The following are excerpts from :

Miller, Kent L., William C. Knudsen, Karl Spenner, "The Dayside Venus Iono-
sphere, I. Pioneer-Venus Retarding Potential Analyzer Experimental Observa-
tions", Icarus, 57, 386-409, 1984.

Copyright 1984 by Academic Press, Inc.
All rights of reproduction in any form reserved.


which has serveral sections which describe the intercalibration of the PVO 
Ion detectors. We have left information about page numbers and section titles
in place and have provided TIFF formated scanned images of the relevant 
figures. Figure captions have been included in this text portion of the 
document.




                         The Dayside Venus Ionosphere
         
     I. Pioneer-Venus Retarding Potential Analyzer Experimental Observations
         
              KENT L. MILLER,* WILLIAM C. KNUDSEN,* AND KARL SPENNER**
         
         *Lockheed Palo Alto Research Laboratory, Department 52-12, Building 
             255, 3251 Hanover Street, Palo Alto California 94304, and 
         **Institut fur Physikalische Messtechnik, D78  Freiburg, 
             BRD, Heidenhofstrass 8, West Germany
         
               Received August 23, 1983; revised January 2, 1984


==============================================================================
Conventions  [] indicate a superstript, {} indicate a subscript 
RPA = Retarding Potential Analyzer 
IMS = Ion Mass Spectrometer 
LP  = Langmuir Probe 
RO  = Radio Occulation 
==============================================================================



         DISCUSSION OF RESULTS
         

 FIG. 9. Median profiles of the particle pressure nik(T{e} + T{i}) 
 within the 65 +/- 5 deg. and 25 +/- 5 deg. SZA intervals. Medians 
 are medians of the local product and not the product of the medians. 
 The altitude scales for the two different SZA intervals are different.

                                     395


The RPA does not have the mass resolution required to resolve atomic ions 
into distinct peaks; the IMS instrument has the mass reslotuion to resolve 
these peaks. 
 
The ratio of C[+] + N[+])/O[+] (~0.07) (Taylor et al.1979a) based on IMS 
results. Use of this ratio makes a 7% change in the value of O[+] and will 
improve the ORPA reported ion temperatures. 
 
At higher altitudes the ratio of O[+]/N{i} is ~0.86. This makes the ratio 
(C[+] + N[+] + O[+])/N{i} ~0.93.  All other combined contribute only 
~7% of the total number density. 
 
The RPA doesn't resolve the ion masses 32(O{2}+), 30(NO+), and 28(CO+ + N{2}+)
into separate peaks. When the RPA peak is analyzed with a 2 ion (mass 32, 29) 
composition, the ratio is within 5% agreement with IMS below 200 km altitude. 
 
Below 160 km altitude the ratio of O{2}[+]/[M29[+] from ORPA is ~5 and from 
OIMS is 10-15. 
 
The shape and magnitude of the RPA determined [O{2}+] profiles differ from  
those reported by the IMS at low altitudes. The IMS density is a factor of  
approximately 2 larger than that measured by the RPA and shows a peak near  
175 km altitude.  
 
The values of CO{2}[+] reported by the IMS are approximately a factor of 2-3  
times larger than the RPA CO{2}[+] results.  
 
The values of O[+] reported by the IMS and RPA are approximately equal in  
the dayside ionosphere.  



                                     396


         ACCURACY
        
        
The estimated accuracy at which the RPA measures N{i}, O[+], O{2}[+] + M29[+],
CO{2}[+], and T{i} is approximately 5% (Knudsen et al., 1979a). 

The accuracy of T{e} is approximately 10% (Knudsen et al., 1979a)


         FIG. 15. Solar longitude variation of normalized T{e}.


                                      404

The inferred accuracy of the RPA total density measurement is within the  
approximately +/- 5% claimed.  
 
The four (RPA, IMS, LP, RO)  experiments are in satisfactory agreement above  
200 km altitude where O+ is approximately 90% of the total ion density.  
 
Below 200 km altitude the total ion density N{i} measured by the IMS  
systematically departs from the other three and reaches a factor of  
approximately 2.5 larger than that reported by the other experiments at an  
altitude of ~165 km.  
 

                                     405

Above 250 km altitude in the dayside ionosphere the peak corresponding to the 
ion group (O[+] + N[+] + C[+]) had a median number density equal to  
approximately 93% of N{i} which is consistent with the composition reported  
by the IMS. 
 
The RPA measurements indicate [O{2}+ + M29+] is approximately 90% of N{i}  
which is close to that (~95%) indicated by the IMS (Taylor et al., 1980).  
 
N{i}, [O+], and (O{2}[+] + M29[+]) are essentially independent measurements  
and N{i} is measured to approximately 5% 


FIG 18. Vertical profiles of median plasma density measured 
    by several Pioneer-Venus experiments in the same solar zenith 
    angle interval.

                                       406

Because the detectability of a minor ion increases with increasing fractional 
density, the possibility exists that the median densities reported for O[+],
(O{2}[+] + M29[+]), and CO{2}[+] may not accurately represent the true median 
in the altitude range





 FIG. 19. Contours of the ratio (n{i,1} + n{i,2})/N{i}, where n{i,1} 
 and n{i,2} are the ion concentrations corresponding to the two major 
 ion peaks measured by the RPA.

                                     407


         REFERENCES 

         KNUDSEN, W. C., J. C. BAKKE, K. SPENNER, AND V.
              NOVAK (1979a). Retarding potential analyzer for the
              Pioneer-Venus orbiter mission. Space Sci. Instrum.
              4, 351-372.

         TAYLOR, H. A., H. C. BRINTON, S. J. BAUER, R. E. 
              HARTLE, P. A. CLOUTIER, AND R. E. DANIEI L 
              (1980). Global observations of the composition and 
              dynamics of the ionosphere of Venus: Implications 
              for the solar wind interaction. J. Geophys. Res. 85, 
              7765-7777. 
 
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