The Advanced Very High Resolution Radiometer (AVHRR) is a broad-band, four or five channel (depending on the model) scanner, sensing in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum. This sensor is carried on NOAA's Polar Orbiting Environmental Satellites (POES), beginning with TIROS-N in 1978.
HRPT data are full resolution image data transmitted to a ground station as they are collected. LAC are also full resolution data, but recorded with an on-board tape recorder for subsequent transmission during a station overpass. GAC data provide daily subsampled global coverage recorded on the tape recorders and then transmitted to a ground station.
The AVHRR sensor provides for global (pole to pole) on board collection of data from all spectral channels. Each pass of the satellite provides a 2399 km (1491 mi) wide swath. The satellite orbits the Earth 14 times each day from 833 km (517 mi) above its surface.
Example swath
AVHRR data are both broadcast continually in direct readout mode and recorded on board the satellite for later playback. The EROS Data Center (EDC) AVHRR Data Acquisition and Processing System (ADAPS), which began operation in May 1987, receives approximately six daytime passes per day of HRPT data over the conterminous United States. Night acquisitions are acquired upon request only. As of March 1990, all data received at EDC are permanently archived. Prior to March 1990, approximately 40 percent of the data received were archived.
The EROS Data Center AVHRR Data Acquisition and Processing System was expanded on June 15, 1990, to acquire LAC and GAC data via a communications satellite for areas recorded throughout the entire globe. Priority is given to LAC acquisitions of the North American continent not covered by EDC's direct reception capabilities and other project specific areas.
NOAA/NESDIS receives both world-wide recorded and direct readout AVHRR data from the Wallops Island, Virginia, and Gilmore Creek, Alaska, stations. Those stations then redirect the data via a satellite relay to NOAA/NESDIS in Suitland, Maryland, where the data are processed, archived, and reproduced.
EDC's ADAPS flow for acquisitions and archiving begins with either direct HRPT reception or re-broadcast DOMSAT LAC/GAC reception. Initial ingest of the data reformatting includes archiving, and creation of browse quick looks, 9-track tapes, and 3480 cartridge tapes.
The NOAA AVHRR processing flow begins with sensor data receipt by the Command and Data Acquisition (CDA) stations (Wallops Island, Virginia and Gilmore Creek, Alaska) where the data are re-broadcast via communications satellites, to NOAA/NESDIS in Suitland, Maryland. The ephemeris data are accessed through the Gridded Earth Location and Determination System (GELDS) software on NAS computers for Level 1b production.
The EROS ADAPS systematic georegistration process references AVHRR data to the Earth's surface. Through modeling the position and attitude of the TIROS satellite platforms and the scanning geometry of the AVHRR sensor, geometric distortions can be minimized. The position of the satellite is determined by an orbital model updated by ephemeris data received daily from NAVY Space Surveillance. The AVHRR sensor model characterizes the non-linear scanning of the sensor mirror. A refinement to the sensor model accounts for the displacement in longitude due to the rotation of the Earth under the satellite. All modeling is referenced to the time of acquisition. As the satellite clock time drifts, a delta time adjustment is applied. Collectively, these models comprise the geometric correction model in ADAPS. The positional accuracy of a systematic georegistration is approximately 5000 m, RMSE.
Precise georegistration positional accuracy of 1000 m RMSE, requires correlation of image features with accurately registered cartographic or image-based maps. A common practice is to use cartographic sources such as Digital Chart of the World (DCW) or hydrography data to extract easily identifiable features such as coastlines, water bodies, and rivers and to correlate them with the matching raw image locations using various techniques. The correlation process determines specific adjustments to be applied to the time, roll, and yaw parameters of the orbital model. The EDC ADAPS uses a variety of techniques depending upon the geographic location of the imagery and the volume of data to be processed.
Spatial Resolution
The average instantaneous field-of-view (IFOV) of 1.4 milliradians yields a LAC/HRPT ground resolution of approximately 1.1 km at the satellite nadir from the nominal orbit altitude of 833 km (517 mi). The GAC data are derived from an on board sample averaging of the full resolution AVHRR data. Four out of every five samples along the scan line are used to compute one average value and the data from only every third scan line are processed, yielding 1.1-km by 4-km resolution at nadir.
Satellite Launch Ascending Descending Service Number Date Node Node Dates -------- ------ ---- ---- ------------------ TIROS-N 10/13/78 1500 0300 10/19/78 - 01/30/80 NOAA-6 06/27/79 1930 0730 06/27/79 - 11/16/86 NOAA-7 06/23/81 1430 0230 08/24/81 - 06/07/86 NOAA-8 03/28/83 1930 0730 05/03/83 - 10/31/85 NOAA-9 12/12/84 1420 0220 02/25/85 - Present NOAA-10 09/17/86 1930 0730 11/17/86 - Present NOAA-11 09/24/88 1340 0140 11/08/88 - 09/13/94 NOAA-12 05/14/91 1930 0730 05/14/91 - Present NOAA-14 12/30/94 1340 0140 12/30/94 - Present
NOAA-B launched May 29, 1980, failed to achieve orbit. NOAA-13 launched August 9, 1993, failed due to an electrical short circuit in the solar array.
Band # Satellites: Satellites: IFOV
NOAA-6,8,10 NOAA-7,9,11,12,14
1 0.58 - 0.68 0.58 - 0.68 1.39
2 0.725 - 1.10 0.725 - 1.10 1.41
3 3.55 - 3.93 3.55 - 3.93 1.51
4 10.50 - 11.50 10.3 - 11.3 1.41
5 band 4 repeated 11.5 - 12.5 1.30
(micrometers) (micrometers) (milliradians)
The record structure of LAC/HRPT Level 1b data sets for each file follows the pattern:
Record 1 TBM (Terabit memory)Header record (122 bytes) Record 2 Data Set Header record (7400 bytes) Record 3 Dummy (7400 bytes) Records 4-n Data records (7400 bytes)
The record structure of GAC data sets for each file follows the pattern:
Record 1 .... TBM (Terabit memory) Header record (122 bytes) Record 2 .... Data Set Header record Record 3-n .. Data records
To place orders and to obtain additional information regarding technical details, ancillary products, and pricing schedules, contact: Customer Services, Eros Data Center OR NOAA/SAA User Assistance
Online requests for these data can be placed via the U.S. Geological Survey Global Land Information System (GLIS) interactive query system. The GLIS system contains metadata and online samples of Earth science data. With GLIS, you may review metadata, determine product availability, and place online requests for products.
The EROS Data Center provides standard AVHRR digital Level 1b and georegistered products on 3480 cartridge, 8 mm cassette, and via network access.
Applications and Related Data Sets
AVHRR data provide opportunities for studying and monitoring vegetation conditions in ecosystems including forests, tundra, and grasslands. Applications include agricultural assessment, land cover mapping, producing image maps of large areas such as countries or continents and tracking regional and continental snow cover. AVHRR data are also used to retrieve various geophysical parameters such as sea surface temperatures and energy budget data.
Additional data sets include the Alaska twice-monthly AVHRR and the U.S. Conterminous bi-weekly composites. These comprehensive time series data sets are calibrated, georegistered daily observations and twice-monthly maximum NDVI composites for each annual growing season.
Global Experimental Bi-Weekly Normalized Difference data, computed from Global Vegetation Index (GVI) data, are analyzed to monitor global vegetation as a potential tool in global climatic studies.
Example scene
TBM Header The TBM Header contains data type and selection parameters. All fields are ASCII except the Channels Selected field which is binary. The overall format follows:
BYTE # # OF BYTES CONTENT
IN FIELD
31-74 44 Data Set Name**
75 1 Total/Selective Copy ("T" or "S")
76-78 3 Beginning Latitude
79-81 3 Ending Latitude
82-85 4 Beginning Longitude
86-89 4 Ending Longitude
90-91 2 Start Hour
92-93 2 Start Minute
94-96 3 Number of Minutes
97 1 Appended Data Selection ("Y" or "N")
98-117 20 Channels Selected (in binary)
** The complete data set name with qualifiers follows the pattern:
NSS.Data-type.Spacecraft-Unique-ID.Year-day.Start-time. Stop-time. Processing-block-ID.Source. The following screens detail this scheme.
Qualifier Valid Entry
--------- ----------
Data-Type HRPT = HRPT
GHRR = GAC (recorded)
LHRR = LAC (recorded HRPT)
Spacecraft- TIROS-N = TN
Unique ID NOAA-A = NA = NOAA-6
NOAA-B = NB
NOAA-C = NC = NOAA-7
NOAA-E = NE = NOAA-8
NOAA-F = NF = NOAA-9
NOAA-G = NG = NOAA-10
NOAA-H = NH = NOAA-11
NOAA-D = ND = NOAA-12
NOAA-I = NI = NOAA-13
NOAA-J = NJ = NOAA-14
Year-day D78141, where "D" identifies this section as a
Julian day delimiter. The "78" identifies the
year the spacecraft began recording data, and
the "141" indicates the Julian day the satellite
began recording.
Start-time S1422, where "S" identifies this group as a
start time delimiter. The "1422" indicates 14
hours and 22 minutes GMT to the nearest minute
to when the spacecraft recording began.
Stop-time E1555, where "E" identifies this group as a end
time delimiter. The "1555" indicates 15 hours
and 55 minutes GMT to the nearest minute of the
spacecraft recording of the last usable data.
Processing- B0017499, where "B" indicates this group is a
Block-ID processing block ID delimiter. The "0017499" is
a seven digit number identifying the spacecraft
revolution number in which data recording began
and the revolution in which the recording
ended. The first five digits identify the
beginning revolution and the last two being the
least significant numbers of the ending
revolution. The revolution number may be off by
one or two digits.
Source Gilmore Creek, Alaska = GC
Western Europe CDA = WE
SOCC (Satellite Operations Control Center) = SO
Wallops Island, Virginia = WI
EDC, Sioux Falls, SD = SD
The binary Data Set Header record format follows:
BYTE # # OF BYTES CONTENT
IN FIELD
1 1 Spacecraft ID
2 1 Data Type
3-8 6 Start Time - time code from first
data frame
9-10 2 Number of Scans
11-16 6 End Time - time code form last data
frame
17-23 7 Processing Block ID (ASCII)
24 1 Ramp/Auto Calibration
25-26 2 Number of Data Gaps
27-32 6 DACS Quality
33-34 2 Calibration Parameter ID
35 1 DACS Status
36-40 5 Zero-filled - spare
41-84 44 44 Character data set (EBCDIC)
85-end variable Spares - Zero-filled to size of data
record (3220 or 14800)
LAC Data Set Information Each LAC data set contains two records per scan. The records are 7400 bytes long and are written in binary format. A design detail follows:
To calculate the size in megabytes of an AVHRR scene follow the formula\listed below:
- Two records at 7400 bytes each .......... 14800 bytes
- Six lines/second capture rate (6 x 60 seconds). 360
lines/minute
- Using an average EROS pass of .................... 12
minutes
- Formula: 14800 x 360 x 12 = 63.9 megabytes
The pre-September 1992 LAC/HRPT data record format:
BYTE # # BYTES CONTENTS
1-2 2 Scan line number from 1 to n
3-8 6 Time code - year, julian day,
milliseconds
9-12 4 Quality indicators
13-52 40 Calibration coefficients
53 1 Number of meaningful zenith
angles and Earth location
points appended to scan (n)
54-104 51 Solar zenith angles
105-308 204 Earth location
309-448 140 Telemetry (header)
449-14104 13656 LAC/HRPT video data
14105-14800 696 Spares
The LAC/HRPT video data contain five (channel) values for each of the 2048 points in a scan. There is a total of 10240 samples (5 channels x 2048 points) in the data.