An evaluation method of the retrieved carbone dioxide column amount derived from short wave infrared measurement

Greenhouse Gases Observing Satellite (GOSAT) and Orbiting Carbon Observatory (OCO) for the purpose of observing greenhouse gases will be expected to launch in late 2008 or in early 2009. OCO and GOSAT will be the first satellite to observe carbon dioxide (CO₂), major greenhouse gases, from space. Global distributions of CO₂ column abundances, retrieved from each GOSAT and OCO data, will be opened to researchers and public users, so it is important to clarify the precision of the data retrieval. If satellite observations are to improve over the existing ground network, monthly averaged column data at a precision of 1% or better, for an 8deg times 10deg footprint are needed [1]. The GOSAT mission was designed to observe CO₂ density with 1% relative precision averaged in a certain period and with 10 km times10 km footprint size. This paper describes an evaluation method of retrieved CO₂ column abundances considering internal and external error sources, respectively. Variance of the internal error, which is derived from spectral fitting residuals, is obtained analytically. Variance of the external error, which is caused by error of given parameters when column abundance is retrieved, is estimated by factorial design. Further, observation situation is set and noises occurred in sensor are generated, retrieval precision is evaluated by numerical simulation. Evaluation results changing noise seed are shown as one example.