Atmos Composition
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Bands 1, 2, 5 and 6 have 20 nm bandwidth;band 3 has a bandwidth of 22 nm and band 4 has a bandwith of 18 nm;bands 7 and 8 have 40 nm bandwidth. [Notes: Gelbstoff (German for "yellow substance") describes amorphous, high molecular weight organic matter with a somewhat polymeric nature.It absorbs strongly in the blue region of the spectrum. The term "Case 2" (and also Case 1) refers to a water "type" defined by its optical characteristics. Case 1 water is clear, open-ocean water, and Case 2 is generally coastal, higher productivity, turbid water. K(490) is the diffuse attenuation coefficient at 490 nm, a measure of optical clarity.] Nominal thermal band radiometric parameters for OCTS (the SIMBIOS-NASDA-OCTS Data Set does not contain thermal band data):
[Notes:Bands 1, 3 and 4 are similar to the wavelength ranges of bands 3, 4, and 5 of the Advanced Very High Resolution Radiometer (AVHRR).Band 4 data from the AVHRR has also been used to investigate turbidity due to suspended sediments, so OCTS data from band 3 could likely also be used for this purpose.] OCTS is a scanning radiometer.The instrument contains the optical system, detector module, and electrical unit.OCTS has a catoptric (reflective) optical system where a rotating mirror is the primary scanning device.This design allows OCTS to cover a wide wavelength range and wide scanning angles. OCTS can also tilt its line of sight along the track to prevent sun glint at the sea surface from interfering with observation.For high sensitivity, each band has 10 pixels aligned to the track.The infrared detectors are cooled at 100 K by a large radiant cooler facing deep space. OCTS optical calibration was achieved using solar light and a halogen lamp as the calibration source.
A brief description of ocean color measurements: When visible light from the Sun illuminates the ocean surface, it is subject to several optical effects.Foremost among these effects are light reflection and absorption.Reflection beneath the water surface is generally inefficient, returning only a small percentage of the light intensity falling on the ocean surface.Absorption selectively removes some wavelengths of light while allowing the transmission of other wavelengths. In the ocean, light reflects off particulate matter suspended in the water, and light absorption is primarily due to the photosynthetic pigments (chlorophyll) present in phytoplankton.These optical interactions produce modified light radiating from the ocean surface, the "water-leaving radiance".Radiometers are instruments that measure radiance intensity at a given wavelength of light.The measured radiance may then be quantitatively related to various constituents in the water column that interact with visible light, such as chlorophyll. The concentration of chlorophyll, in turn, may be used to calculate the amount of carbon being produced by photosynthesis, which is termed primary productivity. OCTS is a spectroradiometer, which means that it measures radiance in specific bands of the visible light spectrum.The advantage of observing the oceans with a space-based spectroradiometer is the global coverage that a satellite provides.The disadvantage is that interfering optical effects, primarily light scattering in the atmosphere, must be accounted for to provide an accurate measurement of the water-leaving radiance. For a more detailed description of how ocean color measurements are accomplished, refer to NASA TM-2000-209966 "Ocean Optics Protocols for SeaWiFS Validation, Revision 2" at http://simbios.gsfc.nasa.gov/Info/ This document updates and supersedes Volumes 5 and 25 of the SeaWiFS Technical Report Prelaunch Series. Another resource is the online discussion From Radiation to Scientific Imagery.
OCTS Mission Data Collection Strategy OCTS visible bands can only view the sunlit Earth.The useful data collection range is limited to solar zenith angles less than 75 degrees, which corresponds to approximately 40 minutes per orbit. OCTS acquires data at a nadir resolution of 700m per pixel (LAC resolution).Under normal operating conditions, each Level 1A OCTS data file was defined by a single tilt segment, i.e., the tilt of the instrument remains constant throughout the data acquisition period. Instrument commands were used to begin data acquisition at the top (northern terminus) of the descending node on the sunlit side of the Earth and at the bottom (southern terminus) of the descending node.
SIMBIOS-NASDA-OCTS data at the Goddard Earth Sciences Distributed Active Archive Center (GES DAAC) are available in HDF (Version 4.0r2), the data format used by the SeaWiFS Project and the Earth Observing System (EOS). HDF is a self-describing, platform-independent format.Toolsfor analysis of this data are described under "Data Access Information" below.The use of HDF allows a large amount of metadata, including calibration, navigation, mission information, and data quality indicators, to be included with each data file. OCTS data was acquired in fine resolution and coarse resolution mode. All raw pixel data were transmitted via X band in fine data transmission mode. One data pixel was subsampled from each 6x6km area and is transmitted at UHF band in coarse data transmission mode. SIMBIOS-NASDA-OCTS data is archived according to the standard remote sensing definitions of Level 1A, Level 2 and Level 3 data. Level 2 data consists of derived geophysical parameters produced using the Level 1a radiances as input data.Level 2 parameters are only produced for GAC data.Level 3 data is global gridded data that has been statistically collected into daily, weekly, monthly, or annualgrid cells, corresponding either to 9 x 9 km equal area grid squares (binned product) or 0.09 x 0.09 degree squares (standard mapped image product).The exact contents of each data level are given below. In addition to the SeaWiFS data described below, ancillary ozone and meteorological data that are utilized in geophysical product algorithms are also available from the DAAC.These products are also in HDF. Ozone and meteorological data for the OCTS mission period were created by the SIMBIOS-NASDA-OCTS data set collaboration and are available at the GES DAAC. Ozone data are from the ADEOS-TOMS (ADTOMS) instrument. SIMBIOS-NASDA-OCTS File Naming Convention A typical SeaWiFS-OCTS file name is in the following format: Oyyyydddhhmmss.<suffix> O represents OCTS, and the subsequent digits represent the Greenwich Mean Time (GMT) year, day of the year(Julian calendar), and hour, minutes and seconds of the start of the first scan line. The suffix describes the actual data type: Level 1A data:
Level 2 data:
Level 3 data, binned product:
Prefixes for the other binned products, which have the same format as the Level 3 Daily binned product:
Level 3 data, standard mapped image (SMI) product:
There are also SMI files corresponding to the 8-day, monthly, and yearly binned products.The suffixes 8D, MO, YR, and CO are inserted in place of DAY in the format shown above. Level 3 browse products:
[The file sizes given are uncompressed volume.Data files are shipped in compressed form. ] Level 1A GAC data:
Level 2 GAC data:
[Notes:The epsilon of the aerosol correction is an atmospheric correction parameterrepresenting the ratio of the aerosol reflectances at 765 and 865 nm. CZCS estimated aerosol reflectance using a single-scattering model; SIMBIOS-NASDA-OCTS accounts for multiple scattering effects with several different aerosol models.] Level 3 Binned Data Products:
* There is one change:The ratio of chlorophyll a concentration to K(490) is also a binned parameter. ** The Level 3 Binned data products consist of 1 main and 12 subordinate HDF files.Each subordinate HDF file corresponds to one SIMBIOS-NASDA-OCTS binned geophysical data product.The main file contains the metadata describing the geophysical data in each of the subordinate files. Level 3 Standard Mapped Image (SMI) Products:
SIMBIOS-NASDA-OCTS data was processed with algorithms identical to the SeaWiFS data atmospheric correction algorithms, using ancillary meteorological and ozone data for the OCTS mission period.The chlorophyll a algorithm (OC40) is similar to the SeaWiFS chlorophyll-a algorithm (OC4).The OC40 algorithm was fit to data in the SeaBAM database corresponding to OCTS band passes. Vicarious calibration was accomplished with data from the Marine Optical Buoy (MOBY), so both SeaWiFS and OCTS are tied to the same in situ source (though the epoch differs).Thisvicarious calibration used identical techniques and assumptions (e.g., maritime aerosols in vicinity of MOBY).
All of the data types described above can be accessed and ordered using the Goddard DAAC's NASDA-SIMBIOS-OCTS Data Browser: SIMBIOS-NASDA-OCTS Data Access All SIMBIOS-NASDA-OCTS data are organized by year, month, and day (if applicable) of acquisition, and data may be found and ordered using the calendar format. For Level 1A and Level 2 GAC data, the browser allows users to specify spatial and temporal search criteria.Spatial criteria may be entered using either an interactive map or by entering numerical latitude and longitude values.Temporal search ranges are entered by year, month, and day.Level 3 gridded data are accessed in a similar fashion through the browser. GAC data can also be searched with a spatial/temporal search engine. After the browser has identified data files meeting the specified search criteria, users may examine browse images before ordering individual data files. Data may be obtained by File Transfer Protocol (FTP), or on tape in either 4mm or 8mm format via mail delivery from the DAAC.Users with slow or uncertain network links to the DAAC should consider acquiring the data on tape, which also applies to users who are requesting large volumes of data. Reading data on tape/unpacking transferred data: Data are available on 4 mm (DAT) tapes and high or low density (8200 and 8500) 8mm EXABYTE tapes. Tapes are created with UNIX utilities "dd" and "tar" on a Silicon Graphics 440 system. The no-swap device and a block size of 63.5 KB are used, which translates to a blocking factor of 127. Tapes may be requested in "dd" or "tar" file format. The data are archived and distributed in compressed format. Each tape distributed by the Goddard DAAC contains printed paper labels with the names of the files it contains in the order they were written. Files are compressed using the standard UNIX "compress" command, indicated by a ".Z" appended to the data file name.An ASCII header file on each tape lists the files on the tape. To read a "tar.Z" format tape on a computer with a UNIX operating system: First uncompress the file by typing "uncompress <filename>.tar.Z". When the uncompression is finished, type the command: tar -xvbf <filename>.tar 127 where xvbf are tar command key arguments as follows:
The fields in < > are system specific and may specify a device, such as a tape drive, or a file directory. The specific parameters depend on your local workstation configuration (e.g., this will be "/dev/8mm1nr" if you read the tape off the 8mm1 tape mdrive on the DAAC computer with the "no rewind" option). 127 is the blocking factor. To read a "tar" format file received by FTP, use the command: tar -xvf <filename>.tar To read a "dd" format tape on a computer with a UNIX operating system, use the command: dd if=<dev> of=<filename> bs=65024 where if=<dev> specifies the tape drive with "no rewind" option (e.g., if=/dev/8mm1nr for the DAAC computer.) of=<filename> specifies the desired output file name bs=65024 indicates the block size in bytes To read a tar.Z file on a PC or Macintosh computer: Reading the file will require an applicationprogram capable of uncompressing and untarring the file.WinZip is an application that has been shown to work on a Windows 95, 98, and NT operating system; free versions are available for download on the World Wide Web.Similar applications for Macintosh (such as StuffIt) should be capable of performing the same operations.WinZip recognizes the UNIX compression and tar format and extracts the file in uncompressed format. HDF is the standard data format of the entire Goddard EOSDIS Version 0 (V0) and the SeaWiFS Project. HDF was developed by the National Center for Supercomputing Applications (NCSA) Software Development Group. The HDF group also supplies HDF utilities that allow file manipulation and conversion on a variety of platforms with UNIX-based operating systems. Additional explanation of HDF can be found at the HDF Web site: http://hdf.ncsa.uiuc.edu/ HDF provides several different "data models" which can be used to store data products. The data models currently provided by HDF include Scientific Data Sets (SDS), 8-bit and 24-bit Raster Image Sets (RIS), Vdatas, and Vgroups. An SDS is a multi-dimensional array, and a Vdata is a binary table.In addition to the data models, HDF allows the inclusion of metadata with each data file.Metadata is referred to as Global Attributes, and includes such information as the mission and sensor characteristics, when and how the data was processed, the downlink station where the data was received, and similar information.Along with that information, the Global Attributes also describe the start and end times of a data file, geographic location, and data quality. The Goddard DAAC also has a discussion of HDF, HDF utilities, and links to several different software packages. http://disc.sci.gsfc.nasa.gov/REFERENCE_DOCS/HDF/gdaac_hdf.html A site for information on HDF, featuring the HDF libraries for PC and Macintosh, HDF-capable software, and links to user groups, is found at: http://www.rsinc.com/noesys/hdfinfo.cfm Processing/Analysis Software Packages The SeaDAS software system was written for the specific purpose of analyzing and processing SeaWiFS HDF data. SIMBIOS-NASDA-OCTS data is SeaDAS-compatible. SeaDAS is a comprehensive image analysis package for all SeaWiFS data products and ancillary data (wind, surface pressure, humidity and ozone) from NMC (National Meteorological Center and TOVS (TIROS Operational Vertical Sounder). All SeaDAS source code is freely available for download via FTP. The use of SeaDAS requires IDL.IDL-Runtime is provided free of charge with SeaDAS.Code developers will require an IDL license. SeaDAS 4.1 Configuration and Requirements Platform: SGI O2,SUN UltraSPARC workstations or PC. Minimum system requirements:
The SeaDAS software requirements:
SeaDAS PC-Linux version: SeaDAS for Linux/PC was originally developed and tested under the following environment:
See above or SeaDAS 4.1 Configuration and Requirements for current operating systems. 2. The general hardware requirements for memory and disk space are the same as for the UNIX version. For further information on the PC-Linux version, go to SeaDAS Linux ReadMe SeaDAS is available for download via anonymous FTP from: ftp://seadas.gsfc.nasa.gov/seadas/ Other packages: The NCSA offers information on numerous software packages that
process HDF files:
Noesys and Transform, now available from Research Systems, Inc., are sophisticated software packages with many capabilities for HDF data files. SciSpy Browser and related information. Research Systems, Inc.
Windows Image Manager also works with SeaWiFS HDF data and allows
transformation to other formats.
HDF Explorer is a low-cost package for Windows PCs.(Note:the Web site has not been updated recently, so no information is available regarding current operating system capability.) All of the volumes (hard copy only) in the SeaWiFS Technical Report Series (NASA Technical Memorandum 104566) may be ordered online.See "The SeaWiFS Technical Report Series" under SeaWiFS at Ocean Color Scientific Documentation The following sites also have information regarding SIMBIOS-NASDA-OCTS data: ADEOS/Midori Home Page (English) Goddard DAAC:
User Services Office
SeaWiFS Project: Web site: SeaWiFS Project Data production and processing:
Science and algorithms
NASDA Web sites: NASDA (Japanese)
Data product elements:
SIMBIOS Project
SeaDAS:
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