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.