Accurate peat depth data is required for site selection, micro-siting of assets within sites, planning ground investigations, and planning civil works. Currently, this data is obtained through manual peat probing, which is unsafe for the operatives taking measurements, often produces inaccurate measurements, is dependent on agricultural and ecological factors for site access, and is slow and labour-intensive with high associated costs and a frequent need for repeated surveys.

The proposed solution is to develop a method of surveying peat depth using geophysical sensors mounted on drones (including frequency-domain electromagnetic (FEM), photogrammetry, LiDAR, radiometric, and ground penetrating radar (GPR) sensors). This method aims to produce peat depth heat maps that are accurate to ±2m or better without ground truthing and ±0.5m or better with ground truthing, estimating the presence of peat up to 8m below ground level. 

Benefits

The key benefits associated with this innovation project are as follows:  

• Safety: The drone-based method will allow surveys to take place without operatives walking across bogs.
• Accuracy: The drone-based method will provide a continuous map and not rely on interpolation. It should also be able to identify and account for obstructions and layers of superficial sediments. This will result in a more accurate estimate of total peat volume and reduce the amount of costly mid-construction redesign needed.
• Environmental/Community Impacts: The drones will be able to operate without disturbing agricultural land or ecosystems.
• Efficiency:  
  • The drone-based method would allow more sites to be surveyed, earlier in the site selection process, and as a result land carbon considerations and construction feasibility considerations could be more easily considered in site selection.
  • Peat probing is often completed on wide grid spacing during early project development and then repeated with closer grid spacing once the site layout has been refined, leading to multiple mobilisation costs. Earlier refinement of the peat thickness model would allow earlier design layout decisions and fewer mobilisations.
  • Drone surveys will be faster – covering a 50 hectare (ha) site with 10m grid spacing with peat probes would take over 40 days – with drone surveys, this may be reduced to as few as 7 days. 
• Cost:
  • Drone surveys are expected to achieve almost a 50% cost reduction per hectare compared to peat probing on a 10m grid (the nearest comparison, because although peat probing can be conducted more cheaply on a wider grid, only a 10m or smaller grid is comparable to the continuous coverage of drone surveys). Drone surveys are expected to cost £1,919/ha while peat probing on a 10m grid averages £3,818/ha.
  • 467 ha of peat surveys would be required for savings from using drones to make up the innovation development cost. This is equivalent to peat surveys for either: 6.7 400kV substations, 15.6 275kV substations, or 23.4 132kV substations. Considering the number of substations to be built and the use of peat surveys for overhead lines and underground cables, it is expected to reach the breakeven point approximately one year after deployment of the innovation, based only on SSEN-T proposed projects.
    • With an estimated uncertainty range, between 356 and 658 ha of peat surveys will likely be required for savings from using drones to make up the innovation development cost.
  • After breakeven, the per-hectare lifetime saving from using drones instead of probing is £1,173 (in 2018 terms). This is the difference between the lifetime cost per-hectare of probing, £2,359, and the lifetime cost per-hectare of drone surveys, £1,186 (in 2018 terms).  
    • With an estimated uncertainty range, savings will likely fall within the range of £828.87 to £1,445.50 per hectare (in 2018 terms).
  • If this innovation (drone surveys) had been adopted for all SSEN-T T3 projects (including T3 132kV, 275kV and 400kV substations, overhead lines and underground cables), total lifetime savings would equal £15.68 million (in 2018 terms). This is hypothetical and assumes that the cost of the innovation was incurred in 2021, with peat surveys carried out from 2022 to 2026. We can assume similar savings will be realised for T4 projects (relative to the scale of investment in T4), which will likely be the first to consistently use drone surveys, since peat surveys are on average completed around 5 years prior to energisation.
    • With an estimated uncertainty range, savings will likely fall within the range of £9 million to £24.6 million.