Aiborne LiDAR in peatland restoration

By Dr Miles Wilson, GIS and Remote Sensing Officer for the North Pennines AONB Partnership

Miles presented a webinar in June 2022 about Airborne LiDAR use in peatland restoration. You can watch the webinar below:

Peatlands in the UK were commonly drained following World War II to increase agricultural land. Drainage has led to habitat loss and decreased biodiversity, deteriorations in downstream water quality, increased downstream flood risk, and increased carbon emissions to the atmosphere. Our restoration work aims to reverse these effects.

At 1983 km², the North Pennines AONB & UNESCO Global Geopark is the second largest AONB in England and contains approximately 900 km² of peatland. Such a vast area would take many years to survey on foot to plan restoration work, so any planning we can do from a desk improves our efficiency in the field and ultimately means we can restore larger areas quicker. Our desk-based planning to date has used aerial photographs collected from aeroplanes or Unoccupied Aerial Vehicles (UAVs), but freely available airborne LiDAR data offer additional information we can use to enhance our planning.

What is LiDAR?

LiDAR stands for “Light Detection and Ranging” and uses pulses of light from a laser to calculate distances to objects by measuring the time for reflected light to arrive back at the sensor. These data can be used to create digital 3D models. Airborne LiDAR has the laser aimed at the ground from an aerial vehicle, most commonly aeroplanes but also possible from UAVs. Airborne LiDAR therefore enables the creation of 3D models of the Earth’s surface (elevation models) and surface objects. LiDAR sensors also measure the strength of the reflected light (called intensity), which partly depends on an object’s composition, for example dark objects reflect less light than lighter objects.

How can peatland restoration use LiDAR?

We follow a five-step methodology in our peatland restoration in the North Pennines AONB:

• Hydrology – emplace dams in gullies to improve water retention
• Slopes – reprofile steep slopes to reduce erosion
• Heather brash – cover bare peat with brash to reduce erosion and maintain water
• Re-start vegetation growth – use lime, fertiliser, seeds and plug plants to kick start vegetation growth to further reduce erosion and retain water
• Re-establish sphagnum – emplace sphagnum clumps to help retain water

LiDAR data products can help us plan for all five restoration steps and enhance what we can gain from aerial photographs:

• Hydrology – elevation data can be used to calculate where water would flow over the surface, where erosional gullies are plus their widths and depths, and what water volume dams might retain
• Slopes – elevation data enable slope angles to be calculated for each square metre of land, which can help us identify where reprofiling is required. We can also identify large areas of low angle slope, which may be dry and require bunding techniques to help retain water
• Heather brash – intensity data can be used to help map bare peat. Bare peat is dark in colour and reflects less light from the LiDAR laser than surrounding vegetation. We can also estimate vegetation heights which may help us identify where to cut heather for brash
• Re-start vegetation growth – intensity and vegetation height data can help us identify areas of poor/thin vegetation that need a helping hand
• Re-establish sphagnum – the LiDAR laser uses a near-infrared wavelength, which is absorbed by water and wet vegetation. Intensity data can therefore give us an idea about areas where vegetation is, or is not, retaining moisture, and guide where we might harvest healthy sphagnum and target planting.

Where do our LiDAR data come from?

The LiDAR data we use are freely available from the Environment Agency and were collected by their Geomatics group as part of the National LiDAR Programme. The National LiDAR Programme aimed to provide complete coverage of England at 1 m spatial resolution over four consecutive winters by the end of 2021.

The Environment Agency collect LiDAR data primarily for flood risk mapping, historically focusing on high-risk areas such as flood plains, urban areas and the coastal zone. However, the need to understand whole catchments meant that the National LiDAR Programme also included upland areas, such as our own AONB.