Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 K. Bramstedt, L. Amekudzi, J. Meyer IFE/IUP Tangent heights in occultation geometry

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Solar Occultation measurement Solar Occultation sequence: –Wait for sun: scanning around 17.2 km –Follow sunrise: scan over solar disk following pre- calculated sun motion –scan continues above the atmosphere up to 290km

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Determine solar disk measured intensities over a scon are fitted with a 4 th order polynomial care has to be taken to exclude intensities containing information from next scan sequence zeros of fitted polynomial gives boudary of solar disk leading to exact position of the center of solar disk upscan downscan

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Fitting the tangent height offset calculate for all scans above the atmosphere the tangent height for pointing to the center of solar disk also read tangent heights given in products (derived from mirror positions) --> gives tangent height offset for altitudes km fit a straight line through these offsets and extrapolate to a tangent height of 25km x xxxxxxxxxxxxxxxxxx tangent height TH offset 25100

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Confirmation from satellite validation

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Retrieved TH offset big OCM OCM Artemis tests update on-board software ver 6

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Lunar occultation lunar occultation –moon is observed in pointing mode –lunar occultatio performed if moon phase > 0.5, moon on nightside –30°S – 90°S tangent height calculation: –moon follower points to brightest point on moon –CFIs gives tangent height for moon centre (th moon ) –assumption: brightest point = center of moon –CFIs also used to calculate tangent height from mirror positions (th mir ) –th offset = th moon – th mir (calculated above TOA) –th mir +th offset is used as tangent height in the atmosphere

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Validation results better than previous approach O 2 A no clear conclusion from validation

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Lunar tangent- height offset larger platform anomalies can be identified 2002 moon pointing wrong phase/latitude dependency has to investigated

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 Conclusion Solar occultation: –very precise and reliable determination of tangent height –confirmed by validation of ozone profiles lunar occultation: –usefull for retrieval, but higher uncertainty –assumption brightest point on moon same as moon center may not be accurate enough in all cases