Ancillary descriptions in the GCMD consists of brief descriptions of Data Centers (Example: National Snow and Ice Data Center), Projects or Campaigns (Example: the Tropical Ocean Global Atmosphere project, TOGA), Platforms (formerly called Sources; example: the spacecraft description for the Terra satellite), and Instruments (formerly called Sensors; example: the remote sensing instrument, AVHRR). Ancillary descriptions provide related background information but do not directly describe the data sets. However, they are usually linked to data sets.