The Special Sensor Microwave/Imager (SSM/I) and Special Sensor Microwave Imager/Sounder (SSMI/S) Brightness Temperature (BT) Climate Data Record (CDR) is derived from radiance measurements at the top of the atmosphere from a number of microwave frequencies delivered by the Remote Sensing Systems (RSS) SSMI and SSMI/S BT. Radiance levels in the atmosphere and land/ocean surface are influenced by a number of factors that make it difficult to directly evaluate BT data. Instead, this CDR is designed to be used by retrieval algorithms to determine a number of geophysical parameters, such as surface wind speed, total column water vapor, rain rate, and sea ice extent. The final record extends from 1987–2023.