Solid State Spectral Line Discriminator for Remote Sensing of Cloud Properties

摘要

The location of the R1 line of ruby, Al2O:Cr(+3), varies with temperature, and near 110 K it coincides with an oxygen absorption line at frequency 14,416.8/cm (in vacuo). This coincidence makes it possible to use a ruby crystal as a spectrally selective element to determine the height of cloud tops, as viewed from space, by measuring the depth of the atmospheric absorption line. Measurements establish that exact coincidence (for the parallel polarization) occurs at approximately 108 K. This means that the actual frequency of the R1 line is approximately 0.4/cm higher than the literature values. The atmospheric line was seen by observing the fluorescence of a thermally scanned ruby crystal. The measured line depth shows excellent agreement with model atmosphere calculations. Calculated performance of a cloud top height sensor predicts a signal to noise ratio of over 100 relative to unit air mass. The effect of using crystals doped with single-isotope chromium was also studied.