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地球物理学与大地测量学(转载)

已有 4536 次阅读 2008-1-12 08:19 |个人分类:时空与重力场|系统分类:科普集锦|关键词:GEOPHYSICS,AND,,GEODESY| GEOPHYSICS, GEODESY

GEOPHYSICS AND GEODESY

LIDAR采集的月形数据,支持了月球形状研究,取得了重要进展。其单枪测量精度为40;在纬度高于七十五度以外的地区,以2度乘以2度(60千米乘以60千米)网格的数据采集和分析完善。

Clementine 在月球重力场研究中提供了超过一年的数据支持。

 

To date, the most thoroughly studied measurements from Clementine are those of the laser-ranging (Lidar) and gravitational-field experiments. Although the Lidar instrument was not designed for scientific studies of planetary topography, it provided a near-global topographic data set that is an important advance over our previous knowledge of lunar shape. The single-shot ranging precision of the Lidar was about 40 m and is comparable to the stated accuracy (100 m) of the spacecraft orbit with respect to the lunar center of mass. The high relief observed is unexpected and interesting. The verification of (previously proposed) degraded, ancient impact basins and the uniquely deep floors of Maria Crisium and Humboltium are other examples of the findings. The fact that the 2° by 2° (60 km by 60 km) grid is complete except at latitudes above 75° makes this set particularly valuable for geophysical studies across regional to global scales. However, because of the data's resolution and the instrument's inability to track over rough terrains (80% of all valid returns were obtained over maria, even though maria cover just 18% of the Moon's surface), the data set is generally not well suited for detailed regional modeling or short-to-medium-scale geophysical characterization of the lunar topography. Improvement in both the horizontal and vertical geodetic control of the Moon is, however, significant. Horizontal control, that is, the accuracy with which we now know the latitude and longitude of features on the Moon, particularly those on the far side, has been improved by about an order of magnitude.8 Similarly, improvement in the geodetic control to about 100 to 200 m vertically from the Clementine observations will prove valuable for registration of various data sets. This knowledge will also be useful for targeting future robotic and human exploration missions.

The gravity results also improve our understanding of the Moon, though to a lesser degree. The lunar highlands are found to be nearly isostatically compensated, whereas impact basins display a wide range of compensation states that do not correlate simply with basin size or age. The lunar crust is apparently thinned under all resolvable basins. Thus the Moon's structure and thermal history are more complicated than was previously believed.

The data on the far-side gravity field contain useful new findings but are poorly constrained with respect to the precise magnitudes of the anomalies owing to the usual problems associated with the tracking of an intermittently obscured spacecraft. Accordingly, significant uncertainty remains about the lunar gravity field, especially the far-side values and high-spatial resolution data; a future mission (including a subsatellite to allow differential tracking) will be required to complete the global gravitational survey of the Moon. In addition, gravitational observations over an approximately 1-year period will be necessary to unambiguously resolve possible tidal signatures that could indicate the presence (or absence) of a molten deep interior.

 

 

Lessons Learned From the Clementine Mission

http://www.nap.edu/html/ssb_html/Clementine/clem-ch2.shtml#geophysics



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