Comparison of atmospheric and cloud background structure observed by MSX satellite imagery in UV, visible, and mid-wave infrared bands

摘要

The MSX Satellite observed background terrain, clouds and atmospheric structure simultaneously in spectral bands ranging from the UV (～200 to 400 nm) through the visible range (400-900 nm) to the mid-wave infrared (MWIR, ～4.5 μm) over a fifteen month operational period. The high spatial and temporal resolution multi-spectral image data sets allow characterization of the background scene structure by statistical and Fourier analysis techniques. In this paper, we use the multi-spectral image observations to compare the Fourier-space (Spatial Power Spectral Density, PSD, and correlation length) descriptors for the various sources of observed structure. Each MSX band views background structure as a unique combination terrain, clouds, and atmospheric temperature and density fluctuation sources having unique statistical and Fourier-space attributes. We selected the MSX image bands to accomplish altitude sounding in that each spectral image represents the background scene structure at an altitude defined by the peak response of the atmospheric weighting function, which is approximately at the altitude of unit optical depth along the sensor LOS. The results of comparing cloud and atmospheric structure properties in the band-selected altitude ranges are twofold. In these scenes, the overall intensity PSD's are characterized by multi-variate distributions in which each component is distinguishable by the PSD slope and the correlation function. For example, the cloud scenes have PSD's and correlation lengths that are distinguishable from atmospheric density and temperature fluctuations. Similarly, the presence of atmospheric gravity wave structure, observed in MWIR scenes, creates identifiable features in the PSD and correlation functions for these bands. The characteristic PSD's most often observed for cloud, and atmospheric structure appear to converge to k~(-5/3) behavior.