A preliminary evaluation of the impact of assimilating AVHRR data on sea ice concentration analyses

In this paper a method to assimilate data from a visual/infrared (VIS/IR) sensor for the purpose of estimating sea ice concentration is investigated. A novel forward model is presented which allows the reflectances and brightness temperatures from the VIS/IR sensor to be assimilated. The VIS/IR data are assimilated in combination with ice concentration retrievals from a passive microwave sensor using 3D variational data assimilation into a 5 km × 5 km grid of sea ice concentrations. Results are compared with those from an experiment which assimilates only the ice concentration retrievals. It is found that the VIS/IR data have a positive impact as ice on the sea ice state through comparison with independent data. The proportion of points correctly identified asice or open water increased in each region studied by including the AVHRR data, with the largest increase being from 0.921 to 0.935. This positive impact is due to the higher resolution of the VIS/IR data as compared with the passive microwave data, that improves the representation of open water in bays and coastal polynyas. There is however, a degradation in the accuracy of the sea ice state in some regions of the analysis from assimilating the VIS/IR data. Possible ways of improving the impact from VIS/IR data are discussed.