January 8, 2004 SEM instrument performance update as of January 8, 2004 Minor errors in satellite orbit location existing for NOAA-14, NOAA-15, NOAA-16, and NOAA-17 during early January, 2004. A software problem in the NESDIS code that computed the sub-satellite location as a function of time occurred beginning at 0000 UT on January 1, 2004. This error was not corrected until January 5, 2004 (for NOAA-15, NOAA-16, and NOAA- 17) and January 6, 2004 for NOAA-14. The error resulted in an approximate one-degree shift westward in the sub- satellite geographic longitude value from its correct value. During the time period that this error existed the true sub-satellite longitude can be recovered be shifting eastward by one-degree the longitudes given in the archive files (e.g. if the longitude given in the archive data is 275.5 degrees East, the correct longitude would be 276.5 degrees East.) The sub-satellite latitude value was not affected. The one-degree error in sub-satellite longitude propagates to a similar error in our calculation of the foot-of-field-line location, geomagnetic longitudes, and geomagnetic local times. The errors introduced are quite small and not believed to be important to the interpretation of the SEM observations. For this reason, the data archived during the time the location error existed have not been reprocessed. The following list provides the exact time intervals that the one- degree longitude error exists in the SEM archive data should a user wish to introduce a correction. NOAA-14 from 0000:00.000 UT on January 1 to 1240:54.697 UT on January 6, 2004 NOAA-15 from 0000:00.000 UT on January 1 to 1222:38.603 UT on January 5, 2004 NOAA-16 from 0000:00.000 UT on January 1 to 1601:25.929 UT on January 5, 2004 NOAA-17 from 0000:00.000 UT on January 1 to 1455:57.812 UT on January 5, 2004 NOAA-12, as of retirement in July, 2002 Archive processing of SEM data from NOAA-12 ended in July, 2002 when the NOAA-17 satellite came on line. The following summarizes the SEM performance on NOAA-12 at the time data processing ended. Total Energy Detector (TED) on NOAA-12 Beginning early in 1998 the logic that identified the 'characteristic energy channel number' and the sensor response within that channel began to operate in a sporadic fashion for the TED 30§ electron sensor. It appears that the telemetered energy channel number and the response within that channel were consistent with one another but that information was not from the energy channel that contained the maximum in the 30§ electron sensor response during each sweep. This problem has continued in a sporadic manner since that time. Care should be taken in using the identification of the 'characteristic energy' and the sensor response within that energy channel for the 30§ electron channel. Apart from this anomaly the NOAA-12 TED continued to operate nominally until data processing was ended. Medium Energy Proton and Electron (MEPED) Telescopes on NOAA-12 The back solid-state detector (of the two-detector element) in the 0§ proton telescope began to exhibit sporadic noise beginning in May of 1996. The problem got progressively worse until by May 1997 that solid-state detector was no longer operational. Because pulses from the back detector in the proton telescope are used to "veto" pulses from the front detector, the noisy back detector rendered the low energy response from the front detector also questionable. Consequently, low energy proton data from the 0§ proton telescope should be treated with caution between May 1996 and May 1997. Greater than 30 keV proton observations from 0§ proton telescope detector are no longer to be trusted after May 1997. The solid state detector in the 90§ proton telescope became noisy beginning July 15, 2000 and produced invalid high count rates in the lowest energy (30-80 keV) channel. Since that date and until data processing ended this detector has degraded still further. Radiation damage to the solid state detectors in both the 0§ and 90§ telescopes has become severe and has the effect of increasing the particle energy thresholds well above their nominal value. It is advised that after 1996 data from those instruments should be treated with caution and after 1999 not used at all. The performance of the MEPED electron telescopes continues to be nominal although after 1996 radiation damage to the solid state detectors in the electron telescopes may have increased the electron energy thresholds above their nominal value. Quite apart from noisy solid-state detectors, radiation damage to the front solid-state detectors in both the 0§ and 90§ proton telescopes has increased, over time, their effective energy thresholds for counting protons. On NOAA-12, evidence of radiation damage first became evident in July 1992 about one-year after launch and was quite significant by July 1994, three-years after launch. Radiation damage occurs sooner in the 90§ proton telescope detector because of the higher proton fluxes routinely viewed by that detector. Conversion of sensor count rates to particle fluxes in physical units without correction for the increased proton energy thresholds will result in an underestimate of the actual fluxes. The exact changes with time in the effective proton energy thresholds are not known. However, a comparison was made between proton telescope observations made by NOAA-12 and by NOAA-15 shortly after NOAA-15 was launched. The comparison indicated that the nominal 30 keV energy threshold in the NOAA-12 90§ instrument had increased to about 75 keV while the nominal 80 keV threshold had increased to about 160 keV. Comparisons were also made between the NOAA-12 and NOAA-15 0§ proton telescopes, but were hampered by the NOAA-12 0§ telescope detector noise problem described above. After crude corrections were implemented to compensate for that problem, the comparison indicated that the nominal 30 keV proton energy threshold in the NOAA-12 0§ instrument had increased to about 50 keV while the nominal 80 keV energy threshold had increased to about 140 keV. These comparisons were done for July-August 1998, after some 6.5 years of NOAA-12 operation. The 0§ and 90§ electron solid-state detector telescopes on NOAA-12 continued to operate properly to end-of-life with no increase in detector noise levels. While radiation damage to the solid-state detectors in the electron telescope detectors proceeds at a slower rate than in the proton detectors (there is a nickel foil that prevents especially damaging low energy ions from access to the solid-state detector in the electron instrument), after 10 years the nominal particle energy thresholds have likely shifted upwards by some unknown, amount. For this reason, the data from the electron solid-state detector telescopes toward the end of the NOAA-12 mission should be used with care. Omni-directional Energetic Ion Detectors on NOAA-12 The high ion energy omni-directional detectors (designed for solar particle events) continued to perform well, with no evidence of degradation, up to the time archiving terminated. Users of these data should be aware that the P6 detector (>16 MeV protons) also responds to electrons of energies greater than several hundred keV. The response is caused by bremsstrahung produced in the Aluminum dome over the detector with the x-ray photon able to deposit enough energy in the solid-state detector to be detected. This response is particularly apparent in regions south of the South Atlantic Anomaly. NOAA-14, as of January, 2004 The NOAA-14 satellite was launched in 1995 and is in its tenth year of operation. We anticipate that if NOAA-18 is successfully launched in 2004, NOAA-14 will be retired. Total Energy Detector (TED) on NOAA-14 NOAA-14 TED observations between 1212 UT on October 25, 1998 and 1626 UT on November 10, 1998 should be discarded because the channeltron high voltage was not set properly. The 300-20,000 eV electron channels in the TED on NOAA-14 had been plagued by a spurious count problem that began about July 1, 1995. This problem stabilized by early 1996 and never became severe enough to render the NOAA-14 TED non- operational. However, TED observations from NOAA-14 between July 1, 1995 and February 4, 2001 should be treated with caution. Beginning on January 12, 2001 an additional source of spurious counts, having the character of electromagnetic interference (EMI), appeared in the NOAA-14 TED. After investigation, the detector pulse threshold discriminator levels were increased to their highest levels and that step eliminated the spurious EMI response. There were a number of intervals between January 12 and February 4, 2001 when the EMI problem rendered data from the NOAA-14 TED unusable. These periods are: January 12 0700 UT to January 12 2030 UT January 15 0800 UT to January 16 1000 UT January 16 1430 UT to January 17 0730 UT January 17 1500 UT to January 18 1130 UT January 20 1530 UT to January 22 0315 UT January 22 2330 UT to January 23 0400 UT January 24 1300 UT to January 24 2030 UT January 26 0630 UT to January 26 1830 UT January 27 2000 UT to January 28 2400 UT January 29 1030 UT to January 30 1400 UT January 31 0900 UT to February 1 1800 UT February 2 0230 UT to February 4 2130 UT Surprisingly, raising the pulse threshold discriminator level not only mitigated the EMI spurious count problem but also eliminated the long-standing and separate spurious count problem. Raising the pulse discriminator thresholds did not appear to have had any negative impact on the instrument's response to natural auroral particle fluxes. Consequently, the TED data after February 4, 2001 may be utilized with some degree of confidence. However, the electron channeltron bias voltages in the NOAA-14 TED remain at their lowest settings. After 10 years of operation, the channeltrons have undoubtedly suffered gain loss that ordinarily would be compensated by increases in bias voltage. We have been reluctant to perform such voltage increases because of concern that the spurious count problem experienced prior to February, 2001 would return. The consequence of this decision may be that the NOAA-14 TED, especially the electron channels, have lost some sensitivity over the years. Medium Energy Proton and Electron (MEPED) Telescopes on NOAA-14 Beginning at instrument turn-on the 90§ proton telescope displayed no response and is regarded as failed. The solid state detectors in the 0§ proton telescope and both the 0§ and 90§ electron telescopes were noisy from instrument turn-on. This noise affected only the lowest particle energy channels (30-80 keV for the proton telescope, >30 keV for the electron telescope) and the data from the higher energy channels are usable up to year 2000 (with the exception noted below.) At that point radiation degradation in the solid state detectors in the proton telescopes would have become significant enough that the effective particle energy thresholds would have increased significantly above their nominal values. In-flight calibration data has shown that the inherent noise levels of solid- state detectors in the NOAA-14 SEM are greater than prior experience, for example on NOAA-12. The noise level in the front detector early in the life of the NOAA-12 0§ proton telescope was about 8 keV energy equivalent compared with about 16 keV on NOAA-14. A similar comparison between solid-state detectors in the NOAA-12 and NOAA-14 electron telescopes shows, for the 0§ telescope, a NOAA- 12 noise level of about 7.5 keV compared to about 11 keV on NOAA-14 and, for the 90§ telescope, about 7.0 keV on NOAA-12 and 9-11 keV on NOAA-14. The high background count rate observed in the 90§ electron telescope on NOAA-14 may be due in large part to an abnormally low electronic discrimination threshold for the >30 keV energy channel in that sensor. In-flight calibrations indicate that this threshold is (and has been since launch) at about 18.5 keV equivalent particle energy loss in the solid state detector compared to a threshold of about 24 keV particle energy equivalent for the 0§ electron telescope discriminator. Beginning in late 1997 (on or about October 1, 1997) the multiplexer that governed the telemetry time-sharing of sensor responses in the >300 keV energy channels from the 0§ and 90§ electron telescopes began to malfunction in an intermittent fashion. The telemetered response from both of the highest energy electron energy channels often became 0 although there were lengthy periods when the multiplexer functioned properly. By early 1999 the multiplexer was malfunctioning more often than not and by mid-1999 seems to have failed entirely. Care should be taken in using the >300 keV electron data from the MEPED electron telescopes after October 1, 1997 - especially when the telemetered sensor responses are zero. Omni-directional Energetic Ion Detectors on NOAA-14 The high ion energy omni-directional detectors (designed for solar particle events) continued to perform well, with no evidence of degradation, up to the end of year 2003. Users of these data should be aware that the P6 detector (>16 MeV protons) also responds to electrons of energies greater than several hundred keV. The response is caused by bremsstrahung produced in the Aluminum dome over the detector with the x-ray photon able to deposit enough energy in the solid- state detector to be detected. This response is particularly apparent in regions south of the South Atlantic Anomaly. NOAA-15, as of 1 January, 2004 Total Energy Detector (TED) on NOAA-15 The TED in the SEM-2 on NOAA-15 continues to operate nominally. The electron gains on all channeltron detectors were checked at the end of 2003 and all are at satisfactory levels. The channeltron bias for the TED electron detector systems is currently at step 3 of 8 and at step 1 of 8 for the TED proton detector systems. Medium Energy Proton and Electron (MEPED) Telescopes on NOAA-15 The electron and proton solid-state detector telescopes on NOAA-15 continue to operate nominally. Detector noise and all electronic threshold levels remain the same since instrument turn-on in July 1998. There is clear evidence of radiation damage to the solid-state detectors in the 0§ and 90§ proton telescopes. The impact of this damage on the effective energy thresholds of these detectors is not well known. However, comparisons between proton telescope observations by NOAA-15 and by NOAA-16 made late in 2001 suggest that at that time the nominal 30 keV energy threshold had increased to about 40 keV while the nominal 80 keV threshold had increased to about 100 keV. The change in effective energy thresholds has certainly become larger since late 2001 but no additional cross-checks have been conducted to quantify any further changes. Omni-directional Energetic Ion Detectors on NOAA-15 The four omni-directional proton detectors also continue to operate nominally. The electronic thresholds remain at the same levels as at launch and there is no evidence of noise on the part of the solid-state detectors. Users of the data should be aware that because the electronic counting threshold on the P6 energy channel in the SEM-2 instrument is set to a much higher value than the case for SEM-1, the response to very energetic electrons is very much reduced in the SEM- 2, P6 detector NOAA-16, as of 1 January, 2004 Total Energy Detector (TED) on NOAA-16 The TED in the SEM-2 on NOAA-16 continues to operate nominally. The electron gains on all channeltron detectors (both the electron and ion portions of the instrument) were checked at the end of 2002 and were found to be below specification. All the NOAA-16 channeltron bias voltages were increased on February 4, 2003 by two steps and the TED performance improved. The channeltron gains were checked again in November, 2003 and the gain of the channeltron in the low-energy, 0§ TED electron detector was found to be below specification. The channeltron bias voltage for the TED electron detector systems was increased by one step (to step 6 of 8) on December 2, 2003. The bias level for the TED proton detector systems is at step 5 of 8. The bias voltage is still not adequate for the 0§, electron low-energy channeltron but, at this time, we are reluctant to increase the bias voltage still further. The contribution to the total integrated electron energy flux flowing into the atmosphere from the <1000 eV electrons is very modest. To increase the bias voltage further to compensate for the loss of sensitivity in that one detector would accelerate channeltron gain degradation in the more important >1000 keV TED electron detectors compromise our ability to compensate for that loss. Medium Energy Proton and Electron (MEPED) Telescopes on NOAA-16 The electron and proton solid-state detector telescopes on NOAA-16 continue to operate nominally with the exception of radiation damage. Detector noise and all electronic threshold levels remain the same since instrument turn-on in September, 2000. Comparisons between the responses of the 0§ and 90§ proton telescopes demonstrated that the effect of radiation damage to the front detectors in the proton telescopes on NOAA-16 became apparent during the latter 6-months of 2003. The impact of the radiation damage on the effective proton energy thresholds in these telescopes has not been quantified. Omni-directional Energetic Ion Detectors on NOAA-16 The four omni-directional proton detectors also continue to operate nominally. The electronic thresholds remain at the same levels as at launch and there is no evidence of noise on the part of the solid-state detectors. The definitive archived data from NOAA-16 for the short period between 86370 seconds and 86400 seconds UT (2359:30 to 2400:00 UT) on August 22, 2001 should be discarded. NOAA-17, as of 1 January, 2004 Total Energy Detector (TED) on NOAA-17 The TED in the SEM-2 on NOAA-17 continues to operate nominally. The electron gains on all channeltron detectors (both the electron and ion portions of the instrument) were checked at the end of 2032 and were found to be within specification. The channeltron bias for the TED electron detector systems is currently at step 3 of 8 and at step 4 of 8 for the TED proton detector systems. Medium Energy Proton and Electron (MEPED) Telescopes on NOAA-17 The electron and proton solid-state detector telescopes on NOAA-17 are operating nominally. Detector noise levels and electronic threshold levels are well within specifications and have been stable. To date there is no evidence to date of significant radiation damage to the solid-state detectors in the proton telescopes. Omni-directional Energetic Ion Detectors on NOAA-17 The four omni-directional proton detectors also continue to operate nominally. The electronic thresholds remain at the same levels as at launch and there is no evidence of noise on the part of the solid-state detectors.