Operational Status of NOAA-16 Level 1B

MEMORANDUM FOR: All NOAA-16 Level 1B Data Users

FROM: Barbara Banks
Chief, Information Processing Division

SUBJECT: Operational Status of NOAA-16 Level 1B Data

On February 27, 2001, the Information Processing Division declared all
level 1B and 1B* data operational. These data are now available to the
user community. Effective immediately any changes to the level 1B/1B*
data will be made in accordance with the policy outlined below.
Investigations of the anomalies seen in the Advanced Very High
Resolution Radiometer (AVHRR) level 1B data are still underway.
However, the Information Processing Division (IPD) has implemented
corrections to improve the level 1B data. In the event that the true
cause of the errors are determined and corrected on-board the
spacecraft, all ground corrections will be discontinued and the user
community will be notified.

Current corrections to the level1B data are as follows: (The Direct
Readout user community should perform similar updates to correct the

All instruments: The along track errors seen in the NOAA-16 instrument
data is under investigation. To correct the earth location data for all
instruments, a pitch type attitude correction of -0.44 degrees should be
applied to the data along with the reported SOCC clock error correction
(see the TBUS bulletin or

AVHRR: An across track error in the AVHRR data is under investigation.
The error seen in the earth location data can be corrected by using a
max scan angle of +/-55.25 degrees instead of +/-55.37 degrees.

HIRS: A mirror misalignment was discovered that is causing an apparent
roll error of +1.8 degrees. To properly earth location the HIRS data it
is necessary to apply a constant attitude correction to adjust for the
across track error. A correction of approximately -1.8 degrees should
be used as a constant roll offset.

HIRS Collocation With Other Instruments: Users that collocate HIRS
with other instruments will not have a problem if they rely on the
corrected earth location data. If they are using the spot numbers to
match up the data then the HIRS data must be shifted before it will
match with the other instruments.

If you have any questions or concerns, please contact Emily Harrod at
301-457-5247 or via e-mail to

March 14, 2000

Current Level 1B Notification Policy (subject to change under the
unified policy and as more structure is added):
Calibration Updates
No Prior Notice - AVHRR visible calibration updates
- Parameter limit changes
1 to 2 weeks notice - STX antenna bias updates

Software and Format Changes
1 to 2 weeks notice - No impact changes, data remains the
same or within threshold (can be extended to 30 days depending on need)
60 to 90 days notice - User updates required because of format

Parallel testing policy - at most 30 days depending on change

Additional Guidelines for Level 1B Updates and Notification
- Plans for future updates will be announced well in advance before
reaching the testing/implementation notification phase. A quarterly
notice announcing plans for possible operational changes and add info on
updates to a web page will be provided . STX - Trending tests are done
every 2 months with RFI updates sent out within a week after tests are
complete. A schedule will be worked out using this information to
perform updates within 2 weeks of receipt of the data. Test results
will be passed on to users along with the notification. When possible,
one week before implementation users will be sent the time (and orbit if
known) indicating when the update will go into operation. On the day
before, information on the first orbit affected by the change will be

- Users are asked to monitor the change when it actually happens and
provide feedback to confirm its successful implementation

- In-house testing will always include instrument scientists and
product area leads.

- Initial test data will be provided when the update announcement is
sent out. Data to cover the defined parallel test period will be
provided. Parallel test data coming up to the implementation date will
be included to allow early switch over for some users.

- The best method of test data transmittal will be worked out on an
individual basis for those users requiring more than a few orbits a day
until a better system is worked out.

All notices can be found on the Pre-Product Processing (PPP) page under
“Level 1B Notices”,
RFI values can be found on the same page by clicking on the satellite
name. Currently, NOAA-15 is the only satellite that has RFI

Thresholds: John Derber of the National Weather Service has provided
information on reasonable threshold values for "small" changes to use
in determining the length time to allow for user testing and
modification before implementation of updates. User feedback is

HIRS Bias Std Dev. Max/Min
1-7 .05 .05 .2
8 .02 .05 .1
9 .1 .2 .5
10-12 .1 .15 .2
12-15 .05 .05 .2
16-19 .1 .2 .5

ALL .02 .05 .1

1,2,15 .1 .15 .2
3-14 .02 .05 .1