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The AVHRR 1 km archive lists over 15,000 polar scenes available from the AVHRR Polar 1 km Level 1b Data Set. The archive has a table with a single line entry for each archived scene. Each scene has 20 columns in the table. Columns are described below.
Users are encouraged to read the data set documentation before using the archive. Those familiar with and interested in the data can select, view, and order images from the archive using a convenient tool that allows subsetting by station, date, time, and hemisphere. Users can also download the entire archive index (approximately 7.3 MB) via anonymous ftp.
For a discussion on interpreting the text information appended to the end of browse images, please visit the ADAPS Programmer's Guide.
Columns:
|
Granule ID Hemisphere Satellite Data Type Receiving Station Start Date and Time |
Pass Direction Number of Lines in the Scene Data Quality Solar Zenith Angle Latitude and Longitude of the Corner |
Column 1: granule ID
The granule ID is the primary identifier when ordering a data granule. The first field identifies the NOAA satellite that acquired the scene. The second field is an abbreviated code indicating either the High Resolution Picture Transmission (HRPT) station that received the data, or in the case of Local Area Coverage (LAC), the hemisphere in which the data were recorded. The third field is the acquisition date (YYMMDD notation). The fourth field is the acquisition start time rounded to the nearest minute in Greenwich Mean Time (HHMM notation). The following is a sample granule ID that illustrates this naming convention.
a11_tms_930915_1438
where:
a11 = satellite (NOAA-11)
tms = receiving station (Trømso, Norway)
930915 = acquisition date (15 September 1993)
1438 = start time in GMT (14:38)
Column 2: hemisphere
An 'N' designates Northern Hemisphere data, and an 'S' designates Southern Hemisphere data.
Column 3: satellite
This column indicates the number of the NOAA satellite from which the data were acquired. Following are acceptable valids for this field:a10 = NOAA-10
a11 = NOAA-11
a12 = NOAA-12 a14 = NOAA-14 a15 = NOAA-15
Column 4: data type
The data are either High Resolution Picture Transmission (HRPT) or Local Area Coverage (LAC) data. Ground stations receive HRPT data via satellite transmission. The satellite records LAC data on tape for downlink later.
Column 5: receiving station
This column identifies the station that received the data, which in turn defines the geographic location of the image. For HRPT data, the three-letter code is the same as the second field of the granule ID name. For LAC data, the three-letter code indicates which ground station received the tape-recorded playback of data. Following are acceptable valids for this field:csy = Casey Station, Antarctica
hbt = Hobart, Australia
lcn = LAC data, Northern Hemisphere
lcs = LAC data, Southern Hemisphere
mcm = McMurdo Station, Antarctica
ngc = Fairbanks, AK
pal = Palmer Station, Antarctica
pas = Prince Albert, Canada
tkz = Tokyo, Japan
s1n = Polar Sea (U.S. Coast Guard cutter)
sfl = Sioux Falls, South Dakota, USA
tkz = Tokyo, Japan tms = Tromso, Norway
ykt = Yakutsk, Siberia, Russia
Columns 6 and 7: start date and time
These columns indicate the date and time of acquisition. Time is expressed in 24-hour Greenwich Mean Time (GMT) and is truncated to HHMM (not rounded). The header files of each scene include the precise start times of scene acquisition, which may be important for geolocating image data from orbit ephemeris data. Users may request the header files for specific scenes by contacting NSIDC User Services.
Column 8: pass direction
This column contains a three-letter code indicating the orbit direction during the beginning, middle, and end of acquisition of the scene. An 'A' indicates an ascending pass (flying toward the northwest). A 'D' indicates a descending pass (flying toward the southeast). The codes 'AAD' or 'DAA' indicate a change in the pass direction during acquisition. In this case, the satellite passed close to the North or South Pole, with the pole included in the scene.
Column 9: number of lines in the scene
Columns 10 and 11: data quality
The first data quality column reports the number of separate gaps (regions of missing or noisy data) in each scene. The second data quality column indicates the number of lines missing from the total number of lines reported in column 9. The data quality columns provide a concise way to characterize the quality of the archived scene. The header file contains a complete listing of the location and number of lines for missing gaps.
Column 12: solar zenith angle
Since the area covered by each AVHRR scene is quite large, the solar zenith angle varies considerably over the scene. A value greater than 90 indicates that the sun is below the horizon at the center of the scene.
Columns 13 through 20: latitude and longitude of the corner points
The latitude and longitude of each of the four corner points of a scene are expressed in decimal degrees. Plotting the four points on a map indicates the area of coverage of the scene, although the notation 'NW,' 'NE',' 'SW,' and 'SE,' is not entirely meaningful for scenes that include a pole. Longitudes range from 0 to 360 degrees east of the prime meridian.
For additional information, please contact NSIDC User Services:
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
Creation date: October 1996
Revision date: June 2001
