AVHRR LAC/HRPT Data Set Document
Summary:
This data set is comprised of data collected by the Advanced Very High
Resolution Radiometer (AVHRR) sensor. Depending on the model, 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. Beginning in 1978, this sensor has been carried on the National
Oceanic and Atmospheric Administration's (NOAA) Polar Orbiting Environmental
Satellites (POES), otherwise known as the Television and Infrared Observation
Satellites-N (TIROS-N) series.
The AVHRR data held in the U.S. Geological Survey's EROS Data Center archives
are acquired in two formats:
- High Resolution Picture Transmission (HRPT)
- Local Area Coverage (LAC)
The HRPT data are full resolution image data transmitted to a ground station
as they are collected. The LAC data are also full resolution data, but are
recorded with an onboard tape recorder for subsequent transmission during a
station overpass.
Table of Contents:
- Data Set Overview
- Investigator(s)
- Theory of Measurements
- Equipment
- Data Acquisition Methods
- Observations
- Data Description
- Data Organization
- Data Manipulations
- Errors
- Notes
- Application of the Data Set
- Future Modifications and Plans
- Software
- Data Access
- Output Products and Availability
- References
- Glossary of Terms
- List of Acronyms
- Document Information
Data Set Identification:
Data Set Introduction:
The normal operating mode of the satellite is for direct transmission of
AVHRR data to Earth continuously in real time. This direct transmission
is called High Resolution Picture Transmission (HRPT). In addition to the
HRPT mode, about 11 minutes of data may be selectively recorded per orbit,
by recorders on board the satellite for later playback. These recorded
data are referred to as Local Area Coverage (LAC) data. The LAC data may
be recorded over any portion of the world as selected by NOAA/National
Environment Satellite, Data and Information Service (NESDIS) and played
back on the same orbit as recorded or during a subsequent orbit.
AVHRR data are raw data as received by the satellite and archived as Level-0
data. Level-1B data are raw data that have been quality controlled,
assembled into discrete data sets, and appended with Earth location and
calibration information (but not applied). The HRPT and LAC data sets have
been combined in this document since they have identical Level-1B formats
and spatial resolutions.
The AVHRR Level-1B data represent a collection of data sets. Each data set
contains one type of data for a discrete time period. Thus, there are
separate AVHRR HRPT and LAC data sets. Time periods are arbitrary subsets of
orbits and may cross orbits (i.e., may contain data along a portion of an
orbital track that includes the ascending node, the reference point for
counting orbits).
Objective/Purpose:
The objective of producing the AVHRR Data Set is to provide long term, global
data of land surface parameters with high temporal frequency coarse resolution
for studying the Earth as an integrated system.
Summary of Parameters:
Band #
|
Satellites:
NOAA-6,8,10 |
Satellites:
NOAA-7,9,11,12,14 |
Instantaneous Field
of View (IFOV) |
| 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 |
10.30 - 11.50 |
10.30 - 11.30 |
1.41 |
| 5 |
band 4 repeated |
11.5 - 12.50 |
1.30 |
| |
(micrometers) |
(micrometers) |
(milliradians) |
Discussion:
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. It is an integral member of
the payload on the advanced Television and Infrared Observation Satellite-N
(TIROS-N) spacecraft and its successors in the NOAA series and, as such,
contributes data required to meet a number of operational and
research-oriented meteorological objectives.
Related Data Sets:
EROS Data Center (EDC):
- Conterminous United States AVHRR Biweekly Composites
- Alaska AVHRR 14-day Composites
- Northern Great Plains Weekly Composites
Land Processes Distributed Active Archive Center (LP DAAC):
- AVHRR 1-km Global 10-day Composites
- AVHRR 1-km Orbital Segments
Investigator(s) Name and Title:
Not applicable.. The AVHRR program is a worldwide data collection effort
supporting programs and projects too great to be enumerated in this
document.
Title of Investigation:
Contact Information:
The AVHRR sensor is a scanning radiometer with either four or five channels,
which is sensitive to visible, near infrared and thermal infrared radiation.
The channels have been chosen to permit multispectral analyses, which provide
improved determination of hydrologic, oceanographic, and meteorological
parameters. The visible (0.5 micron) and near infrared (0.9 micron) channels
are used to discern clouds; land-water boundaries; snow and ice extent; and,
when the data from the two channels are compared, an indication of ice/snow
melt inception. The IR window channels are used to measure cloud distribution
and to determine temperature of the radiating surface (cloud or surface).
Data from the two IR channels are incorporated into the computation of sea
surface temperature.
On later instruments in the series, a third IR channel was added for the
capability of removing radiant contributions from water vapor when determining
surface temperatures. Prior to inclusion of this third channel, corrections
for water vapor contributions were based on statistical means using
climatological estimates of water vapor content.
Sensor/Instrument Description:
Collection Environment:
Source/Platform:
TIROS-N and NOAA-6 through NOAA-14
Source/Platform Mission Objectives:
In 1961, the Department of Commerce was directed by Congress to establish and
operate a meteorological satellite system. This system was to provide for the
continuous observation of worldwide meteorological conditions from space and
to report and process the data obtained for use in weather forecasting. The
main objectives established in the congressional mandate were:
-
to view the global atmosphere regularly and reliably both day and night.
The system was to provide direct readout data to local ground stations within
communication range of the satellite.
-
to provide for sounding the global atmosphere regularly and reliably; to
provide quantitative information for use in numerical weather prediction; to
provide for continuous viewing of weather features; and to collect and relay
meteorological data from remote platforms such as buoys, ships, automatic
stations, aircraft, and balloons.
Key Variables:
Radiance and Imagery > Infrared Wavelengths
Radiance and Imagery > Visible Wavelengths
Principles of Operation:
The EDC AVHRR processing flow begins with sensor data receipt by EDC's HRPT
receiving station, receipt of data rebroadcast via communications satellite,
or receipt of data from the AVHRR Global 1-km Project. All receipts of data
are ingested and archived at the EDC. The processes to ingest the data
include creating an archive tape; creating an inventory metadata file;
creating a metadata file for information systems support; and building browse
files.
Sensor/Instrument Measurement Geometry:
As the spacecraft moves through its orbit, the expected angular distance
between the nadir of adjacent LAC/HRPT scans is approximately 0.0296 degrees
of arc, or 3.2914 kilometers, as measured from the center of the Earth. This
actual value of the average angular distance can vary by up to about 0.1712
kilometer due to variations in satellite height, scan angle and other factors.
The instantaneous field of view (IFOV) for all channels is specified to be
1.3 +/- 0.1 milliradians.
Manufacturer of Sensor/Instrument:
Calibration:
Specifications:
The NOAA/TIROS radiometers have been designed to view cold space and one or
more internal warm blackbodies as part of their normal scan sequences in orbit.
This provides data in the microwave and infrared channels for determining
signal-to-noise and radiometric slopes and intercepts. Unfortunately, there
are no onboard calibration sources for the visible region; in the visible
channels, the calibration used is the calibration determined before launch.
There are other coefficients necessary for in-orbit calibration that must be
derived from prelaunch test data. These include the coefficients to account
for the nonlinearity in the AVHRR's response and the coefficients for
calibrating the temperature sensors in the internal blackbodies of the AVHRR
sensor.
The following affect the calibration of the sensor:
IFOV ............ 1.4 mr
Resolution ...... 1.1 km
Altitude ........ 833 km
Scan Rate ....... 360 scans/minute
Samples/IFOV .... 1.362 samples
Scan Range ...... -55.4 to 55.4 degrees
Samples/Scan .... 2048 samples per channel per Earth scan
Tolerance:
The AVHRR infrared channels were designed for an Noise Equivalent Differential
Temperature (NEdT) of 0.12 degrees Kelvin (at 300 Kelvin), and a signal to
noise ration of 3:1 at 0.5 percent albedo.
Frequency of Calibration:
The AVHRR sensor was designed to view cold space and one or more internal
warm blackbodies for each scan sequence while in orbit.
Other Calibration Information:
In general, radiometric calibration involves exposing a radiometer to sources
of radiation that have been calibrated against primary or secondary standards
and determining a relationship between the output of the radiometer and the
intensity of the incident radiation (radiance).
All the radiometers flown on the NOAA/TIROS satellites undergo extensive
prelaunch testing and calibration by their manufacturers to characterize their
performance. The NESDIS independently analyzes the data from the prelaunch
tests to determine the operating characteristics of the instruments, such as
their signal-to-noise ratios, stability, linearity of response, and
sensitivity. However, characteristics cannot be expected to be the same in
orbit as they were before the launch. One reason is that the thermal
environment varies with position in the orbit, causing sensitivities to vary
orbitally. Also, instrument components age in the several years that usually
elapse between the time of the prelaunch tests and launch, and the aging
process continues during the two or more years the instrument typically
operates in orbit. Therefore, the NOAA/TIROS radiometers have been designed
to view cold space and one or more internal warm blackbodies as part of their
normal scan sequences in orbit.
The AVHRR data are both broadcast continually in direct readout mode (HRPT)
and recorded (LAC) on board the satellite for later playback. The EDC's
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 NOAA receives both worldwide 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.
On June 15, 1990, the EDC's ADAPS system was expanded to acquire data via the
communications satellite relay used by NOAA. The data collected on a daily
basis, consists of global coverage of the world's land masses.
Data Notes:
Field Notes:
Spatial Characteristics:
Spatial Coverage:
The AVHRR sensor provides a global (pole-to-pole) onboard collection of data
from all spectral channels. The 110.8-degree scan equates to a swath width of
27.2 degrees at the Equator centered on the subsatellite track. This swath
width is greater than the 25.3-degree separation between successive orbital
tracks, providing overlapping coverage (side-lap). The satellite orbits the
Earth 14 times each day from 833 kilometers above its surface.
Spatial Coverage Map:
Spatial Resolution:
The IFOV of each channel is approximately 1.4 milliradians leading to a
resolution at the satellite subpoint of 1.1 kilometers for a nominal altitude
of 833 kilometers. The scanning rate of the AVHRR sensor is 360 scans per
minute. The time within each scan line of AVHRR data represents IFOV 1.
These data provide continuous transmission for the HRPT data and selectively
recorded LAC data.
Projection:
Grid Description:
Temporal Characteristics:
Temporal Coverage:
The overall coverage of the archived AVHRR data base is shown in the
following table. However, there may be short gaps in the time ranges
and additional data coverage outside these dates associated with equipment
malfunctions. Start and end dates indicate operational range.
| SATELLITE: |
START DATE: |
END DATE: |
| TIROS-N |
10/19/78 |
01/30/80 |
| NOAA-6 |
06/27/79 |
06/30/86* |
| NOAA-7 |
08/24/81 |
06/07/86 |
NOAA-8
|
06/20/83
01/85 |
06/12/84*
10/31/85 |
| NOAA-9 |
02/25/85 |
11/07/88 |
| NOAA-10 |
11/17/86 |
09/16/91 |
| NOAA-11 |
11/08/88 |
09/13/94 |
| NOAA-12 |
09/01/91 |
present |
| NOAA-14 |
12/30/94 |
present |
* The quality of these data is poor due to excessive noise.
Temporal Coverage Map:
Not applicable.. The temporal coverage map will not be supplied due to the
complexities of the acquisition schedules.
Temporal Resolution:
Each scan of the AVHRR views the Earth for a period of 51.282 milliseconds.
The analog data output from the sensors is digitized onboard the
satellite at a rate of 39,936 samples per second per channel. Each sample
step corresponds to an angle of scanner rotation of 0.95 milliradian. At this
sampling rate, there are 1.362 samples per IFOV. A total of 2,048 samples for
the LAC/HRPT data are obtained per channel per Earth scan, which spans an
angle of +/- 55.4 degrees from the nadir (subpoint view). Successive scans
occur at the rate of six per second or at intervals of 167 milliseconds.
Because the satellite is Sun-synchronous, visible data revisit time is daily.
Infrared imaging is accomplished twice daily with the second visit occurring
during the pass over the dark side of the Earth. Instrument operation is
continuous.
Data Characteristics:
Parameter/Variable:
Depending on the instrument, there are four or five channels, which measure
wavelengths, as outlined previously in the Summary of Parameters. Other
parameters appended include calibration coefficients, Earth location, time
code, quality indicators, solar zenith angles, and telemetry.
Variable Description/Definition:
Each LAC data set contains an individual satellite recorder playback (up to
11 minutes of recorded HRPT data). Each HRPT data set contains the HRPT data
from a CDA contact. Data within each LAC/HRPT data set are arranged in
chronological order with one scan contained in two physical records. Each
record contains 7,440 bytes written in binary format.
The time code consists of the year, day of year, and greenwich mean time
(GMT) time of day in milliseconds. The year is contained in the first 7 bits
of the first two bytes, the 9-bit day of year is right-justified in the first
two bytes, and the 27-bit millisecond GMT time of day is right-justified in
the last four bytes. All other bits are zero. The time code always has the
same format for all Level-1B data sets.
The quality indicators are contained in four bytes. The first byte contains
the status of detected conditions during processing and the last three bytes
contain Data Acquisition and Control Subsystems (DACS) quality indicators. If
the bit is set to one or the on position, then the condition is true.
The calibration coefficients consist of slope and intercept values for each
of the five channels. The use of these coefficients is described in Section
3.3 of the "NOAA Polar Orbiter Data User's Guide". Each value is stored in
four bytes in the following order:
Channel 1 slope coefficient, Channel 1 intercept coefficient
Channel 2 slope coefficient, Channel 2 intercept coefficient
Channel 3 slope coefficient, Channel 3 intercept coefficient
Channel 4 slope coefficient, Channel 4 intercept coefficient
Channel 5 slope coefficient, Channel 5 intercept coefficient
A fixed number of zenith angles and Earth location points are appended to each
scan. However, only the first n zenith angles and the first n Earth location
points have meaningful values (n is defined in byte 53). A maximum of 51
points is possible in a scan. There are 2,048 points in a LAC/HRPT scan line.
However, the solar zenith angles and Earth location data (latitude and
longitude) are sampled every 40 points starting at the twenty-fifth point (25,
65, 105, ..., 1945, 1985, 2025). There are 51 possible solar zenith angles and
Earth location values for each scan line. Each zenith angle requires one byte
(stored as degrees by 2). The latitude and longitude values are each stored in
two-byte fields in 128ths of a degree (east positive).
The telemetry data contain information which may be used to compute
calibration coefficients when these are not included in the data. The
telemetry data are stored in 140-byte units. The first 103 10-bit words are
packed three 10-bit words in four-bytes, right justified. The last four-byte
group contains one 10-bit word with 20 trailing bits. All unused bits are set
to zero. The contents of these 103 words are contained in Table 3.1.2.1-3 of
the "NOAA Polar Orbiter Data User's Guide", which is the entire HRPT minor
frame format. For more information, refer to NOAA Technical Memorandum NESS
107 entitled, "Data Extraction and Calibration of TIROS-N/NOAA Radiometers".
The LAC/HRPT video data consist of five readings (one for each channel) for
each of the 2,048 points in a scan. They are packed as three 10-bit samples
in four bytes, right-justified. The last four-byte group contains two 10-bit
samples with 10 trailing zero bits. The first two bits of each four-byte
group are zero. The 10,240 samples (2,048 points by 5 channels) are ordered
scan point 1 (Channel 1, 2, 3, 4, 5), scan point 2 (Channel 1, 2, 3, 4, 5),
and so forth. For TIROS-N, NOAA-6, NOAA-8, and NOAA-10, there is no sensor
for Channel 5 so Channel 4 data are repeated in the Channel 5 position. The
video data are stored in 2's complement form.
The 16-bit unpacked format for full copy LAC/HRPT data has the same format as
the "packed" data described above except for the video data. The video data
values for each channel are contained in the 10 least significant bits and
the six most significant bits are zero filled.
Unit of Measurement:
Counts which can be converted to radiances.
Data Source:
Data Range:
October 19, 1978, to present.
Sample Data Record:
Data Granularity:
A general description of data granularity as it applies to the IMS appears in
the eosdis Glossary.
LAC/HRPT (varies by scene).
Data Format:
Record structure of LAC/HRPT Level-1B data sets for each file:
Record 1 .... TBM (Terabit memory) Header record (122 bytes)
Record 2 .... Data Set Header record (7400 bytes)
Record 3 .... Dummy (7400 bytes)
Record 4-n .. Data records (7400 bytes)
The TBM Header contains data type and selection parameters. All fields are in
ASCII format except the Channels Selected field, which is binary. The overall
format follows:
BYTE #
|
# of Bytes
in Field |
CONTENT
|
| 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
Header Record Format
The binary Data Set Header record format follows:
BYTE #
|
# of Bytes
in Field |
CONTENT
|
| 1 |
1 |
Spacecraft ID |
| 2 |
1 |
Data Type |
| 3-8 |
6 |
Start Time - time code from last data frame |
| 9-10 |
2 |
Number of Scans |
| 11-16 |
6 |
End Time - time code from 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 7,400 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
LAC/HRPT Data Record Format
| BYTE # |
# of 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 |
Calibrations 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 |
Formulae:
Derivation Techniques and Algorithms:
Data Processing Sequence:
Processing Steps:
The EDC's ADAPS flow for acquisitions and archiving begins with either direct
HRPT reception or with re-broadcast of DOMSAT LAC reception. Initial ingest
of the data reformatting includes archive, and creation of browse quick looks
and cartridge tapes.
The NOAA AVHRR processing flow begins with sensor data receipt by the 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
Determination System (GELDS) software for generation of Level-1B production.
The EDC 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 canning 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 5,000 meter,
root-mean-square-error (RMSE).
Precise georegistration positional accuracy of 1000 meter 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.
Processing Changes:
See NOAA Polar Orbiter Data User's Guide, Appendix E.
Calculations:
Special Corrections/adjustments:
Calculated Variables:
Graphs and Plots:
Sources of Error:
Quality Assessment:
Data Validation by Source:
Confidence Level/accuracy Judgement:
Measurement Error for Parameters:
Additional Quality Assessments:
Data Verification by Data Center:
Limitations of the Data:
Known Problems with the Data:
Prior to June 1981, the Earth location data in the AVHRR Level-1B data may
have been slightly inaccurate due to errors in the TIROS Information
Processor (TIP) clock on board the spacecraft. The 6-byte time code in the
Level-1B data is taken from the TIP clock, which routinely contained errors
of 1.5 to 2.3 seconds.
Usage Guidance:
Refer to the NOAA Polar Orbiter Data User's Guide.
Any Other Relevant Information about the Study:
As of September 8, 1992, the EDC implemented enhancements to the Level-1B
format. These enhancements utilized some of the spare bytes appended to the
end of the header record and the data records. The header record now includes
Osculating Keplerian and Cartesian orbit parameters. The size of data records
was increased in order to improve the accuracy of the solar zenith angle to
one-tenth of a degree.
On November 15, 1994, the following Level-1B data set enhancements were
implemented:
- Current orbital parameters in the header have been switched to four-byte
integers rather than eight byte floating point numbers.
- Calibration algorithms have been updated to remove the effects of sunlight
impinging on the internal calibration target, referred to as Solar Blackbody
Contamination (SBBC). The SBBC detection indicators have been added to the
AVHRR data record quality indicators.
- Navigation software was updated to remove satellite clock errors from the
data time codes.
- Navigation quality control parameters were provided in the header
record.
The 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
large-area image maps (e.g., country maps, continental maps, world maps), and
tracking regional and continental snow cover. The AVHRR data are also used to
retrieve various geophysical parameters such as sea surface temperatures and
energy budget data.
Software Description:
Software Access:
Contact Information:
Data Center Identification:
Procedures for Obtaining Data:
Data Center Status/Plans:
The LP DAAC provides standard AVHRR digital Level-1B products on 8 mm tape
cassette and 3480 cartridge.
Kidwell, K.B., 1995, NOAA polar orbiter data user's guide: Washington, D.C.,
National Oceanic and Atmospheric Administration [variously paged].
Planet, W.G., ed., 1988, Data extraction and calibration of TIROS-N/NOAA
radiometers, NOAA Technical Memorandum NESS 107--Rev. 1: Washington, D.C.,
National Oceanic and Atmospheric Administration, National Environmental
Satellite, Data, and Information Service [variously paged].
Disclaimer: Any use of trade, product, or firm names is for descriptive
purposes only and does not imply endorsement by the U.S. Government.
ADAPS -- AVHRR Data Acquisition and Processing System
ASCII -- American Standard Code for Information Interchange
AVHRR -- Advanced Very High Resolution Radiometer
CDA -- Command and Data Acquisition
DACS -- Data Acquisition and Control Subsystems
DCW -- Digital Chart of the World
DOMSAT -- DOMestic SATellite
EDC -- EROS Data Center
LP DAAC -- Land Processes Distributed Active Archive Center
eosdis -- Earth Observing System Data and Information System
GELDS -- Gridded Earth Location and Determination System
GMT -- Greenwich Mean Time
HRPT -- High Resolution Picture Transmission
IFOV -- Instantaneous Field of View
LAC -- Local Area Coverage
NEdT -- Noise Equivalent Differential Temperature
NESDIS -- National Environmental Satellite, Data and Information Service
NOAA -- National Oceanic and Atmospheric Administration
POES -- Polar Orbiting Environment Satellite
RMSE -- Root Mean Square Error
SBBC -- Solar Blackbody Contamination
TIP -- TIROS Information Processor
TIROS -- Television and Infrared Observation Satellite
URL -- Uniform Resource Locator
EOSDIS Acronym List
Document Revision Date: January 27, 2004
Document Review Date: May 28, 1997
Document Curator: EDC staff
Document URL:
http://eosims.cr.usgs.gov:5725/DATASET_DOCS/avhrr_dataset.html
Example of two stitched orbital passes over Africa and western Europe.(252 kb)