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Landslide Monitoring with GNSS

Many landslides move slowly, by millimetres or centimetres over days to months, before they move fast. Measuring that slow movement shows which ground is active, how fast it is going, and whether it is speeding up.

Grillo Slide measures it with satellite positioning (GNSS).

Why ordinary GPS is not enough​

A phone or a basic GPS receiver knows its position to within a few metres. Landslide movement is far smaller than that, so it would be lost in the error.

RTK (real-time kinematic) positioning removes most of that error. A base receiver at a known, stable point watches the same satellites as a rover on the moving ground. Errors from the atmosphere and the satellites affect both receivers in almost the same way, so the base sends corrections and the rover cancels them out. Over short distances this gets the rover's position relative to the base down to centimetres or better.

A Grillo Slide kit on a slopemoving groundstable groundLTEGrillo Cloudslide.grillo.ioBasereferenceRoverRoverRover2 hopsradio mesh
Rovers on the moving slope report through the radio mesh to the base on stable ground, which uploads over LTE.

When the rover has used the corrections to resolve its position precisely, it reports an RTK Fixed solution. Grillo Slide only uses RTK Fixed readings to measure movement.

Movement is measured against the base​

Every rover's movement is the change in its position relative to the base. That makes the base the reference for the whole site:

  • The base must be on stable ground outside the area that is moving. If the base moves, every rover appears to move by the same amount.
  • The base first surveys its own position by averaging GNSS for several minutes. See Survey the base.
  • Each rover's first valid reading is its baseline, its zero. Later readings are reported as movement east, north, and up from that baseline, in millimetres.

If a device is moved on purpose, reset its baseline so the move is not counted as ground movement. See Reset the movement baseline.

Reading the results​

  • Single readings scatter. Each reading includes a little noise, up to about 2 cm on Grillo Slide. Judge movement from the trend over many readings, not from one point.
  • Vertical is noisier than horizontal. GNSS measures height less precisely than horizontal position, so expect more scatter in the up component.
  • RTK Fixed is about the solution, not the site. It shows the receiver resolved its position, not that the installation is free of errors. A loose mount, a shifting antenna, or nearby reflections can still produce false movement.
  • Steady drift, steps, and acceleration mean different things. Steady drift suggests creep; a sudden step can be real movement or a disturbed device; a rate that keeps increasing deserves urgent attention from a geotechnical specialist.

What affects quality​

FactorEffectWhat to do
Sky viewTrees, walls, and steep slopes block satellitesPlace antennas with as open a sky as possible
ReflectionsSignals bouncing off nearby surfaces bias the positionKeep antennas away from metal, rock faces, and buildings
MountingA mount that leans, settles, or vibrates looks like movementUse rigid, deep mounts; fix antennas firmly
Distance to baseCorrections are less exact far from the baseKeep rovers within the site, near the base
Snow, ice, and vegetationCan cover antennas or tilt mountsInspect after storms and seasonal change

How often to measure​

Grillo Slide takes a reading every 6 hours. That suits slow-moving slopes, where the trend over days and weeks matters most, and lets devices run from a battery and solar panel. It is not designed to catch a sudden failure as it happens; that needs continuous sensors and a dedicated warning system.

Using the data responsibly​

Movement data supports decisions; it does not make them. Interpret it with a geotechnical engineer or geologist who knows the site, and set any response thresholds with them. Grillo Slide does not currently send movement alerts.