P. Flament (U. of Hawaii, USA)
R. Bernstein (SeaSpace Inc., USA)
Announced availability: 1 August 1993
Data Access GMS images, collected by the University of Hawaii, are available upon request from the University Corporation for Atmospheric Research. The images are contained on two CD-ROMs and come with a technical report that describes data collection and processing in more detail. The infrared CD-ROM is also available through the University of Hawaii URL http://satftp.soest.hawaii.edu/pub/.
Background GMS-4 is a Japanese satellite in geostationary orbit over the equator at approximately 140E. The satellite is equipped with the Visible and Infrared Spin Scan Radiometer (VISSR) imaging sensor, which uses the spin motion of the satellite to scan the earth in the East-West direction. GMS begins a North-South scan every hour on the half hour, with four additional scans daily for wind estimation. At the satellite subpoint, the visible (0.5-0.75 um) channel has a resolution of 1.25 km and the infrared (10.5-12.5 um) channel has a resolution of 5 km. This gives approximately 10,000 visible and 2,500 infrared lines and samples for each full-globe image. The visible channel is digitized at 6 bits and the infrared channel at 8 bits. The S-VISSR telemetry is transmitted digitally at 1.7 GHz with a bit rate of 660 kbps. Detailed documentation on the GMS satellite and the VISSR can be found in the GMS User's Guide.
The telemetry from the GMS-4 geostationary satellite was captured in Hawaii during the TOGA COARE Intensive Observation Period (IOP) from November 1992 to March 1993. The images were calibrated into percent albedo or brightness temperature, regridded to the COARE domain (135E to 175E, 10S to 10N with a 5-km square pixel size), and placed on the anonymous internet server satftp.soest.hawaii.edu less than one hour after capture during the IOP.
The images are useful to find relationships between events in a survey or in a time series, and the general weather patterns in the vicinity of sampling platforms. Quantities that can be estimated include reflected shortwave and outgoing longwave radiations, tropospheric winds by tracking clouds, surface roughness from sun glint intensity, and rainfall from cloud top temperatures. Since the images have been remapped to a common geographic grid, temporal statistics should be especially easy to construct.
Data File Information The images on the CD-ROMs are in the form of compressed PostScript files with graphic overlays for the geographic grid, the gray scale wedge and the positions of the moorings and ships. A catalog of the images captured (1,910 infrared and 877 visible images), tools to uncompress and convert the images to binary arrays or Sun raster files, and utilities to map the ISO-9660 names into Unix names for workstation users are also provided.
Caution
As described in the technical report distributed with the disks, the images were only recorded every two hours until 10 December 1992, due to limited archiving facilities. After this date and until the end of the IOP, the full hourly data was archived. Users of the disks should be aware of this sampling peculiarity.
Temporal statistics over the entire period spanned by the data should only be computed using the two-hourly data. Hourly statistics should be limited to the period during which the hourly data are available, i.e., after 10 December 1992. Attempting to compute hourly statistics, such as the diurnal cycle of outgoing longwave radiation, over the entire period, will inevitably lead to estimates biasing the odd hours, because the atmospheric conditions were not stationary during the IOP.
For more information, please contact:
Pierre Flament
University of Hawaii at Manoa
Dept. of Oceanography
1000 Pope Road
Honolulu, HI 96822
USA
email: pierre@mael.soest.hawaii.edu
Phone: (808) 956-6418
FAX: (808) 956-9225
To obtain a copy of the dataset, please contact:
UCAR Communications
P.O. Box 3000
Boulder, Colorado 80307-3000 USA
e-mail: butterwo@ucar.edu
Phone: (303) 497-8601
Fax: (303) 497-8610
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