Information content on temperature and water vapour from a hyper‐spectral microwave sensor

Abstract

This study examines the information content on atmospheric temperature and humidity profiles that could be provided by a future spaceborne microwave sensor with a few hundred radiances in the millimetre and submillimetre spectral domains (ranging from 7–800 GHz). A channel selection method based on optimal estimation theory is undertaken, using a database of profiles with associated errors from the European Centre for Medium‐Range Weather Forecasts (ECMWF) numerical weather prediction model and the radiative transfer model Atmospheric Radiative Transfer Simulator (ARTS) under clear‐sky conditions. The main results indicate that, by increasing the number of channels within the oxygen absorption band around 60 GHz and within the water‐vapour absorption band at 183 GHz, the accuracy of temperature and humidity retrievals in the troposphere and stratosphere (for temperature) would be noticeably improved compared with present and planned microwave radiometers. The channels located in the absorption lines at 118 GHz and above 200 GHz do not bring significant additional information regarding atmospheric profiles under clear‐sky conditions, partly due to greater radiometric noise. With a set of 137 selected channels that contribute to 90% of the total information content (measured by the degree of freedom for signal), it is possible to achieve almost the same performance in terms of variance error reduction as with 276 candidate channels. Sensitivity studies of various prescribed quantities defining the channel selection have been undertaken, in order to check the robustness of the conclusions. They show that none of the choices modifies the above findings.

Information content of OCO-2 oxygen A-band channels for retrieving marine liquid cloud properties

“…It is common practice to select channels based on information content and/or degrees of freedom for signal Mahfouf et al, 2015;Martinet et al, 2014;Rabier et al, 2002), and this approach has already been used in an oxygen A-band and B-band analysis for aerosol retrievals (Ding et al, 2016).…”

THz spectroscopy of the atmosphere for climatology and meteorology applications

“…Maximum impact on the results is provided by the hyper-spectral information on the O2 band around 60 GHz. Mahouf et al [15] found that increasing the number of spectral bands around 55 GHz by a factor of three increases the information content on temperature by a factor of around 1.5. They found a clear benefit, in terms of information content, in increasing the number of spectral channels around the 55 GHz O2 and 183 GHz H2O absorption lines, compared to current and future instruments.…”

“…For water vapour retrieval, the AMSU-B/MHS instruments are widely used in satellite data assimilation systems for numerical weather prediction, even though the limited number of spectral channels provides very poor vertical resolution [10][11][12][13]. A recent European Space Agency (ESA) funded study by Prigent et al [14][15][16] compared the predicted retrieval performance of a future hyperspectral microwave instrument to the predicted performance of the microwave (MW) instruments selected to fly on board the next generation of European operational meteorological satellites (MetOp-SG). For clear sky conditions, the reduction in retrieval uncertainty, compared to a priori information, goes from 2% to 10%, depending on the atmospheric layers, and is more than twice as good as what will be achieved with MetOp-SG.…”

“…Studies for hypothetical hyperspectral microwave sounders [14][15][16] have shown that adding more channels particularly around the O2 (60GHz) and H2O (183 GHz) absorption lines significantly enhances the retrieval capabilities for high accuracy temperature and humidity sounding. Additionally, for accurate retrieval of IWP, it is important that a significant part of the ice particle size distribution is sampled.…”

All-sky Information Content Analysis for Novel Passive Microwave Instruments in the Range from 23.8 GHz up to 874.4 GHz

“…In recent years, also the potential of hyper-spectral sensors in the millimeter/submillimeter wavelength region is explored for clear-sky (Mahfouf et al (2015)) and cloudy-sky (Birman et al (2017)) conditions. Birman et al (2017) find that the information content on hydrometeors can be significantly increased by using a hyper-spectral sensor, but also depends on the assumed microphysical properties of the frozen hydrometeors.…”