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Willson, R. C.

Publications and source records attributed to Willson, R. C..

42 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Absolute radiometry and the solar constant

A series of active cavity radiometers (ACRs) are described which have been developed as standard detectors for the accurate measurement of irradiance in absolute units. It is noted that the ACR is an electrical substitution calorimeter, is designed for automatic remote operation in any environment, and can make irradiance measurements in the range from low-level IR fluxes up to 30 solar constants with small absolute uncertainty. The instrument operates in a differential mode by chopping the radiant flux to be measured at a slow rate, and irradiance is determined from two electrical power measurements together with the instrumental constant. Results are reported for measurements of the solar constant with two types of ACRs. The more accurate measurement yielded a value of 136.6 plus or minus 0.7 mW/sq cm (1.958 plus or minus 0.010 cal/sq cm per min).

Willson, R. C.↗
NASA NTRS1973

Active cavity radiometer.

The active cavity radiometer (ACR) is a pyrheliometer that accurately defines the absolute radiation scale. The physics of the pyrheliometric method and the ACR approach to this method are presented in detail. A mathematical abstraction of the method is generated through a quasi-equilibrium analysis of the power balance of the ACR's cavity detector. An error analysis is carried out on the quasi-equilibrium equation to determine the uncertainties of ACR measurements relative to the absolute radiation scale. The uncertainty of ACR measurements as a function of irradiance level is presented in graphical form.

Willson, R. C.↗
NASA NTRS1973

New radiometric techniques and solar constant measurements.

A series of absolute cavity radiometers, designed to measure solar irradiance, has been developed at the Jet Propulsion Laboratory. Analysis indicates the absolute uncertainty of irradiance measurements made by the most recent devices to be less than plus or minus 0.5 mW/sq cm. In a series of experiments the radiometric scale defined by the JPL instruments has been compared with the International Pyrheliometric Scale (IPS). A systematic 2.2% difference has been observed with the IPS producing consistently lower measurements. The solar constant and spectral distribution have been derived from high-altitude balloon flight measurements made by two types of JPL cavity radiometers. Measurements at 25 km in 1968 produced a solar constant value of 137.0 mW/sq cm. From 1969 measurements at 36 km, a value of 136.6 mW/sq cm was derived, with an estimated absolute uncertainty of plus or minus 0.5%. The solar spectrum information from these experiments agrees most closely with the solar spectrum model of Labs and Neckel (1968).

Willson, R. C.↗
NASA NTRS1972

Experimental comparisons of the international pyrheliometric scale with the absolute radiation scale.

Solar irradiance measurements by instruments (Eppley Angstrom Pyrheliometers) reproducing the International Pyrheliometric Scale (IPS) have been compared with measurements made simultaneously by a number of JPL Active Cavity Radiometers (ACR) and the Practical Absolute Cavity Radiometer (PACRAD). The results of these tests demonstrate a systematic difference between the absolute radiation scale as defined by the ACR and PACRAD measurements and the IPS.

Willson, R. C.↗