using PKZIP (with the -expand option) on MS Windows and UNIX, or with StuffIt Expander on the Mac OS. Versions of the decompression software for MS Windows, Mac OS, and several varieties of UNIX systems are included on the CD-ROMs. You can get newer versions from the PKZIP Web site at http://www.pkware.com/shareware/. ========================================================================= Legend & Additional Sources of Information ------------------------------------------ These are some references for SeaWiFS. Hu, C.M., K.L. Carder, F.E. Muller-Karger. How precise are SeaWiFS ocean color estimates? Implications of digitization-noise errors. REMOTE SENS ENVIRON 76: (2) 239-249 MAY 2001. Hooker, S.B., C.R. McClain. The calibration and validation of SeaWiFS data. PROG OCEANOGR 45: (3-4) 427-465 2000. Barnes, R.A., R.E. Eplee, F.S. Patt, et al. Changes in the radiometric sensitivity of SeaWiFS determined from lunar and solar-based measurements. APPLIED OPTICS 38: (21) 4649-4664 JUL 20 1999. McClain, C.R., M.L. Cleave, G.C. Feldman, W.W. Gregg, S.B. Hooker, N. Kuring. Science quality SeaWiFS data for global biosphere research. SEA TECHNOLOGY 39: (9) 10-16 SEP 1998. Hooker, S.B., C.R. McClain. The calibration and validation of SeaWiFS data. PROGRESS IN OCEANOGRAPHY 45: (3-4) 427-465 2000 McClain, C.R., M.L. Cleave, G.C. Feldman, et al. Science quality SeaWiFS data for global biosphere research. SEA TECHNOL 39: (9) 10-16 SEP 1998.