1. Atmospheric polarisation measured by POLDER Polarisation: Stokes vectors, direction, etc. POLDER Results of analysis of POLDER polarisation data Conclusion / Relevance to SCIAMACHY 28 August, 2003

2. Polarisation Atmospheric light: Stokes vector {I, Q, U, V} Q = I 0° – I 90° U = I 45° – I 135° Q = P I cos 2  U = P I sin 2  P = degree of polarisation  = direction of polarisation V = 0 ; Q and U describe the linear part of polarisation

3. POLDER (ADEOS-I) CCD detector matrix. Bandfilter carousel. Resolution 6 x 7 km 2. Polarisation at 443, 670 and 865 nm. I, Q, and U.

4. Direction of polarisation Comparison between POLDER and single scattering theory:  = ½ atan U/Q

5. Conclusions Direction of polarisation ~ single scattering value. No need to measure it (SCIAMACHY). It’s BETTER not to use a measured value (SCIAMACHY). Spread for a large part determined by measurement errors in POLDER data, especially at larger wavelengths.