of the surface as well as the atmosphere of Mars. Most of the results from 
those experiments (UVS, IRR, IRIS, TV and S-band radio occultation) were used 
in topographic mapping of Mars (Wu, 1978). Sixty thousand photographs from the 
Viking mission make it possible to systematically map the planet Mars. The 
Moon, the Earth's satellite, is mapped from topographic data derived from lunar 
photographs and other remotely sensed data. The following sections describe 
interpretations of those various data. 
S-band Radio Occultation. The S-band radio occultation experiments were 
  
   
   
    
   
  
  
  
  
  
  
  
     
   
    
included in both the Mariner 9 and Viking missions (Kliore, et al., 1973). 
There were 256 usable occultation points scattered between latitudes from 486? 
and -80? from Mariner 9 and about 155 points scattered over the entire Martian 
surface from the Viking mission. At the instant of the spacecraft orbital 
occultation at both entry and exit, the radii of Mars at those points were 
determined by recording the time immediately before and immediately after an 
occultation (Kliore, et al., 1972). The occultation data were received at the 
deep space stations at Goldstone, California, Woomera, Australia, and Cebreros, 
Spain. 
The Mariner 9 occultation points have a wide distribution and have an 
accuracy range of from 0.25km to 1.10km. Therefore, they were used as control 
of the Mars global topographic map using Mariner 9 data (Wu, 1975). The 
comparison of the Mars global map with the 69 occultation points observed from 
the Viking extended mission (Lindal, et al., 1979), shows that the elevation 
differences range from -5 to +2.4km, with an average absolute difference of 
about 0.9km. The average arithmetic elevation difference is only -0.13 km, and 
only 13% of the points compared have elevation differences larger than 2km (WU, 
1979). As shown in Figure 1, elevation differences are almost zero in the 
north and gradually increase to the south 
because the map was originally compiled from data that were sparse and 
unreliable in the south. 
Ultraviolet Spectrometer (UVS). One of the objectives of the ultraviolet 
  
   
   
  
  
  
  
  
    
   
  
    
  
   
    
    
   
   
   
  
spectrometer experiment of Mariner 9 was to measure the composition and 
pressure of the martian atmosphere at the surface of Mars (Barth, et al., 
1972). The reflected ultraviolet intensity is a measure of the number of 
atmospheric scatters. The local pressure can then be determined from these 
intensity measurements, and the variations of local pressure can be interpreted 
to measure the martian topography (Barth and Hord, 1971). There are almost 
7,500 measurements of elevation provided by the UVS experiment along 39 
revolutions (paths 140 to 216) of the Mariner 9 spacecraft; covering the planet 
Mars, from 60? south latitude to 45? north (Wu, 1975). The resolution is about 
30km. 
Infrared Interferometer Spectrometer (IRIS) and Infrared Radiometer (IRR). The 
infrared interferometer spectrometer was experimented with to infer the martian 
atmosphere and surface parameters which include the temperature for a vertical 
temperature structure. It also provides topographic information through the 
absorption of certain bands of CO0,. The local variations are 
claimed to be reliable to 0.5km, But the absolute accuracy is about lkm (Herr 
and Pimentel, 1969, Hanel, et al., 1970, Hanel, et al., 1972). The infrared 
radiometer is used to infer the thermal properties of the martian surface 
(Chase, et al. 1972). The data can also be used to compile a temperature map 
which can be correlated with topographic variations (Cunningham and Schurmeier, 
1969). There are about 4,600 elevation points provided from the infrared 
experiment also observed along the paths of Mariner 9, covering the planet Mars 
from 65? south latitude to 40? north (Wu, 1975). 
  
Earth base Radar Data. From radar observations, altitudes on the martian 
  
   
   
  
surface are calculated from signal time delay. In other words, variations in 
radar travel time to and from Mars are associated with the topographic relief 
  
    
  
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