# Analysis of Mining Waste Dump Site Stability Based on Multiple Remote Sensing Technologies
## 4 Discussion of Experimental Results  
### SBAS Results  
The displacement velocity map along the line of sight (LOS) direction over the Xudonggou dump site is depicted in Figure 8. The Google Earth image was used as background image. As shown in Figure 8, negative displacement rates indicated projected movements away from the satellite platform, whereas positive values indicated projected movements toward the satellite platform. In the study area, a total of 3072 pixels were selected for a time series analysis. Most of the points were located at the platforms or roads and the highest density of PS points was on the south slope. However, only two groups of PS points were selected for the area in which we were interested. These are highlighted by the red and yellow rectangles. As shown in Figure 9, The LOS displacement velocity of PS points basically obeyed the normal distribution. The mean displacement rate over the study area was about \(-1.44\) mm/yr with standard deviation of \(8.22\) mm/yr and approximately \(73\%\) of the pixels showed displacement velocities between \(-9.66\) (\(-1.44\) \(-\) \(8.22\)) mm/yr and \(6.78\) (\(-1.44\) \(+\) \(8.22\)) mm/yr. In statistics, the standard deviation is a measurement used to quantify the dispersion of a set of data values. In the SBAS results, a lower standard deviation indicated that the displacement rates of PS points tended to be close to the mean displacement rate, whereas a higher standard deviation indicated that the displacement rates of the PS points were spread out over a wider range. Generally speaking, a lower standard deviation value is expected in time series InSAR results. This is because most PS points should be more or less stable in a study area and deformation only happens to a small portion of the PS points. The largest displacement velocity along the LOS was \(-42.17\) mm/yr, whereas the lowest was about \(0\) mm/yr. Figure 7: The assumed geometry in the first simulation if the failure surface is a plane. For landslide studies, even if the assumption that deformation only occurs parallel to the slope surface is applied for simplicity, the true deformation direction of PS points in rugged areas is still a complicated issue due to the diversity of local incidence angles. The deformation estimated by SBAS was just a projection of the true deformation onto the LOS direction. If a very high precision DEM is available, the three dimensional projection geometries for all PS points can be automatically derived according to their respective geographic locations. Then, accurate translation from the LOS direction to the slope direction can easily be carried out. Unfortunately, there is no accurate DEM for the Xudonggou dump site to carry out automatic translation for the 3072 PS points. Therefore, geometric translation was only conducted for four points near the terrestrial measurement points for the purpose of cross validation. From May to September 2015, total station measurements were conducted weekly at the study site. The locations of total station measurement points (A1-A8 and B1-B5) are depicted in Figure 1b. The cumulative deformation of the ground measurement points along the slope direction are shown in Figure 10, indicating that the cumulative displacements of the 13 points varied from 29.06 mm to 137.94 mm. Along Platform 1, A8 presented the largest movement (about 117.73 mm), whereas A3  
Figure 8: Displacement velocity along line of sight direction with the Google Earth image used as a background image. Figure 9: Distribution of displacement velocities in LOS direction. presented the smallest deformation (about 46.47 mm). Along Platform 2, B1, B4 and B5 were relatively stable with displacements of 32.87 mm, 51.72 mm and 29.06 mm, respectively. On the other hand, B2 and B3 showed relatively poor stability, with cumulative deformations of about 130.81 mm and 137.94 mm respectively. The deformation of the nearest PS point along the slope was compared with the ground measurement data of Points A3, B1, B2, and B3, respectively.