The EUMETSAT OSI SAF near 50 GHz sea ice emissivity model

Abstract

A sea ice thermal microwave emission model for 50 GHz was developed under EUMETSAT's Ocean and Sea Ice Satellite Application Facility (OSI SAF) programme. The model is based on correlations between the surface brightness temperature at 18, 36 and 50 GHz. The model coefficients are estimated using simulated data from a combined thermodynamic and emission model. The intention with the model is to provide a first guess sea ice surface emissivity estimate for atmospheric temperature sounding applications in the troposphere in numerical weather prediction (NWP) models assimilating Advanced Microwave Sounding Unit (AMSU) and Special Sensor Microwave Imager/Sounder (SSMIS) data. The spectral gradient ratio is defined as the difference over the sum of the SSMIS brightness temperatures at 18 and 36 GHz vertical linear polarisation (GR1836). The GR1836 is related to the emissivity at the atmospheric temperature sounding channels at around 50 GHz. Furthermore, the brightness temperatures and the polarisation ratio (PR) at the neighbouring 18, 36 and 50 GHz channels are highly correlated. Both the gradient ratio at 18 and 36 GHz and the PR at 36 GHz measured by SSMIS are input into the model predicting the 50 GHz emissivity for horizontal and vertical linear polarisations and incidence angles between 0° and 60° The simulated emissivity is compared to the emissivity derived with alternative methods. The fit to real AMSU observations is investigated using the different emissivity estimates for simulating the observations with atmospheric data from a regional weather prediction model

Assimilating SMOS sea ice thickness into a coupled ice‐ocean model using a local SEIK filter

“…Thus, the uncertainty in the observed sea ice concentrations is on average around 10% [ Tonboe and Nielsen , ]. There is, however, an additional source of the errors because of model representativeness.…”

Impact of Ice Surface and Volume Scatterings on the Microwave Sea Ice Apparent Emissivity

“…It is interesting to note that higher σ values, in particular at frequencies of 18.7 and 23.8 GHz, are located at boundaries between first‐year and multiyear sea ice, where two or more different types of ice possibly coexist, resulting in more deformed and roughened sea ice by dynamical processes. Other higher σ areas are found in the Kara Sea and the Laptev Sea, where deformed sea ice is prevalent (Nghiem et al, ; Tonboe et al, ). In summary, except for the boundary area between first‐year and multiyear sea ice, most of Arctic sea ice region shows σ values smaller than 0.3, suggesting that the roughness effect is likely insignificant over the Arctic sea ice for frequencies lower than 23.8 GHz, as noted in Figure .…”

“…Because of the strong dependence of PR on Δ θ , it should be worthwhile to examine in detail the relationship between PR/GR and θ eff to improve our understanding of the optical characteristics of sea ice in terms of roughness and thus various sea ice retrieval algorithms. Here we examine PR and GR relationships to Δ θ using the well‐known parameters, PR18 and GR18V36V, for retrieving sea ice concentration and snow depth (Comiso et al, ; Markus & Cavalieri, ; Spreen et al, ; Tonboe et al, ), i.e., …”

“…Efforts of estimating sea ice emissivity have also been made for assimilating satellite data into the weather forecasting. Tonboe et al () developed an emissivity model for 50 GHz to assimilate Special Sensor Microwave Imager/Sounder (SSMIS) data into the numerical weather forecasting, based on correlations between surface radiances at 19, 37, and 50 GHz. Similar efforts have been made to assimilate Advanced Microwave Sounding Unit (AMSU) measurements but based on the assumption that surface reflections are specular and AMSU channel emitting layers are on the skin surface (Karbou et al, ).…”

Estimating the snow depth, the snow-ice interface temperature, and the effective temperature of Arctic sea ice using Advanced Microwave Scanning Radiometer 2 and Ice Mass Balance buoys data

“…T ef f is defined as the integrated temperature over a layer corresponding to the penetration depth of the given frequency: the larger the wavelength, the deeper the penetration in the medium. The problem is particularly complicated over sea ice, due to its large spatial and temporal variability and the interaction between the radiation and the medium (English, 2008;Tonboe et al, 2013;Wang et al, 2017). The layering and the vertical structure in the snowpack, as well as the scattering from snow grains and voids, are affecting the microwave emission processes (Mathew et al, 2008;Rosenkranz and Mätzler, 2008;Harlow, 2009Harlow, , 2011Tonboe, 2010;Tonboe et al, 2011).…”