# Application of Acoustic Emission Technique in Landslide Monitoring and Early Warning: A Review
## 2 Current Landslide Monitoring Methods
### Limitations of Existing Methods  
Although current methods for monitoring landslides have demonstrated success in identifying hazardous areas and analyzing past incidents, they possess limitations that hinder their effectiveness as reliable early warning systems. Table 5 summarizes the advantages and disadvantages of several traditional slope monitoring methods. Geodetic techniques are constrained by the intermittent nature of data acquisition, which is not suited for the continuous monitoring required for unstable slopes. Additionally, surface measurement techniques fail to capture subsurface kinematics that are critical for understanding buried structures, infrastructure, and processes such as deep-seated soil creep. Furthermore, the interpretation of the results often involves significant uncertainties due to factors such as vegetation density, atmospheric distortions, and terrain irregularities. Geotechnical instrumentation faces challenges related to limited subsurface coverage, as the costly deployment of extensive networks along every potential failure plane at sufficient depths is often impractical. Post-failure detection can delay timely responses, even if full slope coverage is achieved. The high costs associated with these systems prohibit large-scale implementations without continuous government subsidies, which is unsustainable for developing countries, which experience the majority of global landslide disasters each year. Additionally, field instrumentation can become ineffective when access to hazardous areas is obstructed during active failure events. Geophysical methods are limited by resolution constraints and may yield ambiguous results, necessitating integration with additional techniques, as standalone solutions often lack clearly interpretable parameters. Seismic monitoring requires dense station networks for effective source localization, which increases costs and is not feasible over extensive areas. Remote sensing methods are impaired for continuous monitoring due to infrequent revisit periods and dependence on favorable weather conditions for image acquisition. Detected changes typically correspond to displacements that have already occurred, rather than capturing early-stage precursory deformations. Moreover, discrepancies may exist between the surface morphological expressions delineated from optical imagery and the actual shear planes that govern internal slope failure mechanics. \begin{table}
\begin{tabular}{c c c} \hline
**Monitoring Methods** & **Advantages** & **Disadvantages** \\ \hline \multirow{2}{*}{Geodetic Methods} & High precision; direct measurement; less & Limited measurement points; low efficiency; high requirements for the environment. \\ \hline \multirow{2}{*}{Geotechnical Methods} & Strong pertinence; real-time monitoring; combined with engineering practice. & Damage to the rock and soil mass; high maintenance costs; representativeness issues. \\ \hline \multirow{2}{*}{Geophysical Methods} & Large-area detection; non-contact & Damage to the rock and soil mass; high maintenance cost; representativeness issues \\ \cline{2-3}  & measurement; multi-parameter measurement. & Damage to the rock and soil mass; high maintenance cost; representativeness issues \\ \hline \multirow{2}{*}{Remote Sensing Methods} & Macroscopic monitoring; fast data update; not restricted by terrain. & Relatively low precision; dependent on weather and lighting; complex data processing. \\ \hline \multirow{2}{*}{AE Technique} & Early damage sensitivity; possession of a & \multirow{2}{*}{Potential damage to rock and soil masses; high maintenance costs; issues with representativeness.} \\  & natural signal source; applicability in & \\ \cline{1-1}  & multiple fields; comprehensive analysis of & \\ \cline{1-1}  & signal parameters. & \\ \hline \end{tabular}
\end{table} 
Table 5: Comparison of slope monitoring methods. These limitations render existing methods less effective as early warning tools that can be integrated into community-based disaster preparedness strategies.