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Using shaded filter instruments for measurements of sky radiance: retrieval of the apparent sky-view factor from ultraviolet radiation measurements.

There is a growing need for sky radiometric measurements that encapsulate spatial as well as temporal variability. Since the advent of fast data acquisition systems in the 1980s, recent studies have utilized radiation filter instruments deployed in various sky-shading platforms. One cost effective method provides azimuthally averaged sky radiance distribution data at time scales down to fractions of a minute. Successful operation of this scheme requires knowledge of the apparent sky-view factor of the deployed sensor--an artifact of the instrument input optics, instrument filter design, and the instrument shading device employed. We provide a methodology for a determination of the sensor sky-view factor by using the employed shading device and the sun as a light source. The effect of an incorrect determination of instrument sky-view factor is also analyzed in context of the measurements.