Data Set Information
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| DATA_SET_NAME |
PVO VENUS ONMS DERIVED SUPERTHERMAL ION LOCATION V1.0
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| DATA_SET_ID |
PVO-V-ONMS-5-SUPERTHERMALIONLOC-V1.0
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| NSSDC_DATA_SET_ID |
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| DATA_SET_TERSE_DESCRIPTION |
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| DATA_SET_DESCRIPTION |
orbits time 1 1978-12-05T15:06:25.000Z 645 1980-09-10T17:30:20.000Z 4710 1991-12-29T00:40:49.000Z 5055 1992-10-07T19:50:29.000Z The data reduction process has been described in Kasprzaket al. (1987). The method used to reduce the data assumescylindrical symmetry of the ion source. In actual fact, thesource is asymmetrical in its angular response (Guenther, 1989).This can introduce as much as a factor of 2 scatter in the data.No simple solution has been found for modeling this asymmetrysince the actual ion drift vector is unknown. The minimum energyof an ion detectable by the ONMS in this ion mode is 35.9 eV.The maximum transmission is assumed to occur about 10 V abovethis value. On the nightside of Venus the spacecraft potentialis negative and the most probable ion energy is near 40 eV.The ion species regularly monitored include: He+, N+, O+,N+ and/or CO+ and CO2+. Because of the paucity of data at othermass numbers only mass 16 (atomic oxygen) has been reduced to aflux and number density. As part of the reduction process theangle in the ecliptic plane of the apparent ion flow in spacecraftreference frame has been deduced. The flux values are estimatedin the spacecraft reference frame relative to spacecraft ground.The density is computed from the flux by dividing it by a speedcorresponding to 40 eV. No correction has been applied to theangle, density or flux in order to remove the effect of spacecraftvelocity.The dataset fields are:VARIABLE COMMENT-------------------------------------------------------- ORBIT Orbit number MASS Mass number of species 4 He+ 12 C+ 14 N+ 16 O+ 28 CO+ and/or N2+ 30 NO+ 32 O2+ 44 CO2+ BTIME Beginning time -| BTPER Time from periapsis (sec) | BALTIT Altitude in (km) |-- START BSZA Solar zenith angle (deg) | BLAT Local solar time (hr) -| ETIME Ending Time -| ETPER Time from periapsis (sec) | EALTIT Altitude in (km) |-- FINISH ESZA Solar zenith angle (deg) | ELAT Local solar time (hr) -|
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| DATA_SET_RELEASE_DATE |
1996-09-01T00:00:00.000Z
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| START_TIME |
1978-12-05T03:06:25.000Z
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| STOP_TIME |
1992-10-07T07:50:29.000Z
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| MISSION_NAME |
PIONEER VENUS
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| MISSION_START_DATE |
1968-06-01T12:00:00.000Z
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| MISSION_STOP_DATE |
1992-10-07T12:00:00.000Z
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| TARGET_NAME |
VENUS
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| TARGET_TYPE |
PLANET
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| INSTRUMENT_HOST_ID |
PVO
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| INSTRUMENT_NAME |
ORBITER NEUTRAL MASS SPECTROMETER
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| INSTRUMENT_ID |
ONMS
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| INSTRUMENT_TYPE |
QUADRUPOLE MASS SPECTROMETER
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| NODE_NAME |
planetary plasma interactions
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| ARCHIVE_STATUS |
ARCHIVED
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| CONFIDENCE_LEVEL_NOTE |
In order to fit the data, a minimum of 30 points were required in 36 seconds. In addition, the maximum to minimum count ratio was required to be factor of 3 or greater in order to insure that there was a definitive spin modulation. The center 12 seconds of data is divided by the fitting function to derive the equivalent flux for that point. The center of the new fitting interval is adjusted so that it is centered on the expected signal maximum predicted from the previous interval fit. As a result of this method of fitting, discontinuities may exist near minimum angle of attack where one 12 second interval adjoins the next interval.See Kasprzak et al. (1987).Kasprzak, W.T., H.B. Niemann and P. Mahaffy, Observations ofEnergetic Ions on the Nightside of Venus, Journal of GeophysicalResearch, vol. 32, 291-298, 1987.
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| CITATION_DESCRIPTION |
Kasprzak, W., PVO-V-ONMS-5-SUPERTHERMALIONLOC-V1.0, PVO VENUS ONMS DERIVED SUPERTHERMAL ION LOCATION V1.0, NASA Planetary Data System, 1996.
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| ABSTRACT_TEXT |
This dataset contains start and stop times/locations wheresuperthermal ions were detected by the Neutral Mass Spectrometerinstrument aboard the Pioneer Venus Orbiter. The instrument detectedsuperthermal, energetic or fast ions whose energy exceeds 36 eV inthe spacecraft frame of reference. These ions were observed inearly orbits during measurements of the neutral density nearperiapsis, have an erratic and unpredictable signature, and occurat too high an altitude to be due to the neutral atmosphere. When thealtitude of periapsis increased above the point where neutral densitymeasurements could be made, the instrument was configuredspecifically to detect superthermal ions. In general, for orbitnumbers 1 to 645, data were taken from the RPA mode. The gasbackground signal with the filament on is about a factor of 10less in this mode than in non-RPA mode, resulting in a lowerdetection threshold. For orbit numbers above 923, the instrumentwas deliberately configured with the filament off and non-RPAmode data was used. For mass 16 the RPA voltage is about +3.8volts.
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| PRODUCER_FULL_NAME |
DR. WAYNE KASPRZAK
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| SEARCH/ACCESS DATA |
Planetary Plasma Interactions Website
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