GOES-12 Sounder Anomalies

November 25th, 2009 |

channel15loop

Measurements from the GOES-12 Sounder instrument have shown increased noise over the past weeks. The noise in the signal does not occur with any persistence, but it can be very noticeable, as shown in the loop above of gif imagery taken from the UW CIMSS Derived Products Page. The images above are for Channel 15 (4.4 microns, a wavelength used to investigate the upper atmosphere), a channel on the GOES-12 sounder that has shown considerable noise since launch. Note the marked increase in noise, however, for the 2300 UTC image in the loop.

In addition, increased noise is also affecting channels 13 and 14 (4.57 and 4.53 microns, respectively) and channels 16-18 (4.13, 3.98 and 3.76 microns, respectively). Compare the noise in the images from 25 November at 1800 UTC (significant, noticeable noise in Channels 13-17) and at 1700 UTC (Noise noticeable only in the usually noisy Channel 15).

These noisy satellite observations do impact derived products such as Precipitable Water cloud mask: The 1800 UTC product that uses the noisy data from 1800 UTC shows the speckled result of noise over the southern Plains; the 1700 UTC observations that use the cleaner 1700 UTC data, do not contain such speckles.) The affected channels are used to determine the cloud mask. When there is amplified noise — especially if it results in very cold temperatures that are inferred to be high clouds — then a faulty cloud mask is a result. This is especially true at night when the Channel 18 brightness temperature is compared to the Channel Channel 8, and a cloud is inferred if there is a significant difference between the two. See, for example, this image from 01 UTC on 24 November. The speckling in the cloudtop pressure over Texas results from subtle noise signals in the 3.76-micron band (Channel 18). If these sounder data are being used to quantify the presence of clouds, the increasing noise in the shortwave infrared channels may be problematic.

GOES-14, located above the Equator near 105 W, is currently undergoing science testing. A comparison of Sounder band 15 from GOES-12 to the same band on GOES-14 shows the remarkably cleaner signal from GOES-14.

GOES-12 is scheduled to remain the operational GOES-EAST through March of 2010. It will be replaced by GOES-13.

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