Advanced Very High Resolution Radiometer
Encyclopedia
The Advanced Very High Resolution Radiometer (AVHRR) is a space-borne sensor embarked on the National Oceanic and Atmospheric Administration
(NOAA) family of polar orbiting platforms (POES
). AVHRR instruments measure the reflectance of the Earth in 5 relatively wide (by today's standards) spectral bands. The first two are centered around the red (0.6 micrometres, 500 THz) and near-infrared
(0.9 micrometres, 300 THz) regions, the third one is located around 3.5 micrometres, and the last two sample the thermal radiation emitted by the planet, around 11 and 12 micrometres, respectively. The NOAA satellite has equator crossing times of 0730 and 1930 local solar time.
The first AVHRR instrument was a 4-channel radiometer, while the latest version (known as AVHRR/3, first carried on the NOAA-15 platform launched in May 1998) acquires data in a 6th channel located at 1.6 micrometres.
meteorological satellites in orbit at all times, with one satellite crossing the equator in the early morning and early evening and the other crossing the equator in the afternoon and late evening. The primary sensor on board both satellites is the AVHRR instrument. Morning-satellite data are most commonly used for land studies, while data from both satellites are used for atmosphere and ocean studies. Together they provide twice-daily global coverage, and ensure that data for any region of the earth are no more than six hours old. The swath width, the width of the area on the Earth's surface that the satellite can "see", is approximately 2,500 kilometers (about 1,500 miles). The satellites orbit between 833 or 870 kilometers (+/- 19 kilometers, between 516 and 541 miles) above the surface of the Earth.
The highest ground resolution that can be obtained from the current AVHRR instruments is 1.1 kilometre (0.683510010314787 mi), which means that the satellite records discrete information for areas on the ground that are 1.1 by 1.1 kilometers. This smallest recorded unit is called a pixel
. AVHRR data have been collected continuously since 1981.
and environmental degradation because of the comparatively long records of data already accumulated (over 20 years). The main difficulty associated with these investigations is to properly deal with the many limitations of these instruments, especially in the early period (sensor calibration, orbital drift, limited spectral and directional sampling, etc.).
The AVHRR instrument also flies on the MetOp
series of satellites. The three planned MetOp satellites are part of the Eumetsat Polar System (EPS) run by Eumetsat.
NASA
is currently experimenting with the Moderate Resolution Imaging Spectroradiometer (MODIS
) on board the Terra and Aqua earth observation research spacecraft. NOAA and NASA are currently developing a follow-on to AVHRR and MODIS for the operational NPOESS
constellation.
s and radiances in near infrared and infrared channels.
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
(NOAA) family of polar orbiting platforms (POES
Polar Operational Environmental Satellites
The Polar Operational Environmental Satellite project operates a constellation of weather satellites in polar orbits around the Earth. It is a joint effort between the National Oceanic and Atmospheric Administration and the European Organisation for the Exploitation of Meteorological Satellites...
). AVHRR instruments measure the reflectance of the Earth in 5 relatively wide (by today's standards) spectral bands. The first two are centered around the red (0.6 micrometres, 500 THz) and near-infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
(0.9 micrometres, 300 THz) regions, the third one is located around 3.5 micrometres, and the last two sample the thermal radiation emitted by the planet, around 11 and 12 micrometres, respectively. The NOAA satellite has equator crossing times of 0730 and 1930 local solar time.
The first AVHRR instrument was a 4-channel radiometer, while the latest version (known as AVHRR/3, first carried on the NOAA-15 platform launched in May 1998) acquires data in a 6th channel located at 1.6 micrometres.
Operational procedures
NOAA has at least two polar-orbitingPolar orbit
A polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It therefore has an inclination of 90 degrees to the equator...
meteorological satellites in orbit at all times, with one satellite crossing the equator in the early morning and early evening and the other crossing the equator in the afternoon and late evening. The primary sensor on board both satellites is the AVHRR instrument. Morning-satellite data are most commonly used for land studies, while data from both satellites are used for atmosphere and ocean studies. Together they provide twice-daily global coverage, and ensure that data for any region of the earth are no more than six hours old. The swath width, the width of the area on the Earth's surface that the satellite can "see", is approximately 2,500 kilometers (about 1,500 miles). The satellites orbit between 833 or 870 kilometers (+/- 19 kilometers, between 516 and 541 miles) above the surface of the Earth.
The highest ground resolution that can be obtained from the current AVHRR instruments is 1.1 kilometre (0.683510010314787 mi), which means that the satellite records discrete information for areas on the ground that are 1.1 by 1.1 kilometers. This smallest recorded unit is called a pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
. AVHRR data have been collected continuously since 1981.
Applications
The primary purpose of these instruments is to monitor clouds and to measure the thermal emission (cooling) of the Earth. These sensors have proven useful for a number of other applications, however, including the surveillance of land surfaces, ocean state, aerosols, etc. AVHRR data are particularly relevant to study climate changeClimate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
and environmental degradation because of the comparatively long records of data already accumulated (over 20 years). The main difficulty associated with these investigations is to properly deal with the many limitations of these instruments, especially in the early period (sensor calibration, orbital drift, limited spectral and directional sampling, etc.).
The AVHRR instrument also flies on the MetOp
MetOp
MetOp is a series of polar orbiting meteorological satellites operated by the European Organisation for the Exploitation of Meteorological Satellites. The satellites are all part af the EUMETSAT Polar System. It is intended to replace the soon to be retired TIROS network...
series of satellites. The three planned MetOp satellites are part of the Eumetsat Polar System (EPS) run by Eumetsat.
NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
is currently experimenting with the Moderate Resolution Imaging Spectroradiometer (MODIS
MODIS
The Moderate-resolution Imaging Spectroradiometer is a payload scientific instrument launched into Earth orbit by NASA in 1999 on board the Terra Satellite, and in 2002 on board the Aqua satellite...
) on board the Terra and Aqua earth observation research spacecraft. NOAA and NASA are currently developing a follow-on to AVHRR and MODIS for the operational NPOESS
NPOESS
The National Polar-orbiting Operational Environmental Satellite System was to be the United States' next-generation satellite system that would monitor the Earth's weather, atmosphere, oceans, land and near-space environment. NPOESS satellites were to host proven technologies and operational...
constellation.
Calibration and validation
Remote sensing applications of the AVHRR sensor are based on validation (matchup) techniques of co-located ground observations and satellite observations. Alternatively, radiative transfer calculations are performed. There are specialized codes which allow simulation of the AVHRR observable brightness temperatureBrightness temperature
Brightness temperature is the temperature a black body in thermal equilibrium with its surroundings would have to be to duplicate the observed intensity of a grey body object at a frequency \nu....
s and radiances in near infrared and infrared channels.
Launch and service dates
| Satellite name | Launch date | Service start | Service end |
|---|---|---|---|
| TIROS-N | 13 Oct 1978 | 19 Oct 1978 | 30 Jan 1980 |
| NOAA-6 | 27 Jun 1979 | 27 Jun 1979 | 16 Nov 1986 |
| NOAA-7 | 23 Jun 1981 | 24 Aug 1981 | 7 Jun 1986 |
| NOAA-8 | 28 Mar 1983 | 3 May 1983 | 31 Oct 1985 |
| NOAA-9 | 12 Dec 1984 | 25 Feb 1985 | 11 May 1994 |
| NOAA-10 | 17 Sep 1986 | 17 Nov 1986 | Present |
| NOAA-11 | 24 Sep 1988 | 8 Nov 1988 | 13 Sep 1994 |
| NOAA-12 | 13 May 1991 | 14 May 1991 | 15 Dec 1994 |
| NOAA-14 | 30 Dec 1994 | 30 Dec 1994 | 23 May 07 |
| NOAA-15 | 13 May 1998 | 13 May 1998 | Present |
| NOAA-16 | 21 Sep 2000 | 21 Sep 2000 | Present |
| NOAA-17 | 24 Jun 2002 | 24 Jun 2002 | Present |
| NOAA-18 | 20 May 2005 | 30 Aug 2005 | Present |
| NOAA-19 | 6 Feb 2009 | 2 Jun 2009 | Present |
| MetOp-A | 19 Oct 2006 | 20 Jun 2007 | Present |
| TIROS/NOAA dates from USGS website and from NOAA POES Status website | |||
External links
- What is AVHRR? at National Atlas
- Advanced Very High Resolution Radiometer at NOAA
- Advanced Very High Resolution Radiometer at USGS