Abstract

Conventional correlation spectroscopic methods usually require some mechanical motion, e.g. rotating reflecting light choppers, the interchange of reference and empty absorption cells or a pressure modulator. We will describe here an electro-optical method of light modulation which permits correlation-spectroscopic measurements to be made without mechanical motions. The problems of maintaining optical and electronic balance during the measurements do not occur with this new approach. An interesting feature of the electro-optical modulation technique is that it can be made to allow for a Doppler shift between the sample and reference cell; this permits measurements of the earth′s atmosphere to be made from earth orbiting satellites where the Doppler shift may amount to several thermal absorption line half-widths depending on the relative orientation of the spacecraft velocity and the field of view. A Doppler shift comparable to or greater than the half-width of the lines being observed has a profound effect on the spectral correlation. This would make conventional correlation spectroscopy of the stratosphere impossible. The method of Doppler shift compensation also makes possible the determination of that Doppler shift and, therefore, the relative velocity; this provides for the possibility of measuring wind in the atmosphere as will be described in another paper given at this meeting. Finally, the electro-optical modulation technique permits a satellite borne radiometer to determine the thermal profile of the stratosphere in an improved fashion to the pressure modulated radiometer technique.

© 1983 Optical Society of America