Intercomparison of spectroradiometers and Sun photometers for the determination of the aerosol optical depth during the VELETA‐2002 field campaign

Abstract

[1] In July 2002 the VELETA-2002 field campaign was held in Sierra Nevada (Granada) in the south of Spain. The main objectives of this field campaign were the study of the influence of elevation and atmospheric aerosols on measured UV radiation. In the first stage of the field campaign, a common calibration and intercomparison between Licor-1800 spectroradiometers and Cimel-318 Sun photometers was performed in order to assess the quality of the measurements from the whole campaign. The intercomparison of the Licor spectroradiometers showed, for both direct and global irradiances, that when the comparisons were restricted to the visible part of the spectrum the deviations were within the instruments' nominal accuracies which allows us to rely on these instruments for measuring physical properties of aerosols at the different measurement stations. A simultaneous calibration on AOD data was performed for the Cimel-318 Sun photometers. When a common calibration and methodology was applied, the deviation was lowered to much less than 0.01 for AOD. At the same time an intercomparison has been made between the AOD values given by the spectroradiometers and the Sun photometers, with deviations obtained from 0.01 to 0.03 for the AOD in the visible range, depending on the channel. In the UVA range, the AOD uncertainty was estimated to be around 0.02 and 0.05 for Cimel and Licor respectively. In general the experimental differences were in agreement with this uncertainty estimation. In the UVB range the AOD measurements should not be used due to maximum instrumental uncertainties.

Autonomous marine hyperspectral radiometers for determining solar irradiances and aerosol optical properties

“…6) between the two instrument datasets results in a high R 2 (ranging between 0.768 at 870 nm and 0.940 at 500 nm) and an RMSE of between 0.040 (675 nm) and 0.075 (400 nm). This is similar to differences found between LICOR LI1800 spectrometers (Estellés et al, 2006). The 400 nm channel performance was somewhat worse than the other wavelengths using the RMSE Figure 6.…”

“…9). While not perfect, this is approaching the uncertainty of AERONET fielddeployed CIMEL instruments (0.01-0.02) and the level of agreement between different sun photometers when they are compared together in the field (0.01-0.02) using different AOD methodologies (Estellés et al, 2006). LICOR 1800 spectroradiometers calibrated by lamps also have a nominal AOD uncertainty of about 0.02-0.05 (Estellés et al, 2006).…”

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

“…In our case the error in the AOD is mainly conditioned by the error in the measurement of the direct spectral irradiance and the value of the optical air mass in the instant of the measurement. The authors have previously used this method with experimental measurements made at other sites [42] and the values that were obtained were similar to those presented by Kaufman et al [43].…”

“…Nevertheless Estelle´s et al [42] compared the Licor 1800 and Cimel 318 (instrument used in AERONET) results obtained in Veleta 2002 campaign. They concluded that the deviation in the retrieved AOD between both instruments in the visible range is 0.01-0.03, depending on the channel.…”

Physical and optical properties of aerosols over an urban location in Spain: seasonal and diurnal variability

“…The calibration measurements were carried out on completely cloud free days, with low and stable aerosol concentration. The total uncertainty in aerosol optical depth is <±0.02 (Estellés et al, 2006).…”