The transition of satellite InSAR technology to a ground-based system provides a proven risk reduction technology if combined with a critical slope monitoring (CSM) program. Together the technology with the active engagement of a defined program can detect the onset of slope displacement, acceleration, and provide a method to determine slope collapse. Recently, using the radar software, Guardian, and its ability to document surface velocity in intervals of 24-hours or less has allowed for the development of site-specific levels of rockfall risk.

The ground-based InSAR (interferometric synthetic aperture radar) systems and their near real-time capabilities allow for proactive and early warning monitoring. The technical requirements include the ability to operate 24/7 in all weather conditions, acquire data in near real-time, and visually present data in an interpretable format that requires no end user processing. Since slope failure without acceleration is unlikely, the rapid visual presentation of processed data becomes a crucial component for a CSM technology.

The definition of the CSM program not only requires short intervals for data acquisition, processing, and visual presentation but also requires a monitoring professional that can interpret and communicate changes in slope movement. A specific CSM technology requirement demands, acquiring data at a continuous interval of 2-minutes or less, 24 hours per day for the duration of the monitoring project. Also, the CSM technology must be able to transmit alarm messages at the moment thresholds are met, visually present data with various time series plots, including displacement, and velocity maps while acquired radar data is continuously updated and with no end-user processing. A site-specific document called a trigger action response plan (TARP) needs to be prepared at the start of any CSM project. Currently, only the IBIS-FM and ArcSAR radars developed by IDS (Ingegneria Dei Sistemi) GeoRadar can meet the technical requirements of the defined CSM technology.

During a CSM program, the short interval between each data acquisition provides two specific advantages. First, the short acquisition interval decreases interpolation, which automatically increases data confidence. Second, the short intervals also decrease the effects of atmospheric changes that are a part of all data acquisitions. Although the IBIS-FM and ArcSAR radar systems can operate in nearly all-weather conditions, sudden changes in local atmospheric conditions can still exhibit data effects. Both radar systems include active proprietary algorithms that account for ongoing atmospheric changes during acquisitions. In comparison, some remote sensing data acquired from, LIDAR, and total station technologies can be critically affected by sudden changes in local atmospheric conditions.

Combining the near real-time capabilities of an interferometric synthetic aperture radar system with a dedicated professional will decrease risk to people and property by allowing slope movement trends to be identified and observed in near real-time, 24-hours per/day. The paper will discuss the highlights of several successful CSM programs. We describe deployment versatility, the ability to identify the onset of displacement accurately, and the critical identification of the onset of acceleration.

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