Interpreting SAR data over the Bering Sea

April 8th, 2021 |

GOES-17 ABI Band 2 (0.64 µm) and Band 5 (1.61 µm) at 1740 UTC on 8 April 2021 (Click to enlarge)

The toggle above shows GOES-17 ABI Band 2 (“Red Visible” at 0.64 µm) and Band 5 (“Snow/Ice” at 1.61 µm) imagery at 1740 UTC on 8 April 2021. 60ºN and 170ºW lat/lon lines are included in yellow, as well as Nunivak Island.  There is evidence of sea ice extending from south of Nunivak northwestward;  visible 0.64 µm imagery  shows much greater reflectance compared to 1.61 µm snow/ice imagery.  It’s much harder to view the ice edge in the snow/ice channel because reflectances in that channel for ice and water are similar.

Compare the toggle above to the Sentinel-1A Synthetic Aperture Radar (SAR) image at 1735 UTC on 8 April 2021, shown below.   The stark wind difference (red vs. blue) in the SAR wind image below is in reality a change in ocean state, with ice over the red region and open water over the blue.  (Here is the Sea Ice analysis for 8 April from the Alaska Sea Ice Program (ASIP)).  Interpretation of SAR winds requires a knowledge of the presence of ice.

Sentinel 1-A analysis at 1735 UTC on 8 April 2021 (Click to enlarge)