Data Set Information
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| DATA_SET_NAME |
PVO RPA PROC THERM ELEC, ION, PHOTOELEC, LOW RES. V1.0
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| DATA_SET_ID |
PVO-V-ORPA-5-ELE/ION/PHOTO/UADS-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 |
Introduction: The ORPA processed data consist of 4 file types: high resolutionthermal electrons, high resolution superthermal electrons, highresolution ions, and a key parameters file at 12 second sampling. Highresolution data are provided (for the entire orbit / only the portionof the orbit near periapsis) The sample rate of the high resolutiondata is variable and dependent on the telemetry rate and otheroperational considerations. All of these data are derived from thereformatted EDR data (RDR) which contains the raw I-V curve values.The moments of the distributions have been computed by a least squaresfitting algorithm. The low resolution data are resampled from the highresolution files. Data from the entire mission (Dec 5, 1978 - Oct 7,1992) are included in the data set, where possible. The PV RPAis described in considerable detail by Knudsen et al. [1979-1980]. Theprinciples of measurement are also described therein together withsome of the factors affecting the accuracy of the derived quantities.Additional information on the theory of measurement by an RPA ispresented by Knudsen [1966].Sampling: The ORPA instrument sweeps through the ion, electron, andphotoelectron modes in an EIIIP sequence covering 5 spacecraft spinperiods spending one spin period in each mode. A single retarding scancan be completed approximately 40 times in a spin period (0.3 sec).There are various algorithms by which the instrument can decide whichscan to place in the telemetry frame.Please read the instrument description for more details.Data Processing:High resolution data were processing by using an automated leastsquares fitting procedure. Values derived from these fits are providedin the archive. Some of the quantities contained in this submittal ofRPA data to the PDS are erroneous because of bad least-squares fits tothe I-V curves. These bad fits were not detected by the data reductionalgorithms and have not been removed by a trained observer viewing theI-V curves and making an educated judgment. A trained observer,looking at an I-V plot, can rather quickly recognize data that willproduce erroneous fit results but it is difficult to write analgorithm that can recognize all the possible situations and make thenecessary adjustments. High Resolution Electrons:In the electron mode, the ion current to the collector isnegligible with the collector at 47 V, A potentialdifference of 20 V between G-4 and C was found sufficientto suppress most of the secondary electrons produced by ionor electron impact at the collector. The three front gridsG-0, G-1 and G-2 are the energy analyzing grids. They arestepped together from +6.8 to -4.2 V in the coarse scan.The corresponding collector current is measured by anelectrometer and then digitized. The straight line portionis the retarding region, and the logarithmic slope determinesthe electron temperature by the relation: e Delta(V)Te = - - -------------------- k Delta( log (- Ie) )where e is the electron charge; k, the Boltzmann constant;and Ie, the electron current. The left side with largerpositive voltage is the attractive region. The voltageVp at which these two portions of the curve join is thepotential of plasma relative to spacecraft. Vp is expectedto vary from a few volts negative in interplanetary spaceto 1 or 2 V positive in the Venusian ionosphere. For thesimulation it was set to zero. The lower portion of thecurve bends away from the straight-line portion becausethe velocity distribution is not a true Maxwelliandistribution. An additional population of suprathermalelectrons exists with higher energies than the thermaldistribution. High Resolution Ions:The algorithm that scans the data in an ion I-V curve and computesthe initial estimates of the ion quantities must also make a decisionas to what ion mass is represented by a peak in DI [Knudsen et al.,1979; 1980]. The voltage at which the DI peak occurs for a given massmay be substantially smaller or larger than the nominal value becausethe Venus ionosphere is moving relative the planet with a velocitythat can approach that of the spacecraft. Consequently, some peaksin DI have been assigned the wrong mass. The result is not only anerroneous concentration for that mass but also an erroneous ionvelocity and total ion density. It is possible to recognize theincorrect assignments when comparing several I-V curves which areadjacent to each other in time, but the analysis algorithms are notthis sophisticated. A few errors in ion quantities are present in thePDS files resulting from this difficulty. The uncertainties in theion fitting process are included in an ancillary file. High Resolution Suprathermal Electrons:The analysis of a suprathermal electron I-V curve is similarlydifficult. The interpretation of the electron distributionscontributing to the I-V curve depends on the potential of thespacecraft relative to the ambient plasma which, in turn, depends onthe location of the spacecraft and the properties of the ambientplasma. The spacecraft is negative in the dense ionospheric plasma.It is positive in the low density solar wind plasma provided thespacecraft is not in the umbra of the planet. An additionalcomplication arises in that the sign of the current to theelectrometer occasionally changes from negative to positive during asweep. This can occur because the background current, with maximumretarding potential applied to the retarding grids, is compensatedclose to the noise level of the electrometer just before the sweepbegins [Knudsen et al., 1979]. If the background current that hasbeen compensated is significant relative to the saturation currentand changes in the right direction during the ensuing sweep, thetotal current will go through zero and the sign change. Thebackground current can change because the orientation of the rotatingspacecraft relative to the sun changes, because a purely temporalchange occurs or because the location of the spacecraft changes.Switching of the current from one sign to the other with theelectrometer in its most sensitive mode produces a noise spike in-the electrometer that is digitized and becomes part of-the I-Vcurve. Writing an algorithm that recognizes the noise spike and thechange in current sign is difficult because the sign of only thesaturation current and background current of a sweep has beenretained in the I-V data for reasons of minimizing the telemetryrequirements of the RPA. A trained observer, looking at an I-V plot,can rather quickly recognize in most cases when this condition hasoccurred, but it is difficult to write an algorithm that canrecognize all the possible situations and make the necessaryadjustments. Low Resolution Data:The PV PDS LFD SEDR tapes have time tags at 12 second intervals from30 minutes prior to periapsis to 30 minutes after periapsis. Thesetime tags are the tags specified in the first four quantities of eachof the EDR data records. All PV instruments are to report their dataat these common time tags for the purpose of easy intercomparison ofdata. Principal Investigators (PIs) with instruments with a samplingperiod much less that 12 seconds are to report the average ofmeasured quantities over a 12 second interval centered on the timetags. The RPA, because of a low telemetry word assignment, records atmost one current-voltage (I-V) characteristic curve per spacecraftspin period. Except for one set of 14 orbits, the spin period of thePV spacecraft has been about 12 seconds. Thus, RPA physicalquantities are derived at intervals of 12 seconds or more. Since theRPA operates in several modes, a particular quantity such as thermalelectron temperature may be typically measured at much longerintervals. The thermal electron temperature is typically measured ateither approximately 48 or 60 second intervals. In a few orbits, itwas measured at 12 second intervals.The quantities TOTI,- H+, O+, M29+, CO2+, TI, VX, VY, VZ, N1, TL, N2,and T2 are derived by least-squares fitting a strongly non-linearnumerical algorithm to an I-V curve. It is necessary in performingsuch a fit to supply an initial estimate of the quantities that areto be derived. If the estimates are not sufficiently close to thetrue least-squares values, the algorithm may yield a grosslyerroneous value by converging to a relative minimum of the varianceand not to the absolute minimum. Also, it may not converge at all.Although some such erroneous values have been eliminated from ourbasic tables tapes by checking for the magnitude of the variance,some erroneous value are known to be present. Such values can be wayoutside the nominal uncertainty quoted in Table 1.ASCII low resolution data are included as part of the high resolutiondata archive to facilitate browsing of the key parameters of thedataset.Missing values:RPA quantities may be unavailable for assigning to a specific timetag for several reasons as follows: The spacecraft data format in useat the time may not have contained any words for the RPA. The RPA mayhave been turned off for power conservation reasons. The spacecrafttelemetry bit rate and/or data format may have been such that an RPAI-V curve was recorded only at long time intervals. RPA data for aninterval of time, including the time tag, has not been reduced. (RPAdata at the time of this submission have been reduced for only asmall time interval about periapsis: plus and minus approximately 15minutes for the first 800 orbits, plus and minus approximately 30minutes for orbits 800-1300, plus and minus 60 minutes for orbits1300-2890.)Data:Each of the four data file types are described in this section. The 3high resolution data files all contain 17 ephemeris data columnsnecessary for the interpretation of the data. Rather than repeat thedescription 3 times, we will described the ephemeris data columnsonce, and then place the phrase ephemeris(17) in the column namefield of the file description.Ephemeris(17)____________________________________________________________________name type description____________________________________________________________________EPH1 Real Roll spin angle (NRSC - RAMROLL)**EPH2 Real Spin period EPH3 Real Attitude of spin axis X (NRSC - ATTX)**EPH4 Real Attitude of spin axis Y (NRSC - ATTY)**EPH5 Real Attitude of spin axis Z (NRSC - ATTZ)**EPH6 Real Distance from Venus to center of spacecraft, Real X component (ICC_ECLP - XP1SFF)*EPH7 Real Distance from Venus to center of spacecraft, Real Y component (ICC_ECLP - YP1SFF)*EPH8 Real Distance from Venus to center of spacecraft, Real Z component (ICC_ECLP - ZP1SFF)*EPH9 Real Spacecraft velocity X component (ICC_ECLP - DXP1SF)*EPH10 Real Spacecraft velocity Y component (ICC_ECLP - DYP1SF)*EPH11 Real Spacecraft velocity Z component (ICC_ECLP - DZP1SF)*EPH12 Real Distance from Sun to center of spacecraft, Real X component (ICC_ECLP - XPHSFF)*EPH13 Real Distance from Sun to center of spacecraft, Real Y component (ICC_ECLP - YPHSFF)*EPH14 Real Distance from Sun to center of spacecraft, Real Z component (ICC_ECLP - ZPHSFF)*EPH15 Real Venus center velocity, X component (ICC_ECLP)*EPH16 Real Venus center velocity, Y component (ICC_ECLP)*EPH17 Real Venus center velocity, Z component (ICC_ECLP)** Inertial Cartesian Coordinate System - Ecliptic** Non-rotation spin coordinate systemIons (ASCII Table)____________________________________________________________________name type description____________________________________________________________________PDSTIME String UTC at the time of the sweepIORBT Integer Orbit numberTPER Integer Periapsis time (UT)KDAY Integer Periapsis day of yearSWEEP Integer Unique sweep numberTIMI Real Unique time of sweepALTI Real Altitude of sweepSZAI Real Solar Zenith Angle of sweepTOTI Real Total ion densityH+ Real Hydrogen ion densityHE+ Real Helium ion densityO+ Real Oxygen ion densityM29+ Real Sum density of CO+, NO+, N2+ ionsO2+ Real O2+ ion densityCO2+ Real Carbon dioxide ion densityVELI Real Ion bulk velocity component in direction of RPA outTI Real Ion temperaturePHII Real Spacecraft ground potentialCSQ Real Chi square, goodness of curve fitFRSI Real Saturation ion currentBCKI Real Background ion currentephemeris(17)Thermal Electrons(ASCII table):____________________________________________________________________name type description____________________________________________________________________PDSTIME String UTC at the time of the sweepIORBT Integer orbit numberTPER Integer Periapsis time (UT)KDAY Integer Periapsis day of yearSWEEP Integer Unique sweep numberTIME Real Unique time of measurement for sweepALTE Real Altitude of sweepSZAE Real Solar Zenith Angle of sweepTOTE Real Electron densityTE Real Electron temperaturePHIE Real Spacecraft ground potentialFRSE Real Saturation electron currentBCKE Real Background electron currentephemeris(17)Photoelectrons(ASCII table)____________________________________________________________________name type description____________________________________________________________________PDSTIME String UTC at the time of the sweepIORBT Integer orbit numberTPER Integer Periapsis time (UT)KDAY Integer Periapsis day of yearSWEEP Integer Unique sweep numberTIMPH Real Unique time of measurement for sweepALTPH Real Altitude of sweepSZAT Real Solar Zenith Angle of sweepVPPH Real Suprathermal electron spacecraft potential of sweepDENPH1 Real First suprathermal electron density of sweepTEMPH1 Real First suprathermal electron temp of sweepDENPH2 Real Second suprathermal electron density of sweepTEMPH2 Real Second suprathermal ele temp of sweepSDENPH1 Real Least-squares fit statistical uncertainty of DENPH1STEMPH1 Real Least-squares fit statistical uncertainty of TEMPH1SDENPH2 Real Least-squares fit statistical uncertainty of DENPH2STEMPH2 Real Least-squares fit statistical uncertainty of TEMPH2CSQPH Real Chi square, goodness of curve fitFRSPH Real Saturation suprathermal electron currentBCKPH Real Background suprathermal electron currentephemeris(17)Key Parameters File (low resolution - ASCII table):____________________________________________________________________name type description____________________________________________________________________PDSTIME String UT of UADS record time which is defined for all PVO inst providing UADS data.ORBIT Integer Orbit numberTPER Integer Time from periapsisUT Integer Universal timeTOTI Integer Total ion densityH Real Hydrogen ion densityO Real Oxygen ion densityO2 Real O2 ion densityCO2 Real Carbon dioxide ion densityTI Real Ion temperatureVX Real Ion bulk velocity X componentVY Real Ion bulk velocity Y componentVZ Real Ion bulk velocity Z componentF1I Real First ion current, no retarding potentialBKGI Real Background current at start of ion sweep, +37V potentialVPI Real S/C potential at start of ion sweepTOTE Real Total electron densityTE Real Electron temperatureF1E Real First thermal electron current, +6.8V from S/C groundBKGE Real Background current at start of thermal electron sweep, -4.6V potentialVPE Real S/C potential at start of thermal electron sweepN1 Real Cold electron densityT1 Real Cold electron temperatureN2 Real Hot electron densityT2 Real Hot electron temperatureF1P Real First photoelectron current, no retarding potentialBKGP Real Background current at start of photoelectron sweep, -58V potentialVPPE Real S/C potential at start of photoelectron sweep Ancillary Files:The ion fitting process involves both mass and velocitydiscrimination In many cases, one or the other parameter can not bewell determined. As an ancillary component of the high resolution iondata files, we have included an ion uncertainties file. Some of thereasons for the uncertainties in the fits are described in thefollowing section on measured quantities. The ion uncertainty fileshave the following structure:____________________________________________________________________name type description____________________________________________________________________PDSTIME String UTC at the time of the sweepIORBT Integer orbit numberTPER Integer Periapsis time (UT)KDAY Integer Periapsis day of yearSWEEP Integer Unique sweep numberTIMI Real Unique time of measurement for NDSIALTI Real Altitude of NDSI.SZAI Real Solar Zenith Angle of NDSISTOTI Real Estimated uncertainty in total ion densitySH+ Real Least-squares fit statistical uncertainty of H+ ion densitySHE+ Real Least-squares fit statistical uncertainty of HE+ ion densitySO+ Real Least-squares fit statistical uncertainty of O+ ion densitySM29+ Real No significanceSO2+ Real Least-squares fit statistical uncertainty of O2+ ion densitySCO2+ Real Least-squares fit statistical uncertainty C02+ ion densitySVELI Real Ion velocitySTI Real Ion temperatureSPHII Real Spacecraft ground potentialCSQ Real Chi square, goodness of curve fitephemeris(17)RPA Measured QuantitiesThe PV RPA is described together with some of the principles ofmeasurement in some detail by Knudsen et al. [1979,1980]. Many of thefactors affecting accuracy are also described therein. We present inthis section the quantities recorded on the PDS EDR data filesfollowing the four time tag quantities, their nominal uncertainty andmeasurement noise level, and additional limitations of thequantities.Table 1 lists the symbol, quantity, measurement range with units inwhich the quantities are quoted, noise level of measurement, anduncertainty of the measurement for the quantities reported by theRPA. We have included in the list of quantities the vector componentsof the ion bulk velocity even though we do not supply values in thisOct 1988 submission to PDS. TABLE 1SYMBOL QUANTITY RANGE NOISE LEVEL UNCERTAINTYUTC UNIVERSAL TIME OF MEASUREMENT 0 - 8.7x10**7ms - 0.1sTOTI TOTAL ION DENSITY 10 - 1x10**7cm 10 cm-3 10%H+ HYDROGEN ION DENSITY 300 - 10**7cm-3 300 cm-3 10%O+ OXYGEN ION DENSITY 300 - 10**7cm-3 300 cm-3 10%M29+ SUM DENSITY OF CO+,N2+,NO+,O2+ 300 - 10**7cm-3 300 cm-3 10%CO2+ CARBON DIOXIDE ION 300 - 10**7cm-3 300 cm-3 10%TI ION TEMPERATURE 150 - 10,000 K - 10%VX ION BULK VELOCITY, X COMPONENT 0 - 7 km/s 0.4 km/s 0.4 km/sVY ION BULK VELOCITY, Y COMPONENT 0 - 7 km/s 0.4 km/s 0.4 km/sVZ ION BULK VELOCITY, Z COMPONENT 0 - 7 km/s 0.4 km/s 0.4 km/sF1I SATURATION ION CURRENT 0 - 1.3x10-4 A 1x10-12 A 1%BKGI ION BACKGROUND CURRENT 0 - 1.3x10-4 A 1x1O-12 A 1%VPI SPACECRAFT GROUND POTENTIAL -5 - +3 V - 0.1VTOTE ELECTRON DENSITY 102 - 107 cm 3 - -TE ELECTRON TEMPERATURE 300 - 20,000 K - 10%F1E SATURATION ELECTRON CURRENT 0 - 1.3x10-4 A 1x10-12 A 1%BKGE ELECTRON BACKGROUND CURRENT 0 - 1.3x10-4 A 1x10-12 A 1%VPTE SPACECRAFT GROUND POTENTIAL -5 - +3V - 0.1VN1 FIRST SUPRATHERMAL 0 - 107 cm-3 1 cm-3 20% ELECTRON DENSITYT1 FIRST SUPRATHERMAL 0 - 100 eV 0.2 eV 20% ELECTRON TEMPERATUREN2 SECOND SUPRATHERMAL 0 - 105 cm-3 1cm -3 20% ELECTRON DENSITYT2 SECOND SUPRATHERMAL 0 - 100 eV 0.2 eV 20% ELECTRON TEMPERATUREF1P SATURATION SUPRATHERMAL 0 - 1.3x10-4A 1x10-12A 1% ELECTRON CURRENTBKGP BACKGROUND SUPRATHERMAL 0 - 1.3x10-4A 1x10-12A 1% ELECTRON CURRENTVPPE SUPRATHERMAL ELECTRON 0 - +20V - 0.1 - 5V SPACECRAFT POTENTIALUTC: UTC is the universal time in milliseconds assigned to the physicalquantities recorded in this record. UTC will typically, but notalways, lie within plus or minus 6 seconds of the time of dayassigned to the time tag of this record. UTC should be accurate towithin plus or minus 0.1 second.TOTI: TOTI is the total ion density of the plasma in cm-3 and isderived from the FORTRAN expression TOTI=FlI/(VN*e*Area)where F1I is the first ion current measured with zero retardingpotential, VN is the component of ion bulk velocity parallel to theRPA axis derived from the lst-squares analysis when an analysis waspossible, e is the electronic charge, and AREA is the effective areaof the RPA collector (= 0.81 cm2). When a lst- squares analysis isnot possible, VN is the component of the spacecraft velocity inecliptic coordinates parallel to the RPA axis.H+: H+ is the hydrogen ion density. When the RPA is operating in oneof its peaks mode, H+ will be detected and recorded only when itsdensity is greater than approximately 10% of the sum of more massiveion densities. H+ can be the second most abundant ion and still notbe recorded when the RPA is operating in its two peaks mode. Theuncertainty of the H+ density also depends on its density relative tothat of more massive ions. For an H+ density comparable to that ofmore massive ions, the accuracy should be of the order of 10%. Thedetection noise level for H+ is estimated at 300 cm-3. Additionaldiscussion of the RPA ion peak detection capability and limitation isgiven by Miller et al. [1984].O+: O+ is the oxygen ion density. It will be detected in the presenceof more massive ions only when its density is greater thanapproximately 10% of the sum of more massive ions. The RPA does notresolve C+, N+, or 0+. We have assumed in our least-squares fittingthat (CC+] + CN+])/CO+] is constant at 0.07, a value derived from PVion mass spectrometer results.M29+: M29+ is the symbol assigned to the sum density of ions withmass near 32 atomic mass units, CO+, NO+, N2+, O2+. The RPA does notresolve these masses. In performing a least squares analysis, I havepermitted the algorithm to adjust the density of a mass 32 ion and afictitious mass 29 ion in fitting the measured DI peak correspondingto this mass range [Miller et al., 1984].Measurements by the PV IMS have revealed that the density of NO+ canapproach been that although the median density of each of the twomasses varies with altitude in the expected way, on successive sweepsthe least squares analysis can assign all the density to mass 29 forone sweep and to mass 32 in the next. For the PDS files, I haveadded the densities of the mass 29 and 32 ions and entered them underthe symbol M29+. RPA results as well as IMS results show that thepredominant ion mass in the group is 32 in most regions of theionosphere. In future submissions, the sum density of this mass groupwill be submitted under the symbol m32+.C02+: C02+ is the density of the carbon dioxide ion.TI: TI is the ion temperature and is assumed to be the same for allion masses. It is one of the adjustable variables in the least-squaresanalysis of ion sweeps.VX: VX is the x component of ion bulk velocity. The vector ion bulkvelocity is derived from three component velocities parallel to theRPA axis measured in three successive spin periods of the PVspacecraft [Knudsen et al., 1980]. In deriving the vector, it isnecessary to assume that the ion bulk velocity is uniform over theregion of space traversed by the spacecraft in two spin revolutionsof the spacecraft, a distance of about 250 km. The coordinate systemin which VX, VY, and VZ are given will be specified when data aresubmitted.VY: VY is the y component of the bulk ion velocity.VZ: VZ is the Z component of the ion bulk velocity.F1I: F1I is the saturation (first) current measured in an ion I-Vsweep. The retarding potential is programmed to be slightly negativeof plasma potential during this measurement. F1I is measured relativeto the ion current measured with the retarding potential equal to 37Vpositive [Knudsen et al. 1979].BKGI: BKGI is the current to the RPA collector measured just beforethe beginning of an ion sweep with the retarding potential set atapproximately +37V relative to plasma potential.VPI: VPI is the value of the spacecraft potential relative to plasmapotential that is assumed to exist at the time of the ion sweep. Thevalue is derived by interpolating between values of the spacecraftpotential measured in the thermal electron mode.TOTE: TOTE is the total electron density derived from the thermalelectron mode saturation current F1E. The formula used for thispresent PDS submission, in FORTRAN language, is: TOTE = 6.15E9*MAX(0, -3.5E-9 -F1E)~0.847We consider this measure of the total electron density to beapproximate and valid only while the PV spacecraft is within theionosphere.TE: TE is the thermal electron temperature derived using equation (1)in Knudsen et al. [1980]. When the spacecraft is positive relative toplasma potential r a condition existing with the spacecraft in thesun and in a low density plasma the value of TE is representative ofthe secondary electrons trapped in the positive spacecraft potentialwell.F1E: F1E is the saturation electron current measured at the beginningof a thermal electron mode sweep. The front (retarding) grids are ata potential of +6.8 V relative to the spacecraft ground.BKGE: BKGE is the current measured by the RPA electrometer at thebeginning of the thermal electron mode. The front (retarding) grids ofthe RPA are held at a potential of -4.6 V during the measurement.VPTE: VPTE is the spacecraft potential relative to the ambient plasmapotential. It is derived from the thermal electron sweep data asdescribed BY Knudsen et al. [1980]. When the spacecraft is in thesolar wind and exposed to the sun, its potential is typically a fewvolts positive with respect to the solar wind plasma potential. VPTEloses its meaning in this situation.N1: N1 is the density of the low temperature Maxwellian electrondistribution used to fit the suprathermal electron I-V curve[Knudsen et al., 1985].T1: T1 is the temperature of the low temperature Maxwellian electrondistribution.N2: N2 is the density of the high temperature Maxwellian electrondistribution used to fit the suprathermal electron I-V curve[Knudsen et al., 1985]T2: T2 is the temperature of the high temperature Maxwellian electrondistribution.F1P: F1P is the electron current measured by the RPA with zeroretarding potential on the retarding grid.BKGP: BKGP is the electron current to the RPA with the retardingpotential on the retarding grid equal to -58V.VPPE: VPPE is the spacecraft potential relative to the ambient plasmapotential. When the spacecraft is in the solar wind and not in theVenus umbra, the spacecraft is positive, and the potential isinferred from the suprathermal electron I-V curve. When thespacecraft is within the ionosphere or in the Venus umbra, thepotential is either estimated or taken from the potential measured inthe thermal electron mode.Coordinate systems:Non-rotating spin coordinate system (NRSC): The roll angle of the roll reference object will be calculated in this coordinate system as well as the roll angles of the Fs, RIP, RAM, and NADIR signals. The non-rotating coordinate system (Wx, Wy, Wz) is centered at the spacecraft center of mass. The Wz-axis is parallel to the spacecraft spin axis. The Wx-Wy plane is perpendicular to the spacecraft spin axis. The Wx-Wz plane includes the Vernal Equinox of reference. Thus the Wx-axis is at the intersection of the plane perpendicular to the spacecraft spin axis and the plane containing the spin axis and the Vernal Equinox. Roll angles in this coordinate system are measured in the Wx-Wy plane from the roll reference direction.Inertial Cartesian Coordinate System - Ecliptic (ICC-ECLP) The Ecliptic Inertial Cartesian Coordinate System is defined for the reference epoch of 1950.0 The X-direction lies in the Ecliptic Plane and is positive away from the reference body towards the Vernal Equinox which is determined by the line of intersection between the mean Earth equatorial plane and the ecliptic plane of reference. The Y direction is measured outward from the center of the reference body, perpendicular to and east of the the X-axis, and lying in the ecliptic plane of reference. The Z direction is positive toward the north ecliptic pole of reference, from the center of the reference body.
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| DATA_SET_RELEASE_DATE |
1997-09-01T00:00:00.000Z
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| START_TIME |
1978-12-05T02:41:22.816Z
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| STOP_TIME |
1992-10-07T08:16:27.750Z
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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 RETARDING POTENTIAL ANALYZER
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| INSTRUMENT_ID |
ORPA
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| INSTRUMENT_TYPE |
RETARDING POTENTIAL ANALYZER
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| NODE_NAME |
planetary plasma interactions
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| ARCHIVE_STATUS |
PRE PEER REVIEW
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| CONFIDENCE_LEVEL_NOTE |
Some of the quantities contained in this submittal of RPA data to thePDS are erroneous because of bad least-squares fits to the I-Vcurves. These bad fits have not been detected by our currentalgorithms for reduction of the data and have not been removed by atrained observer viewing the I-V curves and making an educatedjudgment.
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| CITATION_DESCRIPTION |
Knudsen, W.C., PVO-V-ORPA-5-ELE/ION/PHOTO/UADS-V1.0, PVO RPA PROC THERM ELEC, ION, PHOTOELEC, LOW RES. V1.0, NASA Planetary Data System, 1997.
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| ABSTRACT_TEXT |
The ORPA processed data consist of 4file types: high resolution thermal electrons, high resolution superthermalelectrons, high resolution ions, and a key parameters file at 12 secondsampling.
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| PRODUCER_FULL_NAME |
DR. WILLIAM C. KNUDSEN
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| SEARCH/ACCESS DATA |
Planetary Plasma Interactions Website
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