Updates for NOAA-16 and 15

On February 15, the following changes will be implemented
- NOAA-16 HIRS earth locations will be corrected by applying a constant
attitude correction to adjust for the across track error. A correction of
-1.8 degrees (error of +1.8 degrees) will be used as a constant roll

- A NOAA-16 HIRS CPIDS file will be updated to change the minimum number
of space FOVs needed to calculate space coefficients from 45 to 40 to
correct the problem where channels 17, 18, and 19 are periodically not

- The software to update the 24-hour calibration coefficients file
header will be modified to use a different algorithm to compute the variance
of the calibration slopes. The current algorithm uses a shortcut version of
the variance formula which is producing negative variances for NOAA-16 and
therefore preventing the automatic update of the slopes used for the level
1B HIRS earth view data. This algorithm change will effect both NOAA-15 and
16 HIRS calibration. On February 15, the algorithm change will be made for
NOAA-16 so that the 24-hour file will begin updating automatically. The
change will be made for NOAA-15 on February 21. Parallel testing is on

Changes on February 15 will be made between 10:30 am and 11:45 am local
time. The updates will be made after the following passes have been
The first orbits processed after the update will be:
The following passes will be received out of sequence and will be affected
by the change

On February 21, the following changes will be implemented:
- The algorithm used to update the NOAA-15 HIRS 24-hour calibration file
will be changed so that updates will happen more readily.

- The preprocessing software will be updated to correct an error in the
attitude algorithm that affects pitch angle adjustments to the earth
location data. This will be a no impact change.

- The along track and across track errors seen in the NOAA-16 instrument
data will be corrected by adjusting the earth location data with a pitch
attitude correction of -0.44 degrees (along track), by using the SOCC
reported clock error (along track), and by using a max scan angle of
+/-55.25 degrees instead of +/-55.37 degrees (across track).

- The preprocessing software will be updated to properly extract the
AVHRR dig-B and analog telemetry data for NOAA-16.

Parallel test data is available on the CEMSCS under the file names P1S and
P1B. Level 1B test data will be made available on the anonymous ftp site
( under the subdirectory pub\test1b\NOAA-16. Those
user that do not have access to the CEMSCS and need 24 hours of level 1B
test data should contact us.

Please contact us if you have any questions or problems.
Thank you for your support in our efforts to resolve the NOAA-16 and 15
problems as quickly as possible.

Emily Harrod/Cecil Paris