Channel Compression of High Resolution Infrared Spectra with Using Hypothetical Channel System

Abstract

A method has recently been shown by Aoki (2004) to compress the number of channels of trace gas remote sounder preserving almost all the information content that the original data has. In this method the weighting function of the original channels is expanded with empirical orthogonal functions (EOFs), and a set of hypothetical radiances, whose weighting functions are the EOFs, are used for the analysis. It has been shown that the radiance data of 240 original channels, which is obtained by the above trace gas sounder, can be compressed to 3 or less channels of hypothetical radiances, loosing negligible information content.
In the present paper, the performance of this method is examined for the simulated radiance data of high spectral resolution in the thermal infrared region that is used for the remote measurements of temperature and humidity vertical profiles. The number of hypothetical channels that is required for preserving the information content of original data has been examined for two different spectral resolutions, 0.1 and 0.3 cm⁻¹. The present study showed that the radiance data of 1200 channels of high spectral resolution 0.1 cm⁻¹ is compressed to less than 23 hypothetical channels with negligible loss of information content in the case of wavenumber region 640-760 cm⁻¹, which is used for the temperature soundings. For the low resolution 0.3 cm⁻¹, the number of hypothetical channels needed becomes smaller than this. In the case of the humidity sounding from the region 1300-1600 cm⁻¹ with the spectral resolution 0.1 cm⁻¹, 3000 channels are compressed to less than 20 hypothetical channels.