Pioneer Venus Orbiter(PVO) Electron Temperature Probe (OETP) Data Bundle
Pioneer Venus Orbiter (PVO) Electron Temperature Probe (OETP) Ionopause Data Description
PD3S_DATA_SET_ID = PVO-V-OETP-5-IONOPAUSELOCATION-V1.0
PDS3_DATA_SET_RELEASE_DATE = 1993-10-01
START_TIME = 1978-12-05T15:07:34.817
STOP_TIME = 1992-10-07T19:46:27.000
PRODUCER_FULL_NAME = DR. LARRY BRACE, DR. ROBERT F. THEIS
Collection Overview
===================
The Ionopause collection gives the orbit-by-orbit times and locations of the ionopause
crossings, which are evident as sharp gradients in Ne at the top of the ionosphere. (These
crossings always occur within 30 minutes of periapsis, so they may be seen in the High
Resolution Ne files).
The ionopause and bow shock crossing times and locations are easily identified in the high
resolution Ne measurements (Theis et al., 1980). These files contain the UT, altitude,
latitude, SZA and local time of each crossing.
On the dayside, the ionopause is taken (somewhat arbitrarily) at the level in the steep
gradient of the ionopause where Ne = 1x102 cm-3. On the nightside, the ionopause is selected
at somewhat lower densities because the absence of spacecraft photoelectrons lowers the Ne
measurement threshold. In both cases, the intent is to identify the ionopause as the point
where the first rise of Ne above the background density occurs. Of course, the ionopause
itself is not a point but is the extend region in which the ionopause density gradient occurs.
Confidence Level Overview
=========================
The ionopause location is selected at that point in the steep gradient of the ionopause where
Ne crosses through the level of 1x102 cm-3. When the spacecraft is in darkness, the pe
background is absent and the ionospheric Ne is also much lower, so the ionopause is identified
as the first rise in Ne above whatever background is present. The ionopause is identified by a
human operator who views each high resolution Ne pass plot on an interactive computer terminal.
He selects the ionopause somewhat subjectively as the time of the first rise above the
background Ne, which may consist of magnetosheath plasma or photoelectrons. The 40 minute pass
plots used for this purpose provide only a 5-10 second accuracy in the crossing times. When
irregularities or waviness in the ionopause produce several ionopause crossings, the outer most
crossing is the only one identified.
References
==========
Brace, L.H., Global Structure of Ionosphere Temperature, in Space Research X. Amsterdam,
The Netherlands: North-Holland, p.633, 1970.
Brace, L.H., 'Orbiter Electron Temperature Probe', L. Colin and D.M. Hunten, Eds. Space
Sci. Rev., Vol.20, No.4, p.454, June 1977.
Brace, L.H., R.F. Theis, and A. Dalgarno, 'The Cylindrical Electrostatic Probes for
Atmosphere Explorer -C, -D, -E', Science, Vol.8, No.4, p.341, Apr.1973.
Brace, L.H., R.F. Theis, J.P. Krehbiel, A.F. Nagy, T.M. Donahue, M.E. McElroy, and A.
Pedersen, 'Electron Temperatures and Densities in the Venus Ionosphere', Science,
Vol.203, p.763, Feb.23, 1979.
Brace, L.H., H.A. Taylor Jr., P.A. Cloutier, R.E. Daniell Jr., and A.F. Nagy, 'On the
Configuration of the Nightside Venus Ionopause', Geophys. Res. Lett., Vol.6,
p.345, 1979.
Brace, L.H., R.F. Theis, H.B. Niemann, H.G. Mayr, W.R. Hoegy, and A.F. Nagy, 'Empirical
Models of the Electron Temperature and Density in the Nightside Venus Ionosphere',
Science, Vol.205, p.102, 1979.
Colin, L., Pioneer Venus Overview, IEEE Transactions on Geoscience and Remote Sensing,
Vol GE-18, No. 1, pp. 5-10, 1980.
Fimmel R.O., Colin L., and Burgess E., 'Pioneering Venus: A Planet Unveiled',
NASA SP-518, 1995.
Hoegy, W.R., and L.E. Wharton, 'Current to Moving Spherical and Cylindrical Electrostatic
Probes', J. Appl. Phys., Vol.44, No.12, p.5365-5371, 1973.
Krehbiel, J.P., L.H. Brace, J.R. Cutler, W.H. Pinkus, and R.B. Kaplan, 'Pioneer Venus
Orbiter Electron Temperature Probe', IEEE Transactions on Geoscience and Remote
Sensing, GE-18, 49, 1980.
Langmuir, I. and H. Mott-Smith, Jr., 'Studies of the Electric Discharges in Gases at Low
Pressures', Gen. Elec. Rev., p.616, Sept.1924.
Mott-Smith, H. and I. Langmuir, 'The Theory of Collectors in Gaseous Discharges', Phys.
Rev., Vol.28, pp.727-763, 1926.
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.
Shai, M.C., 'Formulation of Electrically Conductive Thermal-Control Coatings ', NASA Tech.
Paper 1218, Apr.1978.
Smith, D., 'The Application of Langmuir Probes to the Measurement of Very Low Electron
Temperatures', Planet. Space Sci., Vol.20, p.1721, 1972
Spencer, N.W., L.H. Brace, G.R. Carignan, D.R. Taeusch, and H.B. Niemann, 'Electron and
Molecular Nitrogen Temperature and Density in the Thermosphere', J. Geophys. Res.,
Vol.70, pp.2665-2698, 1965.
Theis, R. F., L. H. Brace, K. H. Schatten, C. T. Russell, J. A. Slavin, J. A. Wolf, The
Venus ionosphere as an obstacle to the solar wind, Advances in Space Research, 1, 47,
1980.
Yang, L., 'Preparation and Evaluation of CVD Rhenium Thermionic Emitters', in The Third
Annual Conference on Chemical Vapor Deposition, F.A. Glaski, Ed., American Nuclear
Society, 1972.
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