The GOES-17 ABI will be operating in Mode 6 as a test starting today, Nov 27 at 1400 UTC through 1700 UTC on Nov 30. Recall in Mode 3, the current default operating mode for GOES-16 and GOES-17 ABI, we get a Full Disk sector every 15-min, a CONUS/PACUS sector every 5-min, and two mesoscale sectors every 1 minute each. In Mode 6, the ABI scans a full disk sector every 10-min, a CONUS/PACUS sector every 5-min, and two mesoscale sectors every 1-minute each. As you can see, the only difference between the two modes is that Mode 6 provides a full disk image more often (six per hour) than mode 3 (four per hour). See table 1 for a comparison between the two scan modes. Also shown is Mode 4, which is also currently an option on the ABI’s. 

How Often Sectors Are Scanned in Each ABI Mode

Figure 1 is a 60 minute snapshot of all four sectors (Full Disk, PACUS, Meso-1, Meso-2) from the GOES-17 ABI in Mode 6 on Nov 27. As a comparison, Figure 2 provides the same snapshop for GOES-16 ABI operating in Mode 3. 

Figures 3 and 4 compare full disk scanning for GOES-17 in Mode 6 and GOES-16 in Mode 3 for a three hour period. During this period, the full disk is scanned by GOES-17 18 times, and by GOES-16 12 times.

Bill Line, NWS

GOES-17 data are preliminary and non-operational at the time of this post.

A Winter Storm delivered snow across a large swath of the US during Thanksgiving weekend. Clearing behind the system revealed the fresh snowfall. As has been discussed in previous blog posts, the increased spectral resolution of the ABI compared to previous GOES Imagers makes it easier to identify/differentiate surface and atmospheric features. By combining multiple channels into channel differences and RGB’s, it makes the job of the forecaster even easier to analyze these complicated scenes.

The scene across the central US behind the system included bare ground, lakes, fresh snow, water clouds and ice clouds. The latter three features are all highly reflective and difficult to differentiate in visible imagery (Fig 1).

Figure 1: 26 November 2018 GOES-16 0.64 um VIS. Full res

By combining the visible channel with the 1.61 um snow/ice near IR channel and the 10.3 um IR window channel, we have one image that contrasts those features while maintaining the 0.5 km high resolution of the VIS (Fig 2). This combination is known as the Day Cloud Phase Distinction RGB. In this example, the max bounds of the green and blue components were lowered to 50 and 40, respectively, while the min red component was decreased to 0. These changes were made in order to best highlight the features I was interested in for this situation (snow vs low clouds vs high clouds in a cold airmass). Bare ground is blue, water bodies are very dark blue to black, snow is green, water clouds are light blue/green, ice clouds are red.

26 November 2018 GOES-16 Day Cloud Phase Distinction RGB. Full res

Bill Line, NWS

With GOES-17 now at the 137.2W GOES-West position (not yet operational, though), Alaska has significantly improved satellite coverage. Imagery from GOES-17 is available every 15-min over Alaska from the full disk sector, and every 1-min (or 30 seconds) in a mesoscale sector upon request (previous generation GOES provided 15-min coverage over Alaska with a 30-min gap every 3 hours). However, spatial resolution is degraded so far from the satellite subpoint over Alaska. A 1 km pixel will have an approximate pixel area of around 4 km over southern Alaska and the Aleutian Islands, degrading to 8+ km over northern Alaska. Figures 1, 2, and 3 show 15-min full disk VIS, IR and WV imagery during the day on 19 Nov. An occluded low pressure system is diagnosed along the southern Alaska coast.

Figure 1: 19 Nov 2018 GOES-17 0.64 um VIS. Full res

Figure 2: 19 Nov 2018 GOES-17 10.3 um IRW. Full res

Figure 3: 19 Nov 2018 GOES-17 6.2 um WV. Full res

Since GOES-17 arrived at GOES-West and dataflow resumed, NWS offices in Alaska have taken advantage of the 1-minute mesoscale sectors.  On the evening of 16 Nov, WFO Juneau requested and was granted a sector through the next evening  for “Winter Storm Warning in area with no RADAR coverage.” During the morning of 17 Nov, WFO Anchorage requested a sector to run through the evening for “Winter Wx Advisory, no radar coverage, models under performing.” These sectors were positioned next to each other, providing widespread 1-min imagery over Alaska. The mesoscale sector coverage from the AWIPS GOES-West perspective is shown in Figure 4. For a more direct view of Alaska, AWIPS users can take advantage of the Alaska perspective, shown in Figure 5. The meridional stretching of the sectors (and embedded pixels) is apparent in the Alaska perspective. The southern extent of the sectors are cut off in the Alaska perspective in this example. Alaska offices have requested mesoscale sectors numerous additional times since the 17th.

Figure 4: 17 Nov 2018 GOES-17 1-min meso-1 and meso-2 sector 0.64 um VIS from GOES-West perspective. Full res

Figure 5: 17 Nov 2018 GOES-17 1-min meso-1 and meso-2 sector 0.64 um VIS from Alaska perspective. Full res

Most derived products are not yet available in AWIPS from GOES-17, but all imagery channels, channel differences, and RGB’s are. The Day Cloud Phase Distinction (DCPD) RGB, which provides great contrast of snow (green) vs low clouds (light blue) vs high clouds (red), benefits from some slight modifications to the recipe. These changes are necessary due to lower reflectance and cooler temperatures over Alaska compared to over CONUS, especially this time of year. Figure 6 shows the default DCPD RGB over Alaska on 17 Nov, while figure 7 shows the same RGB and time period with some adjustments to the RGB component ranges. The max value for the vis/nir components was reduced, and the min value for the IR component was reduced. Similar tweaks can be made to other RGBs in order to make them more usable in cold airmasses.

Figure 6: 17 Nov 2018 GOES-17 1-min Day Cloud Phase Distinction RGB over Alaska. Full res

Figure 6: 17 Nov 2018 GOES-17 1-min *modified for AK* Day Cloud Phase Distinction RGB over Alaska. Full res

As of the writing of this post, GOES-17 imagery is preliminary and non-operational.

Bill Line, NWS

GOES-17 arrived to the 137.2W, GOES-West position, on Nov 13. Dataflow from GOES-17 resumed on Nov 15. The below examples exemplify the scope of ABI sector coverage from the GOES-West position.

GOES-17 full disk sector imagery (updates every 15-minutes when in mode 3, every 5-minutes when in mode 4) from 137.2W includes much of North America (with best coverage over western parts) and much of the Pacific Ocean (with best coverage over eastern parts). The sector includes coverage of Hawaii and Alaska. Below are examples of GOES-17 Full Disk VIS, IR, and WV from 137.2W.

Figure 1: 17 November 2018 GOES-17 15-min Full Disk 0.64 um VIS Imagery from 137.2W. Higher res

Figure 2: 17 November 2018 GOES-17 15-min Full Disk 10.3 um IRW Imagery from 137.2W. Higher res

Figure 3: 17 November 2018 GOES-17 15-min Full Disk 6.2 um WV Imagery from 137.2W. Higher res

GOES-17 CONUS sector imagery (updates every 5-minutes) from 137.2W includes the western 1/3 of the US and Hawaii. Below are examples of GOES-17 CONUS VIS and IR imagery from 137.2W.

Figure 4: 17 November 2018 GOES-17 5-min CONUS 0.64 um VIS Imagery from 137.2W. Higher res

Figure 5: 17 November 2018 GOES-17 10.3 um IRW 5-min CONUS Imagery from 137.2W. Higher res

Like it’s predecessor, GOES-17 has two movable 1-min mesoscale sectors. These sectors can image anywhere within the full disk. Below is an example of the two GOES-17 mesoscale sectors with IR imagery from the default “GOES-West” mesoscale sectors positions.

Figure 6: 17 November 2018 GOES-17 10.3 um IRW 5-min CONUS Imagery from 137.2W. Higher res

Finally, full disk imagery of all 16 GOES-17 ABI channels from the 137.2 GOES-West position.

Figure 7: 17 November 2018 GOES-17 15-min Full Disk All 16 Channel Imagery from 137.2W. Higher res

A reminder that GOES-17 is expected to become the operational “GOES-West” on Dec 10. As of the writing of this post, imagery is preliminary and non-operational.

Bill Line, NWS