Global sea surface temperature measurements from the along-track scanning radiometer (AATSR) on the ENVISAT satellite – an initial assessment

The AATSR sensor has been acquiring data on a continuous basis since the March 2002 launch of the European Space Agency’s environmental satellite, ENVISAT. The sensor is an infrared imaging radiometer which uses similar spectral channels to AVHRR and MODIS with the additional feature of a two-angle view, at nadir and at 55º to nadir. This facility is designed to provide an improvement in atmospheric correction over that achievable by the traditional single-view sensors, especially in the presence of excessive atmospheric aerosol, which do not always have a distinctive spectral signature.

The initial validation programme has been completed, involving comparisons with data from buoys, precision in situ radiometers and data from other satellite sources. The validation results indicate that the AATSR system is producing global SST fields with an accuracy of around 0.3ºC an better in many cases.

Comparisons with data from other satellite systems such as MODIS or AVHRR demonstrate the particular effectiveness of along-track scanning in achieving a useful atmospheric correction in the presence of excessive aerosol loading such as occur during Saharan dust outbreaks in the tropical Atlantic Ocean. AATSR is the third in a series of experimental sensors, which have been collecting SST data since 1991 and the current sensor was funded by the UK’s Department of Environment, Food and Rural Affairs (DEFRA) in order to establish data-continuity for the purpose of climate change detection and monitoring, in support of their programme of climate prediction and research at the UK’s Hadley Centre. An early analysis of the time-series since 1991 indicates trends in global SST within expected limits, demonstrating that the AATSR system can generate data of the quality and stability required for the monitoring of global climate change.