Calibration and data elaboration procedure for sky irradiance measurements

Abstract

The problems encountered in the elaboration of measurements of direct and sky diffuse solar irradiance are the following: (1) to carry out the calibration for the direct irradiance, which consists in determining the direct irradiance at the upper limit of the atmosphere; (2) to carry out the calibration for the diffuse irradiance, which consists in determining the solid viewing angle of the sky radiometer; (3) to determine the input parameters, namely, ground albedo, real and imaginary parts of the aerosol refractive index, and aerosol radius range; and (4) to determine from the optical data the columnar aerosol optical depth and volume radius distribution. With experimental data and numerical simulations a procedure is shown that enables one to carry out the two calibrations needed for the sky radiometer, to determine a best estimate of the input parameters, and, finally, to obtain the average features of the atmospheric aerosols. An interesting finding is that inversion of only data of diffuse irradiance yields the same accuracy of result as data of both diffuse and direct irradiance; in this case, only calibration of the solid viewing angle of the sky radiometer is needed, thus shortening the elaboration procedure. Measurements were carried out in the Western Mediterranean Sea (Italy), in Tokyo (Japan), and in Ushuaia (Tierra del Fuego, Argentina); data were elaborated with a new software package, the Skyrad code, based on an efficient radiative transfer scheme.

Comparison of AERONET and SKYRAD4.2 inversion products retrieved from a Cimel CE318 sunphotometer

“…For the field Prede radiometer, the S 0 calibration is obtained by using an improved Langley plot method (Tanaka et al, 1986;Campanelli et al, 2004a). For the retrieval of , the solar disk scanning method (Boi et al, 1999) is used.…”

Aerosol Optical Properties and Composition over a Table Top Complex Mining Area in a Monsoon Trough Region

“…It measures both direct solar irradiance (every 1 min) and diffuse sky radiation at either 10 min time interval or 0.25 step in air mass at 7 wavelengths (0.315, 0.4, 0.5, 0.675, 0.87, 0.94, 1.02 µm); we opted 10 min interval for this study. Calibration methodology and data reduction procedures or quality checks for this instrument are followed as per Nakajima et al (1996) and Boi et al (1999).…”

Columnar aerosol properties in a Northeastern Atlantic site (Plymouth, United Kingdom) by means of ground based skyradiometer data during years 2000–2008

“…The estimation of the SVA values can be performed by a spatial scanning of the clear sky solar disk which provides better stability and collimation than any laboratory source. This procedure has the added advantage of being applicable in situ (Boi et al, 1999).…”