The Validation Inter-comparison of Polar Mesospheric Clouds from OSIRIS with WINDII

Routine measurements of high altitude limb radiance profiles began in mid July, approximately 60 % of the way through the PMC season. OSIRIS takes a single altitude scan every 2 minutes resulting in an sampling interval of 500 km which should yield about 8 observations per orbit. WINDII has a field of view 150 km wide and takes an image every 100 km. WINDII morphology demonstrates that PMCs are observable at latitudes north of 60 during this time period and recede towards the pole until no longer present below 72 N by August 15. OSIRIS can measure up to the pole. The OSIRIS observations are consistent with this morphology. The peak altitude of 84 km is consistent with the WINDII peak of 83 km. The vertical resolution of OSIRIS is 2 km compared to the 1.1 km vertical resolution of WINDII. The WINDII software was used to process some of the OSIRIS observations into limb scattering ratio profiles and to invert these into volume scattering ratio profiles. WINDII used only 530 nm to measure the PMCs whereas OSIRIS measures from 280 nm to 800 nm with 1 nm resolution. This spectral coverage should make an estimate of the particle size possible. WINDII double FOV measurements indicated that the ice particles are about 25 nm. The detection threshold for WINDII was a scattering ratio of 0.3; by comparison, the detection threshold for OSIRIS is estimated to be about 2, similar to POAM3. The available OSIRIS observations will be statistically compared with the cumulative frequency distribution from WINDII. From these comparisons with WINDII results, the validity and utility of OSIRIS PMCs observations will be assessed. Odin is a Swedish-led satellite project funded jointly by Sweden (SNSB), Canada (CSA), Finland (Tekes) and France (CNES).