MISR abstract

Realmuto, V.J., Moroney, C.M., Davies, R. (2002). The use of MISR Multiangle Image Data to Visualize Cloud Morphology and Motion. Eos Trans. AGU, 83(47), Fall Meet. Suppl. 2002, Abstract # U52A-12

The Multiangle Imaging SpectroRadiometer (MISR), currently orbiting the Earth aboard NASA's Terra spacecraft, acquires image data at 9 distinct viewing angles simultaneously. This multiangle imaging is accomplished through the use of 9 cameras, with one camera providing a nadir view and the remaining cameras providing views 26.1, 45.6, 60.0, and 70.5 degrees fore and aft of nadir. Each camera, in turn, measures scene radiance in 4 spectral bands (red, green, blue, and near infrared). One of the objectives of the MISR mission is to infer the physical properties of atmospheric aerosols, clouds, and land cover (including snow, ice, and vegetation) from angular variations in scene radiance. One step in the operational processing of MISR data is to map these data into a Space Oblique Mercator projection. As a result of this projection, features at elevations above or below the reference ellipsoid (WGS 84) exhibit an apparent displacement, known as parallax or disparity, in the off-nadir images. The disparities exhibited by clouds can be used to estimate the height of the clouds, and cloud-top height maps are an operational MISR data product. Although the 9 MISR cameras acquire data simultaneously, approximately 7 minutes are required to obtain a suite of fore- and aft-viewing images that depict the same scene. This time lag allows MISR to capture the motion of clouds due to winds, and maps of wind direction and wind speed are operational data products. Visualization of the cloud properties measured by MISR presents several unique challenges, such as registration of the angular distribution of radiance above a cloud with its surface morphology and depiction of cloud motion independent of the disparity resulting from cloud height. We will present some of the tools and animation techniques developed to address these challenges. For example, MISR_Shift is an interactive tool that allows us to evaluate the effects of changes (or uncertainties) in cloud height and wind speed estimations on the registration of features across 9 MISR images. We are investigating the projection of image data onto three-dimensional surfaces created from cloud-top height maps as a means of visualizing cloud motion.

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