1. Comparison of Cloud Detection Methods Jane Hurley, Anu Dudhia, Don Grainger University of Oxford

2. Cloud Detection Methods Thresholding radiances or ratios of radiances Mean Radiance L υ Method Colour Index CI Method Singular Vector Decomposition Analysis χ 2 Ratio Method Integrated Radiance Ratio L cloud / L total Method

3. 2) Colour Index (CI) Method CI > Thr CLEAR CI < Thr CLOUDY 1) Mean Radiance Method > Thr CLEAR < Thr CLOUDY cloud in the FOV contributes more radiance than background due to higher T B

4. Use SV clear and SV cloud for given tangent height to do a LSF to mean-subtracted Original signal 15 km 12 km 9 km 6 km EF ≠ 0 → Non-zero fit coefficient to SV cloud ! Singular Vector Decomposition Analysis

5. 3) SVD Ratio Method Compare the goodness-of-fit when signal fit by SV clear only with that when SV clear + SV cloudy used CLEAR CLOUDY 4) SVD Integrated Radiance Ratio Method Compare radiance contributed by SV cloudy to total radiance CLEAR CLOUDY

6. Comparison of Methods L cloud /L total χ 2 Ratio CILυLυ Detection Test Derivatives & Errors Percent Agreement Order Scalar Percent Agreement MORSE Retrieval OVERALL 3 rd 4 th 2 nd 1 st 2 nd 3 rd 4 th 1 st 3 rd 4 th 2 nd 1 st 4 th 1 st 3 rd 2 nd 4 th 2 nd 3 rd 1 st 2 nd 4 th 1 st 3 rd

7. Conclusions and Future Work 4 methods of cloud detection compared Simulated and real MIPAS spectra SVD methods consistently behave best Use ORM to do MORSE retrieval test