ATBD - GHG-CCI
ESA Climate Change Initiative (CCI) Algorithm Theoretical Basis Document Version 2 (ATBDv2) – UoL-FP for the Essential Climate Variable (ECV) Greenhouse Gases (GHG) Page 24 Version 2 – Draft 1 18 March 2013 Saturation Test Band 2 Polarisation S Number of Cross Track Points Cross Track Angle Error (Degrees) Along Track Angle Error (Degrees) 0 4.0x10 -5 Instrument saturation Flag determined from L1B radiance. -1 10 Filters out invalid cross-track values. -0.007 0.007 Reduce geolocation uncertainty. -0.05 0.05 Reduce geolocation uncertainty. A Posterior Error (ppm) 0 1.6 Filters out significantly poor retrievals. Retrieved AOD Aerosol profile 1 Retrieved AOD Aerosol profile 2 0 0.15 Removes any soundings with high AOD. 0 0.15 Removes any soundings with high AOD. Retrieved AOD Total 0 0.2 Removes any soundings with high AOD. Albedo band 1 0 0.45 Removes high-albedo cases (High-gain only) CO2 Ratio 0.96 1.01 Ratio between band 2 and band 3 CO2 H2O Ratio 0.96 1.2 Ratio between band 2 and band 3 H2O Aerosol Ratio 0 3 Ratio between Aerosol 1 and Aerosol 2 AOD It should be noted that all the screen criteria for CO 2 are still under development and may change in the future. 220.127.116.11 Methane Full-Physics Screen Currently the methane full-physics post-screen is the same as the CO2 post-screen as described in Section 18.104.22.168 but updates are expected as the retrieval is further developed. 22.214.171.124 Methane Proxy Screen The methane is post-screened based on the algorithm convergence criteria as above (i.e. outcome =1, cost_div = F, conv_flag = T) as well as on the normalised CHI-Squared value for both the CO 2 and CH 4 . Currently a threshold of 0.4 < CHI-Square CH 4 < 3.0 and 0.4 < CHI-Square CO 2 < 2.0 . Currently all soundings below 60°S are also removed (i.e. Antarctica).
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