Satellite Liaison Blog

By the morning of 10 October 2018, Hurricane Michael was a category 4 storm set to make landfall on the Florida Panhandle coast later in the day. GOES-16 had been providing 1-min satellite imagery over the storm during the days leading up to landfall, and collected 30-second imagery of the storm on the 10th to help support operations.

The VIS/IR sandwich product has been discussed in previous blog posts, and involves combining visible and IR imagery into one display to take advantage of both. The VIS provides high spatial detail, while the IR provides the quantitative brightness temperature information. In the past in AWIPS, users would overlay semi-transparent IR on the VIS to make this product. Recently, the OPG in collaboration with NWS created an RGB that combines the VIS and IR imagery into one. This allows for the high spatial detail of the VIS to show within the IR information noticeably better. The RGB is currently being tested in a few offices and tweaked to best fulfill forecasters needs.

Below is 40 minutes of 30-sec VIS/IR Sandwich RGB imagery over Hurricane Michael (Fig 1) on the 10th, along with corresponding VIS (Fig 2) and IR (Fig 3) imagery.

Figure 1: 10 October 2018 GOES-16 30-sec VIS/IR sandwich RGB. Full res

Figure 2: 10 October 2018 GOES-16 30-sec VIS. Full res

Figure 3: 10 October 2018 GOES-16 30-sec IR. Full res

Zoomed in view on Hurricane Michael center of circulation just prior to landfall (Fig 4).

Figure 4: 10 October 2018 GOES-16 30-sec VIS/IR sandwich RGB. Full res

GOES-16 Derived Motion Winds (DMW’s) were available every 2.5 minutes within the 30-sec meso sector (Fig 5). As one would expect, most of the winds were in the upper levels (0-250 mb = pink). Low level winds (blue) were computed around the outside of the storm.

Figure 4: 10 October 2018 GOES-16 2.5-min VIS, Derived Motion Winds. Reds = upper level, Blues = lower level. Full res

A daylong animation of the storm, including landfall, from GOES-16 5-min CONUS imagery (Fig 5). Note the eye holds together pretty well after landfall before filling in towards sundown.

Figure 4: 10 October 2018 GOES-16 5-min VIS/IR sandwich RGB. Full res

Bill Line, NWS

A compact shortwave trough skirting across the norther-central US/Canada border sent a cold front racing south down the central US plains during the day/evening of October 3, 2018.

GOES-16 15-min full disk water vapor imagery depicted the progression of the shortwave east along the US/Canada border (Fig 1). Since NWS/AWIPS does not display GOES-R full disk imagery at full resolution, I prefer to do my long, large scale water vapor analysis time-matched to the full disk imagery with the full resolution CONUS imagery overlaid. The cold front can also be diagnosed in water vapor imagery surging south through the plains, is especially apparent over the high plains, and forcing the development of convection from Kansas to Michigan.

Figure 1: 3-4 October 2018 GOES-16 15-min water vapor imagery. Full res

IR-Window imagery provides a highly detailed, both spatially and temporally, depiction of the cold air advancing through the plains (Fig 2).

Figure 2: 3-4 October 2018 GOES-16 15-min IR window imagery. Full res

The Land Surface Skin Temperature (Fig 3) and Total Precipitable Water (Fig 4) baseline derived products depict the cold and very dry airmass pushing south into the northern plains behind the front.

Figure 3: 3-4 October 2018 GOES-16 15-min Land Surface Temperature. Full res

Figure 4: 3-4 October 2018 GOES-16 15-min Total Precipitable Water. Full res

Bill Line, NWS

The NWS National Hurricane Center has requested GOES-16 1-min mesoscale imagery to support monitoring of Hurricane Florence since September 5. Previous blog posts have discussed the value of 1-min satellite imagery for analyzing tropical cyclones, particularly for identifying a center of circulation and for monitoring thunderstorm evolution. The Florence center of circulation appeared to have briefly revealed itself in 1-min VIS during the morning of 9 September (Fig 1). Thunderstorms in the vicinity of the storm center quickly obscured the view.

Figure 1: 9 September 2018 GOES-16 1-min visible imagery focused on Hurricane Florence. Full res

By 5 AM Monday, Florence had strengthened to a category 2 storm, with an eye apparent in satellite imagery. The storm was also quite large, as depicted in Figure 2, which shows the storm with respect to the full 1000 x 1000 km (at nadir) 1-min mesoscale sector. The westward shift of the sector is captured in the middle of the animation. Bermuda was well to the north of the forecast path.

Figure 2: 10 September 2018 GOES-16 1-min mesoscale sector 2 visible imagery, over Hurricane Florence. Full res

A little later in the morning on September 10, the NHC requested 30-second imagery over Florence (Fig 3). As a reminder, two sectors of 1-min imagery can be collected, OR one sector of 30-second imagery, from an ABI.

Figure 3: 10 September 2018 GOES-16 30-second visible imagery centered over eye of Hurricane Florence. Full res

Bill Line, NWS

Have you noticed stray light contamination in visible, near-IR and SWIR imagery at night (~0400 – 0600 UTC) recently? Missing pieces of images as well? Odd GLM behavior? This is due to light from the sun directly entering the imaging sensors during a period known as the eclipse season. The eclipse season occurs in the Northern Hemisphere during the Spring (late Feb to mid April) and Fall (late Aug to mid-Oct) every year. During this period, the satellite enters the shadow of the Earth during the late night hours. Sunlight enters the sensors and impacts the VIS/NIR/SWIR imagery and GLM as the satellite enters and leaves the Earth’s shadow. More details on this phenomenon can be found on the NESDIS/OSPO webpage here. According to NESDIS for the current eclipse season:

“Stray light contamination and truncated swaths during the GOES-East Fall 2018 eclipse season will be apparent on ABI imagery: Starting August 8, 2018 from approximately 0415 UTC – 0545 UTC each day in the Northern Hemisphere until September 22, 2018.”

Examples below are from GOES-16 (East) ABI and GLM. Figures 1, 2, and 3 are early in the eclipse season (20 August), and reveal the vertical beam of stray light contamination in ABI imagery. Notice the beam is apparent in the visible and shortwave IR channel, but is not apparent in the IR window channel.

Figure 1: 20 August 2018 GOES-16 5-min 0.64 um VIS. Notice vertical beam of light passing across CONUS. Full res

Figure 2: 20 August 2018 GOES-16 5-min 3.9 um SWIR. Notice warming of features, especially cold cloud tops, as beam of light moves through region. Full res

Figure 3: 20 August 2018 GOES-16 5-min 10.3 um IRW. Full res

Figures 4, 5, and 6 are later in the eclipse season. Stray light is still apparent, as well a canceled frames in all of the channels.

Figure 4: 4 September 2018 GOES-16 5-min 0.64 um VIS. Notice canceled frames and vertical light beam extending south. Full res

Figure 5: 4 September 2018 GOES-16 5-min 3.9 um SWIR. Notice canceled frames and warming of cold cloud tops. Full res

Figure 6: 4 September 2018 GOES-16 5-min 10.3 um IRW. Notice canceled frames. Full res

GLM data are also impacted during the same period, with the solar intrusion causing false events (Fig 7).

Figure 4: 5 September 2018 GOES-16 5-min IRW and 1-min GLM FED. False detections from GLM are apparent over the western half of the US between 0430 UTC and 0445 UTC. Full res

Bill Line, NWS

The default scan mode (as of the writing of this blog post) for GOES-16 (GOES-East), mode 3, provides a full disk image every 15-min, a CONUS image every 5-min, and two movable 1-min sectors. The GOES-East mesoscale sectors have default locations over the eastern half of the United states, and can be positioned anywhere within the full disk upon request. NWS entities have the highest priority for making requests, and any NWS WFO can make a request through their regional request focal point office.

Figure 1: GOES-East Mesoscale Domain Sector coverage for the afternoon of 3 September 2018. The sector over the northern plains covers a SPC slight risk, while the sector over Florida covers TS Gordon. Full res

When making a meso request, individuals should provide: their office, desired begin and end date/time of sector coverage, the center lat/lon of the sector in decimal degrees, and the rationale for the request. Try to make the request early in the day before the event begins, if possible.

In the event of more than two requests, a priority list is consulted. The priority list can be found in the document or slides at this NOAA VLAB page. When offices make a request, they should refer to this list and make sure they use the highest possible reasoning that applies to their CWA.

When deciding on the center lat/lon of the sector, offices should consider the threat not only within their CWA, but also around them. Instead of simply using a lat/lon in the center of the CWA, requestors should choose a lat/lon that covers their area plus as much of the rest of the threat area as possible. For example, choose a lat/lon that will cover most of the SPC convective outlook area, or SPC fire weather outlook area, or WPC excessive rainfall outlook area, etc. Also, try to keep most of the sector in CONUS in order to benefit as many NWS offices as possible. One can visualize the coverage of a sector  given a center lat/lon by consulting this CIRA webpage (Fig 2).

Figure 2: Screenshot from CIRA MDS preview webpage. Full res

Finally, if you think the 1-min imagery will be even remotely helpful in your area, make the request! If there are no requests, the sectors simply scan from their default locations, possibly going unused. National Centers also make requests, but offices should not assume this will happen. For severe threats, SPC will likely make requests for ENH or higher, and often will for SLGT as well. But it is recommended the WFO make the request to ensure coverage, especially for MRGL and SLGT.  And remember, once GOES-17 goes operational as GOES-West, there will be four total 1-min mesoscale sectors to work with!

Bill Line, NWS

You may have noticed a change to the GOES-R RGBs in AWIPS since the May/June 2018 RPM update. A new and improved method for calculating the RGBs was implemented. One of the most notable benefits of this change is that users can now control the ranges of the three RGB components based on the physical units (reflectance, brightness temperature), instead of the 0-255 color range as was the case before (Fig 1). Similarly, when sampling the RGB in AWIPS, users now see the physical units for each of the three RGB components (Fig 1). The new method for computing RGBs may also lead to improved performance on AWIPS workstations. Finally, minor projection issues are resolved with the new method.

Figure 2: 5 August 2018 GOES-16 Day Cloud Phase Distinction RGB, point sampling readout, and Composite Options. Full res

Users are reminded that the default RGB ranges were chosen for a reason, and altering them will change the interpretation of the RGB, potentially negatively.

Below is an example of how a user may alter an RGB (Fig 2 and 3). The “simple” Day Cloud Phase Distinction RGB is great for differentiating various cloud types and clouds from snow from bare land, during the day. In this RGB, however, the green component (0.64 um) becomes saturated fairly quickly (reflectance >78%). So, for example, forecasters cannot interrogate  features atop deep moist convection using this RGB that are otherwise apparent in visible imagery (texture, overshooting tops, etc) . This isn’t necessarily one of the purposes of this RGB, but a forecaster may want to expand it’s capabilities regardless. With the new design, a user can simply load the composite options for the RGB, and adjust the max for the green component up to, say, around 100%.

Figure 2: 5 August 2018 GOES-16 Day Cloud Phase Distinction RGB and point sampling readout. Full res

Figure 3: 5 August 2018 GOES-16 modified Day Cloud Phase Distinction RGB and point sampling readout. Full res

This change allows for details in the visible channel to be apparent in this RGB. However, users must keep in mind the green influence will be less for all features in the RGB. Low water clouds will appear closer to blue than blue/green, and snow will be a darker shade of green. Highly reflective cold cloud tops (deep convection) may appear more red than yellow.

Bill Line, NWS

Severe storms produced large hail (including significant) and tornados across Wyoming and Colorado on 29 July 2018. Strong northwest flow over a moist airmass led to very favorable shear and instability across the region, and a SPC Enhanced Risk for severe was in place. GOES-16 1-min imagery was available to support NWS forecasters during the event. Storms early on produced overshooting tops and above anvil cirrus plumes, a signature indicative of severe and significant severe potential. The plumes appear as smooth cirrus cloud features emanating from the overshooting top and downstream over the storm anvil. Cumulus clouds are also analyzed being drawn into the southern regions of the storms, indicative of strong inflow winds.

Figure 1: 29 July 2018 GOES-16 1-min VIS. Full res

A little later over east-central Colorado, a severe storm developed that produced a measured wind gust of 83 mph, along with hail at least 2.75″ in diameter (baseball). GOES-16 1-min imagery of this storm showed a large and persistent overshooting top and an above anvil cirrus plume (VIS, Fig 2). The corresponding 1-min IRW imagery (Fig 3) shows a large overshooting top (round region of coldest pixels) along with a relatively cooler area immediately downstream of the overshooting top (completing the thermal couplet) and a relatively cool region extending downstream above the anvil (above anvil cirrus plume). Overlaying a semi-transparent IRW on the VIS, we get the sandwich image combination (Fig 4). Radar imagery of the storm showed reflectivity over 80 dBz along with significant beam attenuation, indicating a lot of hail (Fig 5).

Figure 2: 29 July 2018 GOES-16 1-min VIS. Full res

Figure 3: 29 July 2018 GOES-16 1-min IRW. Full res

Figure 4: 29 July 2018 GOES-16 1-min IRW. Full res

Figure 5: 29 July 2018 KPUX 0.5 degree radar reflectivity. Full res

Bill Line, NWS