# Analysis of Mining Waste Dump Site Stability Based on Multiple Remote Sensing Technologies
## 1 Introduction  
Significant amounts of fragmented waste rock and loose top soil are excavated and piled at a certain site during the mining process, making up to several large man-made dumps with heights of more than one hundred meters [1]. The capacity of some waste dumps reaches tens of millions of cubic meters and some even reach hundreds of millions of cubic meters. Because of the loose structures of the dump sites, the unstable slopes pose a threat to local safety due to the high risk of landslide or debris flow, especially after heavy rainfall [2]. Therefore, stability monitoring of waste dumps is essential to ensure the safety of local lives and properties. With the continuous advancement of science and technology, ground surveys such as prism leveling, total station measurements, and GPS measurements are widely used in China. However, it is difficult for ground survey technology to retrieve the deformation patterns of a whole area since it can only accurately measure deformation at a few points. As an important complement to traditional ground survey methods, synthetic aperture radar interferometry (InSAR) has become a popular tool for large area displacement monitoring, especially with the rapid development of timeseries InSAR (TS-InSAR) algorithms such as permanent scatterers interferometry (PSI), small baseline subset (SBAS) analysis [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. Although, it has widespread applications and has been utilized to measure deformation with promising accuracy, it remains difficult to overcome the limitations of 1-D line-of-sight (LOS) measurements caused by the intrinsic side-looking geometry of SAR sensors [15]. Since ground displacements generally happen in both horizontal and vertical directions, how to translate the 1-D LOS measurements to the real displacements of the ground targets is a key problem plaguing the successful application of TS-InSAR technology. At present, the ways of resolving three-dimensional surface displacements can be categorized in three ways [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. The first way is by combining the multi-pass LOS and azimuth measurements generated from SAR observations. For example, three dimensional displacements can be extracted by combining multiple InSAR LOS measurements from at least three viewing angles [16; 17; 18; 28; 29], or by combining InSAR LOS measurements with azimuth measurements from offset tracking (OT) or multi-aperture interferometry (MAI). The second way is to integrate InSAR measurements with GPS data [30; 31; 32; 33; 34; 35; 36]. However, it is often difficult to satisfy the requirements of the above mentioned approaches. The above mentioned approaches all have their drawbacks and are only applicable in certain circumstances. For example, fused multi-pass InSAR LOS measurements can only be applied to areas where multiple stacks of data are available and high precision in the north-south directions is limited to high-latitude regions [18]. The fusion of InSAR LOS measurements with azimuth measurements obtained by OT or MAI has low accuracy in terms of north-south displacements because of the relative insensitivity to slow displacements of OT and MAI [17]. The integration of InSAR measurements with GPS data strongly depends on the number and distribution of GPS observations [35]. Fortunately, as a way to relax the requirements for TS-InSAR analyses, there is a third way that involves simply translating the InSAR measurements according to some prior information [37; 38; 39; 40]. For example, the assumption that displacements only occur parallel to the ground surface can be made for landslides and glacial movements and horizontal deformation can be neglected when analyzing the subsidence of a large area, etc. Other remote sensing technologies, complementary to TS-InSAR, are also necessary for a complete investigation of ground displacement.