4km resolution Global Area Coverage (GAC) Advanced Very High Resolution Radiometer (AVHRR) Level 1B data are available from 1978 - 2013 for the whole globe from NOAA satellites 06 through 12, 14 through 19 and Tiros-N, and from Metop A and B. For details of instrument versions and timespans available for each satellite see the table below.

The AVHRR sensor is carried on NOAA's Polar-orbiting Operational Environmental Satellites (POES) starting with TIROS-N in 1978. Onboard the TIROS-N, NOAA-6, 8 and 10 POES Satellites, the AVHRR Sensor measures in four spectral bands, while on the NOAA-7, 9, 11, 12 and 14 POES Satellites, the sensor measures in five bands. The AVHRR/3 sensor on NOAA-15, 16, 17, 18 and 19 measures in six bands though only five are transmitted to the ground at any time. One data type produced by AVHRR is Global Area Coverage (GAC) which is reduced resolution image data that is processed onboard the satellite taking only one line out of every three and averaging every four of five adjacent samples along the scan line.

The Advanced Very High Resolution Radiometer for TIROS-N and the follow-on satellites is a scanning radiometer with either four or five channels, which are sensitive to visible/near IR and infrared radiation. The instrument channelization has been chosen to permit multispectral analyses which provide improved determination of hydrologic, oceanographic, and meteorological parameters. The visible (0.5 micron) and visible/near IR (0.9 micron) channels are used to discern clouds, land-water boundaries, snow and ice extent, and, when the data from the two channels are compared, an indication of ice/snow melt inception. The IR window channels are used to measure cloud distribution and to determine the temperature of the radiating surface (cloud or surface). Data from the two IR channels is incorporated into the computation of sea surface temperature. By using these two channels, it is possible to remove an ambiguity introduced when clouds fill a portion of the field-of-view. On later instruments in the series, a third IR channel was added for the capability of removing radiant contributions from water vapor when determining surface temperatures. Prior to inclusion of this third channel, corrections for water vapor contributions were based on statistical means using climatological estimates of water vapor content.

The spectral bands are as follows:

The AVHRR GAC data stored at the NEODC are available to registered NEODC users. To obtain access to the data please register as a NEODC user. If you have forgotten your NEODC user ID and/or password, please contact the NEODC helpdesk. Once you have registered, the web browser download link can be found in the online references section below.

NOAA Level 1B (following FGGE terminology) is raw data that have been quality controlled, assembled into discrete data sets, and to which Earth location and calibration information have been appended (but not applied).

Software is available, free of charge, which may assist you in viewing data from AVHRR instruments:

• BEAM: BEAM is an open-source toolbox and development platform for viewing, analysing and processing of remote sensing raster data. Originally developed to facilitate the utilisation of image data from Envisat's optical instruments, BEAM now supports a growing number data formats of other EO sensors such as AVHRR.

Software

Basic ERS & Envisat (A) ATSR and Meris Toolbox (BEAM): BEAM is an open-source toolbox and development platform for viewing, analysing and processing of remote sensing raster data. Originally developed to facilitate the utilisation of image data from Envisat's optical instruments, BEAM now supports a growing number of other raster data formats such as GeoTIFF and NetCDF as well as data formats of other Earth Observation (EO) sensors such as Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Very High Resolution Radiometer (AVHRR), AVNIR, Polarised Radiation Imaging and Spectroscopy Mission (PRISM) and Compact High Resolution Imaging Spectrometer (CHRIS). Various data and algorithms are supported by dedicated extension plug-ins.

Documentation

• NOAA KLM User's Guide (for NOAA-15 and later satellites)
• NOAA Polar Orbiter Data (POD) User's Guide (for NOAA-14 and earlier satellites)

Links to further information

• NOAA information on AVHRR
• ESA information on AVHRR
• EUMETSAT information on AVHRR

For any enquiries concerning the AVHRR GAC data held at the NEODC please contact the NEODC helpdesk