The OCO-2 Total Column Water Vapor layer displays the total gaseous water within a vertical column of the atmosphere over land and ocean and is measured in millimeters (mm). Water vapor (H2O) is one of the retrieved variables in the OCO-2 retrieval algorithm.
Almost all of atmospheric moisture is in the form of water vapor. This water vapor drives the development of weather systems on short time scales and influences the climate on longer time scales. Water vapor is Earth’s primary greenhouse gas and traps more heat than carbon dioxide. The movement of water vapor around the globe helps determine the amount of precipitation a region might receive and helps transport heat from the tropics to the poles.
The Orbiting Carbon Observatory-2 (OCO-2) is a three-channel imaging grating spectrometer that collects cloud-free XCO2 observations continuously over the globe by measuring reflected sunlight in the near-infrared. The OCO-2 Total Column Water Vapor is an ancillary product of the retrieval algorithm used to measure the CO2 concentrations derived from the OCO-2 Level 2 Lite product. OCO-2 makes eight simultaneous, adjacent measurements, each with a spatial resolution of 2.25 km x 1.29 km. These measurements are then mapped onto a 500 m2 grid. The repeat cycle for OCO-2 is every 16 days.
References: Nelson, R. R., et al.: High accuracy measurements of total column water vapor from the Orbiting Carbon Observatory-2, Geophysical Research Letters, 43, doi: 10.1002/2016GL071200, 2016.; GES DISC - OCO-2 Documents; OCO-2 Data Center