PDS_VERSION_ID        = PDS3                                                  
RECORD_TYPE           = STREAM                                                
OBJECT                = TEXT                                                  
  PUBLICATION_DATE      =  " "                                                
  NOTE                        = "Experiment description for the               
                                 Satellite Occultation Experiment conducted   
                                 starting in 1996 through 1997 (DOY 354       
                                 through DOY 215).  Formatted for display     
                                 or printing with up to 78 constantwidth      
                                 characters per line."                        
END_OBJECT            = TEXT                                                  
END                                                                           
                                                                              
                                                                              
     Satellite Occultation Measurement Experiment                             
                                                                              
     The Radio Propagation Team (part of the Radio Science Team) conducted    
occultation experiments during closest approach and during the cruise portion 
of the orbit. The occultation experiments were done at Europa, Ganymede,      
Callisto, and Io.                                                             
                                                                              
     In general, an occultation of the Earth occurs when the spacecraft       
travels behind a body from the Earth's point of view (or, from the space-     
craft's point of view, the body "occults" the Earth).  Ingress occurs when    
the spacecraft disappears behind the body, and egress occurs when the         
spacecraft reappears on the other side.  Right before ingress and right       
after egress, the signal travels from the spacecraft to the Earth through     
the body's atmosphere (or ionosphere).  These are the periods in which        
Radio Science is interested.                                                  
                                                                              
     The atmosphere (or ionosphere) acts like a lens, slightly changing       
the signal as it passes through.  The signal actually "bends" around the      
planet, and a phase change is observed on the Earth.  Since the spacecraft    
position is known, the amount of refraction caused by the atmosphere (or      
ionosphere) can be deduced.  The amount of refractivity is plotted verses     
atmospheric (ionospheric) dept in a refractivity profile.  The current        
model of the atmospheric composition (ionospheric density) of the body,       
which takes into account the types and behavior of the gases (electrons)      
is then altered to account for this refractivity profile.  Temperature and    
pressure profiles can be developed for the atmosphere from this data along    
the ingress and egress radio pathways and electron density profiles can be    
developed for the ionosphere along the same pathways.                         
                                                                              
     For the Satellite Occultation Experiment, the observation begins         
at 10,000 km above the Satellite and continues until ingress.  The            
observation resumes at egress and continues until 10,000 km above the         
Satellite.