Data Set Readme for the SIMBIOS-NASDA-OCTS (Ocean Color and Temperature Sensor) Data Set

SIMBIOS-NASDA-OCTS Data Access

SIMBIOS-NASDA-OCTS Data Browser
SeaDAS (analysis software)

SIMBIOS-NASDA-OCTS Data Set Readme Contents

Data Set Information
Satellite and Instrument Information

Brief instrument overview
A brief description of ocean color measurements

Data Set Organization
SIMBIOS-NASDA-OCTS File Naming Convention
Data Description

Data Processing Information

Data Access Information
Getting Data
Reading data on tape/unpacking transferred data
A bit about HDF
Processing/Analysis Software Packages

References
Points of Contact

Readme for the
SIMBIOS-NASDA-OCTS (Ocean Color and Temperature Sensor) Data Set

Production and distribution of this ocean color data set are funded by NASA's Earth Science Enterprise (ESE) Program. The data are not copyrighted. We request that when you publish data or research results utilizing these data, please acknowledge as follows:

"The authors would like to thank the National Space Development Agency of Japan (NASDA), the SIMBIOS and SeaWiFS Projects (Code 970.2) and the Goddard Earth Sciences Distributed Active Archive Center (Code 610.2) at the National Aeronautics and Space Administration Goddard Space Flight Center, Greenbelt, MD 20771, for the production and distribution of these data, respectively. These activities are sponsored by NASA's Earth Science Enterprise Program and NASDA."

The use of trade names in this document does not imply endorsement by the U.S. Government, NASA, NASDA, or the Goddard DAAC. The DAAC does not provide support for commercial software products or packages.

Data Set Information

This data set consists of satellite measurements of global and regional ocean color data obtained by the Ocean Color and Temperature Sensor (OCTS) in orbit on the MIDORI (formerly ADEOS) platform. The apparent color of the ocean, which can range from deep blue to varying shades of green and ruddy brown, is primarily determined by the concentration and predominant identity of substances and particles in the euphotic (lighted) zone of the upper ocean. Living phytoplankton (which contain chlorophyll and associated photosynthetic pigments), inorganic sediments, detritus (particulate organic matter), and dissolved organic matter all contribute to the color of the ocean.

The first instrument to collect scientific data on the color of the ocean was the Coastal Zone Color Scanner (CZCS), an instrument on the NIMBUS-7 satellite which operated from November 1978 to June 1986. The operational parameters of the SeaWiFS mission were based on the heritage of the CZCS mission and were designed to improve the acquisition and accuracy of ocean color data for global and regional study of ocean biology and related physical oceanographic phenomena.

The temporal range of the data set is November 1996 - June 1997, All of the data products in the SeaWiFS-OCTS data set are stored in the Hierarchical Data Format (HDF), which was developed by the National Center for Supercomputing Applications (NCSA) at the University of Illinois.

Satellite and instrument information

MIDORI was launched on August 17, 1996 by an H-II launch vehicle from the Tanageshima Space Center. Operational OCTS data acquisition commenced on November 1, 1996.

Nominal orbit parameters for the MIDORI satellite:

Orbit - Sun-synchronous
Nominal altitude - 830 km
Equator Crossing - 10:15-10:45 AM, descending node
Inclination - 98.6 deg
Orbital Period - 101 min

Nominal operating parameters for OCTS:
(LAC stands for Local Area Coverage; GAC stands for Global Area Coverage)

Scan Width: +/- 40.0 deg (varies with tilt angle +/- 32.86 to +/- 45.73 deg)
IFOV: Varies with tilt angle: 0.7337 to 1.049 mrad
Scan Coverage: 1400 km
Pixels along Scan: 2222 (LAC), 400 (GAC)
Scan Period: 1.10 Hz (0.9s /scan)
Nadir Resolution: 700 m
Tilt: -20, 0, +20 deg
Digitization: 10 bits/pixel
Revisit Time: ~3 days

Nominal visible band radiometric parameters for OCTS:

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.]

Brief instrument overview:

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.

Data Set Organization

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. Tools for 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 annual grid 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:

L1A_GAC: Level 1A GAC data

L1A_BRS: Level 1A Browse data

Level 2 data:

L2_GAC: Level 2 GAC data

L2_BRS: Level 2 Browse data

Level 3 data, binned product:

L3b_DAY.main: Daily Level 3 binned product main file

L3b_DAY.xff: Daily Level 3 Binned product subordinate file 

(one of 12 geophysical products, ranging from .x00 to .x10)

Prefixes for the other binned products, which have the same format as the Level 3 Daily binned product:

L3b_8D: 8-day binned product

L3b_MO: Monthly binned product

L3b_YR: Annual binned product

L3b_CO: Mission composite binned product

Level 3 data, standard mapped image (SMI) product:

L3m_DAY_CHLO: Daily chlorophyll-a

L3m_DAY_A510: Angstrom coefficient, 520-865 nm

L3m_DAY_L555: Daily normalized water leaving radiance at 565 nm

L3m_DAY_T865: Aerosol optical thickness (tau) at 865 nm

L3m_DAY_K490: Daily K(490) 

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:

L3_BRS_DAY: Daily browse product

L3_BRS_8D: 8-day browse product

L3_BRS_MO: Monthly browse product

L3_BRS_YR: Annual browse product

L3_BRS_CO: Mission composite browse product

Data Description

[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 parameter representing 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:

Data Processing Information

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). This vicarious calibration used identical techniques and assumptions (e.g., maritime aerosols in vicinity of MOBY).

Data Access Information

Getting Data

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:
x indicates that the data are to be read from tape
v requests verbose output; i.e., processed file names will be listed
b states that a blocking factor is specified
f states that an archive name is specified.

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 application program 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.

A bit about HDF:

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:

Memory: 192 MB (regular users), 384 MB (HRPT users)
Disk: 9 GB
Tape Drive: 4MM(DAT) or 8mm Exabyte
Display: 19inches Console or X-terminal, 1280x1024 resolution, 8-bit, 256 colors.

The SeaDAS software requirements:

Operating System: SGI: IRIX 6.3 or 6.5, SUN: Solaris 2.6 or 2.7, PC: Red Hat Linux 6.0, 6.2, 7.0, or 7.1
Languages: C, FORTRAN (for compile-from scratch)
Software Libraries: HDF 4.1r1 (included in SeaDAS 4.0).

SeaDAS PC-Linux version:

SeaDAS for Linux/PC was originally developed and tested under the following environment:

- Gateway 2000 PC with a Pentium II 300 MHz CPU
- Redhat Linux 5.2.
- IDL 5.1 or 5.2.

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:
Software using HDF

Noesys and Transform, now available from Research Systems, Inc., are sophisticated software packages with many capabilities for HDF data files.

Noesys

SciSpy Browser and related information.

Research Systems, Inc.
4990 Pearl East Circle
Boulder, CO 80301
Phone: 303-786-9900
FAX: 303-786-9909
Email: info@rsinc.com

Windows Image Manager also works with SeaWiFS HDF data and allows transformation to other formats.
Windows Image Manager

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.)

References

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:

SeaWiFS Project Home Page

ADEOS/Midori Home Page (English)

SeaDAS Home Page

Points of Contact:

Goddard DAAC:
Web site: Goddard Earth Sciences Data and Information Services Center / Distributed Active Archive Center

Ocean Color Data Support Team

Dr. James Acker
Code 610.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771
USA Email: ocean@disc.gsfc.nasa.gov

User Services Office

Goddard Earth Sciences Distributed Active Archive Center
NASA Goddard Space Flight Center, Code 610.2
Greenbelt, MD 20771
phone: 301-614-5224
fax: 301-614-5268
Email: daacuso@disc.gsfc.nasa.gov

SeaWiFS Project:

Web site: SeaWiFS Project

Data production and processing:

Dr. Gene Carl Feldman
SeaWiFS/SIMBIOS Projects
Code 970.2
Goddard Space Flight Center
Greenbelt , MD 20771
USA
Email: gene@seawifs.gsfc.nasa.gov

Science and algorithms

Bryan Franz
SeaWiFS Project, Code 970.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771
USA
E-mail: franz@seawifs.gsfc.nasa.gov

NASDA

Web sites:

NASDA (Japanese)
NASDA (English)
ADEOS/Midori (English)

Dr. Ichio Asanuma
NASDA/EORC
TRITON SQUARE, X-23
1-8-10 HARUMI
CHUO-KU TOKYO 104-6023
JAPAN
E-mail: asanuma@eorc.nasda.go.jp

Data product elements:

Bryan Franz
SeaWiFS Project, Code 970.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771
USA
E-mail: franz@seawifs.gsfc.nasa.gov

SIMBIOS Project

SIMBIOS Project, Code 970.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771
USA
E-mail: gfargion@simbios.gsfc.nasa.gov

SeaDAS:

The SeaDAS Development Group
Code 970.2
Goddard Space Flight Center
Greenbelt, MD 20771
USA
Email: seadas@seadas.gsfc.nasa.gov
Web site: http://seadas.gsfc.nasa.gov
Phone: (301)286-4759: Mark Ruebens
(301)286-9958: Robert Lindsay

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