Aerosol retrieval over Cape of Good Hope

View larger JPEG image (305 kb)

These Multi-angle Imaging SpectroRadiometer (MISR) images of the Cape of Good Hope were acquired on August 23, 2000.

This first of two image sets, with the four strips, extends from 10 deg. South latitude to just south of the Cape of Good Hope, and are each 40 0 km wide. The left image is a nadir top-of-atmosphere (TOA) image, i.e., the Level 1 product. The image to the right of it is the Da camera (70.5 deg. aft) Level 1 image. It shows the atmospheric and aerosol scattering effect pretty well. The image to the right of that is the retrieved aerosol optical depth at 558 nm, one of the Level 2 products. It captures the general trend of the aerosol; in particular note what appears to be a haze boundary in the Da image in the southern part of South Africa - the aerosol retrieval picks it up, and also the slightly clearer area in the middle. Also, what's very encouraging is that the optical depths on both sides of the coastline are similar, despite coming from two completely different algorithms (one is for land, the other for water). The cloud screening is clearly not working entirely well. MISR is not using cloud thresholding at this point - the cloud screening is being done using a criterion that requires the terrain projected radiances to be a smooth function of angle, for each pixel. Any cloud above the surface will misregister because of parallax and therefore the radiance vs. angle should not be smooth. But this algorithm fails for near-surface clouds and homogeneous, extensive clouds. This will improve as more code elements are implemented. The rightmost image is retrieved land surface "bihemispherical reflectance", or albedo for short, also a Level 2 product. It is an atmospherically-corrected product - we remove ozone absorption, clear atmosphere (Rayleigh) scattering, and scattering from the retrieved aerosol.

These data are all from orbit 3626, path 176, on August 23, 2000.

Image Credit: NASA/GSFC/JPL, MISR Science Teams