Abstract
The Geostationary Carbon Cycle Observatory (GeoCarb) was selected as a NASA Earth Venture Mission in 2016 to measure greenhouse gas concentrations from geostationary orbit with a view of North and South America. The GeoCarb instrument incorporates a high-resolution grating spectrograph operating in four narrow passbands with central wavelengths of 0.765 μm, 1.606 μm, 2.065 μm, and 2.323 μm, each with a dedicated focal plane array. From these bands, oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and solar induced fluorescence (SIF) will be measured. The four bands are observed through a single slit, with a roughly 6 x 2700 km field of view, which can be steered using scan mirrors. GeoCarb is being built at the Lockheed Martin (LM) Advanced Technology Center (ATC) and the spectrograph has recently undergone a series of thermal-vacuum tests (TVAC). During TVAC, the spectrograph was stimulated by multiple external light sources and its spectroscopic performance characterized. We present an overview of the optical design of the instrument, describe the test configurations, and report on the performance characteristics of the spectrograph.
Spectrograph Characterization for the GeoCarb Mission
The Geostationary Carbon Cycle Observatory (GeoCarb) was selected as a NASA Earth Venture Mission in 2016 to measure greenhouse gas concentrations from geostationary orbit with a view of North and South America. The GeoCarb instrument incorporates a high-resolution grating spectrograph operating in four narrow passbands with central wavelengths of 0.765 μm, 1.606 μm, 2.065 μm, and 2.323 μm, each with a dedicated focal plane array. From these bands, oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and solar induced fluorescence (SIF) will be measured. The four bands are observed through a single slit, with a roughly 6 x 2700 km field of view, which can be steered using scan mirrors. GeoCarb is being built at the Lockheed Martin (LM) Advanced Technology Center (ATC) and the spectrograph has recently undergone a series of thermal-vacuum tests (TVAC). During TVAC, the spectrograph was stimulated by multiple external light sources and its spectroscopic performance characterized. We present an overview of the optical design of the instrument, describe the test configurations, and report on the performance characteristics of the spectrograph.