POES SEM Performance Update February 11, 2003 David S. Evans I have finished the clean up of NOAA-12, NOAA-14, NOAA-15, NOAA-16, and NOAA-17 data from 2002 and have some performance information and figures that may be of interest. NOAA-12 We stopped archiving NOAA-12 SEM data as of July 2002. We had been receiving only one or two orbits of NOAA-12 data each day and, with the launch of NOAA-17 in July 2002, there were four full-time operating SEM instruments on POES. Data from the NOAA-12 TED and high energy, omni-directional detectors, when it is received, is still posted on the real-time web pages. The following describes the state of the SEM instrument on NOAA-12 when archiving was stopped. 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 front solid-state detector in the 90§ proton telescope, first became noisy on July 15, 2000, and has continued to degrade with noise background becoming increasingly elevated. The noise count rate in the 90§, 30 - 80 keV channel, began to exceed 1000 counts per second in late July 2000, exceeded 10000 counts per second by late April, 2001, and exceeded 50,000 counts per second in July 2002 when archiving of NOAA-12 data was terminated. The noise levels were not sufficient to trigger the 80-240 keV proton channel in the 90§ proton telescope and those higher energy proton data may be used with caution. Quite apart from noisy detectors, with time radiation damage to the front solid- state detectors in both the 0§ and 90§ proton telescopes has increased 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 should be used with care. 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 able to deposit enough energy in the solid-state detector to be detected. This response is particularly apparent in region south of the South Atlantic Anomaly. With the exception of the misidentification of the energy channel containing the maximum in the differential energy flux for the 30§ TED sensor, the NOAA-12 TED instrument continued to perform well up to the time archiving of data was terminated. When available, the NOAA-12 TED data continue to be used for the 'Auroral Activity' web page. NOAA-14 The state of the MEPED solid-state detector telescopes in the NOAA-14 SEM remains the same as of January 1, 2003 - that is to say very unsatisfactory. All three operating solid-state detector telescopes have had noisy solid-state detectors since launch in early 1995 and the fourth, the 90§ proton telescope, had never worked. The current (as of January 1, 2003) noise level in the 30-80 keV channel of the 0§ proton telescope on NOAA-14 is about 2000 counts per second, and has been at about that level since launch. The detector noise does not affect the higher energy channels. The front solid-state detector in the 0§ proton telescope has undoubtedly suffered radiation damage in launch, but the changes in effective energy thresholds is not known. The current noise level in the >30 keV channel in the 0§ electron telescope is about 500 counts per second while the >30 keV channel in the 90§ electron telescope in about 4000 counts per second. These levels are sufficiently high that conversion of sensor responses to electron fluxes in physical units will have errors, especially for low fluxes. During more intense events, when the sensor count rates are much higher than the noise background rates, the conversion to fluxes will have less error. The >100 keV electron energy channels in both the 0§ and 90§ telescopes are unaffected by the detector noise. Both the 0§ and 90§ electron telescope, >300 keV channels suffered an electronic data multiplexer failure in 1999 and have not operated since. Of the MEPED solid-state detectors, only the three omni-directional detectors continue to operate entirely satisfactorily and those data are used in the web- page 'Solar Proton' display. 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 able to deposit enough energy in the solid-state detector to be detected. This response is particularly apparent in region south of the South Atlantic Anomaly. Beginning in mid 1995, about six-months after launch, the electron sensors in the TED on NOAA-14 began suffering a spurious count problem that was induced by encounters with intense auroral particle fluxes. This problem was never serious enough to declare the data non-usable but serious enough to compromise their value. In early January 2001 the TED background count rates experienced a sudden increase not related to encounters with aurora. Because those background rates seemed to assume a constant value, it was suspected that some sort of electronic interference was responsible. To test that hypothesis the pulse counting threshold levels in the TED electronics were increased to their highest levels. This step did, indeed, eliminate the high background problem but, surprisingly, also eliminated the spurious count problem that had plagued the NOAA-14 TED since late 1995. However, the user of TED data from NOAA-14 should not use archived TED data acquired between January 12, 2001 and February 4, 2001 because the TED was not operating properly. In the past, the magnitude of the spurious count problem was monitored by counting the number of instances the TED background rates exceeded 175 counts per readout over a 10 day period. During the period Jan 1-10, 2001 there were 2360 such instances. During the period March 1-10, 2001 (after the threshold discriminator levels had been increased) this number decreased to 113 instances and has remained low ever since. There is no indication that the increase in detector pulse discriminator level affected the TED instrument capability to properly detecting auroral particles in the energy range 300 to 20,000 eV and so valid auroral particle measurements continue to be made. NOAA-14 had the potential of making 10309 passes over the polar region during 2002. Of that potential, 10032 passes showed up in the data base (191 passes missing). This is a data recovery of 98.1%. Of the 10118 polar passes that were obtained, 10032 had sufficient data to estimate the hemispheric power input, a recovery rate of 99.2%. On November 25, 2002 the archive processing of all SEM-2 data was changed over to new, better documented, software. The new software was designed to not impact either the format or content of the SEM-2 archive files. If any user notices a difference in SEM-2 archive data beginning on that data, we would appreciate being contacted. NOAA-15, SEM-2 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 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 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. 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 2002 and all are at satisfactory levels. NOAA-15 had the potential of acquiring 10390 passes over the polar region during 2002. Of that potential, 10348 passes showed up in the data base (42 passes missing). This is a data recovery of 99.6%, which is even better than 2001. Of the 10348 polar passes that were obtained, 10330 had sufficient data to estimate the hemispheric power input, a recovery rate of 99.8%. NOAA-16 The electron and proton solid-state detector telescopes on NOAA-16 continue to operate nominally. Detector noise and all electronic threshold levels remain the same since instrument turn-on in September 2000. As of the end of 2002 there is no evidence of significant radiation damage to the solid-state detectors in the proton telescope detectors. 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 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. Further increases in bias voltages are planned. The statistics for NOAA-16 data recovery during 2002 were very satisfactory. Of the potential of acquiring 10302 polar passes during 2002, 10247 were logged into the data base. This is a recovery rate of 99.5%. Of the 10247 valid polar passes in the database, 10225 had sufficient data to estimate the hemispheric power input, a success rate of 99.8%. NOAA-17 NOAA-17 was launched in June 2002 and the SEM-2 instrument was activated on July 19, 2002. 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 are stable. The four omni-directional proton detectors are also operating nominally with electronic threshold levels well within specifications and stable. The TED in the SEM-2 on NOAA-17 is operating 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-17 channeltron bias voltages were increased on February 4, 2003 by two steps and the TED performance improved. Further increases in bias voltages are planned. The statistics for NOAA-17 data recovery since turn-on in July 2002 were very satisfactory. Of the potential of acquiring 4900 polar passes since the turn- on, 4877 were logged into the data base. This is a recovery rate of 99.5%. Of the 4877 valid polar passes in the database, 4864 had sufficient data to estimate the hemispheric power input, a success rate of 99.7%. In summary, SEC currently is receiving data on a regular basis from four SEM packages, three of which are operating perfectly and one (NOAA-14) with a crippled MEPED telescope instrument but fully operation TED. The local time coverage provided by these four SEM instruments is unprecedented. We continue to receive about one orbit of NOAA-12 data each day, but have discontinued archiving data from NOAA-12. cc Ron Zwickl Ernie Hildner Joe Kunches Tom DeFoor Rodney Viereck Howard Singer