Detection of smoke is a challenge in regions with clouds. The bright reflectance from clouds can make the subtler (and usually not so bright) smoke features difficult to view. This blog post briefly shows how visible imagery can be manipulated to facilitate smoke detection. The animation above shows visible imagery (GOES-16 Band 2 at 0.64  µm) at 2-km resolution. The sixteen half-km pixel visible reflectances within the larger pixel have been averaged to create the 2-km resolution image, and a square-root enhancement (from 0-100%) has been applied.

August 4 was a day with a smoke pall over much of the upper midwest, as suggested below by HRRR Smoke Model output below. How distinct is that pall in the imagery above, especially in regions of cumulus and cirrus clouds, such as over northeastern Minnesota? Can the visible imagery above be manipulated so that smoke features are enhanced?

The animation below shows 2-km resolution data again (with a square-root enhancement applied), but instead of the mean reflectance value from the 16 1/2-km pixels used, the minimum reflectance of those 16 pixels is shown. The smoke in the air is more noticeable (and the clouds are less noticeable).

You can also display the maximum pixel value of the 16 1/2-km pixels within the 2-km pixel footprint. That’s shown below (also using a square-root enhancement). This brings out the clouds at the expense of smoke detection.

A PowerPoint presentation that contains the imagery above is here. Thanks to Andy Heidinger, NOAA, for these images.

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Shortwave Infrared (3.9 µm) images from GOES-17, GOES-15, GOES-14 and GOES-16 [click to play animation | MP4]

The Caldor Fire (east of Sacramento, California) exhibited unprecedented growth on 17 August 2021 — increasing from 3600 acres burned in the morning to 30,000 acres that evening, with 0% containment — and Shortwave Infrared (3.9 µm) images from 1-minute GOES-17, 15 to 30-minute GOES-15, 15 to 30-minute GOES-14 and 5-minute GOES-16 (above) displayed a rapid expansion of the fire’s thermal anomaly (large cluster of hot pixels, darker black enhancement; the white pixels seen in GOES-15 images were due to a “wrap-around” effect with that satellite’s saturated 3.9 µm detectors). Each of the 4 image panels are displayed in the native projection of that particular satellite.

GOES-17 True Color RGB images created using Geo2Grid  (below) showed the large amounts of smoke (and frequent pyrocumulus clouds) produced by the Caldor Fire.  

GOES-17 True Color RGB images [click to play animation | MP4]

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GOES-16 “Cirrus” channel (1.38 µm) imagery, above, and visible (0.64 µm ), below, shows Tropical Storm Henri to the southeast of the island of Bermuda (at 32.3º N, 64.7º W) shortly after sunrise on 17 August 2021. The cirrus channel shows a compact region of convection and an expanding cirrus shield. Visible imagery, below (click here for the animation in CSPP Geosphere), at a higher resolution (and zoomed in) also shows persistent convection near the center of the storm (according to NHC at 1500 UTC: 30.4º N, 64.3º W). The curvature of the low-level clouds in the visible imagery, below, give some hint to where the surface center is, near the western edge of the convection. (Those low-level clouds are not visible in the ‘Cirrus’ channel animation above because water vapor is absorbing reflected solar radiation at 1.38 µm and the signal from the low clouds is lost).

An analysis of shear at 1500 UTC on 17 August (here, from the CIMSS Tropical site) shows modest northerly shear over the storm.

For more information on Henri, refer to the National Hurricane Center. Current forecasts keep the storm offshore, although swells from the storm could affect beaches along the eastern seaboard of the USA.

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GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

1–minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed Tropical Storm Fred during the 8-hour period leading up to it making landfall along the panhandle of Florida around 1915 UTC on 16 August 2021. Multiple convective bursts developed near the storm center, with some exhibiting cloud-top infrared brightness temperatures of -80ºC or colder (violet pixels). As Fred moved inland, it produced heavy rainfall and strong winds.

A time-matched comparison of Infrared images from GOES-16 and Suomi NPP at 1831 UTC is shown below. The coldest cloud-top infrared brightness temperatures were -74.1ºC with GOES-16 and -79.5ºC with Suomi NPP. The spatial offset is due to parallax that is inherent with GOES imagery. 

1831 UTC Infrared Window images from GOES-16 (10.35 µm) and Suomi NPP (11.45 µm) [click to enlarge]

Views of Fred from 4 GOES (GOES-17, GOES-15, GOES-14 and GOES-16) around 1800 UTC are shown below. 

Infrared Window images of Tropical Storm Fred from GOES-17, GOES-15, GOES-14 and GOES-16 around 1800 UTC (credit: Tim Schmit, NOAA/NESDIS/ASPB) [click top enlarge]

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