France is being laser 3D-mapped to create a tool to identify flood risks, manage mountain forests, check land for farm subsidies, and even find archaeological sites.
The Lidar HD project uses airborne laser beams to create an image from the reflected light that ‘sees through’ vegetation to the solid surface.
Using its two specially equipped Beechcraft planes, state geographic agency IGN has already mapped part of the south east and Corsica, with the Vosges mountains and Rambouillet forest next in line.
Lidar (LIght Detection And Ranging) is a telemetry technique (distance measurement) that uses the properties of light. Whether on land or on board an aircraft, Lidar is based on the same acquisition process: a scanner, whose position and orientation are measured continuously, emits infrared laser pulses towards an object or towards the ground at high frequency then records very precisely the time elapsed between the emission of these pulses and their return to the transmitter in order to deduce the position of the points impacted. At the rate of several hundred thousand pulses emitted per second, the device quickly generates a large quantity of geo-referenced points. The data is then processed to develop 3D digital models: digital terrain models (altimetric description of the ground), digital surface model (altimetric description of the ground and above ground), etc.
It aims to cover all of France by 2025 in the €60million plan. The IGN has hired private aircraft to help, and 10 planes are now involved.
The work is expected to take 7,000 flight hours, with pilots flying in square or rectangular patterns at between 1,000m and 2,000m. They can only gather data on clear days but can also work on clear nights.
In the south east, they are concerned with built-up areas which are at risk of flooding in particular. 3D mapping shows the places at risk and allows modelling of what could happen and how to reduce the risk.
The agriculture ministry sees it as a way to help with forestry management in mountain areas, to check farm subsidy claims and to identify new areas for particular crops.
The maps will be released through the IGN’s Géoportail pages and are free for individual use.
Once completed, the maps can be used for all sorts of things which we have not thought of yet.
The Lidar HD program in numbers:
- 5 years of work
- 7,000 flight hours
- 10 points per square meter on average
- 4 groups of subcontractors in support
- 3 petabytes of data
- 60 million euros estimated budget