The Infrared Sea surface temperature Autonomous Radiometer (ISAR) has been developed to provide accurate and reliable measurements of the radiative sea surface temperature (skin SST) to an accuracy of ±0.1 K without the need of operator intervention. Infrared emission from the sea surface and atmosphere are measured in the spectral waveband 9.8-11 μm. The ISAR system has been specifically designed to address the problem of sea-water spray or rain, which without adequate environmental protection of delicate infrared radiometer fore-optics, could introduce significant errors in the skin SST measurement. Furthermore it provides a self-calibrating infrared radiometer system that can operate autonomously for extended periods when deployed from a ship of opportunity (SOO).

ISAR instruments are operated by a number of institutions around the world:

The Scanning Infrared Sea surface Temperature Radiometer (SISTeR) is a chopped, self-calibrating filter radiometer. Designed and operated by RAL Space, the SISTeR makes highly accurate and traceable measurements of the sea surface skin temperature. The instrument can protect itself against bad weather and can operate unattended for extended periods. SISTeR instruments have been deployed since 1996 on a range of reseach ships and passenger vessels. Currently a SISTeR is deployed on the Cunard Line Queen Mary 2 liner.