Comparing Satellite Estimates for Rainfall

Images

One of the products demonstrated at the Hazardous Weather Testbed (HWT) in Norman in May and June this year was GREMLIN (GOES Radar Estimation via Machine Learning to Inform NWP) a tool created with Machine Learning (by Kyle Hilburn at CIRA) to use ABI and GLM data to create synthetic radar reflectivity fields. (This article describes the product fully). GREMLIN was trained on GOES-16 CONUS data, but in these images it is displayed over American Samoa (the product has been incorporated into the AWIPS machine at WSO Pago Pago), and it’s being compared to hourly estimates of rainfall from CMORPH-2. The images below show 6 fields (at 10-minute intervals) of simulated radar and an hourly CMORPH-2 accumulation derived independently and displayed in RealEarth.

Consider the 15 different animations shown below, that step through an event with rain over the Samoan Islands. In general, the CMORPH-2 hourly accumulations on the right agree in general with where the radar estimates derived from GREMLIN suggest rain might be falling.

GREMLIN MRMS estimates 2210-2300 UTC 16 May 2024 (left) ; CMORPH-2 1-h rain estimates, 2259 UTC on 16 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 2310-0000 UTC 16-17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 2359 UTC on 16 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0010-0100 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0059 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0110-0200 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0159 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0210-0300 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0259 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0310-0400 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0359 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0410-0500 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0459 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0510-0600 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0559 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0610-0700 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0659 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0710-0800 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0759 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0810-0900 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0859 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 0910-1000 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 0959 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 1010-1100 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 1059 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 1110-1200 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 1159 UTC on 17 May 2024 (right) (Click to enlarge)
GREMLIN MRMS estimates 1210-1300 UTC 17 May 2024 (left) ; CMORPH-2 1-h rain estimates, 1259 UTC on 17 May 2024 (right) (Click to enlarge)

What should a user do when GREMLIN does or does not show rain where CMORPH-2 is or is not showing rain accumulation. It should not make a user think “Oh, this is wrong”; rather, it means a user should investigate those regions using other satellite imagery to determine whether or not rains are occurring.

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