CCSD3ZF0000100000001CCSD3VS00002MRK**001 VOL_IDENT: USA_NASA_NSSD_P10F_0003 VOL_CREATION_DATE: 04-21-1997 MEDIUM_DESCRIPTION: sent by e-mail TECHNICAL_CONTACT: Dr. Pradip Gangopadhyay Space Sciences Center, MC-1341 University of Southern California Los Angeles, CA 90089-1341 (213) 740-6340 e-mail: djudge@lism.usc.edu PREV_VOLS: USA_NASA_NSSD_P10F_0002 CCSD$$MARKERMRK**001CCSD3SS00002MRK**002 DATA_SET_NAME: PIONEER UV DATA ARCHIVE DATA_SOURCES: PIONEER 10, ULTRAVIOLET PHOTOMETER EXPERIMENT SCIENTIFIC_CONTACT: SAME AS IN TECHNICAL CONTACT SPACECRAFT_CHARACTERISTICS: Pioneer 10 was launched on March 2, 1972, and carries a Ultraviolet (UV) photometer on board to detect backscattered solar uv light. The spacecraft is moving downstream with respect to the interstellar breeze flowing in to the solar system. In comparison Pioneer 11, launched April 5, 1973, is moving upstream. INVESTIGATION_OBJECTIVES: The primary scientific objective for the USC/UV experiment is to study the interaction of the solar wind with the interstellar medium. The UV photometers onboard the spacecraft Pioneers 10/11 are used to determine the spatial and temporal variations of the intensity of the backscattered solar Lyman alpha at 1216 A and solar Helium line at 584 A. One objective is to study the transition region of the heliospheric boundary. Another is to study the variation of resonance backscattered H 1216 A and He 584 A ultraviolet lines far from the local solar influence which will help us to determine the fundamental characteristics of the nearby interstellar medium. Another objective is to study the effect of solar variability as reflected in the interstellar glow, and comparing them to direct solar UV observations. INSTRUMENT_ATTRIBUTES: A. DESCRIPTION_OF_INSTRUMENT: The University of Southern California ultraviolet photometers onboard Pioneers 10/11 cover two broad spectral regions. The long wavelength channel is sensitive to emissions shortwards of 1400 A which includes the 1216 A emission line. The short wavelength channel is sensitive to shortwards of 800 A which includes the 584 A helium resonance line. The details of the UV photometers, as well as their sensitivity curves, can be obtained in Carlson and Judge, J.Geophys. Res., 79, 3623 (1974). The instrument design was based on the anticipated dominance of hydrogen and helium gases in the interplanetary medium. In the interplanetary space, the measured signal in the long wavelength channel is primarily composed of the H 1216 A line, while the measured signal in the short wavelength channel is primarily composed of the He 584 A line. For a uniform diffuse source that fills the field of view, the relations between the count rate, CR [count/sec], and brightness [rayleigh] are Brightness[Rayleigh] = (CR - 3.0)/S_lw for 1216 A, and Brightness[Rayleigh] = (CR - 3.0)/S_sw for 584 A, where S_lw[count/sec/Rayleigh] and S_sw[count/sec/Rayleigh] are conversion factors for long- and short-wavelength channels respectively. The background count rate is 3 count/sec. The conversion factors, as determined by a pre-launch calibration with a radioisotope thermogenerator, are : S_sw = 7.3 count/sec/Rayleigh S_lw = 4.9 count/sec/Rayleigh. These conversions factors can be applied to all data contained in data flies. The Pioneer 10 long wavelength channel has suffered a gain loss since mid-1986 about 37.5 AU from the Sun. The details of the problem are described in the paper published in J. Geophys. Res., v.98(A9), p. 15185-15192, 1993 by Hall et al. The gain loss was found when the photometer was turned on and off after initiation of spacecraft instrument power sharing on day 271, 1989. By examining earlier data both before and after the instrument was turned off for other operational reasons it was possible to identify the time at which the gain loss began i.e., mid 1986. There has been a further change in gain since late 1990 (~50 AU) after the duty cycle was changed on day 211, 1990. The duty cycle was 5 days on and 2 days off from 1989 day 271 to 1990 day 210 and 2 days on and 5 days off from 1990 day 211. In 1993 and 1994 the duty cycle has been highly aperiodic complicating the data analysis procedure. We discuss here the data analysis and correction procedure for the above three distinct periods. The correction procedure allows application of the same conversion factor s_lw, to all the data. The basis of the procedure is discussed below. Between 1986, day 219 and 1989, day 271, the UV detector was operated nearly continuously. During this period, the instrument was shut down occasionally for about 2 hours to facilitate other spacecraft operations. We have used those days to correct the data during the period. The count rate registered after the instrument turn-on was nearly constant for a few minutes and then decayed to a lower value over a period of some hours. We consider the initial plateau region as the correct data. We had to derive correction factors for those days when the instrument was run continuously. The correction factors were derived by dividing the plateau region data value observed after turn-on by the asymptote data value which the instrument was normally reading. We found that the correction factor increased from 1.1 in mid 1986 to 3.4 in late 1988. We fitted a polynomial curve to these correction factors and thus could calculate the correction factor to the daily average value throughout this period. The data during 1989, day 1 to 1989, day 271 were found to gradually fall below the 1/r curve. We believe that this is not a real scientific finding but is due to the steady depletion of charge as the UV detector was being run continuously in this period. The reason for believing this is that the plateau region values after 1989, day 271 were again on the 1/r curve. Further, if we accept the data in this period there would be a physically unacceptable discontinuity in the data. Thus, we have dropped the the 1989 data till day 271 since no clearly viable correction procedure was available during this period. Now we give the data correction procedure for the period between 1989, day 271 and 1990, day 254. In this period for some days the data are available within a few minutes of the instrument turn-on and the value can be directly read from the decay curve. There are some other days when the data are available quite some time after the instrument turn-on. We determined the data correction for those days as follows: First we chose the day 330, 1989 as our reference curve as we have data within 4 minutes of turn-on and there is a plateau region of 190 counts/sec. Suppose for the day for which we want to determine the count rate the data are available between times t1 and t2 and for which we have data from the reference day also. We summed the data between t1 and t2 for both days, which are called Sum for the day for which we want the count rate, and Sumref for the reference day. Then (Sum/Sumref)*(the reference day plateau data) will yield the correct count rate. Between 1990, day 254 to 1993, day 25 we have used a similar method except for two changes. Firstly, we are using 1992 day 282 as our standard decay curve. Secondly, we are dividing the plateau data by 2. We are doing this as there is evidence that the instrument has suffered a quantized gain change since the duty cycle was changed in 1990, day 211, leaving the instrument off for long periods. The whole decay curve has shifted upwards by a factor of 2. (We can not specify the exact date when this shift occured because of the large gaps in data collection.) If we do not divide by 2 then we have to seek a physical explanation for such a sudden change. Since the UV instrument integrates along its line of sight such a sudden change is impossible without a sudden change in the driving mechanism for the backscattered UV, the solar Lyman Alpha line. There has been no such change in that line. From 1993, day 84 to the end of mission we had to divide the plateau data by 3 since the decay curve had shifted upwards by a factor of 3. The described above correction of experimentally obtained count rates allows one to use the correction factor, S_lw, for the wavelength channel data in the same, consistent way throughout the mission. B. MEASURED_PARAMETERS: Ultraviolet photometers measure count rates of two spectral channels: i) short wavelength channel, and ii) long wavelength channel. C. PERFORMANCE_OF_THE_INSTRUMENT: Both the long and short wavelength channels of the Pioneer 10 UV photometer have functioned normally throughout the time period in FILE_TIME_COVERAGE. The Pioneer 11 UV photometer short wavelength channel has functioned normally throughout the spacecraft mission. However, the long wavelength channel has degraded in sensitivity since the Pioneer 11 Saturn encounter in 1979. DATA_SET_PARAMETERS: The data included in this data set are stored in UV Data Base (UVDB) files. UVDB files contain the following data: MNEMONIC DESCRIPTION DAY Day is stored in the first column in ascii. COR Indicator of the correction of spacecraft orientation is stored in the second column in ascii. DRATLW Daily averaged count rates for the long wavelength channel are given in the third column in ascii. DRATSW Daily averaged count rates for the short wavelength channel are given in the fourth column in ascii. HRADSP Heliocentric distance of the spacecraft in au is given in the fifth column in ascii. CLATSP CLONSP Celestial latitude and celestial longitude of the spacecraft +z axis, taken along spin axis pointing approximately at earth, are given in the sixth and the seventh column in ascii. CLATSU CLONSU Celestial latitude and celestial longitude of the Sun are given in the eighth and ninth column in ascii. CLATEA CLONEA Celestial latitude and celestial longitude of the Earth are given in the tenth and eleventh column in ascii. Note on the coordinate system: Origin of coordinate system is centered at the spacecraft. Celestial longitude is the ecliptic longitude (in degrees) measured from gamma (the first point of Aries) and centered at the spacecraft. Celestial latitude is the respective latitude measured from the ecliptic plane (in degrees). DATA_SET_QUALITY: Criteria for data acceptance are based on both proper functioning of spacecraft telemetry and communication link and the "behavior" of the instrument. All data received when there is an indication of problems in telemetry or data link, are rejected. The instrument behavior is checked in the following way. Data flow consists of the readings of photon counters, which accumulate counts during a telemetry frame period. Telemetry frame period depends on the mode of the communication link and may be in the range between a fraction of a second and several seconds. All experimental data are put together in the form of blocks of 512 consecutive readings of counters. Then all readings, that deviate more than three standard deviations for this particular block, are rejected. DATA_PROCESSING_OVERVIEW: In normal operations, we receive 800 bpi tapes from NASA containing the UV data at its highest resolution. These tapes are then compacted to 1600 bpi tapes for ease of use in USC. Once the 1600 bpi tapes become available various types of averages (daily, hourly etc) can be obtained. All data are given in spacecraft (not ground receiving) time. The data supplied here is daily averaged data which is also averaged over all clock angles. A detailed explanation about clock angles can be found in F.M. Wu, P. Gangopadhyay, H. S.Ogawa and D. L. Judge, Ap. J., 331, 1004 (1988). Briefly, since the UV photometer spins rigidly with the spacecraft making an angle of 20 degrees with the spin axis, its field of view traces out a 1 degree wide cone with a semi-vertical angle of 20 degrees on the sky. The clock angle is the angle between any particular direction and the ecliptic plane measured along the 20 degree cone. Data, accumulated during a day, are used to determine daily averaged count rates for long wavelength and short wavelength channels. All experimental data are put together in the form of blocks of 512 consecutive readings of counters. Then all readings, that deviate more than three standard deviations for this particular block, are rejected. FILE_CLASS_RELATIONSHIPS: There is only one type of data file. LIT_REFERENCES: 1. Carlson R.W. and Judge D. J. Geophys. Res., v.79, 3623, 1974. 2. Carlson R.W. and Judge D. in: Jupiter, p.418, University of Arizona Press, 1976. 3. Wu F.M. and Judge D. Astrophys. J., v. 231, 574, 1979. 4. Wu F.M. and Judge D. J. Geophys. Res., v.84, p.979, 1979. 5. Wu F.M. et al. Astrophys. J., v.239, 389, 1980. 6. Wu F.M. et al. Astrophys. J., v.331, 1004, 1988. CCSD$$MARKERMRK**002CCSD3KS00002MRK**003 VOL_TIME_COVERAGE: 1972-01-01 to 1991-12-31 FILE_NAMING_CONVENTION: UVDB files are named according to the start time of the data contained in the file as follows: UVxxx_yy.DAT. Here xxx stands either for P10 or for P11, yy stands for the year. Hence UVP10_80.DAT means the UV data of Pioneer 10 for January 01 - December 31 of year 1980. FILE_TIME_COVERAGE: UVP10_92.DAT 1992-01-01 to 1992-12-31 UVP10_93.DAT 1993-01-01 to 1993-12-31 UVP10_94.DAT 1994-01-01 to 1994-12-31 UVP10_95.DAT 1995-01-01 to 1995-12-31 UVP10_96.DAT 1996-01-01 to 1996-12-31 CCSD$$MARKERMRK**003CCSD3RF0000300000001 REFERENCETYPE=$VMS; LABEL=ATTACHED; REFERENCE=FORMAT.SFD; LABEL=NSSD3IF0005800000001; REFERENCE=UVP10_*.DAT /* EOF */