Eddy in Lake Michigan

April 8th, 2017 |

GOES-16 Visible (0.64 µm) images, with hourly surface and ship reports plotted in yellow [click to play animation]

GOES-16 Visible (0.64 µm) images, with hourly surface and ship reports plotted in yellow [click to play animation]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

GOES-16 Visible (0.64 µm) images (above) revealed the presence of an eddy in the high-turbidity nearshore waters of southern Lake Michigan on 08 April 2017. The animation was created using 5-minute “CONUS” Sector images; an animation using 1-minute Mesoscale Sector images is available here.

A sequence of Terra and Aqua MODIS true-color Red/Green/Blue (RGB) images viewed using RealEarth (below) showed that the eddy began to develop on 07 April.

Terra and Aqua MODIS true-color RGB images from 07 and 08 April [click to enlarge]

Terra and Aqua MODIS true-color RGB images from 07 and 08 April [click to enlarge]

Eruption of Kambalny volcano in Kamchatka, Russia

March 25th, 2017 |

Himawari-8 Visible (0.64 µm) and Infrared Window (10.4 µm) images [Click to play animation]

Himawari-8 Visible (0.64 µm) and Infrared Window (10.4 µm) images [Click to play animation]

The Kambalny volcano in far southern Kamchatka, Russia erupted around 2120 UTC on 24 March 2017. A Himawari-8 “Target Sector” was positioned over that region — providing rapid-scan (2.5-minute interval) imagery — as seen in a 2-panel comparison of AHI Visible (0.64 µm) and Infrared Window (10.4 µm) data covering the first 7 hours of the eruption (above). Ash plume infrared brightness temperatures quickly became -40ºC and colder (bright green enhancement).

Himarari-8 false-color RGB images [click to play animation]

Himarari-8 false-color RGB images [Click to play animation]

Himawari-8 false-color Red/Green/Blue (RGB) images from the NOAA/CIMSS Volcanic Cloud Monitoring site (above) showed the ash plume drifting south-southwestward during the subsequent nighttime hours. It is interesting to note the formation and subsequent northwestward motion of numerous contrails (darker green linear features) across the region, due to the close proximity of a major Tokyo flight corridor.

True-color RGB images from Terra MODIS, Suomi NPP VIIRS and Aqua MODIS, viewed using RealEarth (below) revealed the long ash plume during the late morning and early afternoon on 25 March. The dark signature of ash fall onto the snow-covered terrain was evident on the Terra and Aqua images, just west of the high-altitude ash plume.

Terra MODIS, Suomi NPP VIIRS and Aqua MODIS true-color RGB images [Click to enlarge]

Terra MODIS, Suomi NPP VIIRS and Aqua MODIS true-color RGB images [Click to enlarge]

26 March Update: a closer view of Terra MODIS true-color images from 25 and 26 March (below) showed that the perimeter of the darker gray surface ash fall signature had fanned out in both the west and east directions.

Terra MODIS truecolor RGB images from 25 and 26 March, with arrows indicating the perimeter of surface ash fall signatures on each day [Click to enlarge]

Terra MODIS truecolor RGB images from 25 and 26 March, with arrows indicating the perimeter of surface ash fall signatures on each day [Click to enlarge]

GOES-16 Mesoscale Sectors: improved monitoring of fire activity

March 19th, 2017 |

GOES-16 Shortwave Infrared (3.9 µm, left) and GOES-13 Shortwave Infrared (3.9 µm, right) images [click to play MP4 animation]

GOES-16 Shortwave Infrared (3.9 µm, left) and GOES-13 Shortwave Infrared (3.9 µm, right) images [click to play MP4 animation]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

The ABI instrument on GOES-16 is able to scan 2 Mesoscale Sectors, each of which provides images at 1-minute intervals. For what was likely a prescribed burn in the Francis Marion National Forest (near the coast of South Carolina) on 19 March 2017, a comparison of 1 minute Mesoscale Sector GOES-16 and 15-30 minute Routine Scan GOES-13 Shortwave Infrared (3.9 µm) images (above; also available as a 50 Mbyte animated GIF) demonstrated the clear advantage of 1-minute imagery in terms of monitoring the short-term intensity fluctuations that are often exhibited by fire activity. In this case,  the intensity of the fire began to increase during 15:15-15:45 UTC — a time period when there was a 30-minute gap in routine scan imagery from GOES-13. The GOES-16 shortwave infrared brightness temperature then became very hot (red enhancement) beginning at 15:46:58 UTC, which again was not captured by GOES-13 — even on the 16:00 UTC and later images (however, this might be due to the more coarse 4-km spatial resolution of GOES-13, compared to the 2-km resolution of the shortwave infrared band on GOES-16). Similar short-term intensity fluctuations of a smaller fire (burning just to the southwest) were not adequately captured by GOES-13.

The corresponding GOES-16 vs GOES-13 Visible image comparison (below; also available as a 72 Mbyte animated GIF) also showed the advantage of 1-minute scans, along with the improved 0.5-km spatial resolution of the 0.64 µm spectral band on GOES-16 (which allowed brief pulses of pyrocumulus clouds to be seen developing over the fire source region).

GOES-16 Visible (0.64 µm, left) and GOES-13 Visible (0.63 µm, right) images [click to play MP4 animation]

GOES-16 Visible (0.64 µm, left) and GOES-13 Visible (0.63 µm, right) images [click to play MP4 animation]

 The rapid south-southeastward spread of the smoke plume could also be seen on true-color Red/Green/Blue (RGB) images from Terra/Aqua MODIS and Suomi NPP VIIRS, as viewed using RealEarth (below).

Terra MODIS, Aqua MODIS and Suomi NPP VIIRS true-color images [click to enlarge]

Terra MODIS, Aqua MODIS and Suomi NPP VIIRS true-color images [click to enlarge]

GOES-16 RGB Imagery in AWIPS

March 15th, 2017 |

0.64 µm, 0.86 µm and 1.61 µm imagery and the computed RGB from GOES-16. 1524 UTC on 15 March 2017 (Click to enlarge)

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.

The ABI on GOES-16 contains 16 Channels, and those channels can be combined into RGB Imagery to highlight features that the individual channels can identify (Click here for general information on RGBs). For example, the ‘Icing RGB’ in AWIPS (also called the ‘Day Land Cloud’ RGB) uses 1.61 µm imagery for the Red component of the RGB, the 0.86 µm for the Green component and the 0.64 µm for the Blue. (This is similar to the oddly-named EUMETSAT ‘Natural Color’ RGB). The toggle above shows the three individual channels, and then the combination in the RGB. A version of the RGB was sent in this Tweet from NWS Lincoln IL.

Cyan regions are those with high values from the green component (0.86 µm) and the blue component (0.64 µm) but little from the red (1.61 µm); such regions include snow on the ground, and/or glaciated clouds. Consider, for example, the toggle below between the 0.86 µm and 1.61 µm imagery.  Lake Effect clouds are distinct over Lake Michigan in both channels, where they show up against the dark background.  Snow on the ground and Water Clouds look very similar at 0.86 µm (or at 0.64 µm, part of the toggle at top of this blog post) and it’s difficult to distinguish clouds from snow over land in a still image.  However, the 1.61 µm imagery is much darker in regions of snow (most of the Midwest United States had snow cover on 15 March 2017).  Water-based clouds show up distinctly against the darker background in the 1.61 µm imagery, and the Lake Effect clouds can be seen easily over Indiana and Michigan. There is apparently some glaciation in the lake effect clouds over land, however, because they do have a cyan tint to them.

Note how the easternmost lake effect band over Lake Michigan shows evidence of glaciation in the clouds.  There is a noticeable change in reflectance between 0.86 µm and 1.61 µm in the toggle below — and that region also shows cyan in the RGB.

0.86 µm and 1.61 µm imagery from GOES-16. 1524 UTC on 15 March 2017 (Click to enlarge)

Over the East Coast, this RGB helps better discriminate between low clouds and high. The example below, also from 1524 UTC on 15 March, cycles through the three channels and then shows the RGB.  The gradual glaciation of the ‘ocean effect’ clouds over the Atlantic is apparent east of New Jersey, as is the glaciation of some of the clouds in the north-south frontal band offshore.  Low clouds are bright in all three channels (0.64 µm, 0.86 µm and 1.61 µm) and therefore appear white-ish in the RGB. Snow on the ground in clear skies is dark in the 1.61 µm imagery and cyan in the RGB.

0.64 µm, 0.86 µm and 1.61 µm imagery and the computed RGB from GOES-16. 1524 UTC on 15 March 2017 (Click to enlarge)

Long-time readers of this blog are familiar with a MODIS-based product that also uses the 1.61 µm channel (in the green and blue) and the visible channel in the red to produce a Snow RGB that has Red snow and cirrus clouds, as shown in this figure from this recent blog post. The key channel for snow-detecting or cirrus-detecting RGBs is the 1.61 µm Channel because ice crystals strongly absorb radiation at that wavelength, reducing the solar reflectance.

Fact sheets are available on the 0.64 µm, 0.86 µm and 1.61 µm Channels on ABI.

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Added, 17 March 2017

Icing RGB at 2002 UTC on 17 March 2017 (Click to enlarge)

The red visible (0.64 µm), veggie band (0.86 µm), snow/ice channel (1.61 µm) and RGB, above, gave information about snowcover in the Northeast in the wake of the strong winter storm on 13-15 March. The demarcation between snow and no snow is particularly apparent in central New Jersey. Note snow/land discrimination in the Veggie Band is reduced compared to the visible (click here for a toggle between the two channels) — because of very strong surface reflectance over bare ground. There are northwest-to-southeast streaks in the RGB imagery from southwestern Ontario into northeastern Pennsylvania. These are present because of cirrus clouds as highlighted by the Cirrus Channel at 1.38 µm.  The RGB is also able to distinguish between low clouds over western Pennsylvania, West Virginia and eastern Ohio (that are mostly white in the RGB) and higher ice-laden clouds that are cyan.

AWIPS Note:  Visible (0.47 µm and 0.64 µm) and Veggie Band (0.86 µm) imagery can show missing data in regions of high reflectance near solar Noon, because albedo values then can exceed 1.  When those bands are then used in RGBs, the missing data points are apparent. A fix on this to allow an albedo >1 is in progress.