Slide Sentinel
Project Leads: Kamron Ebrahimi ([email protected]) and Blake Hudson ([email protected])
Landslides cost the United States an estimated $3.5 billion in infrastructural damage per year and claim the lives of 25-50 people annually. Regularly monitoring the activity of landslides (i.e. frequency and magnitude of deformations) with high spatio-temporal resolution and accuracy can provide valuable early warning information and aid in the interpretation of landslide kinematics. Traditional landslide monitoring techniques often require drilling, which is expensive, time-consuming, potentially dangerous, and limited in serviceability over time.
The Slide Sentinel aims to create a low-cost, easily deployable, landslide monitoring system capable of producing centimeter-level positional readings using RTK GNSS. The system consists of a centralized base station and a network of rover units which may be deployed over the extents of active landslide terrain. Rover units on the network wake at configurable intervals, receive RTK correctional data from the local base station and produce a positional reading. Readings are sent to the base station and are uploaded via an Iridium satellite link to a Google spreadsheet for real-time monitoring of rover movement. Rover units come equipped with a 6 milliG-precision accelerometer capable of waking the device in the event of sudden movement and can be remotely configured from a client portal to increase wake frequency and verbosity. A single base station and rover unit designed to operate in an environment with a clear sky view for 3 months costs ~$1800 USD, and can provide positional readings every two to three hours.
| Rover | Rover Empty |
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| Base | Base Empty |
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Use [RTK GNSS](RTK GNSS) to produce centimeter-level positional readings of rovers on the network
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Produce positional readings every 15 minutes
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Survive in challenging environments for upwards of 3 months with a low-power efficient design
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Produce a scalable network in which a single base can service 6 rovers over an [RF link](Freewave Z9-T/Z9-C)
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Configure rover verbosity and wake interval remotely via Iridium Satcom link
As the Slide Sentinel has matured and garnered more interest, the team has identified a need for a modular plug and play design. The Slide Sentinel is being developed to support a wide suite of GNSS receivers and communication links for better-tailored monitoring solutions.
The first GNSS receiver used in the design was the Skytraq S2525F8-GL-RTK. While extremely low cost (~$70), this receiver required 30 minutes to produce a reliable, accurate positional reading. Over the course of this wake interval a substantial amount of power was consumed by the RF link, making frequent wake intervals difficult. The device also performed poorly in 15m canopied environments, sufficient grounds to halt development against the unit. While this receiver is not a viable solution for rover units deployed in canopied environments, or rovers which need to wake frequently, this receiver would be ideal for a cheap, open-sky monitoring solution with 3 to 4-hour positional readings.
While the Skytraq S2525F8-GL-RTK did not provide the required performance for the Slide Sentinel, field testing this receiver provided the team insight into what makes RTK possible and the different factors one must consider when selecting a GNSS receiver for high multi-path environments.
Recent investments in satellite infrastructure by the EU (Galileo), China (Beidou) and Russia (GLONASS) have made multi-constellation, multi-frequency GNSS possible. Dual-frequency GNSS is the most recent development to hit the low-cost GNSS receiver commercial market, largely carried by the Swift Piksi Multi and Ublox ZED-F9P. Dual-frequency satellite reception allows for the robust correction of ionospheric attenuation by the receiver. While a single frequency GNSS receiver might produce positional readings of around 5 meters, dual-frequency GNSS can provide readings within 30 cm.
All satellites send data over the L band of the radio spectrum (one to two GHz). This band is further sub-divided into three smaller "slices" each about 2 MHz wide over which same satellite signals are simultaneously transmitted.
The Skytraq S2525F8-GL-RTK was the first GNSS receiver tested with the Slide Sentinel, it is ideal for solution on a tight budget, with open sky environments and positional readings every 3 hours.
| Skytraq S2525F8-GL-RTK |
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The Swift Piksi Multi is currently undergoing performance tests. The device can produce RTK fixes quickly (<60 seconds) and accurately in open sky environments, is a dual-frequency receiver, and supports the GPS L1/L2, GLONASS G1/G2, BeiDou B1/B2, Galileo E1/E5b and SBAS1. The downside of this GNSS receiver is its excessive power consumption (~2.9 Watts).
| Swift Piksi Multi |
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The ZED-F9P is the most promising low-cost receiver, and sits between the Swift Piksi Multi and Skytraq S2525F8-GL-RTK. The device is low power (~1 Watt), is dual-frequency and supports GPS L1C/A L2C, GLO L1OF L2OF, GAL E1B/C E5b, BDS B1I B2I, and QZSS L1C/A L2C. While this receiver has not yet undergone performance testing it is likely that its performance to cost ratio will out compete both the Skytraw and Swift receivers substantially.
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Development on the project is currently focused on reducing rover power consumption, designing an efficient base station printed circuit board, improving network scalability and researching commercially available OEM GNSS receivers capable of getting RTK fixes in canopied environments.