The OCO-2 Carbon Dioxide (Difference from Global Mean) is a layer that combines OCO-2 XCO2 (column-averaged dry-air mole fraction) and an estimated daily global trend XCO2 value that is produced by the National Oceanic and Atmospheric Administration Earth System Research Laboratory Global Monitoring Division (NOAA ESRL GMD). It is calculated from daily averaged CO2 data from four surface stations and is subtracted from the OCO-2 XCO2 in order to provide a product that visualizes smaller variations in XCO2 than the raw XCO2 product. This is done because increasing atmospheric CO2 concentrations has resulted in a large range of XCO2 values over the OCO-2 record.
Carbon dioxide (CO2) is an odorless, colorless gas and is the fourth most abundant component of dry air (after nitrogen, oxygen and argon). CO2 is an important greenhouse gas that helps trap heat in the atmosphere. As a part of the carbon cycle, CO2 can be emitted (e.g. from respiration by plants and soils or from wildfires) or absorbed (e.g. from plant photosynthesis or by dissolving into the oceans). Human activities such as the combustion of fossil fuels and biomass burning are sources of CO2.
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 Carbon Dioxide parameter is taken 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: NOAA/ESRL - Global Greenhouse Gas Reference Network, Data Products and Visualization; Ed Dlugokencky and Pieter Tans, NOAA/ESRL; OCO-2 Carbon Dioxide in GIBS/Worldview