CAL_IIR_L2_Track-Standard-V4-51 is the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Infrared Imaging Radiometer (IIR) Level 2 Track, Version 4-51 data product. Data for this product was collected using the CALIPSO IIR instrument. This product contains emissivity and cloud particle data related to pixels co-located to the lidar track. The version of this product was changed to V4-51 to account for a change in the operating system of the CALIPSO production cluster.

CALIPSO was launched on April 28, 2006, to study the impact of clouds and aerosols on the Earth's radiation budget and climate. The CALIPSO satellite comprises three instruments: Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), IIR, and Wide Field Camera (WFC). CALIPSO is a joint satellite mission between NASA and the French Agency CNES (Centre national d'études spatiales).