A multi‐instrument approach for characterizing the atmospheric aerosol optical thickness during the STAAARTE/DAISEX‐99 campaign

Abstract

This work deals with the retrieval of the aerosol optical thickness (AOT) needed to carry out the atmospheric correction of remote sensing data measured in Barrax (Spain) on 4 June 1999 in the framework of 1999 Digital Airbone Imaging Spectrometer Experiment (DAISEX'99). The AOT was estimated through three approaches based on: spectral extinction of direct solar irradiance at ground level, airborne nephelometer measurements at different altitudes, and backscatter lidar in the lower troposphere. We found extremely low AOT values due to a cold Atlantic front that swept across the Iberian Peninsula from west to east producing light rain over the test area on 2 June 1999. The results were solar irradiance extinction: 0.085±0.018; nephelometer: 0.063±0.020; lidar: 0.083±0.030. Nephelometer‐ and lidar‐derived values account for both extinction and absorption, assuming a single scattering albedo value of 0.90. Errors values include measurements and retrieval uncertainties as well as statistical variability.

Column‐integrated aerosol optical properties from ground‐based spectroradiometer measurements at Barrax (Spain) during the Digital Airborne Imaging Spectrometer Experiment (DAISEX) campaigns

“…In the DAISEX campaigns (a detailed description of which is presented in the following section) simultaneous measurements of this type were available for 2 days of the DAISEX‐99 campaign, from a lidar and a nephelometer on board the airborne Avion de Recherche Atmosphérique et de Télédéction (ARAT). Some results related to these have been published by the authors in a previous paper [ Martínez‐Lozano et al , 2002]. In this paper we present the results corresponding to the column‐integrated aerosol optical properties over the Barrax area during all the days of the DAISEX campaign.…”

“…The authors have also estimated, using the Nakajima SKYRAD.PACK code [ Nakajima et al , 1983, 1996], the contribution of the sky radiance to the measured irradiance, due to the fact that the solid angle subtended by the collimators is higher than the solid angle subtended by the sun. The inaccuracy due to the circumsolar radiation, for 500 nm, was 0.6% assuming that the sun was perfectly centered in the instrument's FOV [ Martínez‐Lozano et al , 2002, 2003]. When the Sun was not in the center, the circumsolar radiation would probably be slightly less, and so too the inaccuracy due to this radiation.…”

Design of a sun tracker for the automatic measurement of spectral irradiance and construction of an irradiance database in the 330–1100nm range

“…On the other hand, the authors have also estimated, using the Nakajima's SKYRAD.PACK code [26,27], the contribution of the sky radiance to the measured irradiance, due to the fact that the solid angle subtended by the collimators is higher than the solid angle subtended by the sun. The inaccuracy due to the circumsolar radiation, for 500 nm, was 0.6% assuming that the sun was perfectly centred in the instruments FOV [16,28]. When the Sun was not in the centre, the circumsolar radiation would probably be slightly less, and so too the inaccuracy due to this radiation.…”