GOES-17 Scanning designed to reduce heating-caused data outages

April 24th, 2020 |

GOES-17 Upper Level Water Vapor (Band 8, 6.19 µm) Infrared Imagery, 0400-1620 (Click to animate)

NOAA/NESDIS has modified the GOES-17 Mode 6 scanning schedule during times of increased data-outages related to the faulty Loop Heat Pipe (LHP) mechanism (Blog Post 1, 2, 3 on that subject;  see also here) on GOES-17.  (The OSPO Notification is here).  Between 0600 and 1200 UTC, Full Disk scans are imaged every 15 minutes, rather than every 10;  the two flexible mesoscale sectors (including the one with a default location over Alaska) are scanned every 2 minutes, rather than every minute;  the GOES-17 ‘CONUS’ domain, also known as the PACUS domain, typically scanned every 5 minutes, is not scanned at all.  These modifications will be in place in 2020 from 9 April through 1 May, from 12 August through 1 September and from 14 October through 31 October.  Dates for 2021 (and beyond) have not yet been determined.  The ‘time-time’ chart for this modified scanning is shown below (figure source).

‘Time-Time’ chart for GOES-17 Scanning during Mode 3 Cooling operations. Cyan regions denote no ABI scanning activity, green regions are Meoscale sector scans, pink denotes the full disk scan. Other colors show navigation and calibration times. Note the lack of a 5-minute PACUS scan (Click to enlarge)

This change in scanning strategy mitigates heating-caused imagery losses because it reduces the amount thermal energy absorbed by the ABI when it is pointed towards a warm source (that is, Earth) instead of cold outer space.  By reducing the scanning periods, OSPO reduced (but did not eliminate) the span of time during which time data from many of the infrared channels of the ABI are unusable because of saturated sensors.

Note in the animation above how the time-step changes at 0600 UTC to every 15 minutes, and then changes back to every 10 minutes at 1200 UTC.  A slower animation from 0530 – 0630 UTC (link) shows that increment change more clearly.  Because the so-called CONUS scan does not happen, GOES-17 CONUS scan imagery is not available during this time window;  of course, data are available in the CONUS region via the every-15-minute Full Disk scans.

The image below, courtesy Mat Gunshor, CIMSS, (derived from this website) shows how this Mode 3 Cooling Operations reduces the window when data are unavailable.  The time span when data are unusable (highlighted by the green double-headed arrows) is shorter in 2020 as a result of this new scanning strategy.  Also, the peak Focal Plane Module (FPM) Temperature is reduced, which may have implications for the long-term health of the satellite.

Comparisons between GOES-16 and GOES-17 Low-Level water vapor infrared imagery (Band 10, 7.34 µm).  Julian day 104 from 2019 (left) and 2020 (right).  GOES-16 and -17 Full-Disk imagery at the end of the time series as shown.  Time series plots (bottom) show the Focal Plane Module (FPM) temperature (black) and the GOES-17 – GOES-16 brightness temperature difference (blue) for a region centered on the Equator equidistant between the two satellite sub-points.

GOES-17 ABI Temperature Data Quality Flags (TDQF) thresholds updated

October 2nd, 2019 |

Top: Thumbnails of GOES-17 and GOES-16 ABI Band 12 (9.6 µm) on August 1, 2019. Bottom: Time series of GOES-17 minus GOES-16 brightness temperature for a region located between the two satellites. Also plotted is the GOES-17 Focal Plane Temperature. The reduced duration of the GOES-17 data to be flagged is highlighted. [click to enlarge]

As of 19:45 UTC on August 8, 2019, the new Look-Up-Table (LUT) went into operations for use in the GOES-17 ABI Temperature Data Quality Flags (TDQF). These hotter thresholds are possible due to the recent implementation of the Predictive Calibration algorithm.  Note that the image also includes the percent good (and conditionally usable) values (flagged 0 or 1) for both GOES-16 and GOES-17 ABI. Recall there are 5 Data Quality Flags for ABI data:

  • DQF:percent_good_pixel_qf = 1.f ;
  • DQF:percent_conditionally_usable_pixel_qf = 0.f ;
  • DQF:percent_out_of_range_pixel_qf = 0.f ;
  • DQF:percent_no_value_pixel_qf = 0.f ;
  • DQF:percent_focal_plane_temperature_threshold_exceeded_qf = 0.f

The last one, DQF:percent_focal_plane_temperature_threshold_exceeded_qf, reports what percentage of the images pixels are warmer than the threshold value. Note that the thresholds on both the increasing and decreasing temperatures are also reported in the meta-data.

Near realtime brightness temperature comparisons between GOES-16 and GOES-17, as well as historical comparisons for a region centered on the equator and half way between the two satellites.

From the NOAA Notification:

Product(s) or Data Impacted: GOES-17 ABI auxiliary field change

Date/Time of Initial Impact: August 8, 2019 1945 UTC

Details/Specifics of Change:

The GOES-17 ABI Temperature Data Quality Flags (TDQF) thresholds for the thermal bands have been updated to the values in the table below.  This update will make utilizing the TDQF more effective for flagging saturated data caused by the GOES-17 ABI cooling system anomaly. There will be no impacts to distribution caused by this update.

Table of updated Temperature Quality Data Flag thresholds [click to enlarge]

Table of updated Temperature Quality Data Flag thresholds [click to enlarge]

Update (10/02/2019)

On October 2, 2019, at 17:04 UTC, updates for a number of the ABI GOES-17 DQF thresholds were implemented in the operational system. NOAA Notification: https://www.ospo.noaa.gov/data/messages/2019/MSG2751954.html

Table of updated Temperature Quality Data Flag thresholds

Table of updated Temperature Quality Data Flag thresholds [click to enlarge]. The bold numbers are those values that were updated on October 2nd. 

GOES-17 Loop Heat Pipe data outages reach seasonal peak

August 30th, 2019 |

All 16 GOES-17 Bands, 0750 – 1640 UTC on 30 August 2019 (Click to animate)

The periodic deleterious heating of the GOES-17 Advanced Baseline Imager (ABI) will reach a peak on 30 or 31 August 2019. The effects (in ABI bands 8-16) of the heating are manifest because the Loop Heat Pipe on the GOES-17 satellite does not operate at peak efficiency and cannot dissipate the heat that accumulates as the sun shines directly on the ABI instrument at night. The animation above shows full-disk imagery for all 16 bands on GOES-17 from 0750 UTC through 1640 UTC. Band 12 (9.6 µm) imagery is affected the most by the heating: data are unuseable from 1040 UTC to 1630 UTC; Band 10, the low-level water vapor channel at 7.3 µm is unuseable from 1050 UTC to 1620 UTC. Other infrared bands show different outages. Only Band 14 (11.2 µm) is mostly unaffected, although some striping is apparent between 1210 and 1330 UTC.

Other well-known artifacts are present in the animation. For example, a keep-out zone (or solar avoidance zone, sometimes also called the “Cookie Monster Effect”) is apparent moving across the northern 1/5th of the Globe; this image from 0910 UTC shows the feature. Satellite-Earth-Geometry means the Sun is near the limb of the Earth and the satellite sensors do not scan near the Sun. Stray Light is also present in the imagery. This shows up most distinctly in visible/near-infrared imagery, but its effects are also present in the 3.9 µm imagery.

The figure below, from this blog post, shows predicted maximum focal plane temperatures for each day.  In early September, a rapid cool-down in the peak temperature occurs as the GOES-17 satellite starts entering the shadow of the Earth during night times when it would otherwise be illuminated by the Sun.

Predicted warmest Focal Plane Temperature as a function of Year. Also included: the threshold temperatures when the ABI Detection is affected by the warmer Focal Plane. The step in values near both Equinoxes occurs when a Yaw Flip is performed on the satellite (Click to enlarge)

This website shows comparisons between GOES-16 and GOES-17 for different bands, and includes observations of the focal plane temperature.  The animation below shows the steady increase in the maximum focal plane module (FPM) temperature in August and that warmth’s impact on the Band 12 observations:  there are longer and longer periods of time with no GOES-17 Band 12 data as you move through August (indicated by difference values that are off the chart).

Mean Band 12 (9.6 µm) brightness temperature difference (between GOES-16 and GOES-17, plotted in blue) over a region on 27 July, 2 August, 10 August, 16 August, 22 August and 29 August 2019. The black line shows the Focal Plane Temperature (Click to enlarge)

A similar chart for Band 8 (6.19 µm) is shown below. Band 8 is not affected so severely by the Loop Heat Pipe. (Click here here for a similar chart for Band 14 (11.2 µm)).

Mean Band 8 (6.19 µm) brightness temperature difference (between GOES-16 and GOES-17, plotted in blue) over a region on 27 July, 2 August, 10 August, 16 August, 22 August and 29 August 2019. The black line shows the Focal Plane Temperature (Click to animate)

The intra-band differences on the effects of the excess heat are shown here for values on 29 August for Bands 8 (6.19 µm), 12 (9.6 µm) and 14 (11.2 µm).

Predictive Calibration is now operational for GOES-17

July 25th, 2019 |

Mean GOES17 – GOES16 Brightness Temperature Difference for a 401×1001 pixel footprint centered on the Equator halfway between the GOES-West and GOES-East subsatellite points. On 25 July (Red line), before Predictive Calibration was implemented, GOES-17 showed a warm bias as the Focal Plane Temperature (shown in black) increased, and a cold bias as Focal Plane Temperature decreased. On 26 July (green line), after predictive calibration was implemented, the large positive and negative biases are gone. (Click figure to enlarge)

Solar heating of the ABI instruments (on both GOES-16 and GOES-17) occurs at night around the Equinoxes. As the ABI points down to the Earth to observe the atmosphere and surface, sunlight falls on the ABI, warming it, and the Loop Heat Pipe that is not operating at capacity on GOES-17 does not circulate enough heat to radiators for dissipation to space. So, the temperature of the ABI increases during part of the night, reaches a maximum, and then decreases (as the solar illumination of the ABI decreases).

The change in temperature means that calibration looks at the Internal Calibration Target (ICT) within the ABI that occur regularly will quickly become invalid because of the changing temperature of the ABI. The images below show the temperature of the Focal Plane within the GOES-17 ABI in mid-June, in mid-July and in late July. For the best calibration, the focal plane temperatures would be steady. They are not. Note that the y-axis values are different in the plots. More significant warming is present in the latest plot and those peak values will steadily increase until Eclipse Season starts in late August. This blog post shows the effects of the warming in mid-April of this year. Predictive Calibration accounts for the change in the temperatures in between calibration looks and was implemented in the GOES-17 Ground Station at 1721 UTC on 25 July 2019. The beneficial effects of Predictive Calibration are shown in the figure (courtesy Mat Gunshor, CIMSS) above for ABI band 12; large warm and cold biases have been mitigated. ABI band 8 (6.2 µm) shows similar improvements.

Focal Plane Temperature as measured on the ABI on 19/20 June 2019, times as indicated. Note the baseline value near 81 K for both mid-wave infrared (MWIR, 3.9 µm – 8.4 µm) in red brown and long-wave IR (LWIR 9.6 µm to 13.2 µm) in green that increases to around 82 K around 1300 UTC

Focal Plane Temperature as measured on the ABI on 13/14 June 2019, times as indicated. Note the baseline value near 81 K for both mid-wave infrared (MWIR, 3.9 µm – 8.4 µm) in red brown and long-wave IR (LWIR 9.6 µm to 13.2 µm) in green that increases to around 84.5 K around 1300 UTC

Focal Plane Temperature as measured on the ABI on 24/25 July 2019, times as indicated. Note the baseline value near 81 K for both mid-wave infrared (MWIR, 3.9 µm – 8.4 µm) in red brown and long-wave IR (LWIR 9.6 µm to 13.2 µm) in green that increases to around 88 K around 1300 UTC

Warmest Predicted Focal Plane Temperature as a function of month. Also included: the threshold temperatures for each ABI band when the ABI output is noticeably affected by the warmer focal plane. The step in values near both Equinoxes occurs when a Yaw Flip is performed on the satellite (Click to enlarge)

The image above, (reproduced from this blog post and originally from here) shows the predicted focal plane maximum each day over the course of the year. It also shows at which temperature each band will marginally saturate, meaning that the effects of the warming ABI start to become noticeable.

The animation below shows the GOES-17 ABI Band 12 ‘Ozone Band’ (at 9.6 µm) that, according to the figure above is one of the first (along with Bands 10 — 7.34 µm — and 16 — 13.3 µm) to show the effects of the warming focal plane. Brightness temperatures warm before 1300 UTC and cool after 1300 UTC, and the amount of noise/stripeyness in the imagery increases  (This is most apparent at the northern edge of these 5-minute PACUS images).  These are all manifestations of the warming and cooling focal plane temperatures.

GOES-17 ABI Band 12 imagery on 18 July 2019, 0826 to 1501 UTC (Click to animate)

One week later, on 25 July 2019, below, the effects of the heating because the Loop Heat Pipe and radiator are not working at capacity are even more evident. The imagery exhibits a warm bias before 1300 UTC and a cold bias after 1300 UTC and the stripeyness of the image increases. Predictive calibration will mitigate the warm and cold bias.

Comparisons between individual bands from GOES-16 and GOES-17 for Full Disk and CONUS/PACUS views (in both cases in regions between the subsatellite points to minimize the effects of view angle) are available at this link, or also through this link.

GOES-17 ABI Band 12 imagery on 25 July 2019, 0836 to 1511 UTC (Click to animate)


======== ADDED, After Predictive Calibration was turned on ============
The animation below shows GOES-17 ABI Band 12 for the same time period as above, 0836-1511 UTC, but for the day after Predictive Calibration was implemented. You no longer see changes in observed brightness temperature that result from the warming focal plane temperatures. There is still some striping; this is associated with detector saturation and that striping will become more obvious in the next week and will lead to missing data. Predictive Calibration will not mitigate the issue of missing or striped data due to saturated sensors. Predictive Calibration is designed to mitigate warm biases before saturation, and cold biases after saturation.

GOES-17 ABI Band 12 imagery on 26 July 2019, 0836 to 1511 UTC (Click to animate)

The animation below (click to animate) shows both 25 July (left, before Predictive Calibration) and 26 July (right, after Predictive Calibration).

GOES-17 ABI Band 12 imagery from 0836 to 1511 UTC on 25 July 2019 (left, without predictive calibration) and on 26 July 2019 (right, with predictive calibration) (Click to play large animation)

You can view a short video on this topic here.