Abstract
Abstract. The Precision Solar Spectroradiometer (PSR) is a new spectroradiometer developed at Physikalisch-Meteorologisches Observatorium Davos – World Radiation Center (PMOD–WRC), Davos, measuring direct solar irradiance at the surface, in the 300–1020 nm spectral range and at high temporal resolution. The purpose of this work is to investigate the instrument's potential to retrieve integrated water vapour (IWV) using its spectral measurements. Two different approaches were developed in order to retrieve IWV: the first one uses single-channel and wavelength measurements, following a theoretical water vapour high absorption wavelength, and the second one uses direct sun irradiance integrated at a certain spectral region. IWV results have been validated using a 2-year data set, consisting of an AERONET sun-photometer Cimel CE318, a Global Positioning System (GPS), a microwave radiometer profiler (MWP) and radiosonde retrievals recorded at Meteorological Observatorium Lindenberg, Germany. For the monochromatic approach, better agreement with retrievals from other methods and instruments was achieved using the 946 nm channel, while for the spectral approach the 934–948 nm window was used. Compared to other instruments' retrievals, the monochromatic approach leads to mean relative differences up to 3.3 % with the coefficient of determination (R2) being in the region of 0.87–0.95, while for the spectral approach mean relative differences up to 0.7 % were recorded with R2 in the region of 0.96–0.98. Uncertainties related to IWV retrieval methods were investigated and found to be less than 0.28 cm for both methods. Absolute IWV deviations of differences between PSR and other instruments were determined the range of 0.08–0.30 cm and only in extreme cases would reach up to 15 %.
Highlights
Water vapour is a very important component of the thermodynamic state of the atmosphere (Hartman et al, 2013), being a greenhouse gas with relatively high concentrations
In this study we developed tools to retrieve integrated water vapour (IWV) using Precision Solar Spectroradiometer (PSR) recordings, adopting two different approaches, one using single wavelength channels and another retrieving from a wider spectral region, the latter being impossible with filter radiometers
Considering that absorption of water vapour is higher in the 910–950 nm region, all calculations were performed for PSR channels in the spectral range
Summary
Water vapour is a very important component of the thermodynamic state of the atmosphere (Hartman et al, 2013), being a greenhouse gas with relatively high concentrations. From a climate change perspective, it is considered to be a feedback agent (Soden and Held, 2006). It is an important component of the hydrological cycle and estimations of it are used in meteorological forecast models Water vapour in the atmosphere has been monitored through radiosondes and provided through measurements of vertical profiles of humidity. These measurements are limited to relatively infrequent (radiosonde) launches; during the last decades methods have been developed to retrieve IWV from other devices: Published by Copernicus Publications on behalf of the European Geosciences Union
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