Active Sensing of CO2 Emissions over Nights, Days, and Seasons

The Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission was recommended by the National Research Council in the report entitled Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. The ASCENDS mission is considered the scientific and technological next step following Japan's Greenhouse gases Observing SATellite (GOSAT) mission and the NASA Orbiting Carbon Observatory (OCO) mission. NASA HQs has taken two actions, which demonstrate the agency's commitment to carbon observations: re-flight of OCO to replace the original OCO mission that failed to reach orbit and acceleration of the ASCENDS mission.

Using an active laser measurement technique, ASCENDS will extend CO2 remote sensing capability to include uninterrupted/all-season coverage of high-latitude regions, nighttime observations with sensitivity in the lower atmosphere, and measurements in partly cloud conditions. The ASCENDS mission, thereby, expands significantly the sampling of the atmosphere, and it avoids some of the potential biases inherent with the passive system.

A central issue for any mission is the mapping of the observations with their uncertainties into information, including uncertainties, regarding the subject of interest—in this case, terrestrial and oceanic surface fluxes of CO2. In this regards, ASCENDS, OCO, and GOSAT are fundamentally difference from most space-based missions in which one is observing more directly the subject of interest. In the case of ASCENDS and the other CO2 missions, the purpose of the atmospheric measurement is to determine fluxes at the surface—perhaps distant from where the atmosphere is observed. This paper presents quantitative information on mapping observations with their uncertainties to uncertainties regarding terrestrial and oceanic surface fluxes of CO2. It will also briefly review the history of ASCENDS and its current status.