Stray Light in GOES-13 Imagery

August 27th, 2014
GOES-13 3.9 µm infrared channel images (click to play animation)

GOES-13 3.9 µm infrared channel images (click to play animation)

GOES-13 is currently in Autumn Eclipse Season, when the Earth-Satellite-Sun geometry means that solar energy can reach the satellite sensors directly. NOAA NESDIS has software to mitigate the effects of Stray Light in the Sensor Processing System (SPS) that transforms the raw GOES Imager data to navigated and calibrated (GVAR) data. However, earlier this month, the SPS at Wallops inadvertently omitted the Stray Light Correction. The animation above, from 16-27 August, shows how Stray Light intruded into the 3.9 µm imagery on the GOES-13 Imager; on 25 August the Stray Light Correction was turned back on, and the final two images show no major Stray Light effects over the satellite view (Stray Light is still recorded in outer space). The animation above is for 5:15 UTC, when Stray Light affected the eastern part of the full disk scan. At 4:45 UTC, Stray Light affected the western part of the disk, and at 05:00 UTC, the central part of the disk.

Click here for more about the Stray Light Correction.

Fix for GOES-13 Sounder Pixel Drop-outs

March 24th, 2014
GOES-13 Sounder 10.7 µm imagery without and with Processing Software changes (click to enlarge)

GOES-13 Sounder 10.7 µm imagery without and with Processing Software changes (click to enlarge)

The GOES-13 (GOES-East) Sounder instrument has been experiencing data anomalies that manifest themselves as missing pixels (link, link). These errors occurred because of slight fluctuations in the speed of the sounder filter wheel, resulting in a time offset. Processing software expects the data to be present at a certain time, but because of the filter wheel speed fluctuations, data were not present when expected. All 19 spectral bands on the GOES-13 Sounder were affected.

Missing data can now be reclaimed using a modified version of the SPS (Sensor Processing System), the ground software that makes the GVAR data stream. GOES Engineers have been testing this software change. The test software modifications properly handle the slight differences in the timing of the data. As of this time, a date has not been slated for operational implementation by NOAA NESDIS.

An example with all 19 bands of the GOES-13 Sounder is shown below, with the current pixel drop-outs (top) and after the software changes were applied (bottom) as part of off-line testing (image toggle).

GOES-13 Sounder imagery (all 19 bands) [click to enlarge]

GOES-13 Sounder imagery (all 19 bands) [click to enlarge]

GOES-13 Sounder imagery (all 19 bands) produced with new processing software [click to enlarge]

GOES-13 Sounder imagery (all 19 bands) produced with new processing software [click to enlarge]

Changes to the routine GOES-13 Scanning Schedule

March 4th, 2014
GOES-13 10.7 µm images (click to play animation)

GOES-13 10.7 µm images (click to play animation)

Tests are underway this week to determine the impact of augmented GOES-13 (GOES-East) imager coverage. The animation above shows the coverage for routine scanning on 3 March 2014 between 1645 UTC and 1945 UTC. CONUS, Extended Northern Hemisphere and Full Disk images are included. The Optimized GOES-East schedule is available at this link. Note the presence of solar RFI (radio frequency interference) in the 1645 UTC image; solar contamination resulted in no 1702 UTC image at all, as expected (link).

The difference in CONUS coverage is shown below in the toggle of the 1732 UTC image from 3 March and the 1730 UTC image from 4 March. The Optimized Image scan allows for more routine scanning of the Caribbean Sea, for example.

GOES-13 10.7 µm images at ~1730 UTC on 3 and 4 March (click to enlarge)

GOES-13 10.7 µm images at ~1730 UTC on 3 and 4 March (click to enlarge)

Side-by-side views of GOES-13 10.7 µm images.  CONUS from 3 March, 1732 UTC (left) and Optimized CONUS from 4 March, 1730 UTC (right) (click to enlarge)

Side-by-side views of GOES-13 10.7 µm images. CONUS from 3 March, 1732 UTC (left) and Optimized CONUS from 4 March, 1730 UTC (right) (click to enlarge)

A side-by-side image of the regular and optimized CONUS scans is shown above. Note that the optimized scan has a slightly different time (Nominal times for each image are in the panel labels). Thus, batch jobs that access imagery by time must be altered. Side-by-side imagery for the entire test period is below. The 1645 UTC imagery should cover the same domain, but RFI interference is different on the two days. The test period ends before the 1902 UTC image. In the animation below, the CONUS images at half-past the hour show the increase in domain size.

Side-by-side views of GOES-13 10.7 µm images, 1645 UTC through 1902 UTC on March 3 2014 (Left, default schedule) and March 4, 2014 (right, optimized schedule). (click to animate)

Side-by-side views of GOES-13 10.7 µm images, 1645 UTC through 1902 UTC on March 3 2014 (Left, default schedule) and March 4, 2014 (right, optimized schedule). (click to animate)

Four-hour animation of Puerto Rico Regional Sector, 17-20 UTC on 4 March 2014 (click to enlarge)

Four-hour animation of Puerto Rico Regional Sector, 17-20 UTC on 4 March 2014 (click to enlarge)

As noted above, the optimized scan strategy significantly improves coverage in the Caribbean. In fact, the Puerto Rico Regional Sector is now almost completely covered. The animation above shows that sector for 2 hours with the expanded coverage during the test, and the subsequent two hours. Compare, for example, the 1830 UTC image, during the test, to the 1931 UTC image after the test (image toggle comparison).

GOES-13 Navigation anomalies due to a maneuver

February 19th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

A GOES-13 (GOES-East) North/South Station Keeping maneuver was performed on Wednesday, February 19, 2014, beginning 1145 UTC, and ending at 1945 UTC (Link). During this time, the navigation of the satellite degraded mostly in the north-south direction. At 1945 UTC, after the maneuver ended, the navigation snapped back to normal. (Compare the 1932 and 1945 UTC images).

Navigation error tracking is available online for some geostationary satellites. For example, this link, off this page, shows landmark errors from MTSAT. NOAA’s OSPO maintains a site for GOES satellites; however, results are posted weekly. (Link).