# The Role of Earth Observation, with a Focus on SAR Interferometry, for Sinkhole Hazard Assessment
## 4 The role of Earth Observation in Sinkhole Hazard Assessment
### Detecting Precursors to Sinkhole Development
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Project** & **Geological Details** & **SAR System Parameters** & **Processing Parameters** & **Precursor Parameters** & **Sinkhole Parameters** \\ \hline  & Event: & & & & \\  & 3 sinkholes/subsidences—1 & SAR: Ground-based & & & & \\  & filled before collapse. & Band: Ku & Technique: Repeat-pass & & & \\  & Geology: & Resolution: 1 m & interferometry & Behaviour: non-linear, & 1.5-2.5 m \\  & Dolomite limestone. & Repeat: Daily & Projection: Vertical & rapid increase & Depth: 2 m \\  & Trigger Groundwater & Incidence \(\sim 10^{\circ}\) & & & \\  & abstraction. & & & & \\ \hline  & Event: 3 sinkholes & SAR: COSMO-SkyMed & Technique: Repeat-pass & & \\  & Geology: Evaporite & Band: X & interferometry & & \\  & Geology: Evaporite & Resolution: 3 m & Pair selection: Sequential & Behaviour: Non-linear & Diameter: 13 m \\  & Trigger: Decreasing water & Repeat: 16 days Seneca: 20 & Surface model: LiDAR 0.5 m & increase & \\  & levels & Incidence angle: 41\({}^{\circ}\) & Projection: Vertical & Lead time: 16-90 days & \\ \hline  & Event: Subsidence basins & & & & \\  & associated with hundreds of & SAR: ALOS PALSAR & Technique: Repeat-pass & & \\  & sinkholes & Band: L & interferometry & & \\  & 2007-2008, [10] & Geology: Evaporite & Polarisation: HH & Pair selection: Overlapping & \\  & Trigger: Seismic events & Scenes: 6 & Surface model: None & & \\  & and/or salt dissolution & & & & \\ \hline  & Event:sinkholes and & & & & \\  & subsidence & SAR: ERS-1 and ERS-2 & & & \\  & Geology: Evaporite & Band: C & & & \\  & Geology: Evaporite & Incidence angle: 23\({}^{\circ}\) & Surface model: Low resolution & & \\  & trigger: Water level decrease & Scenes: 16 & Projection: 2D Ascending and descending tracks & & \\  & or dissolution of salt layers & & & \\ \hline Arizona, USA, & Event: 3 Subsidence & SAR: ERS-1, ERS-2 and & & & \\  & associated with sinkholes & ALOS PALSAR & Technique: Repeat-pass & & \\  & Geology: Evaporite & Band: C + & interferometry & & \\  & Trigger: Salt dissolution & Scenes: 6 Eks, 28 ALOS & & \\ \hline  & Event: Subsidence surround 2 & & & \\ Texas, USA, & large existing sinkholes & SAR: ALOS PALSAR & & & \\
2006-2008, [4] & Geology: Evaporite & Band: L & & \\  & Trigger: salt dissolution and & Scenes: 3 & & \\  & water abstraction & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of investigations for which precursors to sinkhole development were successfully detected. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline  & Event: Subslidence surround 2 & SAR: Sentinel-1A & Technique: Multi-dimensional & Diameter: 500 m & Diameter: 100 m \\ Texas, USA, 2015 & Large existing Sinkholes & Band: C & S0 AS & Magnitude: 0.01–0.04 m & Dept: 34 m \\
[\%] & Trigger: set dissolution and water abstraction & Resolution: \(5\times 20\) m & Devent: descending tracks & & Rate: 0.03-0.014 m/year & Dept: 34 m \\ \hline  & Event: Sinkhole & & & & & \\ Gathering, South & Geology: Dolemie Triggers: & SAR: TerraSAR-X & Technique: Repeat-pass & Diameter: 90 m & Diameter: 2–15 \\ Africa, 2015 & Leaking servidules and ineffective stormwater & Sand: X & Protection: LOS & Magnitude: 0.067 m & m \\  & & Senesed: & Passed: & Parkin selection: Sequential & Behaviour: Non linear & Depth - 7 m \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\ \hline  & Event: Sinkhole & SAR: UAVSAR & Technique: Repeat-pass & Diameter: 400 m & \\ Louisiana, USA, 2012, [5, 11] & Geology: Evaporite & Senes: 2 & Interferometry & Magnitude: 0.260 m & Diameter: 110 m \\  & Trigger: Collapse of a brine & Resolution: 7 m & Projection: 2D Ascending + & Lead time: 1 m & \\  & well.