Monitoring weather and climate from space

AVHRR

The Advanced Very High Resolution Radiometer (AVHRR) provides global imagery twice a day, at 1 km resolution (at nadir), in the visible and infrared bands of the electromagnetic spectrum. The instrument measures reflected solar energy and radiated thermal energy from land, sea, clouds and the atmosphere. AVHRR/3 is a multi-purpose imaging instrument used for global monitoring of cloud cover, sea surface temperature, ice, snow and vegetation cover characteristics.

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.

Other applications include aerosols and fire detection.

In addition, 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.

AVHRR/3 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 utilizes 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.

More in-depth information can be found in the

AVHRR/3 is manufactured by [External link] ITT Exelis in Fort Wayne, Indiana under contract to NASA.

AVHRR Summary Budgets

  Scan Rate   6 Hz (0.1667 secs)  
  Scan Type   Continuous scan  
  Pixel IFOV (3dB beamwidth)   0.0745° (square)  
  IFOV size at Nadir   1.1 km  
  Sampling at Nadir   0.87 km  
  Earth View Pixels / Scan   2048  
  Swath   ± 55.37°  
  Swath   ± 1464 km  
  Spectral Range   0.6 to 12 µm  
  Lifetime   Five years (three years design life)  
  Power   29 W  
  Size   300 mm x 360 mm x 800 mm  
  Mass   33 kg  
  Data rate   1.4 Mbps  
 
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