Photon-counting polarizing radiometer

Photon counting is used in this instrument to obtain high precision in the measurement of the intensity, degree of polarization, and orientation of the plane of polarization of light in the natural environment. The dual-channel configuration, with four interference filters in each channel, provides the possibility of measurements in eight narrow spectral intervals in the wavelength range 0.32-0.90 microm. Operation of the device, including rotation of the polarizing prism, selection of the filters, orientation in azimuth and elevation, and other mechanical processes, is controlled completely by a small electronic computer. The measurements are reduced to the physical quantities of interest on a real-time basis by the computer, which also is used to record the data on magnetic tape and print them out on a high speed printer as desired. Field operation has shown the instrument to be fast and reliable for measuring the intensity and polarization of sunlight, which may be of interest for characterizing atmospheric processes or the physical properties of natural surfaces.