Landslide mapping: assessing geological hazards using drones

26/11/2021

Landslide mapping: assessing geological hazards using drones

When a 14 meter fissure appeared on a hillside in the Georgian capital, geological experts deployed the senseFly eBee X drone to study the landslide and help assess reinforcement operations with an aerial survey of the high-risk area.


Type of mission – Disaster managementOutputs – Orthomosaic, DSM
Area – 2,523 km/ 252 ha / 623 acTotal images – 889
Drone – eBee X with Aeria XProcessing time – 4h30
Accuracy – 1.6 cm / 0.6 inProcessing software – PIX4Dmapper
RTK/PPK – YesLocation – Tbilisi (Georgia)
Flights needed – 2Data provided by – Vitali Machavariani, Georgian National Environmental Agency


In March 2021 the earth broke open on the Vashlijvari slope, a hillside located near a road connecting two residential areas of Tbilisi, Georgia’s capital. The colossal size of the cracking – 14 meters deep and around half a million cubic meters of torn landmass – alerted experts to respond quickly in order to prevent the width from increasing and the slope from sliding off completely.

If a debris flow were to happen, and because of the proximity of the landslide to urban zones, people’s lives and properties were at stake. 

Drone mapping of the Vashlijvari landslide in Tbilisi, Georgia
Aerial imagery of the landslide captured with the senseFly eBee X + Aeria X camera and processed with PIX4mapper. Two residential areas surround the site.

Tbilisi City Hall collaborated with international geologists and specialists from the Georgian National Environmental Agency to overcome the challenges of this geological hazard. The first was the danger of monitoring the land subsidence, the velocity of the soil and aperture of the open surface cracks in situ all while keeping workers safe.

The other was the need for a rapid assessment of the situation and its growing risks, such as the threat of the landslide consuming the nearby road network, causing substantial cost and damage to infrastructure. 

Landslide mapping of the Vashlijvari slope showcased a 14 meter fissure in Tbilisi
The landslide fissure was 14 meters deep. Using a fixed-wing drone to assess the situation was safer than employing terrestrial tools.

Aerial surveys with a drone for landslide mapping

The team of experts decided to use the eBee X fixed-wing drone to assess the geological hazard.

“When you have to be accurate, you choose the best possible way to achieve high-quality datasets. With the senseFly drone and the endurance battery (offering up to 90 mins of flight time) we could cover several square km per day. This means several days of savings if we surveyed with other tools”

Vitali Machavariani, from the National Environmental Agency Hydrometeorological Department. 

Orthomosaic map of the Vashlijvari landslide, captured with the senseFly eBee X and processed with PIX4Dmapper
Area mapped for this mission. The processing time in PIX4Dmapper was less than 5 hours for a total of 889 images captured.

The specialists monitored the landslide process over a few weeks. This dataset is one of the outputs generated during the study. The large area surveyed to create the orthomosaic and Digital Surface Model (DSM) was 2,523 km2 (252 ha / 623 ac). A total of 889 images were collected in two flights and processed with PIX4Dmapper in less than 5 hours. 

Precision was crucial to this mission. With this in mind, the team used the senseFly Aeria X photogrammetry camera and enabled the RTK/PPK option of the eBee X drone. Four checkpoints were used to verify the georeferenced accuracy of the RTK/PPK data and achieve an overall RMS error of 1.6 cm (0.6 in).

“Without the eBee X RTK/PPK solution, it would be much more time consuming to complete the survey with quadcopters and get sufficient, reliable data for decisionmakers”, adds Machavariani. 

High-resolution DSM and orthomosaic maps to assess geological hazards

“The generation of high-resolution aerial imagery with a drone is a crucial part for assessment of different types of geological hazards, combined with detailed DSM (Digital Surface Model) which allowed a detailed evaluation of the slope morphological features”, states Vitali Machavariani.

Indeed, thanks to the maps generated with the drone data, the team of experts could study the volume, curvature and movement of the landslide, to detect its direction, type, velocity, depth, and at the same time identify cracks and flow accumulation.

Drone mapping to assess geological hazards in the Vashlijvari slope, Georgia
The orthomosaic map allowed a detailed study of the landslide features and the debris flow risk.

The eBee X mapping and the digital outputs generated with PIXDmapper were essential for the landslide’s recovery efforts, which consisted of reinforcement and drainage. In August 2021 Tbilisi Mayor proclaimed the site stabilized.

This story was sourced from an entry in the 2021 senseFly & Pix4D Photogrammetry Awards, in the Disaster Management category.