Alisal Fire in Southern California

October 12th, 2021 |

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

GOES-17 (GOES-West) True Color RGB images created using Geo2Grid (above) showed the transport of smoke from the Alisal Fire in Southern California on 12 October 2021. The dashed line in the images is Highway 101 — a portion of which was closed, as the wind-driven fire raced toward the coast. Late in the day some low-altitude smoke began to move eastward along the coast, eventually reducing the surface visibility to 6 miles at Santa Barbara.

During the preceding overnight hours (at 0916 UTC or 2:16 am PDT), a comparison of Suomi-NPP VIIRS Shortwave Infrared and Day/Night Band images (below) revealed the thermal signature and nighttime glow of the fire. The VIIRS imagery was downloaded and processed via the SSEC/CIMSS Direct Broadcast ground station.

Suomi-NPP VIIRS Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

The Suomi-NPP overpass time of the fire region was actually 0926 UTC — and a time-matched comparison of Shortwave Infrared images from GOES-17 and Suomi-NPP (below) demonstrated that the superior spatial resolution of VIIRS instrument (~375 meters, vs ~2 km for the ABI on GOES-17) provided a more accurate depiction of the areal coverage of the fire.

Shortwave Infrared images from Suomi-NPP (3.74 µm) and GOES-17 (3.9 µm) [click to enlarge]

===== 13 October Update =====

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

On 13 October, GOES-17 True Color RGB images (above) showed that as offshore wind speeds relaxed, a shift to onshore flow recirculated some of the smoke inland — with smoke briefly reducing the surface visibility to 1.5 miles at Santa Barbara airport (below). Farther to the south, residual smoke from the previous day of burning was also evident, with some of it traveling as far as Isla Guadalupe (Guadalupe Island) nearly 400 miles away.

Time series of surface observation data from Santa Barbara Municipal Airport [click to enlarge]

Caldor Fire approaches South Lake Tahoe

August 31st, 2021 |
Suomi NPP and NOAA-20 (as indicated) VIIRS Day Night Band visible (0.7 µm) imagery, 11-31 August 2021 (Click to enlarge). Sacramento CA is at the western edge of the imagery, and Reno NV is along the northern boundary.

Day Night Band imagery collected from the VIIRS-Today website, above, shows night-time snapshots of the Caldor Fire (discussed previously here, here and here on this blog) as it formed and moved towards Lake Tahoe in August 2021. On 31 August, the last day of the animation, the fire was close enough to the city of South Lake Tahoe that evacuation orders for that town have been issued.

The longer animation, below, shows the evolution of the Caldor Fire and the Dixie Fire complex as well (and is an update to this blog post).

Suomi NPP and NOAA-20 (as indicated) Day Night Band Imagery, 9 July – 31 August 2021 (Click to enlarge)

VIIRS imagery can also be used to outline burn scars from the fire. The ‘False Color’ RGB image below, from 30 August 2021 (from this url at VIIRS Today), depicts just how large the burn scar (the brownish region in the imagery) from the Dixie Fire is.

NOAA-20 False Color imagery from 30 August 2021 (Click to enlarge)

Smoke from wildfires in Northern California

August 25th, 2021 |

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

GOES-17 (GOES-West) True Color RGB images created using Geo2Grid (above) showed the diurnal variation of smoke from the Dixie Fire, Beckwourth Complex, Caldor Fire and Tamarack Fire in Northern California on 25 August 2021. Early in the day, smoke from the previous day of fire activity that had settled into valleys was evident — but as daytime heating continued, this valley smoke was ventilated and mixed to higher altitudes, with new smoke plumes eventually developing as the fire activity ramped up again. Occasional pyrocumulus clouds were produced by the larger, hotter fires.

===== 26 August Update =====

In GOES-17 True Color RGB images on 26 August (below), less cloudiness allowed a clearer view of the smoke from these wildfires.

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

In a toggle between Suomi NPP VIIRS True Color RGB and False Color RGB images (below), the large wildfire burn scars appear as shades of reddish-brown in the False Color image (these VIIRS images were downloaded and processed by the SSEC/CIMSS Direct Broadcast ground station). At that time, dense smoke from the Caldor Fire was restricting surface visibility to 3/4 mile at South Lake Tahoe, California.

Suomi NPP VIIRS True Color RGB and False Color RGB images [click to enlarge]

Enhancing Smoke Detection with Red Visible imagery

August 18th, 2021 |
GOES-16 Visible Imagery (0.64  µm), 1501-1857 UTC, 4 August 2021 (Click to enlarge) 2-km resolution shown, using mean pixel values

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?

HRRR Smoke forecast of Vertically Integrated Smoke at 1500 UTC on 4 August 2021, an 8-hour forecast from the 0700 UTC Model Run (Click to enlarge)

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).

GOES-16 Visible Imagery (0.64  µm), 1501-1857 UTC, 4 August 2021 (Click to enlarge) 2-km resolution shown using minimum pixel values

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.

GOES-16 Visible Imagery (0.64  µm), 1501-1857 UTC, 4 August 2021 (Click to enlarge) 2-km resolution shown using minimum pixel values

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