Mission preparation and technology development of the Tropical Carbon Mission

University of Glasgow with University of Leicester and STFC ATC

Project Funded in the CEOI-ST EO9 Call for Mission and Technology Studies in preparation for future ESA Earth Explorer Missions

Fast Track Project

On average less than half of the carbon dioxide (CO2) emitted by human activities stays in the atmosphere, with the remaining balance taken up by global oceans, terrestrial vegetation and soils. There are substantial uncertainties associated with the location, strength and durability of these natural components of the carbon cycle. The tropics and sub-tropics are regions of key importance for the global carbon cycle which store large amount of carbon in its forests and soils. These diverse and productive ecosystems are subject to rapid environmental change due to extensive deforestation and urbanisation, with consequent changes in hydrology and regional carbon balance and subsequently the global climate. However, CO2 flux estimates of the tropics and sub-tropics are poorly constrained by the existing network of surface measurements. Consequently, how the tropics affect the global carbon budget remains poorly characterized compared to other ecosystems on the planet, and currently we cannot even determine with confidence if tropical ecosystems are a net source or a sink of carbon.

The Tropical Carbon Mission (TCM) concept will provide unique observations of CO2 over the tropics with the precision and frequency that are required by scientists and policy makers. TCM will be launched in a low inclination orbit of 35 degrees, which will precess within tropical latitudes to maximize the frequency and coverage of cloud-free scenes over and downwind of tropical landmasses. The TCM comprises three instruments developed from current technology: 1) a short-wave IR (SWIR) multi-view spectrometer that will measure CO2, carbon monoxide (CO), methane (CH4), and oxygen (O2); 2) a coboresighted aerosol imager; and 3) a wide-view cloud imager. The maturity of the technology minimizes the overall risks and costs to the mission. Aerosols represent the largest source of systematic error in the retrieval of CO2 at SWIR wavelengths. The adopted multi-view approach, building on work developed by MISR, will improve the characterization of atmospheric aerosols and cirrus prevalent over tropical latitudes.

The primary science objective of TCM is to reduce the overall uncertainties in the magnitude and distribution of tropical CO2 fluxes such that we can determine with certainty whether in any particular two-week period the tropics is a net source or sink of CO2. By better estimating tropical fluxes, we also improve the efficacy of existing surface measurement networks to help estimate extra-tropical CO2 fluxes. The secondary science objectives of TCM are to: 1) reduce the uncertainties in the magnitude and distribution of CO and CH4; and 2) improve source attribution of observed variations in CO2 by using concurrent measurements of CO and CH4. The tertiary science objective of TCM is to complement global survey CO2 measurements from low-Earth orbiting instruments such as follow-on mission to GOSAT and OCO-2.

This study supports the science and technology development of the TCM concept necessary to raise the science and technology readiness levels in preparation for the upcoming ESA Earth Explorer 9 competition. The work programme consists of concurrent and complementary activities focused on technology development and mission preparation. We substantially build on the TCM mission concept originally developed as a bilateral mission with NASA JPL, and address the key recommendations from the RAL Space and JPL TeamX concurrent design facility studies. Technology developments build on these studies and recent experience with the GreenHouse gas Observations of the Stratosphere and Troposphere (GHOST) spectrometer and recent science innovations associated with aerosol characterization.