Microwave radiometer antenna size and the spatial resolution of sea ice concentration

The figure is showing the simulated microwave radiometer sea ice concentration for effective antenna sizes between 1 and 11 m. The sea ice concentration is computed using an imaging simulator, a constant incidence angle at 56 degrees and a satellite altitude of 800 km. With these geometrical parameters the spatial resolution on the ground is then proportional with the electromagnetic wavelength divided by the antenna diameter.

The reference sea ice concentration is derived from the brightness of cloud-free MODIS scenes at 250 m x 250 m pixel size. The MODIS pixel brightness across the image may vary slightly as a function of solar angle and albedo (snow type and sea ice type), leading to uncertainties in the derived ice concentration. However, here it is just used as the reference and it does in fact provide a realistic spatial distribution of ice at the right scale for input to the model and as a reference for comparison. Each of these 250 m x 250 m ice concentration pixels is assigned a microwave brightness temperature using standard tie points for ice and water and linear mixing between 0 and 100 % for the range of MODIS pixel brightness values.

For each 250 m x 250 m brightness temperature pixel 2D elliptical Gaussian-shaped antenna patterns where dimensions depend on the antenna size are folded with the high resolution reference to simulate brightness temperatures at 19v and 19h and 37v and 37h as it would be measured on the satellite with different effective antenna aperture sizes between 1 and 11 m. The simulations of brightness temperatures are then used as input to the Bristol algorithm using the standard tie points also used in the reference.

The figure shows that the improvement in spatial resolution is much larger from 1 to 2 m than for 5 to 6 m and the way to increase resolution (in this simple set-up) is to measure at higher electromagnetic frequencies.