Abstract
Sea ice concentration algorithms using brightness temperatures (<i>T<sub>B</sub></i>) from satellite microwave radiometers are used to compute sea ice concentration (<i>c<sub>ice</sub></i>), sea ice extent, and generate sea ice climate data records (CDRs). Therefore, it is important to minimize the sensitivity of <i>c<sub>ice</sub></i> estimates to geophysical noise caused by snow/sea ice thermal microwave emission signature variations, and presence of water vapor and clouds in the atmosphere and/or near-surface winds. In this study, we investigate the effect of geophysical noise leading to systematic <i>c<sub>ice</sub></i> biases and affecting <i>c<sub>ice</sub></i> standard deviations (STD) using simulated top of the atmosphere (TOA) <i>T<sub>B</sub></i>s over open water and 100 % sea ice. We consider three case studies for the Arctic and the Antarctic and eight different <i>c<sub>ice</sub></i> algorithms, representing different families of algorithms based on the selection of channels and methodologies. Our simulations show that, over open water and low <i>c<sub>ice</sub></i>, algorithms using gradients between V-polarized 19 GHz and 37 GHz <i>T<sub>B</sub></i>s shows 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 <i>c<sub>ice</sub></i> 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 have the highest noise levels.
Highlights
S ATELLITE microwave brightness temperatures (TB) measured at atmospheric window frequencies and used for estimating sea ice concentration are sensitive to noise from the atmosphere and variability in surface emissivity and temperature, here referred to as geophysical noise [1]
If we look at the correlations where the r2 > 0.5 (|r| >= 0.71) the NASA team cice is correlated with the following snow parameters: snow depth (Hs), snow surface density (SnSD), average snow density (ASnD) and snow water equivalent (SW E) in the Ross Sea first-year sea ice (FYI) profile
Main requirements to cice algorithms over sea ice for making climate data records (CDRs) are: 1) low sensitivity to surface noise, 2) low sensitivity to weather (W V and cloud liquid water (CLW) in the atmosphere and open water surface wind), 3) adjustment to climatological changes in noise terms, and
Summary
S ATELLITE microwave brightness temperatures (TB) measured at atmospheric window frequencies and used for estimating sea ice concentration (cice) are sensitive to noise from the atmosphere and variability in surface emissivity and temperature, here referred to as geophysical noise [1]. This geophysical TB sensitivity varies with electromagnetic frequency and polarization. The atmospheric emission and extinction is small (dryer atmosphere than over open water), compared to the high emission from the sea ice background, except at near 90 GHz, where the TBs are sensitive to W V and CLW over ice [3]. Over sea ice we distinguish between surface and atmospheric noise
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