GAIN COMPENSATED PHOTOPOLARIMETER FOR AIRBORNE MEASUREMENTS OF SKYLIGHT POLARIZATION,

The design and performance of a simple battery operated, electronic-servo governed photoelectric polarimeter are presented and discussed. A rotating Glan prism is used as the analyzer. Measurements of the degree of linear polarization and relative intensity variations can be made in four narrow spectral intervals band width approximately equals 150 A centered on wavelengths 3620, 4010, 5010 and 5990A. The variations in the intensity of the incoming light beam are compensated by varying the gain of the photomultiplier tube with the use of a programmable high voltage supply governed by an electronic servo the error signal for which is derived from the instantaneous value of the photosignal after rectification. Variations in intensity of three to four orders of magnitude can easily be accommodated with the present system. Because of its light weight, reasonably low power consumption and characteristic requirement of a single operational command, the polarimeter is eminently suited for use when both the operation and data acquisition are to be interfaced with a telemetry system as in a high altitude balloon flight. Author