PVO-V-OMAG-3--SCCOORDS-HIRES-V1.0 PVO VENUS MAG CALIBRATED SC COORDINATES HIGH RES V1.0 Dataset Overview This dataset contains full resolution magnetometer data from the Pioneer Venus Orbiter spacecraft beginning with orbit 3602 (Oct 16, 1988) and continuing until the orbiter was lost in the Venusian atmosphere (orbit 5055, Oct 7, 1992). The dataset differs from the high resolution magnetometer dataset from the previous orbits due to an anomaly in the multiplexer that controlled the sampling of the magnetometer sensors. During orbit 3602, and for the remainder of the mission, the spacecraft downlink contained magnetometer data from only the P sensor. The P sensor is the sensor which is aligned with the spacecraft spin axis, nominally in the direction of the ecliptic normal. After the anomaly was first detected, the magnetometer team made a substantial effort to recover the average magnetic field vector using the single sensor data. Since the sensor is not perfectly aligned with the spacecraft spin axis, a small amount of spin modulation is present in the sensor data. In theory, the amplitude of the spin plane field can be determined from the amplitude of the spin modulation and knowledge of the true sensor mounting geometry. In practice, this turned out to be a very difficult task because the spin axis of the spacecraft is not sufficiently constant in body-fixed coordinates. Data Processing This dataset has been calibrated to account for sensor zero levels, gains, and geometry. The data are given in units of nanoTesla. The data are at the full downlink sampling resolution. They have not been resampled during the data processing procedure. After the anomaly, the onboard calibrate signal continued to function and the calibration of the instrument was repeatedly checked. No change in gain was detected. The technique used to check the zero levels earlier in the mission could not be used after the anomaly occurred. Since the operations were limited to the low power available on the spacecraft, and since the magnetometer became a low priority instrument, it was not possible to check the zero levels to the levels desirable. However, it is clear that towards the end of the mission the zero levels had drifted significantly. It is recommended that these data be used principally in a variometer mode, i.e. for changes only. The dataset contains the following columns: Column Description ___________________________________________________________________________ UT S/C event time (UT) of the sample P1 Measured value of the P sensor at the sample time P2 Measured value of the P sensor at the sample time + 38 microsecs P2 Measured value of the P sensor at the sample time + 76 microsecs Bz The derived value of the spacecraft z-axis aligned magnetic field component at the sample time . Data Sampling The data ''P'' columns are values which have been sampled from the P sensor directly. The magnetometer samples each sensor 38 microseconds after the previous sensor sample. The data processing procedure uses the P1 sample to determine the Bz value and hence it is sampled at the start of sweep (time-tag) time. Ancillary Products Other datasets on the CD-ROM are the Ephemeris which contains spacecraft position in Venus Solar Orbital coordinates, spacecraft altitude, solar zenith angle, Venus centered longitude and latitude, spacecraft spin axis components, celestial longitude and latitude of the spacecraft, celestial longitude of the earth, and the Sun-spacecraft range. Other ancillary datasets are the: 1) phase and offset which contains the phase amplitude of sun synchronous modulation of the 4 signals (E100, E730, E5.4 and E30K), and offsets of the G sensor. 2) The engineering dataset which contains temperatures, magnetometer modes, magnetometer sample format, magnetometer spin average select, telemetry data format, telemetry bit rate, spacecraft spin period, pulse time, the difference between the Sun pulse time and the Rip pulse time, and the pulse time flag. CONFIDENCE_LEVEL_NOTE These data have been reprocessed several times during the course of the mission. Each successive reprocessing has eliminated some of the problems found in earlier version of the data. Please bring to the attention of the original investigator any suspicious section of data. No zero level correction has been applied to the data. References: Russell, C.T., R.C. Snare, J.D. Means and R.C. Elphic, 'Pioneer Venus Orbiter Fluxgate Magnetometer', Ieee Trans. Geo. Elec., vol. GE 18, no. 1 p. 32, 1980. /* Elphic R.C., C.T. Russell, J.A. Slavin, L.H. Brace, and A.F. Nagy, 'The location of the dayside ionopause of Venus: Pioneer Venus Orbiter Magnetometer observations', Geophys. Res. Lett., vol. 7, no. 8, p. 561, 1980. /* Elphic R.C., C.T. Russell, J.A. Slavin, and L.H. Brace, 'Observations of the dayside ionopause and ionosphere of Venus', J. Geophys. Res., vol. 85, no. A13, p. 7679, 1980. /* Luhmann J.G., R.C. Elphic, C.T. Russell, and J.A. Slavin, 'Observations of large scale steady magnetic fields in the nightside Venus ionosphere and near wake', Geophys. Res. Lett., vol. 8, no. 5, p. 517, 1981. /* Russell C.T, J.G. Luhmann, and R.C. Elphic, 'The distant bow shock and magnetotail of Venus: Magnetic field and plasma wave observations', Geophys. Res. Lett., vol. 8, no. 7, p. 843, 1981. /* Elphic, R.C., C.T. Russell, and J.G. Luhmann, 'The Venus ionopause current sheet: Thickness length scale and controlling factors', J. of Geophys., vol. 86, no. A13, p. 11,430, 1981. /* Luhmann J.G., C.T. Russell, L.H. Brace, H.A. Taylor, W.C. Knudsen, F.L. Scarf, D.S. Colburn and A. Barnes, 'Pioneer Venus observations of plasma and field structure in the near wake of Venus', J. Geophys. Res., vol. 87, no. A11, p. 9205, 1982. /* Russell, C.T., J.G. Luhmann, and J.L. Phillips, 'The location of the subsolar bow shock of Venus: Implications for the obstacle shape', Geophys. Res. Lett., vol. 12, no. 10, p.627, 1985. /* Phillips,J.L., J.G. Luhmann, and C.T. Russell, 'Magnetic configuration of the Venus magnetosheath', J. Geophys. Res., vol. 91, no. A7 p. 7931, 1986. /* Saunders, M.A., and C.T. Russell, 'Average dimension and magnetic structure of the distant Venus magnetotail', J Geophys. Res., vol.91, no.A5 p.5589, 1986. /* McComas,D.J., H.E. Spence, C.T. Russell, and M.A. Saunders, 'The average magnetic field draping and consistent plasma properties of the Venus magnetotail' J. Geophys. Res., vol 91, no. A7, p. 7939, 1986. /* Phillips, J.L., and C.T. Russell, 'Upper limit on the intrinsic magnetic field of Venus', J. of Geophys. Res, vol. 93, no. A3, p. 2253, 1987. /* Russell, C.T., E. Chou, J.G. Luhmann, P. Gazis, L.H. Brace and W.R. Hoegy, 'Solar and interplanetary control of the location of the Venus bow shock', J. of Geophys. Res, vol. 93, no. A6, p. 5461, 1988. /* Russell,C.T., 'Magnetic flux ropes in the ionosphere of Venus', Geophysical Monograph, vol. 58, p. 413 /* Orlowski D.S., and C.T. Russell, 'ULF waves upstream of the Venus Bow Shock: Properties of one-hertz waves ', J. Geophys. Res., vol. 96, no. A7, p. 11271, 1991.