AVHRR3
The six channel Advanced Very High Resolution Radiometer/3 (AVHRR/3) was first flown on NOAA-15 in May 1998 .The AVHRR is used for remotely determining cloud cover and the surface temperature. Channel 3A was specifically designed for snow and ice detection. An experimental global snow and ice detection algorithm using the experimental Clouds from AVHRR (CLAVR) processing system was developed by the National Oceanic and Atmospheric Administration's (NOAA) National Environmental Satellite, Data, and Information Service (NESDIS). The instrument measures reflected solar (visible and near-IR) energy and radiated thermal energy from land, sea, clouds, and the intervening atmosphere.
Objectives
The primary purpose of AVHRR was originally to provide global cloud imagery for meteorological purposes. That objective is still retained, but many other applications have developed around the use of this versatile instrument. These will continue to be supported by the new version. Mapping of sea ice and sea surface temperatures are important oceanic applications, while vegetation mapping in its various specialised forms is a primary land application, of importance also in waterways. These and many other applications, such as glacier extent, snow cover and crop yield forecasts, will form the basis of AVHRR objectives when flown on NOAA and now the Metop-A satellite.
Instrument
The AVHRR/3 is a six-channel imaging radiometer which detects energy in the visible and infrared (IR) portions of the electromagnetic spectrum. The instrument measures reflected solar (visible and near-IR) energy and radiated thermal energy from land, sea, clouds, and the intervening atmosphere. The instrument has an instantaneous field-of-view (IFOV) of 1.3 milliradians providing a nominal spatial resolution of 1.1 km (0.69 mi) at nadir. A continuously rotating elliptical scan mirror provides the cross-track scan, scanning the Earth from ± 55.4° from nadir. The mirror scans at six revolutions per second to provide continuous coverage.
The AVHRR/3 provides spectral and gain improvements to the solar visible channels that provide low light energy detection. Channel 3A, at 1.6 microns, provides snow, ice, and cloud discrimination. Channel 3A will be time-shared with the 3.7- micron channel, designated 3B, to provide five channels of continuous data. An external sun shield and an internal baffle have been added to reduce sunlight impingement into the instrument’s optical cavity and detectors.
Characteristics:
| Band | Wavelength (µm) | Resolution (m) | Swath Width (km) |
Typical Use |
|---|---|---|---|---|
| Band 1 (VIS) | 0.58 to 0.68 | 1100 (4000) | 3000 | Daytime cloud and surface mapping |
| Band 2 (NIR) | 0.725 to 1.1 | 1100 (4000) | 3000 | Land-water boundaries |
| Band 3A (NIR) | 1.58 to 1.64 | 1100 (4000) | 3000 | Snow and ice detection |
| Band 3B (TIR) | 3.55 to 3.93 | 1100 (4000) | 3000 | Night cloud mapping, sea surface temperature |
| Band 4 (TIR) | 10.3 to 11.3 | 1100 (4000) | 3000 | Night cloud mapping, sea surface temperature |
| Band 5 (TIR) | 11.5 to 12.5 | 1100 (4000) | 3000 | Sea surface temperature |
Data Access
General Data Product Level Definition
Data from five of the channels are transmitted continuously and in full 1.1 km resolution within the HRPT (High Rate Picture Transmission) data stream. At any time, two channels are selected for transmission as analogue data in the APT (Automatic Picture Transmission) data stream on NOAA satellites. For APT, every third scan line is selected, while across-scan the sampling is adjusted to reduce the perspective effect due to the Earth's curvature and the satellite altitude, giving approximately 4 km resolution. The APT system will be replaced by a new digital Low Rate Picture Transmission (LRPT) system to be implemented on Metop and on later NOAA satellites.
The NOAA series Platform and MetOp-A Programme
The NOAA-POES series are regarded as the backbone of the US meteorological program. The current POES series satellites are named simply NOAA-9 through NOAA-17 in order of launch. The program has evolved over several years starting in 1960 with TIROS. The philosophy of NOAA is to maintain at least two operational satellites in complementary orbit. The POES satellites will operate till 2010.
All NOAA-POES satellites have a circular, sun-synchronous polar orbit with a nominal flight height of 833 km. The even numbered satellites cross the equator at local solar times of approximately 7:30 and 19:30, while the odd-numbered satellites cross the equator at local solar times of approximately 2:30 and 14:30.
For further details concerning the NOAA satellites look at the NOAA internet sites ( NOAA - documentation ).
The Meteorological Operational satellite programme is a new European undertaking providing weather data services that will be used to monitor climate and improve weather forecasts. The MetOp programme’s series of three satellites has been jointly established by ESA and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), forming the space segment of EUMETSAT's Polar System (EPS). MetOp-A has been designed to work in conjunction with the NOAA satellite system whereby the two satellites fly in complementary orbits. MetOp-A’s polar orbit is Sun synchronous, so that the satellite track along the Earth is always at the same local time, in this case in the mid-morning. NOAA will continue to operate its mid-afternoon orbit satellite service as part of the Polar Orbit Enviromental Satellites (POES) system.
The MetOp satellites, have been designed to embark instruments provided by NOAA, EUMETSAT, ESA and other European partners. MetOp will have different
performances than the actual NOAA system due to a platform designed with high pointing accuracy, full on board recording capacity, digital high rate and low
rate communication system, encryption capability and an increased payload.
Other Instruments on the Metop-A platform include the Advanced Scatterometer ASCAT, the Global Ozone Monitoring Experiment GOME-2, the Global positioning system Receiver for Atmospheric Sounding GRAS, the High Resolution Infrared Sounder IASI, the Microwave Humidity Sounder MHS, the Advanced Microwave Temperature Sounder AMSU.
MetOp’s main objectives are to furnish data for operational meteorology and climate monitoring. Many of the above instruments will give detailed information on the atmospheric temperature/humidity profiles, essential for weather forecasting.
Links
Contact
If you would like to have more information about the AVHRR 3 data, please contact wdc@dlr.de.