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topographic mapping, for example, during 349 days in 
Martian orbit, the instruments for five of the six 
experiments (Masursky et al., 1970) of Mariner 9 
provided measurements of the surface and 
atmosphere of Mars. Most of the results of these 
experiments were used to compile the early version 
contour maps of Mars (Wu, 1975, 1978). The 
following is a brief description for each of these data 
sources. 
2.2.1 S-band Radio occultation: The S-band radio 
occultation experiments were included in all Mariner 
missions, including the Mariner 9 (Kliore et al., 1973). 
The radius of Mars can be determined at the instant of 
the spacecraft orbital occultation at both entry and exit 
by recording the time immediately before and 
immediately after an occultation (Kliore et al., 1972). 
A total of 256 usable occultation points from Mariner 9 
mission were used. The two Viking missions added 
about another 155 points that make occultation points 
having a wide distribution over the entire Martian 
surface. The uncertainty of the  occultation 
measurements used range from 0.25 km to 1.10 km 
(Kliore et al., 1973; Christensen, 1975), therefore, 
they were used as one source of primary controls for 
the derivation of the Mars planetwide control network. 
2.2.2 Ultraviolet Spectrometer (UVS): The major 
objectives of the UVS experiment were to measure 
structure, composition, and pressure of the Martian 
atmosphere (Barth et al., 1972). The local pressure 
at the surface can thus be converted to topographic 
values (Barth and Hord, 1971). The UVS experiment 
provided about measurements of elevation along 39 
orbital nadir tracks, covering 60°S to 45°N latitudes. 
The measurement precision depends on the weather. 
Data were used only for the early version of the 
1:25,000,000-scale global topographic map of Mars 
(Wu, 1975). 
2.2.3 Infrared Interferometer spectrometer (IRIS) 
and Infrared Radiometer (IRR): The infrared 
interferometer spectrometer was used to infer the 
Martian atmosphere and surface which include the 
temperature for a vertical temperature structure. It 
also provides topographic information through the 
absorption of certain bands of carbon dioxide. The 
absolute accuracy is about 1 km (Herr and Pimentel, 
1969; Hanel, et al., 1970; Hanel et al., 1972). The 
infrared radiometer is used to infer the thermal 
properties of the Marian 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 Schumeier, 1969). There 
are about 4,600 elevation points provided from the 
infrared experiment also observed along the tracks of 
Mariner 9 in the same regions covered by the UVS 
experiment, covering the planet Mars from 65? south 
latitude to 40?north (Wu, 1975). 
965 
2.3. Earth Based Radar Data 
Radar observation of Mars were initiated in 1963 
(Goldstein and Gillmore, 1963). Elevation on the 
Martian surface are calculated from signal time delay. 
In other words, variations in travel time to and from 
Mars are associated with the topographic relief on the 
Martian surface. The resolution of the observations 
can be as small as 8 km and the precision of the 
height measurements ranges from 75 m to 200 m ( 
Pattenngill et al., 1971, 1973; Downs et al., 1971, 
1973; Goldstein et al., 1970). However this precision 
is simply a direct translation from the time 
measurements of the observations. 
Along with sensor data from Mariner 9 , more than 
15,000 data points on Mars topography observed from 
Goldstone Observatory, California and Haystack 
observatory, Massachusetts, were used in this 
experiment for compiling both the early and the current 
versions of contour maps of Mars. All the information 
of Earth-based radar data used can be found in Wu's 
publication (Wu, 1975). For local relief, the radar data 
seem to be very reliable but for global topography, the 
ephemeris and the figure of Mars used as the datum 
are important factor for radar observations. 
More than 2,700 radar points from the oppositions of 
1967, 1969, and 1971 at Haystack Observatory, and 
more than 13,000 points from the oppositions of 
1969,1971, and 1973 at Goldstone Observed were 
used for the Mars project. The coverage of these 
points from these two observatories is approximately 
from south 22.5° latitude to north 25° latitude. the exact 
location of each year's opposition of Haystack and 
Goldstone observatories are shown in Wu's 
publication (Wu, 1975) 
3. MARS COORDINATE SYSTEM AND MAP 
PROJECTIONS 
3.1 Mars Coordinate System 
In 1972 the Mariner 9 Geodesy/Cartography Working 
Group of the Television Team selected the Martian 
zero-meridian to pass through a particular small crater 
which is approximately at the center of a larger crater. 
The large crater was then named Airy (in honor of the 
late director of the Greenwich observatory, Sir George 
Biddell Airy, who installed a transit instrument to be 
used to define the prime meridian on the Earth in 
1884) and the small crater Airy-0. The longitudes of 
this new system increases to the west. The Airy-0 is 
located at -5.19° south of the Martian equator (de 
Vaucouleure et al., 1973) 
Reports from the IAU Working Group on Cartography 
Coordinates and Rotational elements of the planets 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996