Simulated Geophysical Noise in Sea Ice Concentration Estimates of Open Water and Snow-Covered Sea Ice

Sea ice concentration algorithms using brightness temperatures (T-B) from satellite microwave radiometers are used to compute sea ice concentration (c(ice)), sea ice extent, and generate sea ice climate data records. Therefore, it is important to minimize the sensitivity of c(ice) estimates to geophysical noise caused by snow/sea ice thermal microwave emission signature variations, and presence of WV and clouds in the atmosphere and/or near-surface winds. In this study, we investigate the effect of geophysical noise leading to systematic c(ice) biases and affecting c(ice) standard deviations (STD) using simulated top of the atmosphere T(B)s over open water and 100% sea ice. We consider three case studies for the Arctic and the Antarctic and eight different c(ice) algorithms, representing different families of algorithms based on the selection of channels and methodologies. Our simulations show that, over open water and low c(ice), algorithms using gradients between V-polarized 19-GHz and 37-GHz T(B)s show the lowest sensitivity to the geophysical noise, while the algorithms exclusively using near-90-GHz channels have by far the highest sensitivity. Over sea ice, the atmosphere plays a much smaller role than over open water, and the c(ice) STD for all algorithms is smaller than over open water. The hybrid and low-frequency (6 GHz) algorithms have the lowest sensitivity to noise over sea ice, while the polarization type of algorithms has the highest noise levels.

Automated summary

This study investigates the sensitivity of sea ice concentration algorithms to geophysical noise and finds that different channels and methods have different effects on the results. The algorithms using gradients between 19 GHz and 37 GHz T(B) show the lowest sensitivity to geophysical noise, while algorithms using the near-90 GHz channel show the highest sensitivity. Over sea ice, all algorithms have smaller c(ice) standard deviations compared to open water, with hybrid and low-frequency algorithms having the lowest sensitivity to noise.