GOES-16 and Fog Detection

October 18th, 2017 |

GOES-16 Brightness Temperature Difference (10.3 µm – 3.9 µm) “Fog Product” from 0202 – 0357 UTC on 18 October 2017 (Click to animate)

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

Stratus and Fog formed over the valleys of Kentucky (and in surrounding states) early on 18 October 2017 (It was there on 17 October as well). When was the fog first obvious from Satellite imagery? It very much depends on the spatial resolution of the Satellite viewing the scene. The Brightness Temperature Difference field (10.3 µm – 3.9 µm) from GOES-16, shown above, can be used to identify regions of stratus clouds that are made up of water droplets. Carefully examine the animation; the time when fog is definitively present over valleys of eastern Kentucky (around 84º W Longitude) is around 0327 UTC.

GOES-16 has 2-km resolution (at the sub-satellite point — 89.5º W Longitude during GOES-16 Check-out); this is superior to GOES-13’s nominal 4-km resolution at the subpoint (75º West Longitude). The GOES-13 Brightness Temperature Difference Field (10.7 µm – 3.9 µm) at 0330 UTC shows no distinct indication of Fog/Stratus over eastern Kentucky. A series of animations of the GOES-13 Brightness Temperature Difference field, from 0215-0345 UTC, from 0415-0500, from 0545-0700 and from 0700-0815 suggest GOES-13 identified the region of fog about 4 hours after GOES-16, at 0730 UTC.

The GOES-13 vs. GOES-16 toggle below, from 0700 UTC on 18 October 2017, shows how the resolution improvement with GOES-16 facilitates earlier detection of fog and stratus as it develops overnight.

Toggle between 0700 UTC 18 October 2017 Brightness Temperature Differences from GOES-13 (10.7 µm – 3.9 µm) and GOES-16 (10.3 µm – 3.9 µm) (Click to enlarge)

Fog/stratus in the Strait of Juan de Fuca

May 20th, 2017 |

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

As seen in a Tweet from NWS Seattle/Tacoma (above), a plume of fog/stratus moved rapidly eastward through the Strait of Juan de Fuca on 20 May 2017. A closer view of GOES-16 Visible (0.64 µm) images (below; also available as an MP4 animation) shows the formation of “bow shock waves” as the leading edge of the low-level fog/stratus plume encountered the sharply-angled land surface of Whidbey Island at the far eastern end of the Strait near sunset — surface observations indicated that the visibility at Naval Air Station Whidbey Island was reduced to 0.5 mile just after the time of the final 0327 UTC image in the animation.

GOES-16 Visible (0.64 µm) images, with hourly plots of surface reports [click to play animation]

GOES-16 Visible (0.64 µm) images, with hourly plots of surface reports [click to play animation]

A Suomi NPP VIIRS Visible (0.64 µm) image with RTMA surface winds (below) indicated that westerly/northwesterly wind speeds were generally around 15 knots at 21 UTC (just after the primary fog/stratus plume began to move into the western end of the Strait). Four hours later, there was a northwesterly wind gust of 27 knots at Sheringham, British Columbia (CWSP).

Suomi NPP VIIRS Visible (0.64 µm) images, with RTMA surface winds plotted in cyan [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) images, with RTMA surface winds plotted in cyan [click to enlarge]

During the following nighttime hours, a Suomi NPP VIIRS infrared Brightness Temperature Difference (11.45 – 3.74 µm) “Fog/Stratus Product” image at 0910 UTC (below) revealed that the fog/stratus plume covered much of the Strait (especially along the Washington coast), and that the leading edge had begun to spread both northward and southward from Whidbey Island. In addition, note the presence of a linear ship track (darker red enhancement) extending southwestward from Cape Flattery.

Suomi NPP VIIRS Infrared brightness temperature difference (11.45 - 3.74 µm)

Suomi NPP VIIRS infrared Brightness Temperature Difference (11.45 – 3.74 µm) “Fog/Stratus Product” image, with RTMA surface winds plotted in cyan [click to enlarge]

Bill Line (NWS Pueblo) showed the nighttime fog/stratus monitoring capability of a GOES-16 infrared Brightness Temperature Difference product:


On a side note, in the upper right portion of the GOES-16 (as well as the VIIRS) visible images one can also see the hazy signature of glacial sediment  flowing from the Fraser River westward into the Strait of Georgia. Longer-term changes in the pattern of this glacial sediment are also apparent in a comparison of Terra MODIS true-color Red/Green/Blue (RGB) images (source) from 20 April, 07 May and 20 May 2017 (below).

 

Terra MODIS true-color RGB images [click to enlarge]

Terra MODIS true-color RGB images [click to enlarge]

Fog/stratus dissipation: 1-minute GOES-16 vs 15-30 minute GOES-13

April 4th, 2017 |

GOES-16 0.64 µm Visible (left) and GOES-13 0.63 µm Visible (right) images, with surface reports of fog plotted in yellow [click to play animation]

GOES-16 Visible (0.64µm, left) and GOES-13 Visible (0.63 µm, right) images, with surface reports of fog plotted in yellow [click to play animation]

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

Widespread fog and stratus had developed across southern Alabama and western Georgia during the pre-dawn hours on 04 April 2017. After sunrise, a comparison of 1-minute interval GOES-16 and 15-30 minute interval GOES-13 visible imagery (above) demonstrated the advantage of more frequent scans to monitor the dissipation of fog and stratus. The improved spatial resolution of the GOES-16 0.64 µm “Red visible” band — 0.5 km at satellite sub-point, vs 1 km for GOES-13 — also aided in the detection of smaller-scale river valley fog features.

Fog Detection using GOES-16 Channel Differences

March 6th, 2017 |

GOES-R IFR Probability Fields at 1230 UTC on 6 March 2017 (Click to enlarge)

Note: GOES-16 data shown on this page are preliminary, non-operational data and are undergoing on-orbit testing.

Here is what this blog post will show: It is vital to tweak the supplied default AWIPS Enhancements so that important atmospheric information is better highlighted.

GOES-R IFR Probability fields (Click here for a website that shows many examples), shown above, use present GOES Data and Rapid Refresh Data to forecast the probability that IFR conditions exist. (There are also Low IFR Probability fields and Marginal VFR Probability fields as well, data from this site). The inclusion of surface information via the Rapid Refresh Model output (that details low-level saturation) is vital to screen out false fog detection (regions where mid-level stratus does not extend to the surface) and to highlight IFR conditions that exist under cirrus that block the satellite detection of low clouds.

GOES-16 data in AWIPS includes pre-defined channel differences judged to have utility in Decision Support Services. One of these is Fog detection (the infrared Brightness Temperature Difference between 3.9 µm and 11.2 µm) that extracts information at night based on emissivity differences from water-based clouds at those two wavelengths. This is a product that can detect stratus clouds at night, if cirrus clouds do not block the satellite’s view. If those stratus clouds extend to the surface, then fog is a result. A GOES-16 Channel Difference field, shown below with the default AWIPS enhancement, contains information about the fog/low clouds that are present over North Dakota, and over Texas (click here for a graphic from the Aviation Weather Center that highlights regions of IFR conditions — Dense Fog Advisories were issued on 6 March over North Dakota).

The Fog signal in the Brightness Temperature Difference field at night occurs when the value is negative; the default color enhancement, below, contains a lot of color gradations that grab the eye in regions where the Brightness Temperature Difference is positive; for Fog Detection, those extra colors in regions of positive difference are needless visual clutter.

Brightness Temperature Difference fields (3.9 µm – 11.2 µm) over the United States, 1227 UTC on 6 March 2017 (Click to enlarge)

To get useful information from this field, alter the Brightness Temperature Difference enhancement to highlight negative values. That has been done in the toggle below with the IFR Probability field. Fog regions over North Dakota and Texas are apparent.  (Note that the scale for the Brightness Temperature Difference field here has also been flipped — click here to toggle between the two Brightness Temperature Difference field enhancements).

GOES-R IFR Probability fields and GOES-16 Brightness Temperature Difference fields, ~1230 UTC on 6 March 2017 (Click to enlarge)

GOES-R IFR Probability fields and GOES-16 Brightness Temperature Difference fields, ~1230 UTC on 6 March 2017 (Click to enlarge)

It is vital to tweak the supplied default AWIPS Enhancements so that important atmospheric information is better highlighted.