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| Earth Resources Observation and Science (EROS) |
The Advanced Very High Resolution Radiometer (AVHRR) data set is comprised of data collected by the AVHRR sensor and held in the archives of the U.S. Geological Survey`s EROS Data Center. Carried aboard the National Oceanic and Atmospheric Administration`s (NOAA) Polar Orbiting Environmental Satellite series, the AVHRR sensor is a broad-band, 4- or 5-channel scanning radiometer, sensing in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum.
The EROS Data Center houses AVHRR High Resolution Picture Transmission (HRPT) data and Local Area Coverage (LAC) data. The HRPT data are full resolution image data transmitted to a ground station as they are collected, while LAC data (also full resolution data) are recorded with an onboard tape recorder for subsequent transmission during a station overpass.
The objective of the AVHRR instrument is to provide radiance data for investigation of clouds, land-water boundaries, snow and ice extent, ice or snow melt inception, day and night cloud distribution, temperatures of radiating surfaces, and sea surface temperature. The AVHRR data collection effort also provides opportunities for studying and monitoring vegetation conditions in ecosystems, including forests, tundra, and grasslands with applications that include agricultural assessment, land cover mapping, production of large-area image maps (e.g., country maps, continental maps, world maps), and evaluation of regional and continental snow cover.
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
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 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 EDCs direct reception. NOAA/NESDIS receives both world-wide recorded and direct readout AVHRR data from the Wallops Island, Virginia, and Gilmore Creek, Alaska, stations. These stations then redirect the data via a satellite relay to NOAA/National Environmental Satellite, Data and Information Services in Suitland, Maryland, where the data are processed, archived, and reproduced. The EROS Data Center ADAPS system was reconfigured in July of 1997 to acquire LAC via electronic transfer from NOAA/NESDIS, replacing the DOMSAT communications link.
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, 3480, and 3490 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). 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 NDVI composites for each annual growing season. Global Experimental Bi-Weekly Normalized Difference data, computed from (GVI) data, are analyzed to monitor global vegetation as a potential tool in global climatic studies.
| Satellite Number | Launch Date | Ascending Node | Descending Node | Service Dates |
|---|---|---|---|---|
| TIROS-N | 10/13/1978 | 1500 | 0300 | 10/19/1978 - 01/30/1980 |
| NOAA-6 | 06/27/1979 | 1930 | 0730 | 06/27/1979 - 11/16/1986 |
| NOAA-7 | 06/23/1981 | 1430 | 0230 | 08/24/1981 - 06/07/1986 |
| NOAA-8 | 03/28/1983 | 1930 | 0730 | 05/03/1983 - 10/31/1985 |
| NOAA-9 | 12/12/1984 | 1420 | 0220 | 02/25/1985 - 05/11/1994 |
| NOAA-10 | 09/17/1986 | 1930 | 0730 | 11/17/1986 - Present |
| NOAA-11 | 09/24/1988 | 1340 | 0140 | 11/08/1988 - 09/13/1994 |
| NOAA-12 | 05/13/1991 | 1930 | 0730 | 05/14/1991 - 12/15/1994 |
| NOAA-14 | 12/30/1994 | 1340 | 0140 | 12/30/1994 - Present |
| NOAA-15 | 05/13/1998 | 1930 | 0730 | 05/13/1998 - Present |
| NOAA-16 | 09/21/2000 | 1400 | 0200 | 09/21/2000 - Present |
| NOAA-17 | 06/24/2002 | 2200 | 1000 | 06/24/2002 - 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 Number | NOAA Satellites: 6, 8, 10 | NOAA Satellites: 7, 9, 11,12,14 | NOAA Satellites: 15, 16, 17 | IFOV |
|---|---|---|---|---|
| 1 | 0.58 - 0.68 | 0.58 - 0.68 | 0.58 - 0.68 | 1.39 |
| 2 | 0.725 - 1.10 | 0.725 - 1.10 | 0.725 - 1.10 | 1.41 |
| 3 (A) | 1.58 - 1.64 | 1.30 | ||
| 3 (B) | 3.55 - 3.93 | 3.55 - 3.93 | 3.55 - 3.93 | 1.51 |
| 4 | 10.50 - 11.50 | 10.30 - 11.30 | 10.30 - 11.30 | 1.41 |
| 5 | band 4 repeated | 11.50 - 12.50 | 11.50 - 12.50 | 1.30 |
| (in micrometers) | (in micrometers) | (in micrometers) | (in 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
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
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:
Example swath
Example scene
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
NOAA-K = NK = NOAA-15
NOAA-L = NL = NOAA-16
NOAA-M = NL = NOAA-17
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)
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.
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