{"id":50528,"date":"2023-02-16T18:17:00","date_gmt":"2023-02-16T18:17:00","guid":{"rendered":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/?p=50528"},"modified":"2023-02-17T16:17:41","modified_gmt":"2023-02-17T16:17:41","slug":"sar-data-over-american-samoa-part-v","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/50528","title":{"rendered":"SAR Data over American Samoa, part V"},"content":{"rendered":"\n
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GOES-18 Band 13 Clean Window infrared (10.3 \u00b5m) imagery, and SAR winds from RADARSAT-2, 0550 UTC (left) and 1650 UTC (right) on 16 February 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

Two more SAR data collections occurred over American Samoa waters on 16 February, as shown above. (This is part of an ongoing special collection<\/a> that extends through early March). As with most previous observations, winds around American Samoa were light. Consider these ASCAT observations from MetopC at ca. 2040 UTC on 16 February 2023<\/a>, for example, taken from this site<\/a>. Observed winds are uniformly around 10 knots.<\/p>\n\n\n\n

The most notable feature in the 0550 UTC winds above is the arc of showers to the northeast of American Samoa, shown below. Imagery from this time is also available at this website<\/a>, both wind fields<\/a> and Normalized Radar Cross Section (NRCS) fields<\/a>. NRCS data suggests that the peak winds — those values exceeding 20 knots — might be where SAR energy is reflecting off ice in clouds, leading to a SAR-derived wind that is too strong.<\/p>\n\n\n\n

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RADARSAT-2 SAR winds, 0548 UTC on 16 February 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

How long do the winds in the SAR field above persist? The mp4 animation below (click here for an animated gif<\/a>) from 0000 UTC to 2000 UTC tracks the cloud feature associated with the SAR observations at 0548 UTC to the east, but that feature is very difficult to discern in the second SAR overpass at 1650 UTC.<\/p>\n\n\n\n