An automatic all sky scanning radiometer

Abstract

A microcomputer controlled all sky scanning radiometer covering the short wave (0.3–3.0 μm) and long wave (3.0–80.0 μm) regions and using a pyroelectric detector has been constructed for continuous automatic measurement of sky radiance. Angular distributions of short, long, and total wave sky radiance are recorded and plotted at each solar hour angle from which irradiances of tilted surfaces are computer calculated. Measurement of the local earth surface radiance facilitates estimation of short wave earth surface albedo and net income of radiation to variously oriented black surfaces. Total scanning, computation, and plotting time for each hour angle observation is 8 min.

Comparison of infrared radiometrie, observed and sunshine‐derived cloud cover

“…The radiometer employed in the present work was constructed at The University of Calgary and has been described in detail by Coombes and Harrison (1982). It has been operated continuously since 1 July 1983 in a rural location 25 km from Calgary together with instrumentation for routinely monitoring wind, temperature, rainfall and surface albedo.…”

“…The technique for estimating cloud cover is based on the observed statistical and temporal variations of individual and average N(Q, <J>) values for each ring. Details of the statistical analysis leading to the radiometer cloud cover (CPR) can be found in a publication by Coombes and Harrison (1985).…”

“…It would also be useful if such a technique could be adapted to the automatic weather stations now being developed for use in remote locations where manpower is difficult to maintain. Coombes and Harrison (1985) have given details of a radiometric technique for estimating cloud cover that is based on the difference in near-infrared radiance between clear and cloudy skies. This technique was developed on the basis of radiometer data accumulated over the period 10 September to 15 October 1984 using all-sky photographs of cloud cover taken at the radiometer site.…”

Calibration of a three‐component angular distribution model of sky radiance

“…Details of the radiometer are given by Coombes and Harrison (1982). The radiometer records both short (0.3-3.0 μηι) and long (3.0-80.0 μΐη) wavelength sky radiance at 95 equally spaced sky positions (θ, φ) over the sky dome once every 20 min.…”

Comparison of model and indirectly measured diffuse sky irradiances of tilted surfaces

“…Complete details of the instrument have been given by Coombes and Harrison (1982). The long-wavelength data are used to estimate cloud cover C as described by Coombes and Harrison (1985).…”