The very talented AVHRR
AVHRR stands for Advanced Very High Resolution Radiometer.
“Very high resolution” is a bit of a misnomer. This is because its spatial resolution is actually very coarse at 1.1 km.
So the “very high resolution” refers to its day temporal resolution and revisit times.
Because of its high temporal resolution, AVHRR offers services in monitoring wildfires, flooding risk and even volcanic eruptions.
AVHRR spectral bands and specifications
The Advanced Very High Resolution Radiometer is a multispectral sensor with six spectral bands.
This includes red, thermal, mid and near-infrared bands. But over time, their spectral ranges have varied.
For example, AVHRR/3 channel characteristics are as follows:
|Band 1||Red||0.58-0.68||Urban, vegetation, snow/ice, daytime clouds|
|Band 2||Near IR||0.725-1.00||Vegetation, land/water boundaries, snow/ice, flooding|
|Band 3A||Mid IR||1.58-1.64||Vegetation, snow/ice detection, dust monitoring|
|Band 3B||Thermal||3.55-3.93||Surface temperature, wildfire detection, nighttime clouds, volcanic eruptions|
|Band 4||Thermal||10.30-11.30||Surface temperature, wildfire detection, nighttime clouds, volcanic eruptions|
|Band 5||Thermal||11.5-12.50||Sea surface temperature, water vapor path radiance|
AVHRR uses and applications
Because of AVHRR quick revisit times, it has several monitoring applications. For example, AVHRR monitors vegetation change, active wildfires, flooding risk and even volcanic eruptions.
AVHRR is the backbone for the 1km global land cover product. We use global land cover to understand the human footprint on the land and its environmental impact.
The AVHRR land cover product differentiates forest types, grass, shrub, cropland and water.
By using its red and NIR band, AVHRR applies normalized difference vegetation index (NDVI).
Because of its high revisit time, it’s capable of monitoring vegetation change on a daily basis.
We can interpret vegetation change over time by comparing NDVI over decades of data.
Other remote sensing applications and uses from AVHRR include measuring regional soil moisture, climate change, physiographic features.
By using the thermal bands, we get a better understanding of sea surface temperatures (pictured below).
40+ year history of AVHRR data
From NOAA-6 to NOAA-19, NOAA Polar-Orbiting Environmental Satellite (POES) satellites have been the primary carrier of AVHRR. But there have been other satellites equipped with Advanced Very High Resolution Radiometer.
For example, Television and Infrared Observation Satellite (TIROS) was the first to use AVHRR in 1978. The 4-channel radiometer on TIROS was later replaced with the 5-channel AVHRR/2.
Finally, MetOp-A and B have been launched with this sensor. To this day, AVHRR still collects satellite imagery of our changing planet. That makes it more than 40 years AVHRR has been in orbit making it one of the longest running sensors.
Satellites equipped with AVHRR
The table below lists all of the satellites that have carried the AVHRR instrument.
|Satellite||Launch Day||End Mission|
|Television and Infrared Observation Satellite (TIROS)||October, 1978||January, 1980|
|NOAA-6||June, 1979||November, 1986|
|NOAA-7||June, 1981||June, 1986|
|NOAA-8||March, 1983||October, 1985|
|NOAA-9||December, 1984||May, 1994|
|NOAA-10||September, 1986||September, 1991|
|NOAA-11||September, 1988||September, 1994|
|NOAA-12||May, 1991||December, 1994|
|NOAA-14||December, 1994||May, 2007|
|NOAA-16||September, 2000||June, 2014|
|NOAA-17||June, 2002||April, 2013|