全国一等水准点高程近20年变化分析

我国于1991—1999年建设的国家第二期一等水准网复测与2012—2015年建设的国家一等水准网成果相隔近20年。受地壳运动、经济建设、地下水开采与回灌等因素的影响,许多地区出现了不同程度的地表沉降和季节性地表起伏,造成区域高程成果发生了不同程度的变化,影响了高程基准的维护及高程成果的使用。本文通过分析两期一等水准重合点、统计分析我国一等水准点20年高程变化量及其变化趋势,并从两期水准网测量设备、措施及测量精度的差异,重力异常改正计算所采用的重力基准、正常重力公式及重力数据的差异,网形结构差异,水准测量周期、水准环闭合周期的差异,地壳垂直运动与局部地表形变影响等4方面进行了两期高程变化的原因分析。研究表明:(1)国家一等水准网点高程近20年发生了不同程度的变化,许多区域出现了严重沉降;(2)地壳垂直运动及局部地表形变是引起高程变化的主要因素;(3)国家一等水准网应进行定期复测更新,复测时应尽量缩短水准测量周期,全网水准测量周期不应超过5年[1]、力争3年内完成。

Elevation change analysis of the national first order leveling points in recent 20 years

National Administration of Surveying, Mapping and Geoinformation of China performed the first order leveling campaign for the second time from 1991 to 1999 and the latest leveling campaign from 2012 to 2015, respectively. The time span of two leveling campaigns was about 20 years, due to the influence of crustal movement, economic construction, groundwater exploitation and recharge, the ground surface settlement with different degree and seasonal surface relieves occurred in some regions, which led to various changes of regional elevation and affected the maintenance of height datum and the application of elevation results. The first order leveling coincidence points in the two periods and their changes and trends were analyzed. The reasons for the change of elevation were analyzed from four aspects, which are the difference of measuring equipment, measures and measuring accuracy of leveling network in two periods, the difference of gravity datum, normal gravity formula and gravity data adopted by correcting computation of gravity anomaly, the difference of configuration structure, the difference of leveling period and closure period of leveling ring as well as the influence of vertical crustal movement and local surface deformation. Through this analysis, we can conclude that the serious ground surface settlement occurred in some regions during the recent 20 years. The vertical crustal movement and local surface deformation are the major factors affecting the elevation changes. The first order leveling should be monitored on a regular period which should be no more than 5 years and strives for 3 years.