Technical Note: Improved total atmospheric water vapour amount determination from near-infrared filter measurements with sun photometers

Abstract

Abstract. In this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We employ gaussian-shaped filters as well as actual filter transmission curves, mainly AERONET data, to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. Published parameterized transmittance functions are applied to the data to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. The moderateresolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940-nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10 −6 to 10 −4 , and typical response curves of commercially available silicon photodiodes are included into the calculations.It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is mainly underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. Further investigations will use experimental data from field campaigns to validate these findings.

Evaluation of the new ESR network software for the retrieval of direct sun products from CIMEL CE318 and PREDE POM01 sun-sky radiometers

“…New algorithms for the retrieval of CWV have been proposed during the past few years (Mavromatakis et al, 2007;Campanelli et al, 2010). The Mavromatakis et al (2007) method proposes an improvement to the Bruegge et al (1992) method for CIMEL instruments, and is expected to be implemented on the sunrad code for mode 2.…”

“…The Mavromatakis et al (2007) method proposes an improvement to the Bruegge et al (1992) method for CIMEL instruments, and is expected to be implemented on the sunrad code for mode 2. The Campanelli et al (2010) algorithm was proposed for its use on the SKYNET PREDE sky radiometers and currently is undergoing validation.…”

Calibration of a water vapour Raman lidar with a kite-based humidity sensor

“…It may still be specific to the conditions experienced in the Balearic sea during this period. While several previous studies have warned about a slight dry bias (Pérez-Ramirez et al, 2014) or wet/dry biases and drifts below 0.3 cm depending on the Cimel sun photometer used (Torres et al, 2009), this much stronger effect (up to 1 cm) has not been reported elsewhere, to our knowledge, despite multiple works on the subject (Estellés et al, 2007;Martinez-Lozano et al, 2007;Mavromatakis et al, 2007;Ortiz de Galisteo et al, 2010). It should be investigated further, by comparison to GPS network retrievals for instance, in similar conditions.…”

Error source in AOD retrieval from filter radiometer data in the UV due to filter band function

“…The same effect affects other atmospheric component optical depths, like ozone or water vapor (Mavromatakis, Gueymard, & Franghiadakis, 2007), thus having a strong impact in their content determination. For aerosol studies, UV region is especially sensitive due to the strong ozone absorption.…”