Total column water vapour retrieval from S-5P/TROPOMI in the visible blue spectral range

Abstract

Abstract. Total column water vapour has been retrieved from TROPOMI measurements in the visible blue spectral range and compared to a variety of different reference data sets for clear-sky conditions during boreal summer and winter. The retrieval consists of the common two-step DOAS approach: first the spectral analysis is performed within a linearized scheme and then the retrieved slant column densities are converted to vertical columns using an iterative scheme for the water vapour a priori profile shape, which is based on an empirical parameterization of the water vapour scale height. Moreover, a modified albedo map was used combining the OMI LER albedo and scaled MODIS albedo map. The use of the alternative albedo is especially important over regions with very low albedo and high probability of clouds like the Amazon region. The errors of the total column water vapour (TCWV) retrieval have been theoretically estimated considering the contribution of a variety of different uncertainty sources. For observations during clear-sky conditions, over ocean surface, and at low solar zenith angles the error typically is around values of 10 %–20 %, and during cloudy-sky conditions, over land surface, and at high solar zenith angles it reaches values around 20 %–50 %. In the framework of a validation study the retrieval demonstrates that it can well capture the global water vapour distribution: the retrieved H2O vertical column densities (VCDs) show very good agreement with the reference data sets over ocean for boreal summer and winter whereby the modified albedo map substantially improves the retrieval's consistency to the reference data sets, in particular over tropical land masses. However, over land the retrieval underestimates the VCD by about 10 %, particularly during summertime. Our investigations show that this underestimation is likely caused by uncertainties within the surface albedo and the cloud input data: low-level clouds cause an underestimation, but for mid- to high-level clouds good agreement is found. In addition, our investigations indicate that these biases can probably be further reduced by the use of improved cloud input data. For the general purpose we recommend only using VCDs with cloud fraction <20 % and AMF >0.1, which represents a good compromise between spatial coverage and retrieval accuracy. The TCWV retrieval can be easily applied to further satellite sensors (e.g. GOME-2 or OMI) for creating uniform, long-term measurement data sets, which is particularly interesting for climate and trend studies of water vapour.

Estimation of the Precipitable Water and Water Vapor Fluxes in the Coastal and Inland Cities of China Using MAX-DOAS

“…MAX-DOAS is usually used in the study of atmospheric pollution, but there is a gap in meteorological research (PW and WVF). In recent years, measuring the atmospheric water vapor VCD and profile based on MAX-DOAS has been continuously studied [15,[21][22][23][24][25][26][27], providing a new method for studying PW and WVF. Because of its simple structure, high temporal and spatial resolution, easy maintenance, and remote control, MAX-DOAS has great advantages over traditional atmospheric water vapor measuring instruments.…”

A semi-empirical potential energy surface and line list for H<sub>2</sub><sup>16</sup>O extending into the near-ultraviolet

“…Water vapour is a major absorber of light in the terrestrial atmosphere, and it interferes with atmospheric retrievals from the microwave to the near-ultraviolet (Lampel et al, 2015). The water molecule dissociates at 41 145.92 cm −1 (Boyarkin et al, 2013), and there are almost no rovibrational transitions beyond that. Although the absorption of water vapour in the near-ultraviolet is known to be weak, particularly when compared to features in the infrared, it obscures retrievals of electronic spectra of important (from an atmospheric and pollution monitoring perspective) molecules with trace abundances in the terrestrial atmosphere (Fleischmann et al, 2004;Cantrell et al, 1990;Stutz et al, 2000).…”

Boundary layer water vapour statistics from high-spatial-resolution spaceborne imaging spectroscopy

“…More TCWV means relatively more absorption at H2O absorption wavelengths relative to other wavelengths. This applies to TCWVVSWIR from missions including MERIS (Bennartz and Fischer, 2001;Guanter et al, 2008), MODIS (Diedrich et al, 2015;Gao and Kaufman, 2003), TROPOMI (Borger et al, 2020;Schneider et al, 2020), SCIAMACHY (Noël et al, 2004), GOME (Noël et al, 1999), GOME-2 (Grossi et al, 2015) and OCO-2 (Nelson et al, 2016). These instruments vary in spectral range and sampling, but all must contend with the measured spectra responding to properties other than TCWV.…”