2008-04-22 MepOp Orbital Maneuvers
It has come to our attention that during instances when the MetOp satellite exercises orbital maneuvers the entire SEM-2 instrument is turned off. Unfortunately the data processing software does not recognize when the SEM-2 data processing unit (DPU) has been turned off and so assumes that the data received from the TED and MEPED detectors, that had been turned off, are valid in spite of the fact those data are zero-fill during these periods. The TED and MEPED instrument ON-OFF flags in the daily archive files are not properly set to OFF at these times.
Those periods of time during which the SEM-2 instrument on MetOp were turned off are:
April 19, 2007 between 0819:58 and 1616:14 UTC
April 24, 2007 between 0000:00 and 1359:27 UTC
July 12, 2007 between 0922:22 and 1538:22 UTC
Sept. 18, 2007 between 1454:10 and 2400:00 UTC
Sept. 19, 2007 between 0000:00 and 1402:58 UTC
Jan. 31, 2008 between 0921:30 and 1538:33 UTC
April 8, 2008 between 0732:23 and 2400:00 UTC
April 9, 2008 between 0000:00 and 0437:58 UTC
The TED and MEPED ON-OFF flags in the MetOp archive files for these days have been corrected and the corrected files are available.
2008-01-07 Revised NOAA-16 file for day 2007-07-09
It was discovered that orbital data contained in the NOAA-16 archive file for July 9, 2007 (day 190) was incorrect for times after 2035:11 UT. A revised NOAA-16 archive file for that day has been produced that eliminated records with incorrect orbital information.
2007-03-23 Revised NOAA-18 archive files
Revisions to NOAA-18 archive data files for July 23-24, 2005 and for the entire period July 11, 2006 through December 26, 2006 were necessary because incorrect calibration data for the TED instrument were used. These revisions impacted only the TED auroral particle energy flux values and many of the data quality flags. All of the MEPED data in the original archive data files were correct.
Users of TED data for these periods are advised to download the revised archive data files for NOAA-18.
2005-08-16 ERRATA: Software errors in unpackSem2.c since year
2000.
It has been brought to our attention by a user of POES SEM-2 data
that the C language archive unpacking routine returns anomalous
sensor values during periods where there are data missing as flagged
by 999. We have examined that code and uncovered two significant
errors in the C version of the code that have existed since 2000.
Both errors involve the way the C unpacker implements missing data
flags. The first error centered around the fact that missing data
flags associated with sensor data from the second half of the 32-second
archive record were being improperly unpacked from the binary archive
record. The consequences of that error were that TED and MEPED sensor
values during periods when data were missing were often improperly
flagged with valid data being set to -999. indicating missing data,
while entries that should have been flagged as missing data were
given count values of 19988488, the highest count value possible.
The second error also involved the implementation of missing data
flags and impacted P8 and P9 omni-directional detector data throughout
an entire 32-second archive record. The P8 and P9 data share the
same data word in the TIROS data format and readouts alternate between
the two. In the archive record the data listing for P8 alternates
between valid data readouts and values set to 0 in the archive format
while the P9 data alternates in the same fashion but with valid
readouts when the P8 value is zero. The existing documentation explains
this and a user is expected to extract only the appropriate entries
when using P8 and P9 data. During instances when data were missing,
the C unpacker assigned the missing data flag (-999.), in both the
P8 and P9 data, to the entry appropriate to 'no data' while the
entries appropriate to valid data were given count values of 19988488.
This count value is unphysical for P8 and P9 data.
Both these errors would have impact upon any analysis that had
not recognized these unphysical sensor count.
The FORTRAN version of the archive record unpacker did not have
either of these problems.
David S Evans <David.S.Evans@noaa.gov>
Corrected sofware (unpackSem2_v2.c) is now available
for distribution.
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