<title>Measurements of polarization of targets of differing albedo and shadow depth</title>

There are many measurements of polarization made with non- imaging polarimeters. Such measurements have been made in the laboratory, of the sky and of the ground. These measurements can be interpreted only when subsidiary information enables identification of the surface under study. Some measurements have been made with imaging polarimeters based upon film, but these were limited in radiometric accuracy by the medium, or by lack of sensitometry. Some investigators fabricated a polarimeter from videcon cameras, but this study was also limited by radiometric fidelity. With the advent of digital cameras with linear focal plane radiometric response, and software retaining this linearity in extracting the image from the camera, greater radiometric accuracy has been achieved. We report here measurements of polarization which we show to be related to scene radiance. The radiance levels covered include a wide dynamic range and facilitate study of low radiance levels in general previously inaccessible to measurement using an imaging device. We also include data from previous measurements with non-imaging devices and show that they are compatible with data collected using a digital camera. There is an inverse linear relationship between the logarithm of the polarization in recorded radiance and the logarithm of the recorded radiance in data obtained with both imaging and with non-imaging polarimeters.