1. Stray light from the upper and lower stray light rows An update of the GDPS algorithm

2. Upper Image taken from SD251 (DPM)

3. Why change the GDPS algorithm? The response in the LSA and USA is column dependent. LSA response is mostly similar though different from the USA. In the UV-2 and VIS sub-channels column dependence of the signal in the LSA and the USA roughly resembles that of the illuminated profile. LSA/USA responses are different for radiance, irradiance and WLS measurements Typically, the LSA/USA response is about 1 percent of the response in the directly illuminated profile, for the UV-2 and VIS sub-channels. In the UV-1 sub-channel, the response in the LSA/USA is very low and does not clearly resemble that of the illuminated profile. LSA/USA responses change over the orbit

4. The new GDPS algorithm Corrections are still applied per sub-channel. Applicable area (3) remains unchanged. The definition of USA and LSA remains unchanged. The UV-1 sub-channel will have a separate USA_UV1 and LSA_UV1 defined. Areas much closer to the directly illuminated area of the UV-1 sub-channel signal levels are higher (better S/N) better correlation with the illuminated UV-1 signal. Measured responses in the USA/LSA (and USA_UV1/LSA_UV1) are averaged. Averaged response is multiplied by a column dependent factor. Linear interpolation between the USA and LSA signals.

5. Upper USA_UV1 LSA_UV1  Linear row dependence   Wavelength dependence  Image taken from SD251 (DPM)

6. LSA and USA are different

7. LSA/USA resemble direct signal

8. LSA/USA different per measurement mode

9. LSA/USA orbital dependence

10. Errors in the old GDPS version

11. Origin of LSA/USA signal (1)

12. Origin of LSA/USA signal (2)

13. Stability of OPF parameters: validating assumptions The signal in the LSA and USA (or USA_UV1 and LSA_UV1) contains stray light The stray light signal as measured in the LSA and USA is indicative for the stray light in the directly illuminated areas. The assumed spectral shape of the USA/LSA correction is constant in time, most notably within an orbit. The USA/LSA correction can be clearly separated from the spectral stray light correction.