Satellite-based remote sensing of atmospheric CO<sub>2</sub> holds the promise to greatly improve our understanding of the processes which regulate atmospheric CO<sub>2</sub> and the global carbon cycle. However, the required precision and resolution of such measurements needed to characterise sources and sinks of CO<sub>2</sub> on regional scales presents strong instrument design challenges. One type of remote sensing instrument which has been proposed to measure the integrated-column concentration of CO<sub>2</sub> is a Gas-Filter Correlation Radiometer (GFCR). As a technique, a GFCR is a radiometer which uses a sample of the gas of interest as a spectral filter for that gas in the atmosphere. In this paper we present a "strawman" design for a GFCR satellite instrument to remotely sense atmospheric CO<sub>2</sub>. This design, which includes multi-pass CO<sub>2</sub> and O<sub>2</sub> gas cells with path lengths of up to 10 metres, demonstrates that such an instrument can be built within the constraints of a satellite environment.
A unique optical configuration of a Gas-Filter Correlation Radiometer (GFCR) is described. This configuration, known as a Simultaneous-View Correlation Radiometer (SVCR), was designed for surface-viewing nadir remote sensing of atmospheric trace gases in the near-infrared. It provides simultaneous measurement of both the gas-filter and correlation channels of the GFCR, minimising noise induced by geo-spatial variations in the surface reflectivity. We analyse the reduction in the sensitivity of the SVCR to noise in input radiance in comparison to a sequential gas-density state GFCR.
WINDII is an imaging, field widened Michelson interferometer built by Canada and France for flight on NASA's Upper Atmosphere Research Satellite, which was launched September 12, 1991. Its primary purpose is to measure winds in the 80-300 km region of the atmosphere by measuring the Doppler shift of the airglow emissions. This paper discusses the design, testing and performance of the baffle system used for daytime observations.