Performance of Radiative Transfer Models in the Microwave Region

Abstract

We compared two fast radiative transfer models, Community Radiative Transfer Model (CRTM) and Radiative Transfer for TIROS Operational Vertical Sounder (RTTOV), with the LBL model Atmospheric Radiative Transfer Simulator (ARTS). We used the measurements from Advanced Technology Microwave Sounder (ATMS) and the Global Precipitation Measurement Microwave Imager (GMI) for evaluation of the radiative transfer models. The models in comparison with the observations and each other performed very well with a mean difference less than 0.5 K for the temperature sounding channels operating near the oxygen absorption band at 60 GHz. There was a difference of up to 1 K among the models as well as compared with the observations for humidity sounding channels operating around water vapor absorption line at 183 GHz. The mean difference between the simulations and observations was up to 6 K for surface sensitive channels. Water vapor and surface sensitive channels also showed to be more sensitive than the temperature sounding channels to the spectroscopy models used to calculate the absorption coefficients. There was a small difference, less than 0.1 K, between brightness temperatures calculated using traditional boxcar and actual Sensor or Spectral Response Functions, except for a difference of 0.25 K for ATMS Channel 6. Double difference technique showed about 1 K difference between water vapor channels from ATMS instruments onboard N20 and National Polar‐orbiting Partnership (NPP). However, comparison of a new version of ATMS/NPP observations recently generated using an enhanced calibration algorithm with ATMS/N20 observations showed that the differences between the two instruments are less than 0.5 K after improving the ATMS/NPP calibration.

Water vapour radiometry in geodetic very long baseline interferometry telescopes: assessed through simulations

“…The PWR98 model for water vapour attenuation was used (Rosenkranz 1998). See Moradi et al (2020) for an assessment of water vapour attenuation models. The attenuation of liquid cloud water is taken from Ellison (2007).…”

Why and How Does the Actual Spectral Response Matter for Microwave Radiance Assimilation?

“…The reason why actual SRF generates different TBs compared with boxcar was also not discussed. The conclusion in Moradi et al (2020) that "the differences (between TBs simulated using boxcar and real SRFs) ultimately depend on how much the real SRFs are different from the expected boxcar SRFs" was also studied in this paper. According to the simulating results in Section 3, the more different SRFs do not necessarily induce more different simulated TBs, the differences depend on the balance of several deformations on the passband.…”

“…Moradi et al. (2020) used the actual SRFs of ATMS to simulate TB then compared with the results of boxcar SRFs by different RTMs. The reason why actual SRF generates different TBs compared with boxcar was also not discussed.…”

“…Zou et al (2013) evaluated the impacts of ATMS laboratory SRF with CRTM and Monochromatic RTM, but they did not discuss how the actual SRF affects TB simulations. Moradi et al (2020) used the actual SRFs of ATMS to simulate TB then compared with the results of boxcar SRFs by different RTMs. The reason why actual SRF generates different TBs compared with boxcar was also not discussed.…”

Implementation of a Discrete Dipole Approximation Scattering Database Into Community Radiative Transfer Model

“…As a result, all-sky simulations conducted using the lookup tables generated using the Mie theory for the frozen particles largely deviate from the observations (Baordo & Geer, 2016;Eriksson et al, 2015Eriksson et al, , 2018Geer & Baordo, 2014). Although CRTM has a good accuracy in simulating clear-sky observations from the input profiles (Moradi, Goldberg, et al, 2020), using Mie theory to generate the scattering lookup tables is known to limit the accuracy of the CRTM all-sky calculations (Sieron et al, 2017).…”