Data Set Information
DATA_SET_NAME V15/V16 VENUS ROE 5 OCC ELECTRON DENS V1.0
DATA_SET_ID V15/V16-V-ROE-5-OCC-ELECTRON-DENS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview==================This dataset contains 29 ionospheric electron density profiles(EDS files) derived from Venera 15 and 16 radio occultation data.A total of 155 profiles are believed to be available and it ishoped that all will eventually be archived. These profiles wereproduced by A. L. Gavrik, who worked on the Venera 15 and 16 radiooccultation experiment, and prepared for the PDS by P. Withers.The DATA/ directory contains one .TAB file and one .LBL file for eachoccultation. Each .TAB file contains a series of altitudes andelectron densities for an occultation. The LBL file containsinformation about how to read the data and some ancillary informationabout the data acquisition (time, location, etc.).Each .TAB file in the ANC/ directory obeys the following namingconvention:ANCYYYYMMDDHXXXQV.TABwhere YYYY is the year of the occultation (e.g. 1983), MM is themonth (e.g. 10), DD is the day of the month (e.g. 12), H is aletter corresponding to the hour of the occultation, as discussedin the next sentence, XXX is either V15 for Venera 15 occultationsor V16 for Venera 16 occultations, Q is either N for ingress or X foregress, and V is a version label (e.g. A for the first version). Anoccultation time of 05:54:00 has hour 05 and H is 'F'. Similiarly, an hourof 00 leads to H being A, 01 to B, 02 to C, and so on until 23 to X. Thusfilename ANC19831012FV15NA.TAB corresponds to an ingress occultation on1983-10-12 at a time with hour 05 by Venera 15, first version. Each.LBL file in the ANC/ directory is named in a corresponding manner.The same naming convention is used in the EDS/ directory, with thereplacement of 'ANC' in the filename with 'EDS'.Dates and times used to produce these filenames are in the Moscowwinter timezone, not UTC. This is discussed further in the sectionheaded 'Timing'.Parameters==========Each .TAB file in the ANC/ directory contains the following items.Name of spacecraft (V15 or V16) SCTDate of occultation, Moscow winter time MOSCOW_WINTER_DATETime of occultation, Moscow winter time MOSCOW_WINTER_TIMELatitude of occultation, degrees north LATITUDELongitude of occultation, degrees west WEST_LONGITUDESolar zenith angle of occultation, degrees SOLAR_ZENITH_ANGLEName of original file supplied by A. L. Gavrik ORIG_FILENAMEThe name of the original file supplied by A. L. Gavrik may containuseful information. These files appear to follow some naming convention,but this convention has not yet been fully understood. For instance,information on the occultation summarized in file ANC19831012FV15A.TABwas originally delivered in a file named 0566_b15.012.Each .TAB file in the EDS/ directory contains the following items.Altitude, km ALTITUDEElectron density, number per cubic centimeter ELECTRON_DENSITYThe altitude is presumed to be relative to a sphere of radius 6052 km.Uncertainties in these parameters are not specified precisely.Uncertainty in absolute altitude is less than 2 km. Relativealtitudes for a given occultation are significantly more accurate.Uncertainty in electron density varies with altitude, being smallerat high altitudes than at low altitudes as a result of the dataprocessing techniques used. Hence the smallest electron densitiesreported at low altitudes are significantly smaller than thesmallest reported at high altitudes. Uncertainty in electron densityat high altitude varies between 200 and 5000 electrons per cubiccentimeter, with a typical value of 500 electrons per cubic centimeter.This value is sensitive to fluctuations in the total electron content(i.e. electrons per unit area) along the ray of the radio signal.Hence it is influenced by properties of the solar wind along the lineof sight at the time of the occultation. Uncertainty in electrondensity near the ionospheric peak is approximately 10000 to 20000electrons per cubic centimeter.Timing======All dates and times reported in this dataset are in the Moscow wintertimezone, not UTC. This time zone is currently three hours ahead of UTC.Times have not been converted into UTC in order to (A) eliminate thepossibility of introducing an error and (B) retain flexibility in thecase that delivery of additional profiles from the Venera 15 and 16radio occultation experiments involves Moscow summer time.Data Processing===============Data processing is described in the documents listed in the REF.CATfile and in some of the other files in the CATALOG/ directory. Theprincipal equations used were:N(p) = (-2 m f c) / (v-perp e^2) x integral from r=p to r=infinity of df dr / sqrt(r^2 - p^2)and p = H + L c df / (v-perp f)where N is electron density, p is the impact parameter of the radioray, m is the electron mass, f is the frequency, c is the speed oflight, v-perp is the line-of-sight component of the velocity of thetransmitter with respect to the receiver, e is the elementary charge,df is the residual frequency change caused by the ionosphere ofVenus, H is the distance of closest approach of the ray to Venus, andL is the separation between the spacecraft and Venus. These equationsare in Gaussian units, inserting 4 pi eps-0, where eps-0 is thepermittivity of free space, to the numerator of the right hand sideof the first equation converts them into SI units.
DATA_SET_RELEASE_DATE 3000-01-01T00:00:00.000Z
START_TIME 1965-01-01T12:00:00.000Z
STOP_TIME N/A (ongoing)
MISSION_NAME VENERA 15 AND 16
MISSION_START_DATE 1983-06-02T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME VENUS
TARGET_TYPE PLANET
INSTRUMENT_HOST_ID V16
V15
INSTRUMENT_NAME RADIO OCCULTATION EXPERIMENT
INSTRUMENT_ID ROE
INSTRUMENT_TYPE RADIO SCIENCE
NODE_NAME planetary plasma interactions
ARCHIVE_STATUS PRE PEER REVIEW
CONFIDENCE_LEVEL_NOTE Data Coverage and Quality=========================Given the small number of available occultations, data coverage islimited. No gaps have been identified in individual profiles.Uncertainties in the ionospheric electron densities are not knownprecisely, as discussed above.Limitations and Caveats=======================These data products come from two Soviet spacecraft whose operationsended over 25 years ago. Therefore the documentation and other aspectsof the dataset are not as complete as would be expected for a currentNASA mission. Nevertheless, it is felt that archiving the dataset inits current state, thereby preserving it for posterity, is betterthan risking that it be lost irrevocably.
CITATION_DESCRIPTION A. L. Gavrik, Yu. A. Gavrik, P. Withers, S. Joy, Venera 15 and 16Radio Occultation Ionospheric Electron Density Profiles,Version 1.0, V15/V16-V-ROE-5-OCC-ELECTRON-DENS-V1.0,NASA Planetary Data System, 2010.
ABSTRACT_TEXT This dataset contains 29 ionospheric electron density profiles (EDS files)derived from Venera 15 and 16 radio occultation data. A total of 155profiles are believed to be available and it is hoped that all willeventually be archived.
PRODUCER_FULL_NAME PAUL WITHERS
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