NOAA-18, All instruments, Turn on constant roll & clock corrections, 15 March 2006- Issued: 10 March 2006; time issued 1845 UTC

Date/Time(UTC) Message Issued:
10 March 1845 UTC

Satellite(s) Involved:

Instrument(s) Involved:
Clock Corrections - All Instruments
Roll Correction - AVHRR

Product(s) Involved/Affected:

Date/Time(UTC) of Initial Implementation:
10 March 2006, 1755 UTC (test system only)

Details/Specifics of Change:
Our product areas have expressed concern that the earth location errors seen in NOAA-18 AVHRR data are looking worse. We have been operating with no earth location data corrections turned on. To remove some of the errors seen in the AVHRR data, we will do the following
- Turn on clock drift corrections - The SOCC is performing daily spacecraft clock corrections to remove the drift error. However, there is still a residual error left from each update. We will turn on clock corrections in our level 1B preprocessor to remove what we consider the residual error. The error as report on 06 March is -229 milliseconds(ms) with a residual drift effect of about 1.3 ms per day.
- Turn on constant attitude corrections - In examining the HRPT and LHRR data, we have observed a roll error of approximately +0.1 degrees. We will turn on constant attitude corrections in the level 1B preprocessor to apply a correction for this error in GHRR, LHRR, and HRPT data.

The changes where implemented on our parallel test system today, 10 March 2006, around 1755 UTC beginning with the following passes.
We expect to put the changes into operations on 15 March 2006. Another email will be issued identifying the actual implementation time.

Contact Person(s) Name/Email/Phone Number for Questions:
Emily Harrod, 301-457-5247 ext 117
I-Yan Wang, 301-457-5257 ext 118

Web site(s) that contain other relevant information (where applicable): - History of level 1B notices - All user notices - SOCC polar satellite status - SOCC geostationary satellite statuss - SOCC morning reports

* Emily D. Harrod
* Computer Operations Branch
* Pre-Product Processing Group
* E/SP11, Federal Building #4, room 0318
* 5200 Auth Road
* Suitland, Maryland 20746-4304
* voice 301-457-5247 ext 117
* fax 301-457-5199
* email