The Advanced Very High Resolution Radiometer (AVHRR) multi-purpose imaging instrument is used for global monitoring of cloud cover, sea surface temperature, ice, snow and vegetation cover characteristics.
AVHRR provides global imagery twice a day, at 1 km resolution (at nadir), in the visible and infrared bands of the electromagnetic spectrum.
What is AVHRR?
AVHRR is an across track scanner that senses the Earth’s outgoing radiation from horizon to horizon in six channels (three solar channels in the visible-near infrared region and three thermal infrared channels), with a spatial resolution of 1km at nadir.
The instrument utilises a 20 cm diameter collecting telescope of the reflecting Cassegrain type. Cross-track scanning is accomplished by a continuously rotating scan mirror that is directly driven by a brushless DC motor. The three thermal infrared detectors are cooled to 105 K by a two-stage passive radiant cooler.
The data from the six channels is simultaneously sampled at a 40 kHz rate and digitised to 10 bits within the instrument. In-flight calibration for the IR channels is provided by deep space view and an internal warm target whose temperature is monitored to an accuracy better than 0.1 K.
AVHRR has applications within operational meteorology — measuring cloud properties (height, temperature, phase); land analysis — supplying data for calculating vegetation indices, soil moisture, snow cover, and land surface temperature (skin); ocean analysis — supplying data for deriving sea surface temperature and sea ice concentration, and aerosols and fire detection.
AVHRR supports the IASI mission with sounding geolocation; cloud characterisation within the IASI FOV, and support to scene inhomogeneity quantification for the correction of the IASI spectral response.