Measuring the point-spread function of sea ice in situ

In this paper, we describe an experiment to measure the point spread function (PSF) of Arctic ice that was conducted by personnel of the Naval Ocean Systems Center in 1985. SRI International designed and developed the instrumentation. In April, data were collected on refrozen leads in pack ice concentrated near the Beaufort Gyre. The location was about 200 miles from the North Pole at approximately 86 degrees north and 88 degrees west. PSF measurements were made with a Hasselblad camera and a pulsed Lambertian (cosine) source gated to the camera. Recently, SRI digitized the film data with a charge-coupled device (CCD) camera and performed a digital analysis of the images. Results from two sites of new and first- year ice, 0.66 m and 2.1 m thick, respectively, are presented. Because of the strong multiple scattering by sea ice, and the limited area of the ice surface that could be imaged by the camera, the data obtained only partially characterize the PSF of the ice. The paper concludes with suggestions for improving future sea ice PSF measurements.