Mode 4 Testing for both GOES-16 and GOES-17

October 1st, 2018 |

GOES-17 upper-level water vapor infrared imagery (6.19 µm) from 1425-1550 UTC on 1 October (Click to animate)

GOES-17 Data shown in this post are preliminary and non-operational.

Continuous Full Disk (Mode 4) Testing is occurring on October 1 2018.   Mode 4 is the highest data flow rate for the ABI and results in a Full Disk image every 5 minutes.  No mesoscale sectors are produced during Mode 4 operations.  Five-minute CONUS imagery can be produced by subsecting the 5-minute Full-Disk Imagery.  This testing started at 0000 UTC on 1 October and will end at 0000 UTC on 2 October.

The animation above shows GOES-17 Full-Disk imagery for the upper-level water vapor imagery (6.19 µm) with a 5-minute cadence.  The GOES-16 animation for the same time and location is below.

GOES-16 upper-level water vapor infrared imagery (6.19 µm) from 1425-1550 UTC on 1 October (Click to animate)

Careful inspection of the imagery from the two satellites might reveal differences in brightness temperatures between the two instruments. This difference is due to view-angle differences. When the satellite is scanning near the limb, computed brightness temperatures will be cooler because more information detected by the satellite comes from the upper part of the atmosphere. Compare, for example, brightness temperatures just west of former Pacific Hurricane Rosa just west of Baja California. GOES-17, at 89.5 W Longitude, sees warmer temperatures than GOES-16 at 75.2 W Longitude. GOES-16’s view is more oblique, and is through more of the colder upper atmosphere.

GOES-16 and GOES-17 upper-level water vapor infrared (6.19 µm) imagery at 1500 UTC on 1 October 2018 (Click to enlarge)

(Update: GOES-16 returned to Mode-3 scanning at 1549 UTC on 1 October. Continuous Full Disk scanning on GOES-16 lead to degradation of derived products).

Update #2: Animations of 5-minute Full Disk GOES-17 Mid-level Water Vapor (6.9 µm) and “Red” Visible (0.64 µm) images from 0000-2355 UTC on 01 October are shown below.

GOES-17 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-17 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play MP4 animation]

One interesting feature on GOES-17 Visible imagery was the east-to-west progression of sun glint off the water of the Amazon River and its tributaries, beginning near the mouth of the river in northeastern Brazil and ending in Ecuador (below).

GOES-17 "Red" Visible (0.64 µm) images [click to play MP4 animation]

GOES-17 “Red” Visible (0.64 µm) images [click to play MP4 animation]

GOES-17 Status and Transition to Operational GOES-West

September 26th, 2018 |

Graphic showing Pixel sizes for Bands 1, 3 and 5 (0.47 µm, 0.86 µm, and 1.61 µm) when GOES-17 is on station at 137º W Longitude. The GOES-West CONUS domain (where 5-minute scanning is routine) is shown in dashed white; GOES-West default Mesoscale Sectors (where 1-minute scanning is routine) are shown in solid white.

This blog post contains information on GOES-17 and its transition to the operational GOES-West satellite at 137º W Longitude (a link is here). Much as the Advanced Baseline Imager (ABI) imagery from GOES-17 is preliminary and non-operational, the information in this blog post is also preliminary, and it will be updated as needed.

The 16 ABI Channels all passed beta status in August. (At that point, GOES-17 data started flowing over the GOES Re-Broadcast [GRB]). Beta Provisional means that there are issues remaining in the individual channels, but they have been identified and are being addressed. Provisional status is expected to occur on 28 November 2018 this year — when the satellite is on station at 137 W. When that provisional status occurs, GOES-17 data will start flowing into NOAA’s CLASS archive (link).

NOAA/NESDIS announced on 26 September that the GOES-17 Drift from the test position at 89.5º W will start on 24 October 2018 at 1740 UTC, reaching its location as GOES-West (137º W) on 13 November 2018. Because ABI data are not transmitted when GOES-17 is moving, this means GOES-17 data will not be available for those 3 weeks. (When GOES-16 transitioned from the test position at 89.5º to its present GOES-East location at 75.2º, the data were missing for 14 days, from 30 November 2017 to 14 December 2017. GOES-17 will move at 2.5º per day, faster than GOES-16 did during its transition.

At about the same time that GOES-17 moves, GOES-15 will be shifted eastward from 135º W to 128º W. This shift starts 23 October 2018 at 2015 UTC and is predicted to end on 1 November 2018 at 1900 UTC. In contrast to GOES-R, however, GOES-15 can continue to transmit data as it moves. When GOES-15 is at its new location, the GOES-15 GVAR stream will be bounced off of GOES-14 (located at 105º W).

All 16 ABI Channels from 00:07 to 23:57 UTC on 30 August 2018 (Click to view mp4 animation)

The GOES-17 Advanced Baseline Imagery (ABI) is affected by malfunctioning Loop Heat Pipes (LHPs) on the spacecraft. Loop Heat Pipes dissipate heat, and because heat around the ABI is not dissipated, the energy emitted by the warmed satellite contaminates the ABI sensors: the ABI will measure energy coming from the Earth but also from the satellite itself. The bottom line is that during the night hours, the sun warms the satellite faster than it can cool.

The animation above (courtesy Tim Schmit, NOAA/NESDIS and CIMSS) shows the effects of the malfunctioning LHP on the worst day. During the night time, longwave infrared imagery (that is, longer than 3.9 µm) deteriorates in quality for several hours around local midnight. (The animation also includes a solar exclusion zone before that deterioration)   Before sunrise, as the ABI is shaded more and more by the GOES-17 spacecraft, the imagery becomes useable again.

This effect varies with season. The plot below (from Dan Lindsey, NOAA/NESDIS at CIRA), shows the solar declination with respect to the satellite. As the value gets smaller, solar forcing on the ABI increases. The minimum value would occur at Equinoxes, but the time around the Equinoxes is also Eclipse Season for the satellite: it moves through the Earth’s shadow around local midnight, and that passage through the shadow mitigates heating effects. Thus, the maximum solar forcing on the ABI occurs about 3.5 weeks before the Equinox, and again about 3.5 weeks after.

Sun angle at local midnight for GOES-17. Heating of the ABI is stronger as the angle decreases. Blue shading indicates Eclipse Seasons when solar forcing at satellite midnight is mitigated by the spacecraft’s passage through the Earth’s shadow. (Click to enlarge)

The plot below (courtesy Mat Gunshor, CIMSS) shows how the Focal Plane Module (FPM) Temperature changes as a function of time. Without solar forcing (that is, during the day when the ABI is in GOES-17’s shadow), the FPM temperature is around 80 K. At night, when sunlight hits ABI, FPM temperatures increase, and the peak value, around 105 K, happened at the end of August. A similar value will occur in October when Eclipse season is over.

Focal Plane Module Temperature for Longwave IR (Band 14), August through mid-September 2018 (Click to enlarge)

The reported effect of this extra heat on ABI data availability has evolved since May (when reports of data availability for only 12 hours were common), as a team of Scientists and Engineers from NOAA, NASA and Harris Company have gained a better understanding of the problem and how the effects of the heat can be mitigated. The current best estimates are that ABI Channels 7 (3.9 µm) and below (visible and near-infrared) will operate within design specifications throughout the year. The majority of the time will be when all channels provide good data throughout the day, but there will also be times, when solar forcing warms the ABI, that causes ABI data to be contaminated and likely unusable for a period around local satellite midnight (that is, midnight at 137 W Longitude). The water vapor channels (8, 9 and 10 at 6.19 µm, 6.95 µm, 7.34 µm), Ozone Channel (12, at 9.6 µm) and CO2 Channel (16, at 13.3 µm) will have 4-6 hours of bad or missing data; the infrared cloud phase/SO2 channel (11, at 8.46 µm) and the Dirty Window Channel (15, at 12.3 µm) will have around 3 hours of missing data; Window channels 13 and 14 (10.3 µm and 11.2 µm, respectively) will likely transmit useable data even during the warm season. However, data from those two window channels may be biased. This is all still under investigation, and these estimates are valid as of mid-September 2018. Scientists and engineers are still working to mitigate the problem and to adjust the way ABI is calibrated given the non-optimal operating temperature. The times of the year when data is most likely to be affected by LHP problems will be as the satellite approaches and exits Eclipse Seasons.

Top: GOES-17 Full Disk 12.3 µm Infrared Brightness Temperatures; Bottom: Time series of GOES-16 and GOES-17 Band 15 (12.3 µm) Brightness Temperatures averaged over a region (of size 401×401) centered over Florida from 00:02 UTC to 23:57 UTC on 30 August 2018 (Click to play mp4 animation)

The animation compares GOES-16 and GOES-17 “Dirty Window” 12.3 µm infrared brightness temperatures averaged in a 401×401-sized box centered over Florida.  There is excellent agreement before and after the issues associated with extra heating because of faulty LHPs.

Note that GOES-15 data may be used to supplement GOES-17 data during the times of data outage, although no decision has been made to operate GOES-15 long term.

Animations that show the evolution of the 16 channels through satellite midnight are available in PowerPoints here and here.

Fixed-Grid Format Data flowing in AWIPS

June 19th, 2018 |

AWIPS imagery of GOES-16 Low-Level Water Vapor (7.34 µm) at 1527 and 1532 UTC on 19 June (Click to enlarge)

Until today, GOES-16 Data that flowed into AWIPS was remapped twice: First, from the observational perspective (that is, how the satellite views it) to a spherical fixed-grid projection that approximates the Earth, and then to a Lambert Conformal projection with (for infrared data) 2-km resolution over the Globe. That Lambert Conformal data was then shipped to AWIPS, where the data were again re-projected into the observational perspective desired by the meteorologist.

The 2-km resolution of the data shipped to AWIPS before today is applicable only at the sub-satellite point (nadir) for GOES-16. Thus, the second remap was suggesting better resolution than was warranted by the data. Additionally, the number of data points needed to be sent was very big.

At 1532 UTC on 19 June, the first fixed-grid format data were directly shipped to AWIPS; remapping to a Lambert Conformal projection is no longer done upstream of AWIPS. The toggle above shows the difference in the 7.34 µm “Low-Level” Infrared Water Vapor imagery over the coast of Oregon, near 46º N, 124º W (very far from the GOES-16 sub-satellite point at 0º N, 75.2º W), in the AWIPS CONUS projection.  At 1532 UTC, after the double remap is removed, the pixels are more distinct, and as expected they splay away from the sub-satellite point.

Removing a remapping in the data processing means that pixel-sized extremes — such as overshooting tops, or fires — and gradients will be better represented in the data.  Consider the Clean Window (10.3 µm) Infrared imagery below of strong convection over the Gulf of Mexico east of Texas.  Overshooting tops Brightness Temperatures are colder and the tops themselves more distinct after 1532 UTC than at 1527 UTC.

AWIPS imagery of GOES-16 Clean Window Infrared Data (10.3 µm) from 1347 to 1612 UTC on 19 June. The animation pauses on the last double-remapped image at 1527 UTC, and the first fixed-grid format image at 1532 UTC (Click to enlarge)

 

See also this blog postThis training also discusses the remapping.  And here (or here) is the National Weather Service announcement on the change.

The 3.9 µm channel at night over very cold cloud tops

May 17th, 2018 |

GOES-16 ABI Infrared Imagery from 3.9 µm (Upper Left), 10.3 µm (Upper Right), 8.5 µm (Lower Left) and 12.3 µm (Lower Right), 0747 – 0832 UTC on 15 May 2018 (Click to enlarge)

When cloud top temperatures are very cold, the 3.9 µm imagery will have characteristics that suggest a noisy signal.  The 45-minute animation above shows a cold cloud top east of Florida in 4 different infrared channels:  3.9 µm (Upper Left), 10.3 µm (Upper Right), 8.5 µm (Lower Left) and 12.3 µm (Lower Right).  That the 3.9 µm image shows noise is not a new problem, as it was present in legacy GOES imagery as explained here.  At very cold temperatures the relationship between radiance (detected by the satellite) and temperature is highly non-linear, because of the character of the Planck function for that wavelength, meaning a very small change in radiance — within the noise — causes a large change in temperature (Compare the first two figures at this link for legacy GOES, for example).

Examine the two figures for GOES-16 below. They show the Planck curves for Band 14 (11.2 µm) and Band 7 (3.9 µm). Two things are apparent. Band 7 (3.9 µm), by design, covers a larger range of temperatures. In addition, very small changes in detected radiance (“counts”) at cold temperatures cause very big changes in the 3.9 µm brightness temperature. The relationship between detected radiance and very cold temperatures is much smoother at 11.2 µm.  The 3.9 µm band lacks precision compared to the other window channels, such as the 11.2 µm, for very cold temperatures. 

Plot of discrete values of Radiance vs. 11.2 µm brightness temperatures (190 K to 420 K) according to the Planck Relationship (Click to enlarge)

Plot of discrete values of Radiance vs. 3.9 µm brightness temperatures (190 K to 420 K) according to the Planck Relationship (Click to enlarge)

A zoomed-in view for cold brightness temperatures between 190 and 230 K (-83.15º C to -43.15º C) is shown below. If a true temperature of 208 K is being sensed by the satellite at the two wavelengths, it will be well-resolved at 11.2 µm, but the 3.9 µm detection will jump between 205 K and 210 K: the nature of the relationship between radiance and brightness temperature is such that there is less precision at the colder end at 3.9 µm. In the 30 K range from 197-227 K, just 12 possible bits are available in the 3.9 µm band (12 out of 2^14 — 16,384; recall that Band 7 on ABI has the highest bit depth of all the channels).  A change of just one count is a large difference in 3.9 µm brightness temperature.

Users need smarter ways to enhance the coldest 3.9 µm to prevent the flashing pixels evident in common traditional color and black-and-white enhancements.  Consider creating a color enhancement that shows only one color at temperatures colder than, say, -40º C, because the detector does not precisely distinguish between the coldest temperatures.  In other words, don’t highlight the noise!  Conversely, don’t use the 3.9 µm imagery at night to discern cloud-top features.   During the day, solar radiation at 3.9 µm reflected off cloud tops causes an increase in apparent brightness temperature so this quantization noise does not occur.

Plot of discrete values of Radiance vs. 11.2 µm brightness temperatures (190 K to 230 K) according to the Planck Relationship (Click to enlarge)

Plot of discrete values of Radiance vs. 3.9 µm brightness temperatures (190 K to 230 K) according to the Planck Relationship (Click to enlarge)

As noted above, this is not a new problem. An image (produced using McIDAS-X) of an Mesoscale Complex over the Great Plains of the United States from GOES-16 is here at 10.3 µm and here at 3.9 µm; the same image from GOES-15 is shown here at 10.7 µm and here at 3.9 µm. In both shortwave images, speckling at very cold cloud top temperatures is apparent.

(Thanks to Mat Gunshor, CIMSS, and Tim Schmit, NOAA, for figures and comments on this entry)