An assessment of cirrus heights from MISR oblique stereo using ground-based radar and lidar at the Tropical Western Pacific ARM sites



[1] We compare cirrus presence and heights (CTHs) using oblique stereo by the Multiangle Imaging SpectroRadiometer (MISR) with measurements from ground-based cloud radar and lidar sensors at the Tropical Western Pacific (TWP) sites operated by the U.S. Department of Energy Atmospheric Radiation Measurement Program. Precise point-wise comparisons, limited to only 195 coincident cases, showed that the total number of cirrus retrieved using oblique-stereo analysis improved to 70% from 39% using the standard-stereo technique. The stereo technique detects cloud with the highest contrast, which is often at lower altitude. The oblique-stereo technique's efficiency depends on the thickness and number of underlying cloud layers. A histogram approach allowed similar regions to be compared statistically with many more samples and showed three distinct peaks at ≈13 km, 15 km, and 19 km related to deep convective clouds, tropical tropopause layer (TTL) cirrus, and overshooting convective clouds, respectively. Most differences between the satellite and ground-based measurements resulted from a number of cases of invalid cloud comparisons (14%), blunders from edges and broken clouds (7%), low contrast stereo mismatches (4%), and under-estimation of CTHs (3%). Overall, the oblique-stereo analysis detected a cirrus-top layer in 65% of all the valid coincident cases, mostly <1 km in thickness. The oblique-stereo derived cirrus CTHs differed from the heights of cirrus-top layers from ground-based cloud radar and lidar by −0.5 ± 1.0 km, validating the MISR retrievals. This suggests global thin cirrus retrievals are possible with the oblique-stereo technique after the screening of occasional blunders.