NOAA-16 Along Track Error

After observing AVHRR images from NOAA-16 since we turned on corrections
based on a pitch attitude error, we are convinced that the along track error
is not due to a pitch error. The error appears as a clock error.

On Tuesday, April 17, we will switch the level 1B process to correct the
along track error using a +1 second in addition to the normal clock error.
This will improve the earth location data out along the limbs. The
improvement will be most significant in the higher latitudes. The user
will see changes in the earth location data that will improve the quality
with the clock correction offset reflecting a different range from current.
Also, the attitude correction information will become zero with the constant
attitude correction flag set to zero in the header record.

Normally, changes such as this (turning clock corrections on/off; turning
attitude corrections on/off) would be done immediately with short notice to
the user community. These are considered no impact changes to maintain or
improve the quality of the data or to correct problems that are making the
data unusable.

Please notify us, if you need test data. If this will create a problem for
you, please contact either myself or Vincent Tabor (
or phone 301-457-5247). Cecil Paris is on detail to another office for at
least 60 days and will not be available to address your inquiries.

Thank you.

* Emily D. Harrod
* Product Systems Branch
* Pre-Product Processing Group
* E/SP13, Federal Building #4, room 0318
* 5200 Auth Road
* Suitland, Maryland 20746-4304
* voice 301-457-5247
* fax 301-457-5199
* email