Calibration and data elaboration procedure for sky irradiance measurements.

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.

Use of sky brightness measurements from ground for remote sensing of particulate polydispersions.

The software code SKYEAD.pack for retrieval of aerosol size distribution and optical thickness from data of direct and diffuse solar radiation is described; measurements are carried out with sky radiometers in the wavelength range 0.369-1.

Aerosol features retrieved from solar aureole data: a simulation study concerning a turbid atmosphere.

The characteristics of the solar aureole were evaluated for several cases of a turbid atmosphere in the 3° ≤θ≤30° interval of scattering angles; for each case, the features of the aerosol were retrieved from the simulated aureole data. Computations were carried out with a recently set up radiative transfer code that uses the approximated delta-M method, corrected further for the 1st and 2nd scattering orders. Results showed that the software tested can work out both the direct and the inverse aureole problems with great accuracy and efficiency in several different situations, so it can reliably be used for handling experimental data measured in the field with an aureolemeter.

Reliability of the polar nephelometer for the measurement of visibility in fog.

The relation between the extinction coefficient of light at lambda = 0.55 microm and the scattered intensity was studied as a function of the scattering angle and the wavelength, in connection with its use in the measurement of visibility with the polar nephelometer. Computations used 239 spectra of natural fogs; they considered 181 scattering angles, 22 wavelengths from 0.

Backscattering, extinction, and liquid water content in fog: a detailed study of their relations for use in lidar systems.

A solution to the single-scattering lidar equation to infer optical extinction, liquid water content W, and visibility in a fog through a monostatic pulsed lidar, requires the use of the relations, and combinations of them, between backscattering coefficient beta, extinction coefficient sigma, and W. To this end, beta and sigma have been computed for 239 droplet size spectra and forty wavelengths from 0.25 to 12 microm, together with W, and the three relations beta vs sigma, W vs sigma and sigma(0.