The GeoCarb Mission

This paper presents an update on the NASA Earth Venture-2 Mission, Geostationary Carbon Cycle Observatory (GeoCarb), which would provide measurements of atmospheric carbon dioxide (CO₂), methane (CH₄), and carbon monoxide (CO) from geostationary orbit. The GeoCarb mission would deliver daily maps of column integrated mixing ratios of CO₂, CH₄, and CO over the observed landmasses at a spatial resolution of roughly 5 x 10 km, which will establish the scientific basis for CO₂ and CH₄ flux determination at ecosystem/weather relevant time and space scale.

The instrument would exploit the four spectral regions: The Oxygen A-band for pressure and aerosols, the weak and strong bands of CO₂ near 1.61 and 2.06 microns, and a region near 2.32 microns for CO and CH₄. The O₂ and CO₂ bands are very similar to the instruments aboard OCO-2, and so we envision OCO-2 in geostationary orbit with the addition of a fourth channel to measure CO and CH₄, but without an oceanic capability. The O₂ A-band also provides for retrieval of Solar Induced Fluorescence (SIF).

The GeoCarb Mission persistent fine-scale daily mapping measurements, under changing conditions also enable significant advances on an important range of CO₂ biotic issues, including: CO₂ fertilization, change in primary production because of nitrogen deposition, and the influence of broad climatic patterns on terrestrial sources and sinks. This probes the mechanisms of the observed inter-annual variability in the atmospheric concentration of CO₂. In sum, GeoCarb attacks the primary question of the nature of the net terrestrial sink of CO₂.

Wetland ecosystems, rice paddies and livestock are major, and highly uncertain, sources of CH₄. Several approaches have been used to scale up from measurements at individual plots to estimations of CH₄ emissions at the landscape scale. However, there has been little large-scale top-down validation. Industrial sources are also poorly quantified. The GeoCarb Mission’s high space- and time-measurements of CH₄ enable important analyses of human impacts via agriculture and industry vs. natural phenomena on methane sources.