Evaluating aerial LiDAR and other approaches to avian flight height measurement – ReSCUE Project Validation Study Report

Evaluating aerial LiDAR and other approaches to avian flight height measurement – ReSCUE Project Validation Study Report

BTO Research Report, 2025

Citation

Rhoades, J., Feather, A., Harwood, A., Banks, A. & Boersch-Supan, P.H. 2025. Evaluating aerial LiDAR and other approaches to avian flight height measurement – ReSCUE Project Validation Study Report. BTO Research Report 796: British Trust for Ornithology, Thetford, Norfolk
Download file

Overview

This report investigates the accuracy and reliability of seabird flight height data that are used to mitigate impacts of offshore wind farms on seabird populations.

Through a set of trials, we set out to validate Light Detection and Ranging (LiDAR)-coupled Digital Aerial Surveys (DAS), and to a lesser extent size-based methods. Additional technologies evaluated in the trials included bird-borne Global Positioning System (GPS) telemetry tags and human-operated laser rangefinders.

We found that the comparative performance of the two LiDAR-coupled Digital Aerial Survey suppliers varied based on system differences and weather conditions during surveys, particularly in terms of detection rates from different sensors. LiDAR flight height measurements, however, proved to be accurate and precise for both suppliers, with measurement uncertainties on the scale of centimetres. In contrast, size-based DAS estimates had uncertainties on the order of tens of metres.

Findings from this study will directly inform the development of best practice guidance for seabird flight height data collection and analysis, supporting impact assessments for offshore wind farms while minimising ecological risks to seabird populations.

Abstract

  1. The ReSCUE project investigates the accuracy and reliability of seabird flight height data to mitigate impacts of offshore wind farms on seabird populations.
  2. A set of validation trials was conducted onshore at Predannack airfield in Cornwall (19—30 August 2024) and offshore near the Flamborough and Filey Coast (FFC) Special Protection Area (SPA) in September 2024.
  3. The focus of the trials was to validate Light Detection and Ranging (LiDAR)-coupled Digital Aerial Surveys (DAS), and to a lesser extent size-based methods. Additional technologies evaluated in the trials included bird-borne Global Positioning System (GPS) telemetry tags and human-operated laser rangefinders (LRFs).
  4. Onshore trials used static and suspended target arrays of artificial birds and moving targets (drones) to explore detection rates, flight height accuracy, and flight height precision under controlled conditions.
  5. Offshore trials examined the real-world performance of LiDAR-coupled DAS systems under varying flight altitudes.
  6. Two aerial survey providers, here referred to as Supplier 1 and Supplier 2, participated in the trials using different instrumentation and data collection approaches. Both suppliers provided LiDAR-based height measurements, and Supplier 1 provided size-based DAS height estimates.
  7. We found that the comparative performance of the two LiDAR-coupled DAS suppliers varied based on system differences and weather conditions during surveys, particularly in terms of detection rates from different sensors. LiDAR flight height measurements, however, proved to be accurate and precise for both suppliers, with measurement uncertainties on the scale of centimetres. In contrast, size-based DAS estimates had uncertainties on the order of tens of metres.
  8. Inaccurate target size determination in the imagery was the primary driver of DAS height estimate errors. Heterogeneity in target sizes, intended to mimic natural body size variation, was a secondary driver.
  9. Results of GPS telemetry and LRF trials provided insights into precision and accuracy and the ability of tracking data to capture dynamic flight patterns, complementing data from aircraft-based technologies.
  10. GPS data showed flight height uncertainties on the scale of tens of metres, whereas LRF measurement achieved accuracy and precision on the scale of metres under optimal conditions, but sampling efficiency and reliability was challenging with these devices.
  11. Findings from this study will directly inform the development of best practice guidance for seabird flight height data collection and analysis, supporting impact assessments for offshore wind farms while minimising ecological risks to seabird populations.

This work was commissioned by Natural England as part of the ReSCUE (Reducing Seabird Collisions Using Evidence) project, with funding from The Crown Estate and Natural England’s Species Recovery Programme. The ReSCUE project forms part of the Offshore Wind Evidence and Change (OWEC) programme, led by The Crown Estate in partnership with the Department for Energy Security and Net Zero and Department for Environment, Food & Rural Affairs. The Offshore Wind Evidence and Change programme is an ambitious strategic research and data-led programme. Its aim is to facilitate the sustainable and coordinated expansion of offshore wind to help meet the UK’s commitments to low carbon energy transition whilst supporting clean, healthy, productive, and biologically diverse seas. The ReSCUE project is led by Natural England, and delivered as part of the Natural England/BTO Research Partnership providing the evidence needed to support nature’s recovery and people’s experience of the natural world.

Scroll down