基于Morlet小波技术的北京平原地面沉降周期性分析

北京市地面沉降自20世纪60年代发现以来一直呈快速发展的趋势。不均匀地面沉降导致建筑物开裂、地基下沉，损害地下管道工程等基础设施，威胁城市安全。为了研究地面沉降发展的特征，分析其演化趋势，本文选取2011—2014年的27景Radarsat-2数据，采用干涉点目标分析技术，获取该时段北京平原区地面沉降时序监测信息；在此基础上，结合Morlet小波分析方法，根据相干点密度差异选取4个典型地面沉降区，分析其地面沉降多尺度演变特征。结果表明：地面沉降速率在空间分布上存在差异性，最大沉降速率为162.70 mm/a，年均沉降速率50.08 mm/a；地面沉降在时间域具有明显的局部周期性变化特征。在28 T （1 T表示1个24 d的时间段）的时间尺度下，存在着约13.3月的时间周期，不同位置还存在不同的不稳定震荡周期。

Periodical Analysis of Land Subsidence in Beijing Plain Based on Morlet Wavelet Technology

Land subsidence in Beijing has been developing rapidly since it was discoverd in the 1960s.Uneven ground deformation can destory buildings,and urban infrastructures such as underground pipelines,threatening urban security.In order to analyze the characteristics and the evolution trend of land subsidence in Beijing plain,27 scenes of Radarsat 2 data from 2011 to 2014 were collected,and the interference point target analysis (IPTA) technology was performed,to obtain the time series land subsidence information.On this basis,four land subsidence areas were selected representatively,and multi-scale evolution characteristics of land subsidence were analyzed through Morlet wavelet tranform respectively.The results show that the maximum subsidence rate is 162.70 mm/a while the average rate is 50.08 mm/a,and subsidence rates are quite different among these areas in spatial distribution.Moreover,the wavelet transforms analysis indicates that the land subsidence present obvious local periodic variation characteristics in the time domain.In particular,at the time scale of 28 T (1 T represents a perod of 24 d),there is a time period of about 13.3 months,with different unstable oscillation periods in different positions.