NOAA KLM User's GuideAppendix M |
The NOAA-15 S-band antenna anomaly was attributed to a mismatch of materials. The STX-1, STX-2, and STX-3 high gain antennas were fabricated using a non-conductive center core with four conductive strips coiled around it. A metal transition tab was attached to an end of each strip and is used to complete the antenna's electrical path. Regrettably, the metal transition tab and the center core had very different thermal expansion properties. As the STX antennas went in and out of sun conditions the material mismatch condition caused these tabs to experience a small movement. These movements introduced stresses and the tabs eventually cracked due to metal fatigue. The antenna's electrical path was then compromised.
The lost NOAA-15 STX down linkcapability was successfully recovered through the use of an operationalwork-around (as described in this appendix). The satellite's data sources were switched to use differently designed antennas, the STX-2 omni and the STX-4 omni.
A corrective redesign to future NOAA satellite antennas was performed. Starting with NOAA-16 the antennas now include stress relief in critical areas and a change of materials to better match the thermal expansion properties. A flight quality antenna was fabricated and subjected to 3675 thermal cycles. No electrical performance degradation was noted. The tested antenna was then disassembled, inspected, and the design was confirmed for flight.
The AMSU-B instruments on NOAA-16 and NOAA-17 were modified before launch to augment the radio frequency shielding within the receiver. Therefore their susceptibility to interference is much reduced compared with NOAA-15.
For NOAA-16 any interference effects are below the noise level of the instrument, so no correction tables are needed.
For NOAA-17 there is low-level interference on Channels 18 and 19. These biases are associated with STX-2 and STX-3. The maximum Earth view bias is 2K for Channel 19 and 1K for Channel 18.
The biases were characterized during the post-launch checkout period, and correction tables issued. Because the spacecraft transmitters are stable there is no need for any additional correction tables or bias detection schemes.
This appendix is an attempt to document the bias characteristics of the AMSU-B instrument for the NOAA KLM spacecraft. The changes are ordered chronologically in this appendix, beginning with the most recent to the earliest changes (note that the tables are numbered in reverse order because of this arrangement).
RFI corrections for the NOAA-15 SARR transmitter were updated in August of 2004. Corrections for the other transmitters remain unchanged. Count corrections for Earth views 1,5,10...90, Space view (91) and Target view (92).
Table M.9-1 AMSU-B RFI CorrectionsNOAA-15, Version 2.4 (13 August 2004).
| View | Channel # 16 | Channel # 17 | Channel # 18 | Channel # 19 | Channel # 20 |
|---|---|---|---|---|---|
| 1 | 0 | -10 | 24 | -434 | -173 |
| 5 | 0 | 0 | 22 | -421 | -180 |
| 10 | 0 | 6 | 14 | -408 | -178 |
| 15 | 0 | 10 | 8 | -344 | -162 |
| 20 | 0 | 11 | 4 | -246 | -143 |
| 25 | 0 | 10 | 0 | -147 | -125 |
| 30 | 0 | 7 | -3 | -79 | -104 |
| 35 | 0 | 3 | -5 | -41 | -81 |
| 40 | 0 | 0 | -7 | -26 | -59 |
| 45 | 0 | -2 | -7 | -35 | -44 |
| 50 | 0 | -5 | -5 | -55 | -73 |
| 55 | 0 | -6 | -2 | -93 | -46 |
| 60 | 0 | -8 | 0 | -168 | -70 |
| 65 | 0 | -7 | 4 | -277 | -102 |
| 70 | 0 | -7 | 8 | -386 | -136 |
| 75 | 0 | -7 | 10 | -461 | -144 |
| 80 | 0 | -6 | 12 | -491 | -139 |
| 85 | 0 | -5 | 12 | -472 | -121 |
| 90 | 0 | -5 | 9 | -389 | -83 |
| 91 | 0 | -2 | 1 | -74 | -16 |
| 92 | 0 | 0 | -2 | -25 | -15 |
Table M.9-1 AMSU-B RFI CorrectionsNOAA-15, Version 2.4 (13 August 2004).
| View | Channel # 16 | Channel # 17 | Channel # 18 | Channel # 19 | Channel # 20 |
|---|---|---|---|---|---|
| 1 | 0 | 0 | 0 | 0 | 0 |
| 5 | 0 | 0 | 0 | 0 | 0 |
| 10 | 0 | 0 | 0 | 0 | 0 |
| 15 | 0 | 0 | 0 | 0 | 0 |
| 20 | 0 | 0 | 0 | 0 | 0 |
| 25 | 0 | 0 | 0 | 0 | 0 |
| 30 | 0 | 0 | 0 | 0 | 0 |
| 35 | 0 | 0 | 0 | 0 | 0 |
| 40 | 0 | 0 | 0 | 0 | 0 |
| 45 | 0 | 0 | 0 | 0 | 0 |
| 50 | 0 | 0 | 0 | 0 | 0 |
| 55 | 0 | 0 | 0 | 0 | 0 |
| 60 | 0 | 0 | 0 | 0 | 0 |
| 65 | 0 | 0 | 0 | 0 | 0 |
| 70 | 0 | 0 | 0 | 0 | 0 |
| 75 | 0 | 0 | 0 | 0 | 0 |
| 80 | 0 | 0 | 0 | 0 | 0 |
| 85 | 0 | 0 | 0 | 0 | 0 |
| 90 | 0 | 0 | 0 | 0 | 0 |
| 91 | 0 | 0 | 0 | 0 | 0 |
| 92 | 0 | 0 | 0 | 0 | 0 |
| View | Channel # 16 | Channel # 17 | Channel # 18 | Channel # 19 | Channel # 20 |
|---|---|---|---|---|---|
| 1 | 0 | 0 | 0 | -2 | 0 |
| 5 | 0 | 0 | 0 | -2 | 0 |
| 10 | 0 | 0 | 0 | -2 | 0 |
| 15 | 0 | 0 | 0 | -2 | 0 |
| 20 | 0 | 0 | 0 | -4 | 0 |
| 25 | 0 | 0 | 0 | -9 | 0 |
| 30 | 0 | 0 | 0 | -16 | 0 |
| 35 | 0 | 0 | 0 | -25 | 0 |
| 40 | 0 | 0 | 0 | -29 | 0 |
| 45 | 0 | 0 | 0 | -29 | 0 |
| 50 | 0 | 0 | 0 | -25 | 0 |
| 55 | 0 | 0 | 0 | -21 | 0 |
| 60 | 0 | 0 | 0 | -18 | 0 |
| 65 | 0 | 0 | 0 | -15 | 0 |
| 70 | 0 | 0 | 0 | -5 | 0 |
| 75 | 0 | 0 | 0 | -2 | 0 |
| 80 | 0 | 0 | 0 | -6 | 0 |
| 85 | 0 | 0 | -5 | -21 | 0 |
| 90 | 0 | 0 | -10 | -34 | 0 |
| 91 | 0 | 0 | -16 | -81 | 0 |
| 92 | 0 | 0 | 0 | 0 | 0 |
| View | Channel # 16 | Channel # 17 | Channel # 18 | Channel # 19 | Channel # 20 |
|---|---|---|---|---|---|
| 1 | 0 | 0 | 0 | 0 | 0 |
| 5 | 0 | 0 | 0 | 3 | 0 |
| 10 | 0 | 0 | 0 | 3 | 0 |
| 15 | 0 | 0 | 0 | -3 | 0 |
| 20 | 0 | 0 | 0 | -13 | 0 |
| 25 | 0 | 0 | 0 | -18 | 0 |
| 30 | 0 | 0 | 0 | -19 | 0 |
| 35 | 0 | 0 | 0 | -22 | 0 |
| 40 | 0 | 0 | 0 | -30 | 0 |
| 45 | 0 | 0 | 0 | -40 | 0 |
| 50 | 0 | 0 | 0 | -37 | 0 |
| 55 | 0 | 0 | 0 | -30 | 0 |
| 60 | 0 | 0 | 0 | -19 | 0 |
| 65 | 0 | 0 | 0 | -7 | 0 |
| 70 | 0 | 0 | 0 | 0 | 0 |
| 75 | 0 | 0 | 0 | 2 | 0 |
| 80 | 0 | 0 | 0 | 3 | 0 |
| 85 | 0 | 0 | 0 | 3 | 0 |
| 90 | 0 | 0 | 0 | 3 | 0 |
| 91 | 0 | 0 | -8 | -20 | 0 |
| 92 | 0 | 0 | 0 | 0 | 0 |
| View | Channel # 16 | Channel # 17 | Channel # 18 | Channel # 19 | Channel # 20 |
|---|---|---|---|---|---|
| 1 | 0 | 0 | 0 | 0 | 0 |
| 5 | 0 | 0 | 0 | 0 | 0 |
| 10 | 0 | 0 | 0 | 0 | 0 |
| 15 | 0 | 0 | 0 | 0 | 0 |
| 20 | 0 | 0 | 0 | 0 | 0 |
| 25 | 0 | 0 | 0 | 0 | 0 |
| 30 | 0 | 0 | 0 | 0 | 0 |
| 35 | 0 | 0 | 0 | 0 | 0 |
| 40 | 0 | 0 | 0 | 0 | 0 |
| 45 | 0 | 0 | 0 | 0 | 0 |
| 50 | 0 | 0 | 0 | 0 | 0 |
| 55 | 0 | 0 | 0 | 0 | 0 |
| 60 | 0 | 0 | 0 | 0 | 0 |
| 65 | 0 | 0 | 0 | 0 | 0 |
| 70 | 0 | 0 | 0 | 0 | 0 |
| 75 | 0 | 0 | 0 | 2 | 0 |
| 80 | 0 | 0 | 0 | 0 | 0 |
| 85 | 0 | 0 | 0 | 0 | 0 |
| 90 | 0 | 0 | 0 | 0 | 0 |
| 91 | 0 | 0 | 0 | 0 | 0 |
| 92 | 0 | 0 | 0 | 0 | 0 |
March 15, 2001
An AMSU-B trending test was conducted on 3 March 2001. Channels 19 and 20 of the SARR table were affected, as well as Channel 19 of the STX-2 omni table. Transmitters STX-2 omni, STX-4 omni and SARR(A) are active. Count corrections for Earth views 1,5,10...90,Space view (91) and Target view (92).
| Transmitter: STX-2 Omni, Mean transmitter power: 114.0 counts> | |||||
| View | Channel # 16 | Channel # 17 | Channel # 18 | Channel # 19 | Channel # 20 |
|---|---|---|---|---|---|
| 1 | 22 | -218 | -30 | -91 | 87 |
| 5 | 21 | -249 | -15 | -92 | 93 |
| 10 | 18 | -245 | -1 | -85 | 89 |
| 15 | 13 | -208 | 7 | -69 | 72 |
| 20 | 8 | -138 | 11 | -48 | 48 |
| 25 | 5 | -67 | 11 | -27 | -24 |
| 30 | 2 | -24 | 10 | -9 | 6 |
| 35 | 1 | -15 | 7 | 0 | -1 |
| 40 | 0 | -16 | 4 | 2 | -2 |
| 45 | 0 | -23 | 0 | 4 | -2 |
| 50 | 0 | -28 | -1 | 4 | -2 |
| 55 | 0 | -33 | -3 | 1 | 0 |
| 60 | 0 | -23 | -3 | -2 | 4 |
| 65 | 0 | -12 | -2 | 0 | 7 |
| 70 | 0 | 0 | -1 | 2 | 8 |
| 75 | 0 | 1 | 0 | 3 | 6 |
| 80 | 0 | -1 | 1 | 0 | 3 |
| 85 | 0 | -2 | 2 | -2 | 4 |
| 90 | 0 | -3 | 4 | -1 | 6 |
| 91 | 0 | 0 | 0 | 0 | 0 |
| 92 | 0 | 0 | 0 | 0 | 0 |
An AMSU-B trending test was
conducted on 4 December 2000 and was based on internal consistency and comparisons with NOAA-16. This revision includes corrections for
anomalous bias, revised following trending tests of 3-4 November 2000 and updated for November drift. Only the channel 19 Earth-view SARR
table was affected. The STX-2 omni antenna was substituted for the STX-2 high-gain antenna. Transmitters STX1, STX2, STX3 and SARR(A) are
active. Counts corrections for Earth views 1,5,10...90, Space view (91) and Target view (92). November 9, 2000
An AMSU-B trending test was conducted on 3-4 November 2000. Results were as expected, i.e. a small change in the Channel 19 SARR interference, and
otherwise no significant change. Results agree well with those obtained by other methods, including comparison with NOAA-16.
The only change in the new bias correction is the SARR table for channel 19. Changes range from -0.8K (around
pixel 50) to +1.7K (pixel 20). The last update was issued in June 2000.
The STX-2 omni antenna was substituted for STX-2 high-gain. Transmitters STX1, STX2, STX3 and SARR(A) are
active. Count corrections for Earth views 1, 5, 10...90, space view (91) and Target view (92).
July 10, 2000 An AMSU-B bias trending test was conducted on 27-28 June 2000. Results of this test, plus monitoring of daily mean brightness temperatures and NWP model
comparisons, show that an update to the bias correction tables is required. The last update was issued in May 2000. Channel 19 bias due to SARR interference,
and to a lesser extent channel 20, is continuing to drift at up to 1K per month, depending on scan position. This does not appear to be directly related to temperature
change, or any other external factor. This time only the SARR table has been updated. STX-2 has not changed. AMSU-B Bias corrections, Version 2.0, 10 July 2000. STX-2 omni was substituted for STX-2 high-gain per Nigel Atkinson (UKMO). The other active transmitters include STX1, STX2, STX3 and SARR(A). Counts corrections for Earth
views 1, 5, 10...90, space view (91) and Target view (92).
May 4, 2000 An AMSU-B bias trending test was conducted on 26-27 April 2000. Results of this test, plus monitoring of daily mean brightness temperatures, show that a minor
update to the bias correction tables is required. The last update was issued in January 2000. Only the STX-2 and SARR tables have been updated. Differences are as follows: Channel 16: None Channel 17: Maximum change 1.3K, mainly affecting pixels 1-30. This is probably not an instrument change but rather an improvement in the characterization method.
Globally-averaged brightness temperatures were showing unrealistic structure between pixels 1-30, which has now been removed. Channel 18: None Channel 19: Maximum change 1.7K at pixels 1-10. This is real, and is probably associated with a change in thermal forcing. The bias pattern changed slightly
around 13th April, coinciding with a change from falling instrument temperatures to rising. Note that channel 19 shows the largest EMI effects and
is therefore the most sensitive to environment changes. Channel 20: None AMSU-B Bias corrections, Version1.9, 4 May 2000 includes corrections for anomalous bias. Revised following trending tests of 26-27 April 2000. STX-2 Omni substituted for STX-2 high-gain per Nigel Atkinson (UKMO). The other active transmitters include
STX-4 Omni and SARR. The STX-4 Omni does not appear to cause any interference, so there is no table for it. January 10, 2000: Revised following trending testsof 23 December 1999. STX-2 Omni antenna substituted for STX-2 high gain antenna. Transmitters STX-2 Omni, STX-4 and SARR(A) are operational per Nigel
Atkinson (UKMO). It should be noted that there is no correction table for STX-4 because it does not contribute to the interference with the AMSU-B instrument. January 4, 2000: After re-configuring the STX antennas on NOAA-15, the previous AMSU-B bias has been minimized and stabilized. The monitoring of this new configuration since September 28, 1999
has shown little change in the bias. Therefore, it has been decided to declare the NOAA-15 1b, 1b* AMSU-B Level 1b an operational product as of January 6,
2000. Bias correction updates will still be implemented to perform bias corrections as deemed necessary by the instrument scientists. December 1, 1999: Updated values for the antenna
bias will be implemented for NOAA-15. The changes are in response to the request to update the AMSU-B RFI Correction tables with data submitted by the
UK Meteorological Office (UKMO) on Nov. 12, 1999. The first orbits to be processed will be: NSS.HRPT.NK.D99335.S1709.E1721.B0806464.GC
scheduled to be ingested at 12:09 pm local time and NSS.GHRR.NK.D99335.S1535.E1707.B0806364.GC
scheduled to be ingested at 12:23 pm local time. November 24, 1999: The following updates to the
AMSU-B RFI bias corrections are based on the October 1999 trending tests (performed by the UKMO). These are the following differences compared with the previous version: 1) Only STX-2 and SARR have
changed (the other transmitters are not used operationally now, so the old values remain). 2) The largest change is for SARR in channel 19. Maximum change=3K. Would not expect any obvious difference in imagery products, but the new version
gives a much flatter scan-dependence when
compared with NWP model background. 3) Have left channel 18 completely unchanged. Changes in channels 17 and 20 are less than 1K. 4) Channel 16 uses a new technique involving AMSU-A to remove the unwanted effects of scene variation, the RFI corrections for this channel should be more
accurate than before (probably about 0.2K). Other channels should be within 1K. Channel 19 is the one most likely to drift with time. For RFI corrections, the users don't have to use the values in the Level 1b header if they don't want to. November 11, 1999: AMSU-B Bias corrections, Version 1.7, includes corrections for anomalous bias revised following trending tests of Oct 1999. STX-2 omni substituted for STX-2
high-gain. Based on October 1999 data. Transmitters STX1, STX2, STX3 and SARR(A) counts corrections for Earth views 1,5,10...90, Space view (91) and Target view (92).
Mean transmitter power in counts, ID=4. November 4, 1999: Since the launch of NOAA-15, the three high-gain antennas connected to three of the four NOAA-15 transmitters (STX), specifically STX-1, STX-2 and STX-3,
have experienced increasing performance degradation. In addition, STX-1 and STX-3 radio frequency interference is being received by the AMSU-B instrument.
The STX-1 high-gain HRPT antenna (1698.0 Mhz) is degraded to a level where small dish (1 m) users experience a significant number of HRPT dropouts, in many
cases rendering the data unusable. NOAA/NESDIS has reconfigured thespacecraft in an effort to maintain many of the missions of NOAA-15; i.e., readout of the full stored GAC data, HRPT direct
readout (which also includesthe HIRS and AMSU data), and HRPT Level 1b acquisitions at the NOAA CDAs. At 0100 UTC on 28 September 1999,
NOAA/NESDIS moved the HRPT service from STX-1 to the STX-2 OMNI antenna (1702.5 MHz). This transmitter/antenna combination has been tested with small dish
receiving stations, and has been found to provide satisfactory reception under most conditions. (The EIRP for the STX-2 OMNI is equal to or greater than 24
dBm over 90% of a sphere). The STX-2 transmissions are Right Hand Circularly polarized and compatible with existing HRPT antenna systems. This change is
permanent. APT service is not affected. Because of these antenna interference problems, all Level 1b AMSU-B data from NOAA-15 received between
launch and Sept. 28, 1999 should be considered unusable. A new bias correction table for the STX-2 OMNI antenna was included in the NOAA-K CPIDS AMSU-B
preprocessor since Sept. 15, 1999, and is therefore included in the AMSU-B data set header record. These bias corrections must be applied by the user. September 28, 1999: Table M.9-2 gives the bias corrections for AMSU-B for transmitters: STX2 Omni, STX3 and SARR(A). The
corrections (in counts) are provided for Earth views 1, 5, 10...90, Space view (91) and Target view (92) and the mean transmitter power is also given. January 4, 1999: The S band transmitters on NOAA-K have been shown to interfere with AMSU-B. The effect is largest on channels 17 and 19 but has been shown to be present in
the other channels also. The errors are largest in the Earth views, but space views and to a lesser extent internal target views are also affected. This appendix
describes the UK Meteorological Office (UKMO) recommendations for correcting the data. The largest Earth view biases are in channels 17 and 19, with a strong scan-dependence and maximum errors of approximately 40K when the STX-1 and SARR transmitters
are active. Since these transmitters are normally switched on all the time, the bias appears constant. The largest space view effect is in channel 17 when the STX-3 transmitter is active. This transmitter is currently used for data dumps to a ground station, typically
for 5-10 minutes per orbit (not every orbit). When the transmitter is on, the space view counts rise by the equivalent of approximately 5K and the internal target view counts
rise by approximately 1K. These rises cause errors in the calibration and result in Earth view brightness temperature errors of typically 2.5K at a scene
temperature of 200K, decreasing to1K at warm scene temperatures. The correction scheme described below applies both to users of the NESDIS Level 1b product and to users who receive the HRPT transmissions directly. When the scheme is
implemented, it is expected that the overall error will be reduced to approximately 1K for all channels. Note that on 13thOctober 1998, an additional bias appeared, which was largest on channel 17 (up to 60K additional error) but was present to some extent
on all channels. This new bias has been present on every orbit since then, and is present for typically 75% of every orbit. See Section M.10 for
further discussion of this problem. M.1 DISCUSSION The AMSU-B Level 1b dataset currently provides the following primary information: Space view counts and internal target counts are also present in the Level 1b dataset
but are not required by the user once the polynomial coefficients have been calculated. The Level 1b dataset is derived from the Level 1a dataset, which contains only raw instrument telemetry (i.e.
no conversion coefficients). In August 1998, a modification was made to the NESDIS Level 1b format to include information on the S-band transmitter status and output power levels. Thus, for any scan
line it is possible to determine which transmitters were on. This information is stored in the analog telemetry data field. In general, some of the transmitters are only
used during data downlinks (currently, STX-2 and STX-3) while others are on continuously (currently, STX-1 and SARR). The information available in the
Level 1b dataset is as follows: STX-1, STX-2, STX-3 and STX-4 status; STX-1, STX-2 and STX-3 output power; SARR-A and SARR-B output power. All values are in
the range 0 to 255 counts (representing analog voltages in the range 0 to 5.1 volts). For users of direct HRPT transmissions, the transmitter information may
be extracted from the TIP data which is embedded in the HRPT data frame - see Section M.8 for details. The correction scheme may be summarized as follows: The advantages of including the correction information in the Level 1b header are as follows: The advantages of making the space view and internal target view corrections at the Level 1A-Level 1b stage are as follows: Recent ground-based Electromagnetic Compatibility (EMC) measurements on the F3 instrument have shown that the counts (or temperature) error due to
interference is proportional to transmitter power. This cannot be verified at present on the spacecraft since the transmitter powers do not vary
significantly. However, it is recommended that the correction algorithm should make some allowance for future variations in transmitter power. The transmitter
powers reported in the analog telemetry are sufficiently noise-free that they can be relied on to provide an instantaneous measure of power. Errors due to
digitization of the analog powers are less than 0.5 percent, which would contribute less than 0.2K error if these powers were used to scale the AMSU-B
corrections (as outlined in sections M.3 and M.4). Strictly speaking the relationship between analog counts and actual transmitter power level is not linear. However, for the purpose of AMSU-B bias removal, a
linear relationship may be assumed, particularly since the transmitters are normally either fully on (with nearly constant power level) or fully off (with zero counts).
M.2 INFORMATION TO BE STORED IN THE HEADER Rather than attempting to identify which channels are susceptible to which transmitters, corrections are provided for all channels and transmitters. Thus,
some corrections may be zero. Transmitter - STX-1, STX-2, STX-3 and SARR. (STX-4 is not normally used, so may be ignored. Also, no distinction is made between SARR-A and SARR-B: only
one of these will be active at any given time). The count corrections are stored in the AMSU-B header record at byte offset 1001 (420 2-byte integers). The bias corrections in the header are given for 5
channels, 21 views, and 4 transmitters, in that order. The 21 views include 19 Earth scene views (views 1, 5, 10, 15, 20, ..., 85, 90) followed by cold and
warm calibration views. The order of the 4 transmitters is STX-1, STX-2, STX-3, and SAR. Transmitter reference powers - mean power at the time the above corrections were derived. The reference transmitter powers are stored at byte offset 1849 (four 2-byte integers, scaled by 10 x value in counts, i.e. a precision of 0.1 counts). The mean
transmitter power at which the bias corrections were determined are given for each transmitter, in the order STX-1, STX-2, STX-3 and SAR. This section applies to users of HRPT direct transmissions, or to users of raw GAC or LAC data. The transmitter powers for each scan line can be found at byte offset 2793-2802 in the AMSU-B data record (five 2-byte integer values, corresponding to STX1,
STX2, STX3, SARR-A and SARR-B). Note that since the update time of the analog parameters giving transmitter status is eight seconds, one or two AMSU-B scans before a transmitter switch-on
or switch-off could be wrongly corrected, both at this stage and at the later stage (see below) when scan-dependent corrections are made. To indicate this, a
scan-line quality flag is set if a transition was detected within ±3 scan lines of the one being calibrated. The quality flag is bit 4 of the quality indicator
at byte offset 25-28 in the AMSU-B Level 1b data record. For comparison purposes, the NESDIS Level 1b product will contain the uncorrected calibration coefficients in the 'secondary' coefficients locations
(byte offset 121-180 in the data record). These secondary coefficients are not normally used. Quality flags will be calculated based on the primary coefficients.
M.4 ADDITIONAL TASKS FOR THE LEVEL 1b USER The transmitter powers for each scan line can be found at byte offset 2793-2802 in the AMSU-B data record (5 2-byte integer values, corresponding to STX1,
STX2, STX3, SARR-A and SARR-B). Example FORTRAN subroutines to correct the Earth-view data are provided in Section M.7 M.5 DERIVATION OF CORRECTION DATA The correction data are obtained by examining the periods immediately before and immediately after a transmitter turn-off or turn-on. Changes in raw counts
are measured. By examining several on/off occasions a measure of the repeatability may be obtained. It is preferable to work in units of raw counts in order
to ensure that the space view, target view and Earth view corrections are independent. Also, it is known that the interference occurs in the 'back end' of the
receiver, i.e. after the stages which have the largest gain variations, so a correction in counts is more appropriate. The initial set of correction data (see Section M.9) are derived from the six transmitter on-off tests conducted between 24th August and
3rdSeptember 1998. Three of these were conducted over land areas ( Note that this is an objective test based purely on the AMSU-B data itself. It does not rely on any particular radiance forward model, though comparisons with forward models
can provide a useful additional check on the consistency of the AMSU-B radiances. M.6 INTERPOLATION METHODS The AMSU-B bias correction curves are essentially smooth curves that have been fitted to experimental data. Although there is insufficient space in the Level 1b
header to provide corrections for all pixels, it is possible to show that by providing corrections at five pixel intervals there is no significant loss of accuracy,
provided a suitable interpolation scheme is implemented. In other words, interpolation errors can be made small compared both with uncertainties in the bias and with
instrument noise. A simple linear interpolation method is simple to code and would result in interpolation errors of up to 0.5C; for many applications such errors may be acceptable.
However, to achieve the best results higher order interpolations are required. Many users will have access to cubic spline library routines, and these will give excellent results - within 1 or 2 counts of the original data values from which
the correction tables were derived. Alternatively, quadratic interpolation may be used in which a quadratic curve is provided between each pair of table samples. Any gradient discontinuities at the
table sample points will be small provided the second derivative of the correction curve is slowly varying relative to the sample spacing of the table. This is a
reasonable assumption for the AMSU-B application because of the underlying smooth nature of the correction curve. The overall accuracy is within 1 or 2 counts. This is
the method used in the example in Section M.7, and is nearly as simple to code as the linear interpolation. It is recommended as an
alternative to the use of cubic spline library routines. M.7 FORTRAN EXAMPLES Two example subroutines are provided below. The first may be used to interpolate the bias correction tables
in an AMSU-B Level 1b header. The second may be used to apply corrections to Earth-view data. M.8 LOCATION OF TRANSMITTER POWER DATA
Table M.9-5. AMSU-B Bias Corrections for NOAA-15, Version 1.9 (4 May 2000).
Transmitter: STX2 Omni, Mean transmitter power: 112.0 counts
View
Channel # 16
Channel # 17
Channel # 18
Channel # 19
Channel # 20
1
22
-218
-30
-84
87
5
21
-249
-15
-86
93
10
18
-245
-1
-79
89
15
13
-208
7
-63
72
20
8
-138
11
-44
48
25
5
-67
11
-25
24
30
2
-24
10
-10
6
35
1
-15
7
-1
-1
40
0
-16
4
1
-2
45
0
-23
0
1
-2
50
0
-28
-1
-1
-2
55
0
-33
-3
-4
0
60
0
-23
-3
-6
4
65
0
-12
-2
-6
7
70
0
0
-1
-4
8
75
0
1
0
-2
6
80
0
-1
1
-1
3
85
0
-2
2
-1
4
90
0
-3
4
-3
6
91
0
0
0
0
0
92
0
0
0
0
0
Transmitter: SARR, Mean transmitter power: 210.0 counts
View
Channel # 16
Channel # 17
Channel # 18
Channel # 19
Channel # 20
1
0
-10
24
-423
-166
5
0
0
20
-394
-165
10
0
6
14
-387
-168
15
0
10
8
-337
-164
20
0
11
4
-247
-152
25
0
10
0
-144
-131
30
0
7
-3
-64
-105
35
0
3
-5
-20
-77
40
0
0
-7
-2
-51
45
0
-2
-7
-6
-33
50
0
-5
-5
-18
-25
55
0
-6
-2
-38
-31
60
0
-8
0
-76
-47
65
0
-7
4
-144
-70
70
0
-7
8
-223
-90
75
0
-7
10
-293
-101
80
0
-6
12
-335
-100
85
0
-5
12
-332
-87
90
0
-5
9
-288
-75
91
0
-2
1
-74
-16
92
0
0
-2
-25
-15
Table M.9-2. AMSU-B Bias Corrections for NOAA-15 (as of 28 Sept 1999).
Transmitter: STX2 Omni, Mean transmitter power: 112.0 counts
View
Channel # 16
Channel # 17
Channel # 18
Channel # 19
Channel # 20
1
0
-263
-30
-102
98
5
0
-288
-15
-105
100
10
0
-263
-1
-97
93
15
0
-204
7
-80
77
20
0
-137
11
-57
54
25
0
-77
12
-32
29
30
0
-34
10
-13
8
35
0
-14
7
-4
0
40
0
-13
4
-3
-1
45
0
-20
0
-5
1
50
0
-26
-1
-7
3
55
0
-27
-3
-7
3
60
0
-23
-3
-6
2
65
0
-15
-3
-4
0
70
0
-6
-1
-3
0
75
0
-1
0
-2
0
80
0
-5
1
-1
0
85
0
-11
2
0
0
90
0
-7
4
0
0
91
0
0
0
0
0
92
0
0
0
0
0
Transmitter: STX3 Mean transmitter power=95.0 counts
View
Channel # 16
Channel # 17
Channel # 18
Channel # 19
Channel # 20
1
23
-48
33
-42
36
5
17
-40
25
-43
32
10
11
-16
18
-33
19
15
7
-2
14
-18
4
20
3
-6
12
-7
0
25
0
-26
14
-12
12
30
-1
-51
17
-21
29
35
-3
-62
19
-16
28
40
-4
-59
19
-5
12
45
-4
-49
16
0
0
50
-4
-36
12
-4
-4
55
-3
-25
9
-12
-1
60
-3
-16
7
-19
2
65
-2
-8
6
-17
0
70
0
-9
5
-10
-3
75
0
-28
3
-6
0
80
1
-50
0
-6
9
85
3
-52
-4
-9
12
90
4
-39
1
-9
13
91
6
-100
-1
-17
22
92
2
-17
1
0
1
Transmitter: SARR Mean transmitter power=209.9 counts
View
Channel # 16
Channel # 17
Channel # 18
Channel # 19
Channel # 20
1
9
-1
36
-582
-214
5
0
-1
20
-556
-217
10
-6
2
20
-520
-215
15
-9
0
21
-456
-206
20
-9
-4
19
-363
-191
25
-7
-3
13
-252
-168
30
-3
2
6
-146
-138
35
0
6
1
-70
-104
40
4
6
-1
-27
-71
45
6
2
-2
-9
-47
50
7
-2
0
-10
-34
55
6
-3
3
-22
-34
60
5
-2
6
-53
-47
70
1
-7
7
-187
-90
75
0
-7
7
-257
-100
80
1
-4
9
-304
-98
85
3
-2
12
-316
-87
90
8
0
7
-291
-71
91
0
-2
1
-74
-16
92
0
0
-2
-25
-15
!+
!ROUTINE: AMB_INTERPOLATE_EX
!
!DISCLAIMER: The UK Meteorological Office does not guarantee the correctness
! of this program and takes no responsibility for its use.
!
!PURPOSE: Example subroutine to interpolate AMSU-B bias correction values.
! Quadratic interpolation - assumes 2nd derivative of correction
! curve is approximately constant between input table points.
!
!VERSION 1.0 12 Oct 1998 N C Atkinson, UKMO
!
!ARGUMENTS Integer*2 CorrTable(5,21,4) Correction table in Level 1b header at byte offset 1001
! Integer*2 CountsCorr(5,90,4) Interpolated Earth-view corrections
!##############################################################################
SUBROUTINE INTERPOLATE_EX(CorrTable,CountsCorr)
INTEGER*2 CorrTable(5,21,4)
INTEGER*2 CountsCorr(5,90,4)
INTEGER Tx,Chan,Pix,Pix1,Pix2,P1,P2
REAL F,FF
REAL Grad(5,19,4) !First derivative of correction curve
!
! Calculate Gradients
!
DO Chan=1,5
DO Tx=1,4
DO Pix=2,18
Grad(Chan,Pix,Tx) = 0.1*(CorrTable(Chan,Pix+1,Tx) -
CorrTable(Chan,Pix-1,Tx))
ENDDO
Grad(Chan,1,Tx) = 2*Grad(Chan,2,Tx) - Grad(Chan,3,Tx) !Special case
Grad(Chan,19,Tx) = 2*Grad(Chan,18,Tx) - Grad(Chan,17,Tx)
ENDDO
ENDDO
!
! Interpolate
!
DO Pix=1,90
P1 = Pix/5 + 1 ! 1 to 19 !Find nearest 2 points in table
P2 = Pix/5 + 2 ! 2 to 20
Pix1 = (P1-1)*5 !0 to 90
Pix2 = (P2-1)*5 !5 to 95
IF (Pix1 .EQ. 0) Pix1=1
!##############################################################################
!+
!ROUTINE AMB_EarthCORRECT_EX
!
!DISCLAIMER The UK Meteorological Office does not guarantee the correctness
! of this program and takes no responsibility for its use.
!
!PURPOSE Example subroutine to correct AMSU-B Earth-view counts for bias
! errors. First convert the I*2 instrument telemetry (byte offset
! 1481-2560) to positive I*4 array. Returns with corrected Earth-view
! counts.
!
!VERSION 1.0 12 Oct 1998 N C Atkinson, UKMO
!
!ARGUMENTS
! Integer*4 Earthcounts(540) AMSU-B sensor data converted to I*4
! Integer*2 CountsCorr(5,90,4) Earth-view correction tables,
! from subroutine INTERPOLATE_EX
! Integer*2 TxPow(5) Actual powers, from analog telemetry
! Integer*2 TxPow_ref(4) 10 X Ref Powers, in Level 1b header,
! byte offset 1849
!##############################################################################
SUBROUTINE AMB_EarthCORRECT_EX(Earthcounts,CountsCorr,TxPow,
& TxPow_ref
INTEGER*4 Earthcounts(540) !AMSU-B sensor data
INTEGER*2 CountsCorr(5,90,4) !Earth-view Correction tables
INTEGER*2 TxPow_ref(4) !From Level 1b header
INTEGER*2 TxPow(5) !From analog telemetry
INTEGER*2 ECorr(5,90) !Overall correction: 5 channels, 90 views
INTEGER Chan,Sample,I,Tx
REAL F
!
! Initialise
!
DO Chan=1,5
DO I=1,90
ECorr(Chan,I) = 0
ENDDO
ENDDO
!
! Calculate current corrections
!
DO Tx=1,4
IF (Tx.LT.4) THEN
F = TxPow(Tx)/(0.1*TxPow_ref(Tx))
ELSE !Use sum of SARR-A and SARR-B powers
F = (TxPow(Tx)+TxPow(Tx+1))/(0.1*TxPow_ref(Tx))
ENDIF
IF (F.GT.0.01) THEN
DO Chan=1,5
DO I=1,90
>ECorr(Chan,I)=ECorr(Chan,I)+NINT(CountsCorr(Chan,I,Tx)*F)
ENDDO
ENDDO
ENDIF
ENDDO
!
! Apply current corrections, overwriting the original counts values
!
DO Chan=1,5
Do Sample=1,90
I = (Sample-1)*6 + Chan + 1
Earthcounts(I) = Earthcounts(I) + ECorr(Chan,Sample)
ENDDO
ENDDO
RETURN
END
!##############################################################################
Note: The TIP data are contained in HRPT minor frame 1 (of 3) at HRPT word 104-623.
M.9 BIAS CORRECTION TABLES
AMSU-B Bias corrections, Version 1.1, 22 Sept 1998, UKMO
Table M.9-1 gives the bias corrections for AMSU-B for transmitters: STX1, STX2, STX3 and SARR(A). The corrections (in counts) are provided for Earth views 1,
5, 10...90, Space view (91) and Target view (92) and the mean transmitter power is also given.
| Table M.9-1. AMSU-B Bias Corrections for NOAA-15 (as of 22 Sept 1998). | ||||||
| Transmitter: STX-1 Mean transmitter power = 111.3 counts | ||||||
| View | Channel 16 | Channel 17 | Channel 18 | Channel 19 | Channel 20 | |
|---|---|---|---|---|---|---|
| 1 | 45 | -514 | 12 | -101 | 113 | |
| 5 | 43 | -555 | 27 | -117 | 132 | |
| 10 | 44 | -595 | 38 | -132 | 147 | |
| 15 | 45 | -612 | 44 | -140 | 159 | |
| 20 | 48 | -617 | 45 | -148 | 171 | |
| 25 | 52 | -626 | 40 | -161 | 182 | |
| 30 | 55 | -603 | 31 | -166 | 183 | |
| 35 | 56 | -502 | 22 | -143 | 162 | |
| 40 | 57 | -362 | 15 | -106 | 128 | |
| 45 | 55 | -246 | 9 | -78 | 97 | |
| 50 | 50 | -170 | 7 | -59 | 77 | |
| 55 | 43 | -126 | 13 | -44 | 68 | |
| 60 | 36 | -105 | 24 | -33 | 66 | |
| 65 | 28 | -98 | 29 | -30 | 64 | |
| 70 | 22 | -98 | 31 | -30 | 61 | |
| 75 | 18 | -98 | 35 | -27 | 58 | |
| 80 | 18 | -86 | 38 | -19 | 52 | |
| 85 | 23 | -56 | 38 | -9 | 41 | |
| 90 | 34 | -33 | 39 | 3 | 34 | |
| 91 | 0 | -21 | -6 | -9 | 11 | |
| 92 | 0 | 4 | 0 | 0 | 7 | |
Note: The TIP data are contained in HRPT minor frame 1 (of 3) at HRPT word 104-623.
M.9 BIAS CORRECTION TABLES
AMSU-B Bias corrections, Version 1.1, 22 Sept 1998, UKMO
Table M.9-1 gives the bias corrections for AMSU-B for transmitters: STX1, STX2, STX3 and SARR(A). The corrections (in counts) are provided for Earth views 1,
5, 10...90, Space view (91) and Target view (92) and the mean transmitter power is also given.
| Table M.9-1. AMSU-B Bias Corrections for NOAA-15 (as of 22 Sept 1998). | |||||
| Transmitter: STX-1 Mean transmitter power = 111.3 counts | |||||
| View | Channel 16 | Channel 17 | Channel 18 | Channel 19 | Channel 20 |
|---|---|---|---|---|---|
| 1 | 45 | -514 | 12 | -101 | 113 |
| 5 | 43 | -555 | 27 | -117 | 132 |
| 10 | 44 | -595 | 38 | -132 | 147 |
| 15 | 45 | -612 | 44 | -140 | 159 |
| 20 | 48 | -617 | 45 | -148 | 171 |
| 25 | 52 | -626 | 40 | -161 | 182 |
| 30 | 55 | -603 | 31 | -166 | 183 |
| 35 | 56 | -502 | 22 | -143 | 162 |
| 40 | 57 | -362 | 15 | -106 | 128 |
| 45 | 55 | -246 | 9 | -78 | 97 |
| 50 | 50 | -170 | 7 | -59 | 77 |
| 55 | 43 | -126 | 13 | -44 | 68 |
| 60 | 36 | -105 | 24 | -33 | 66 |
| 65 | 28 | -98 | 29 | -30 | 64 |
| 70 | 22 | -98 | 31 | -30 | 61 |
| 75 | 18 | -98 | 35 | -27 | 58 |
| 80 | 18 | -86 | 38 | -19 | 52 |
| 85 | 23 | -56 | 38 | -9 | 41 |
| 90 | 34 | -33 | 39 | 3 | 34 |
| 91 | 0 | -21 | -6 | -9 | 11 |
| 92 | 0 | 4 | 0 | 0 | 7 |
| Transmitter: STX-2 Mean transmitter power = 114.3 counts | |||||
| View | Channel 16 | Channel 17 | Channel 18 | Channel 19 | Channel 20 |
| 1 | 0 | 0 | 0 | 0 | 0 |
| 5 | 0 | 0 | 0 | 0 | 0 |
| 10 | 0 | 0 | 0 | 0 | 0 |
| 15 | 0 | 0 | 0 | 0 | 0 |
| 20 | 0 | 0 | 0 | 0 | 0 |
| 25 | 0 | 0 | 0 | 0 | 0 |
| 30 | 0 | 0 | 0 | 0 | 0 |
| 35 | 0 | 0 | 0 | 0 | 0 |
| 40 | 0 | 0 | 0 | 0 | 0 |
| 45 | 0 | 0 | 0 | 0 | 0 |
| 50 | 0 | 0 | 0 | 0 | 0 |
| 55 | 0 | 0 | 0 | 0 | 0 |
| 60 | 0 | 0 | 0 | 0 | 0 |
| 65 | 0 | 0 | 0 | 0 | 0 |
| 70 | 0 | 0 | 0 | 0 | 0 |
| 75 | 0 | 0 | 0 | 0 | 0 |
| 80 | 0 | 0 | 0 | 0 | 0 |
| 85 | 0 | 0 | 0 | 0 | 0 |
| 90 | 0 | 0 | 0 | 0 | 0 |
| 91 | 4 | -26 | 0 | -13 | 10 |
| 92 | 0 | 0 | 0 | 0 | 0 |
| Transmitter: STX-3 Mean transmitter power = 95.0 counts | |||||
| View | Channel 16 | Channel 17 | Channel 18 | Channel 19 | Channel 20 |
| 1 | 23 | -48 | 33 | -42 | 36 |
| 5 | 17 | -40 | 25 | -43 | 32 |
| 10 | 11 | -16 | 18 | -33 | 19 |
| 15 | 7 | -2 | 14 | -18 | 4 |
| 20 | 3 | -6 | 12 | -7 | 0 |
| 25 | 0 | -26 | 14 | -12 | 12 |
| 30 | -1 | -51 | 17 | -21 | 29 |
| 35 | -3 | -62 | 19 | -16 | 28 |
| 40 | -4 | -59 | 19 | -5 | 12 |
| 45 | -4 | -49 | 16 | 0 | 0 |
| 50 | -4 | -36 | 12 | -4 | -4 |
| 55 | -3 | -25 | 9 | -12 | -1 |
| 60 | -3 | -16 | 7 | -19 | 2 |
| 65 | -2 | -8 | 6 | -17 | 0 |
| 70 | 0 | -9 | 5 | -10 | -3 |
| 75 | 0 | -28 | 3 | -6 | 0 |
| 80 | 1 | -50 | 0 | -6 | 9 |
| 85 | 3 | -52 | -4 | -9 | 12 |
| 90 | 4 | -39 | 1 | -9 | 13 |
| 91 | 6 | -100 | -1 | -17 | 22 |
| 92 | 2 | -17 | 1 | 0 | 1 |
| Transmitter: SARR Mean transmitter power = 209.9 counts | |||||
| View | Channel 16 | Channel 17 | Channel 18 | Channel 19 | Channel 20 |
| 1 | 9 | -1 | 36 | -582 | -214 |
| 5 | 0 | -1 | 20 | -556 | -217 |
| 10 | -6 | 2 | 20 | -520 | -215 |
| 15 | -9 | 0 | 21 | -456 | -206 |
| 20 | -9 | -4 | 19 | -363 | -191 |
| 25 | -7 | -3 | 13 | -252 | -168 |
| 30 | -3 | 2 | 6 | -146 | -138 |
| 35 | 0 | 6 | 1 | -70 | -104 |
| 40 | 4 | 6 | -1 | -27 | -71 |
| 45 | 6 | 2 | -2 | -9 | -47 |
| 50 | 7 | -2 | 0 | -10 | -34 |
| 55 | 6 | -3 | 3 | -22 | -34 |
| 60 | 5 | -2 | 6 | -53 | -47 |
| 65 | 3 | -4 | 7 | -112 | -69 |
| 70 | 1 | -7 | 7 | -187 | -90 |
| 75 | 0 | -7 | 7 | -257 | -100 |
| 80 | 1 | -4 | 9 | -304 | -98 |
| 85 | 3 | -2 | 12 | -316 | -87 |
| 90 | 8 | 0 | 7 | -291 | -71 |
| 91 | 0 | -2 | 1 | -74 | -16 |
| 92 | 0 | 0 | -2 | -25 | -15 |
Amended November 21, 2000 Amended December 8, 2000 Amended March 15, 2001 Amended August 10, 2001 Amended July 23, 2002 Amended August 17, 2004
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