Satellite Liaison Blog

No, VIIRS did not capture a Donut dropping powdered sugar near the North Pole! On 12-13 Aug 2022, the VIIRS Snowmelt RGB revealed a Polar Mesoscale Cyclone depositing fresh snow across the Arctic, which was apparent under the clear skies in its wake (Fig 1 and 2). The unique combination of spectral channels, not available on GOES-R series ABI, allows for one to differentiate fresher snow cover from older snow cover and ice (see other examples here and here). In this case, the most recent snow cover is obvious as a trail of a relatively lighter shade of blue atop the darker shades of the older snow cover. In fact, one may note three distinct shades of blue, or snow ages, in this domain. The background/oldest snowpack on ice appears as the darkest shade of blue, the most recent swath the lightest, and a series of swaths perpendicular to the recent swath that exhibit shades of blue somewhere in the middle (Fig 3).

The Snowmelt RGB can be useful operationally, including at lower latitudes, for determining the type of precipitation that has fallen (rain, snow, freezing rain), assessing the blowability or runoff/flooding potential of snow cover, and as a tool to determining cloud microphysics. The VIIRS Snowmelt RGB can be viewed online at the CIRA SLIDER, and very soon, to a CIRA SLIDER – VIIRS CONUS sector to better accommodate the viewing of VIIRS imagery over CONUS.

Bill Line (NESDIS/STAR), Curtis Seaman (CIRA), John Forsythe (CIRA), Carl Dierking (UA/GINA)

GOES-West Operational Interleave began today (8/1) at 1700 UTC, and will continue through Sep 6. What does this mean to NWS users? GOES-West ABI Imagery (single-band imagery, band differences, RGBs) is now from GOES-18. Other GOES-West products, such as from GLM, and ABI derived products (cloud products, TPW, DMWs, etc) remain from GOES-17. Hence, “Interleave”. Why? GOES-18 ABI Imagery reached Provisional Validation maturity on July 28, meaning it is suitable for the broad user community. We are also entering a GOES-17 ABI Warm Period, which results in degraded GOES-17 LWIR imagery due to the cooling system failure. Therefore, the GOES-18 imagery will be distributed instead of that from GOES-17 from 8/1 to 9/6. The transition on 8/1 was successful, with GOES-18 imagery appearing in NWS AWIPS, as well as webpages like CIRA SLIDER and the STAR GOES Image Viewer.

From an AWIPS SBN perspective, no changes were needed at the individual locations. GOES-West imagery (from GOES-18) is loaded from the menu system as one normally would. Procedures containing GOES-West imagery load as usual. If you load imagery from the product browser, you will notice the addition of GOES-18 to the “Satellite” drop-down. The GOES-18 label will now appear in the product legend. GOES-West meso sector requests will continue as usual, with the meso sector imagery coming from GOES-18.

One may notice vertical striping at night in the Nighttime Microphsyics RGB and Nighttime Fog Difference. Details of the subtle GOES-18 Ch07 “Barcode Artifact” can be found here.

The transition from GOES-17 to GOES-18 imagery at 1700 UTC is shown below in various Imagery products. All examples begin with GOES-17, and transition to GOES-18 after 1700 UTC (midway through each animation). All examples are saved from AWIPS (SBN dataflow), with the exception of Geocolor, which was captured from CIRA SLIDER. Since we are already entering the warm period, the imagery degradation can be seen in the impacted GOES-17 imagery.

Starting with Ch08 Water Vapor imagery, the transition from GOES-17 to GOES-18 at 1700 UTC is obvious, as the horizontal striping associated with the cooling system failure is apparent in the GOES-17 portion of the animation, but abruptly disappears in the GOES-18 portion. The GOES-18 imagery appears as one would expect, similar to that from GOES-16.

GOES-17 Ch13 is not as impacted by the cooling system failure, and therefore, the transition to GOES-18 is very smooth with no noticeable changes in imagery.

Split Window Difference imagery, which is used for the detection of blowing dust and moisture gradients, appears significantly cleaner in the GOES-18 imagery. Channel differences typically enhance noise present in imagery.

The Airmass RGB, which includes multiple LWIR channel differences, is also notably improved with the transition to GOES-18.

The Nighttime Microphsyics RGB, which also employs multiple IR channel differences, exhibits significant noise in the GOES-17 portion, and very little in the GOES-18 portion. Note, this animation is during the daytime, so influence of the ch07 “Barcode Artifact” is not apparent here in GOES-18 imagery.

GOES-17 to GOES-18 1-min mesoscale sector imagery is shown in the next animation. The transition to GOES-18 after 1700 UTC is not discernible.

The transition is also seamless in Geocolor imagery, shown in the final figure from GOES-17 and GOES-18 full disk imagery.

Bill Line, NESDIS/STAR and CIRA

GOES-18, the third satellite in the GOES-R series, launched on March 1, 2022. First light ABI imagery from 89.5W was released on May 11 and can also be found here and here. GOES-18 completed its drift to the ~GOES-West position on June 6. Early GOES-18 ABI imagery from this position can be found here and here and in the article/video here. The cooling system on the GOES-18 ABI was redesigned in order to prevent the issues that plague the GOES-17 ABI during certain time periods (GOES-17 LHP info). The redesign was successful, as the cooling system on GOES-18 is working as expected. GOES-18/GOES-17 interleave begins on August 1, meaning NWS users will be viewing GOES-18 imagery in AWIPS (instead of GOES-17) through September 6 (during the ABI Warm Period).

There is a minor artifact apparent in the GOES-18 Channel 07 3.9 um “shortwave IR” channel and associated multispectral products (band differences and RGBs). This artifact is not related to the cooling system, which is working correctly on GOES-18 ABI. Since this artifact is noticeable in some imagery products at times, it is important to acknowledge its appearance in the single-channel imagery as well as in multispectral imagery products. Given its appearance in imagery as a dynamic series of vertical striping, as you will see below, the artifact has been dubbed the “Barcode Artifact”. A Satellite Book Club Webinar discusses the issue in detail (link). This post will introduce the impact of the “Barcode Artifact” on the various imagery products available in NWS AWIPS that leverage the 3.9 um channel. The GOES-18 Transition to Operations page here also includes information on the Barcode Artifact (Downloadable PowerPoint). All of the imagery in this blog post was created in AWIPS from the CMIP files.

Summary up front: The “Barcode Artifact” is most apparent in band differences involving the 3.9 um band and in RGBs using those band differences. Most notable to NWS users is the presence of the artifact in the Night Fog Difference and Nighttime Microphsyics RGB. The artifact is most noticeable in cold scenes such as overnight, and in cold cloud tops. The vertical striping is very subtle in the 3.9 um single band imagery and associated RGBs (FireT RGB). The artifact appears to mostly serve as an annoyance, and should not impact a forecasters ability to analyze the imagery and diagnose relevant features.

The “Barcode Artifact” is not easily seen in single-band 3.9 um imagery. Therefore, routine day-to-day monitoring of the single-band 3.9 um imagery, such as for wildfire hot spots, when using typical ranges and colormaps, will not be impacted. The example in Figure 1 is of the single-band 3.9 um imagery over the western US from 12Z on July 23 to 12Z on July 24 with the AWIPS default rainbow colormap and default range of -109C to 127C. Compare the GOES-18 example in Fig 1 with the GOES-17 example in Fig 2. The imagery appears almost identical, but a keen eye can spot differences in the cold cloud tops over the southeast portion of the scene, as well as over the ocean during the overnight periods, with shifting and subtle vertical striping present in the GOES-18 imagery and not GOES-17.

Some may prefer a grayscale colormap when viewing 3.9 um imagery (black = warm to white = cold BTs), such as that shown in Figure 3, still with the default range. In this example, the only apparent artifact is again barely observed in the cold storm tops to the southeast and over the ocean overnight.

Using the same grayscale colormap, but spreading the range of colors across a smaller range of values (0C to 32C), the artifact finally becomes more apparent (Fig 4). The series of inconsistent vertical striping is detectable to the human eye at night across the full scene (start and end of animation), but especially offshore and in clouds. In comparison, the artifact is not present in similarly stretched GOES-17 imagery (Fig 5).

The Fire Temperature RGB leverages the single-band 3.9 um channel for hot spot detection. A day/night example over wildfires in Idaho reveals no noise that would hinder a forecasters ability to diagnose hot spots or other features (Fig 6). In this RGB, only values greater than 0C in the 3.9 um band contribute to the red component (relatively warm BTs), hence a lack of striping.

Another vital role of the 3.9 um channel is for low cloud and fog detection, when combined with the longwave IR clean window (10.3 um) channel in the “Night Fog” difference. This is where the the artifact becomes more noticeable in areas. In this blog post, the 10.3 um – 3.9 um difference is used with the AWIPS default fogdiff_blue colormap. Positive values, or light blue to dark blue, represent liquid cloud tops (lower-level clouds and fog), shades of gray to black are ice cloud tops (higher-level clouds).

During the same period and in the same location as in Fig 1, an array of vertically oriented stripes or bands is readily apparent shifting across the scene in the Night Fog Difference (Fig 7). The artifact is most apparent at night (start and end of loop), and in both cloud tops and clear skies over land and water. Despite the artifact, the various cloud features across the domain are still easily diagnosed and differentiated by the professional analyst. If users are aware of this artifact, other than being a slight annoyance, there should be little to no impact on ones ability to perform cloud analysis. In some instances, a cloud feature falling on the gradient of colors in a given colormap may appear to flash in and out artificially, particularly in the coldest of scenes (Alaska example below). Animations of images help the user to comprehend close to the actual cloud location/appearance.

Figure 8 includes a corresponding animation of the Night Fog difference from GOES-17. Notice the presence of horizontal striping during the nighttime hours, which are associated with the cooling system issue. The vertical “Barcode Artifact” apparent in the previous GOES-18 example is not detectable in the similarly scaled GOES-17 imagery.

Of course, the fog difference is an important component to a couple of AWIPS RGBs, namely the Nighttime Microphysics RGB. The vertical striping appears similarly in the RGB as it does in the fog difference, as is shown in Figure 9 zoomed in over southern CA and adjacent waters during the overnight period. GOES-17 imagery of the same product and timeframe does not show the artifact (Fig 10).

The more advanced “Geocolor” product also leverages the Night Fog difference (for low clouds) at night to highlight low clouds and fog as blue. The vertical striping appears similar across the region of low clouds as in previous examples, with analysis of low clouds still able to be accomplished (Fig 11).

The Day-Snow Fog RGB also incorporates the (reverse) Fog Difference (Fig 11-2). Vertical striping is not observable in this example, which isn’t surprising given it is a daytime and low-level application.

This fog difference is also included in the Day Cloud Convection RGB. In this case, the difference is leveraged during the day to differentiate small ice particles in the cloud top as a sign of active updraft regions, yellow in the RGB (Fig 12). The artifact is barely detectable in the cold storm tops in this RGB and example, and the important features and colors can be analyzed as with GOES-16 and GOES-17.

The previous examples are from the GOES-18 5-min PACUS sector, but the “Barcode Artifact” appears similarly across the Full Disk Sector and Mesoscale sectors. The example below reveals the appearance of the artifact in mesoscale 1-min Nighttime Microphysics RGB imagery off the southwest US coast on the morning of June 9 (Fig 13).

Alaskan NWS users will also notice the “Barcode Artifact” in GOES-18 imagery. Given the longer cool season, longer nights in the winter, and cooler temperatures overall, the artifact should appear more often in this imagery. The examples in Figures 14, 15, and 16 show GOES-18 1-min grayscale Ch07 single band imagery (-60C to 100C), the Fog Difference (-15C to 15C), and Nighttime Microphysics RGB from 12Z to 15Z on the morning of June 30 over the Aleutian Islands. The artifact is present across the cool scene, especially in the high-level cloud tops, but the various cloud features are still diagnosed and differentiated. As alluded to previously, some areas of low clouds (blue) in cool air mass cases such as this one appear to flash in and out due to the dynamic pattern of the vertical striping.

From around Hawaii, the the Fog Difference is shared during an overnight period (Fig 17). The banding is much less obvious compared to over Alaska, given the relatively warmer scene involved.

This post shared GOES-18 examples of imagery products, available in NWS AWIPS, that include the 3.9 um channel as a component, in order to characterize the impact of the “Barcode Artifact”. While the artifact is not readily apparent in the single-band imagery, it becomes obvious in channel differences (such as the Night Fog Difference), and multispectral products (RGBs and Geocolor) that leverage the differences, as a series of shifting vertical striping. The artifact is most apparent in cold scenes, such as at night, and in relatively cold cloud tops. In most situations, analysis of a scene should not be significantly hampered by the noise, and the user will view it as a slight annoyance. In particularly cold scenes, and depending on the colormap and range used, a given cloud feature may appear to flicker. Engineers continue to work toward a solution to the GOES-18 Channel 07 “Barcode Artifact”.

This CIMSS Satellite Blog also shares information about the “Barcode Artifact”.

Bill Line, NESDIS/STAR and CIRA

A long-lived thunderstorm traveling across northeast Colorado produced a reported Tornado near Fort Morgan, CO late in the afternoon on 6 July 2022. Partially overlapped GOES-West mesoscale sectors yielded 30-second imagery over the region. Recall, the partially overlapped 30-sec imagery cannot be viewed by default in AWIPS, but a simple menu addition unlocks the capability. Figure 1 shows the two GOES-West 1-min mesoscale sectors, offset in time by 30-sec, with the overlap region containing the 30-sec imagery highlighted in yellow.

Focusing on the supercell thunderstorm associated with the tornado report, a clear and long-lived Above Anvil Cirrus Plume, indicative of a particularly strong storm, is present through the 75 minute period (Figure 2). Also notable from the imagery is the orientation of the NWS Tornado warning polygons and Tornado LSRs with respect to the thunderstorm, and updraft region in particular, to the southwest. This is due to parallax, as the thunderstorm top is oriented away from the satellite sub-point, which in the case of GOES-West viewing the central high plains, is an orientation to the north and east of the ground feature. See this post for a graphic on parallax.

Bill Line, NESDIS/STAR and CIRA