Mission-Tracking Data. By using Lunar Orbiter IV tracking data and laser
ranging data, gravity coefficients of the lunar gravity field were developed by
W.L. Sjogren (Ferrari, et al., 1980). Based on the newly derrived gravity
field, a new topographic datum of the Moon has been derived in terms of
spherical harmonics of fith-degree and fifth-order with the sixth-degree
sectorial terms (Wu, 1981b). From the results of the celestial mechanics
experiment of Mariner 9 (Jordan and Lorell, 1975), the topographic datum of
Mars has also been derived based on the fourth-degree and fourth-order
spherical harmonics of the Martian gravity field (Wu, 1981b). These two datums
have been adopted to be the 0-elevation reference surface of all topographic
maps of the Moon and Mars.
Pioneer Venus Radar Altimeter Data. With a wavelength of 17cm, the radar
altimeter aboard Pioneer Venus covered about 93%, between 74° North latitude
and 63° south, of the Venusian surface. The resolution of the radar altimeter
data is about 150km with an accuracy of about 200m (Masursky, et al., 1980).
Using the Pioneer Venus altimeter data, a preliminary global topographic map of
Venus has been compiled at a scale of 1:50,000,000 with a contour interval of
lkm. As shown in Figure 2, Venus has a relief difference of 13km. The terrain
of Venus consists of 8% highland (6053-6062km); 65% upland rolling plains
(6051-6053km), and 27% lowland (6049-6051km) (Masursky et al., 1980).
Fig. 2. PRELIMINARY TOPOGRAPHIC MAP OF VENUS--EQUATORIAL REGIION. (Map was
compiled, at a scale of 1:50,000, using radar altimetry data of the
Pioneer Venus mission. The contour interval is lkm. Elevations
are referred to a mean radius of 6051.5km).
28
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