# Applications of Satellite Radar Imagery for Hazard Monitoring: Insights from Australia
## 7 Geomorphological Changes
### Example Case-Study: Geomorphological Monitoring in Remote Areas (Northern Territory)  
To demonstrate this application in an Australian environment, we select two areas (see Figure 2A for locations) that experience significantly different levels of precipitation, using SAR and InSAR to map geomorphological changes linked to precipitation. The first location (Figure 10) experiences an annual rainfall of 1700 mm (see Figure 3 for applications of SAR to monitor flooding in this region), and the second (Figure 11) is located in a desert environment, experiencing an annual rainfall of 300 mm [29]. In the region of high precipitation, we initially use the method described in Section 3.1.1 and Sentinel-1 backscatter intensity imagery acquired over a one-year period between 20170108 and 20171222 to delineate the floodplain extent. Open flood plains are identified by high-intensity values in Figure 10A and high COV in Figure 10C, whereas sparse forest is identifiable throughout Figure 10A and B by the texture created by contrasting canopy/ground SAR responses, with increased COV (see Section 3.1.1; red in Figure 10C) in regions where the penetration of the SAR signal beneath the canopy allows the detection of temporary floodwaters. Figure 10: Monitoring geomorphological changes in the Wildman coastal plain, Northern Territory, using Sentinel-1 between 20170108. and 20171222. (**A**,**B**) Maximum and Minimum pixel-values of VV intensity, respectively, throughout the observation period with the location of D shown by the green box. (**C**) Map of the COV, Minimum, and Maximum Gradient of VV intensity derived from the SAR time-series as in Figure 3. (**D**) InSAR-derived velocities showing negative LoS velocities on the floodplain banks. In Figure 10D, InSAR is used to measure relative differential LoS velocities across the floodplain banks. Negative LoS velocity is observed on the floodplain banks relative to the (assumed stable) surrounding sparsely vegetated forest. This signal may be attributed to the ablation of fine-grained sediments from the floodplain banks such that small baseline interferometric coherence is not lost (e.g., [74]), but the resulting change in land surface height is measurable. Alternatively, a conceivable explanation for the signal is the shrinking of surficial sediments as they dry or that the observed phase signal is directly related to the soil moisture change and not surface displacement (e.g., [75]). Moreover, we note the importance of accounting for the noise/coverage trade-off related to incorporating intermittently coherent pixels (occurring over vegetated areas and other temporally dynamic land covers) into the phase-to-displacement inversion procedure [35; 76; 77]. The contrasting, near-desert environment shown in Figure 11 experiences precipitation events from November to April, when fine-grained surficial sediments are prone to mobilization at rates dependent upon precipitation, slopes, and soil permeability/roughness. As in Figure 10D, InSAR measurements using images acquired between 20170504 to 20190314 were used to identify regions of relative surface velocities that may provide insight into sediment transport and/or swelling/shrinkage due to changes in water content (e.g., [35; 74]). Positive LoS displacements are identified corresponding to temporary ponds or salt lakes in flat areas (e.g., area labelled d in Figure 11), and negative LoS velocities are observed proximal to topographic gradients (e.g., areas labelled a, b, c in Figure 11). Figure 11: Mapping areas of active geomorphological changes in a desert environment, Northern Territory, using InSAR analysis of Sentinel-1 data between 20170504 and 20190314. (**A**) LoS velocities. Squares highlight the areas with LoS velocities >15 mm/yr in magnitude (a, b, and c are areas of negative LoS velocities; d is an area of positive LoS velocities). (**B**) Digital Elevation Model (ALOS 3D, JAXA, 2019) of the same area.