Pioneer Venus Orbiter (PVO) Ion Mass Spectrometer Data Bundle Pioneer Venus Orbiter (PVO) Ion Mass Spectrometer High-Res Data Collection Description PDS3_DATA_SET_ID = PVO-V-OIMS-3-IONDENSITY-HIRES-V1.0 START_TIME = 1978-12-05T14:41:18.480 STOP_TIME = 1992-10-07T00:00:00.000 PDS3_DATA_SET_RELEASE_DATE = 1993-10-01 PRODUCER_FULL_NAME = DR. PAUL CLOUTIER Collection Overview =================== The Pioneer Venus Orbiter (PVO) Ion Mass Spectrometer High-Res Data Collection contains data from the Orbiter Ion Mass Spectrometer (OIMS) experiment and orbit attitude data for orbits 1-5055, including data for the period periapsis +/- 30 minutes for each orbit (1978-12-05 - 1992-10-07). The collection is divided into multiple files which contain 1 orbit. The user should be able to easily get to any desired orbit by selecting the appropriate file. Data ==== The data are provided in fixed length records (ASCII) with each record consisting of 118 fields totaling 953 bytes. The record structure is described below. Each record represents one complete OIMS experiment data cycle (normally 6.3 seconds but this time can vary with the bit rate). Within each record there are 55 samples of mass and the density associated with that mass. The sequence of masses within a record will normally follow the OIMS 'explore' mode, but this sequence may vary when the experiment is occasionally in the 'explore-adapt' mode. To compute the time associated with a particular mass and density, the dwell time element (element 5) should be used along with the time of day (element 3). The dwell time is time interval (milliseconds) between samples. Thus, for the 'Nth' sample, the time would be computed as follows: TIME = UT = (N - 1) * DWELL/1000 (where UT is the time of day) The user should be aware that some of the densities have been coded. For example, the values 999 and 9.9999e+04 are the missing data values for mass and density, respectively, for that point. (This can be due to several reasons such as telemetry interference or a gap in the data occurred.) Also, a negative value of density represents a 'flagged' data point and should be used with caution. Column Data Type Bytes Description =============================================================================================== PVO TIME ASCII_String 15 PVO TIME indicates the time of the sample as a two field value in the format YYDDD SSSSS.SSS, where YY is the 2-digit year, DDD is the day-of-year (Jan 1 = 001), and SSSSS.SSS is the second-of-day (space padded on the left). A value of 99999.999 for FSEC indicates that the value of FSEC was unavailable. This column can be parsed into its constituent elements using the format I2,I3,X,F9.3 DWELL ASCII_Integer 6 Dwell time (time interval between samples, msec). DWELL = (TIME - UT)*1000/(n-1) BITS ASCII_Integer 6 Bit Rate (bits/sec) LAT ASCII_Real 7 Venusian Latitude (deg) LON ASCII_Real 8 Venus Longitude (deg) ALT ASCII_Real 10 Altitude (km) SZA ASCII_Real 9 Solar Zenith Angle (Sun-Venus-PVO) (deg) SHA ASCII_Real 9 Solar Hour Angle (hr) MASS1 ASCII_Integer 4 Mass of Sample number 1 (AMU) DEN1 ASCII_Real 10 Number density of Sample 1 (ions/cm^3) MASS2 ASCII_Integer 4 Mass of Sample 2 (AMU) DEN2 ASCII_Real 10 Number density of Sample 2 (ions/cm^3) . . . . . . . . . . . . MASS55 ASCII_Integer 4 Mass of Sample 55 (AMU) DEN55 ASCII_Real 10 Number density of Sample 55 (ions/cm^3) Confidence Level Overview ========================= Bad data have been excluded or flagged by using negative values for density. Users should still use caution when interpreting these data. No error estimates for the densities are provided. References ========== Brinton, H.C., L.R. Scott, M.W. Pharo, III, and J.T.C. Coulson, The Bennett ion-mass spectrometer on Atmosphere Explorer-C and -E, Radio Sci., vol. 8, 323, 1973. Taylor, H.A., Jr., H.C. Brinton, S.J. Bauer, R.E. Hartle, T.M. Donahue, P.A. Cloutier, F.C. Michel, R.E. Daniell, Jr., B.H. Blackwell, Ionosphere of Venus: First observations of the dayside ion composition near dawn and dusk', Science, vol. 203, 752, 1979." Taylor, H.A., Jr., H.C. Brinton, S.J. Bauer, R.E. Hartle, P.A. Cloutier, F.C. Michel, R.E. Daniell, Jr., T.M. Donahue, R.C. Maehl, Ionosphere of Venus: First observations of the effects of dynamics on the dayside ion composition, Science, vol. 203, 755, 1979. Colin, L., Pioneer Venus Overview, IEEE Transactions on Geoscience and Remote Sensing, Vol GE-18, No. 1, pp. 5-10, 1980." Nothwang, G.T., Pioneer Venus Spacecraft Design and Operation, IEEE Transactions on Geoscience and Remote Sensing, Vol GE-18, No. 1, pp. 5-10, January 1980. Grebowsky, J. M., W.T. Kasprzak, R.E. Hartle, K.K. Mahajan, T.C.G. Wagner, 'Superthermal Ions Detected in Venus' Dayside Ionsheath, Ionopause, and Magnetic Barrier Regions', J. Geophys Res., vol. 98, no. E5, 9055, May 25, 1993. R. O. Fimmel, L. Colin, and E. Burgess, 'Pioneering Venus: A Planet Unveiled', NASA SP-518, 1995.