THE CORRELATION ANALYSIS OF SUBSIDENCE MONITORING BY D-INSAR AND THE CHANGE OF URBAN CONSTRUCTION LAND

The change of urban construction land affect the subsidence directly or indirectly, the method of D-InSAR has centimeter level or even millimeter accuracy that can provide a reliable and accurate data for the research of correlation analysis of subsidence monitoring by D-InSAR and the change of urban construction land. This article takes Guiyang, Nanning city as example, using 3m level TerraSAR data to construct the Subsidence model by interferometric measurement, then compared with the Chinese national land use change remote sensing survey database at the same measure time to have a correlation analysis GIS research between subsidence and the change of urban construction land. The results shows that the integral correlation coefficient achieved 0.78 between subsidence and the change of urban construction land, the major construction area and the high density construction area are with severe land subsidence. In addition, the correlation coefficient increased from the main city to the suburbs, indicates that some of the main city causes permanent settlement and is difficult to recover. It also shows that some area subsidence caused by long-term mining or other natural factors has no strong correlation with the change of urban construction land, therefore, the results of D-InSAR subsidence monitoring have a reaction on urban construction planning, guiding urban planning to high stability, low settlement area.


INTRODUCTION
The routine monitoring ways of ground subsidence is mainly by levelling, GPS measurement, stratified standard measurement and so on.These ground measurements can only measure subsidence information at sparse points on the ground, lack of spatial density, difficult to cover large areas and The interference phase at point P is: The phase caused by the line of sight to the deformation ΔRd is: The amount of the left side of the above formula can be calculated from the phase and orbital parameters of the interference pattern, and then the line of sight of each point of view to the deformation variable ΔRd is obtained, then the entire area of the surface deformation is calculated.

General Situation and Data Preparation
Nanning City is located in the southwest of China, is the capital of Guangxi Province, it is the northern Gulf Economic Zone and the core cities in southern China.
The crust is relatively stable in the area, but there is a lot of groundwater exploitation in the old city.The crust is relatively stable in the area, but there is a lot of groundwater exploitation in the old city.In order to analyse the correlation between the data results, the TerraSAR-X monitoring data with the resolution of 3m at same period with the monitoring spot were selected.The incident angle was 33 degrees, and the experiment was selected The Nanning area in January and August, a total of six high-repeat coverage of the same track TerraSAR data for differential interference measurement.In order to study the correlation between the all-weather remote sensing monitoring plots and the regional subsidence, the spot of new construction and the subsidence were superimposed (as shown below)， In the figure, the fragmented spots shows the new construction land data of the all-weather change survey, and it is found that the core construction area appears positively correlated with the degree of settlement, especially like XiXiangTang District in the northwest and LiangQing District in the south, Both of the settlement funnel with a higher higher construction intensity.In order to express the correlation between the data objectively, the mean settlement value covered by the spot represent the degree of subsidence of the plots, the density of the plots in the radius of 500 m near the plots is taken as the concentration of the plots, then obtain the correlation between the degree of subsidence and the degree of plot concentration.The correlation index:

Data Processing
Through the above calculation method, the correlation between the the degree of plot settlement and the degree of concentration is 0.78, which is close to the high correlation.

CONCLUSIONS AND PROSPECTS
In this experiment, the settlement results of January 2016 to August 2016 in Nanning area were calculated by DInSAR.Two large settling funnels were found in the northwest and southern regions, and there is a high positive correlation with all-weather city change monitoring spots, indicates that the planning and construction work in the region is towards to the wrong spatial orientation.We will explore the reasons for the formation of sedimentation funnel in the future, control the settlement from the source.
Figure 1. Figure of "Double track" method Differential interferometry (DINSAR) imaging geometry (in the case of a three-track method) is shown as below, Δ Rd is the line of sight to the deformed.A1 and A2 are the two satellite locations where the satellite is imaged in the same area.The first SAR image is obtained before the surface deformation occurs, and the second SAR image is obtained after the surface deformation.The phase of the interference pattern formed by the two SAR images both contains the terrain information of the area and the observation during the deformation of the surface information.

Figure 2 .
Figure 2. Figure of "Three-track" method All-weather remote sensing monitoring is a project carried out by the Ministry of Land and Resources to monitor annual changes in urban construction data changes, the development of city border.Aiming to analyse the technical results of the land use credit file by analysing the monitoring results of each city.In the case of SAR orthographic imaging monitoring in Nanning area, the two time nodes monitoring are distributed in January 2016 and August 2016, and more than 500 urban construction spot are extracted through the refinement of human-computer interaction work.

Firstly
, estimate the baseline image of the pairs SAR image to be processed, he spatial baseline length of the three pairs of images is 24m, 57m, 46m, the time baseline length is 204 days, 211 days, 213 days.The SRTM 90m grid is selected as the base DEM data.eliminate the influence of orbit error, the DEM registration strategy is taken into account in the spectral offset calculation to ensure that the local terrain information.

Figure
Figure 5.Construction monitoring spots and settlement result Distribution of correlation index It is also found that Xixiangtang District is the old city of Nanning City, and occurred many cracking events by settlement, this place is also one of the most serious areas of groundwater exploitation.High positive correlation shows that the urban planning decision-making does not take the surface subsidence factor into consideration.There will be a hidden danger of settlement prevention and control work with sustained high-intensity construction.The city's urban development should focus on the smaller settlement of the study results, rather than strengthen the construction in the settlement funnel，In addition, governance work should be taken into account of two larger sedimentation funnel areas in XiXiangTang District and LiangQing District, forming a scientific planning and construction distribution.