A prescribed burn in Montana, as viewed from GOES-15, GOES-16 and GOES-13

January 2nd, 2018 |

GOES-15 (left), GOES-16 (center) and GOES-13 (right) Shortwave Infrared (3.9 µm) images, with plots of hourly surface reports [click to play MP4 animation]

GOES-15 (left), GOES-16 (center) and GOES-13 (right) Shortwave Infrared (3.9 µm) images, with plots of hourly surface reports [click to play MP4 animation]

A prescribed burn the SureEnough fire — in central Montana was viewed by GOES-15 (GOES-West), GOES-16 (GOES-East) and GOES-13 Shortwave Infrared (3.9 µm) imagery on 02 January 2018. The images are shown in the native projection for each of the 3 satellites.

Due to the improved spatial resolution of the GOES-16 3.9 µm Shortwave Infrared band (2 km at satellite sub-point, vs 4 km for GOES-15 and GOES-13) and the more frequent image scans (routinely every 5 minutes over CONUS for GOES-16), an unambiguous thermal anomaly or fire “hot spot” was first evident on GOES-16 at 1707 UTC, just southeast of Lewistown (station identifier KLWT). The GOES-16 fire thermal signature was also hotter (black pixels) compared to either GOES-15 or GOES-13.

GOES-13 will cease transmission on 3 January 2018 [Update: 8 January]

January 2nd, 2018 |

GOES-13 Visible (0.63 µm) Image, 1745 UTC on 2 January 2018 (Click to enlarge)

The GOES-13 Satellite, operational as GOES-East from April 2010 through December 2017 (with a notable interruption) will be turned off sometime after 1500 UTC on Wednesday 3 January 2018. (Update: due to an impending East Coast winter storm, GOES-13 deactivation was postponed to 8 January)

The visible Full Disk image above, from 1745 UTC on 2 January 2018, is one of the last fully illuminated visible image the satellite will process.  (The first processed full disk visible image, from 22 June 2006, can be viewed here.)

On 28 December 2017, GOES-13 imagery included a view of the Moon, as shown here (and zoomed in here).  Future GOES-East imagery from GOES-16 will not include images of the Moon.  GOES-16 will scan the moon when it is near the horizon (and there are occasional GOES-16 mesoscale sectors placed over the Moon for calibration purposes).  However, GOES-16 imagery is remapped to Earth points before being broadcast to the public.  The Moon (happily) is not on the Earth and its points will not be remapped.

Thank you GOES-13 for your long years of service.  A full-resolution version of the image above is available here.

When Water Vapor Channels are Window Channels

January 2nd, 2018 |

GOES-16 Low-Level Water Vapor Imagery (7.3 µm), 1322 UTC on 2 January 2017 (Click to enlarge)

The very cold and dry airmass over the eastern half of the United States during early January 2018 is mostly devoid of water vapor, a gas that, when present, absorbs certain wavelengths of radiation that is emitted from the surface (or low clouds). That absorbed energy is then re-emitted from higher (colder) levels. Typically, surface features over the eastern United States are therefore not apparent. When water vapor amounts in the atmosphere are small, however, surface information can escape directly to space, much in the same way as occurs with (for example) the Clean Window channel (10.3 µm) on GOES-16 (water vapor does not absorb energy with a wavelength of 10.3 µm). The low-level water vapor (7.3 µm) image above, from near sunrise on 2 January 2018, shows many surface features over North and South Carolina, Kentucky, Tennessee and southern Illinois. The features are mostly lakes and rivers that are markedly warmer than adjacent land. (In fact, Kentucky Lake and Lake Barkely in southwest Kentucky are also visible in the 6.9 µm imagery!)

Weighting Functions from 1200 UTC on 2 January for Davenport IA (left), Lincoln IL (center) and Greensboro NC (right) for 6.2 µm (Green), 6.95 µm (blue) and 7.3 µm (magenta), that is, the upper-, mid- and lower-level water vapor channels, respectively, on ABI. Peak pressures for the individual weighting functions are noted, as are Total Precipitable Water values at the station (Click to enlarge)

GOES-16 Weighting Functions (Click here ) describe the location in the atmosphere from which the GOES-16 Channel is detecting energy.  The upper-level (6.2 µm) and mid-level (6.95 µm) weighting functions show information originating from above the surface.  Much surface information is available at Greensboro, with smaller proportional amounts at Davenport and Lincoln.

The “Cirrus” Channel on GOES-16’s ABI (Band 4, 1.38 µm) also occupies a spot in the electromagnetic spectrum where water vapor absorption is strong.  Thus, reflected solar radiation from the surface is rarely viewed at this wavelength.  The toggle below, between the ‘Veggie’ Channel (0.86 µm) and the Cirrus Channel (1.38 µm) shows that some surface features — for example, lakes in North Carolina — are present in the Cirrus Channel.

ABI Band 3 (0.86 µm) and ABI Band 4 (1.38 µm) (That is, Veggie and Cirrus channels) at 1502 UTC on 2 January 2018 (Click to enlarge)

Whenever the atmosphere is exceptionally dry, and skies are clear, check the water vapor channels on ABI to see if surface features can be viewed. A few examples of sensing surface features using water vapor imagery from the previous generation of GOES can be seen here.