LiDAR (Light Detection And Ranging) has been used as a highly accurate method to map terrestrial assets such as trees and the topography of an area for some time. A series of pulses are fired from the LiDAR system in an aircraft, which then travel down to the earth and reflect back up to a sensor on the LiDAR system. Once the pulse hits an object and reflects back to the sensor, the difference in return timings allows an accurate picture to be created*.
A series of points are captured and mapped with an accurate X, Y, Z location which is tracked via GPS. As the scan takes place, data is digitally recorded which calculates the height of the surface that it meets. The resolution is measured as point density, meaning that data received can be used to make 3D representations of the target in the form of a point cloud, a dataset that represents objects or space. To find out more about LiDAR, why not read our blog ‘Lifting the lid on LiDAR’?
By taking the extensive knowledge and experience gained in a terrestrial setting, the APEM team have made complex hardware and software modifications to develop a completely new system. This combination has allowed APEM to create a bespoke system that is suitable for use in the offshore environment.
Trials undertaken in 2019 gave APEM’s remote sensing and marine consultancy teams the confidence to map bird flight heights to within a one metre tolerance. This refined approach allowed us to get a sufficient number of points per square metre whilst also capturing ultra-high resolution still images suitable for species level ID.
By flying a LiDAR survey in a bespoke system setup with a high resolution digital aerial survey, we are able to combine the two data sets to calculate a bird’s flight height above the sea with a high degree of confidence.
Noise captured on LiDAR (such as moisture in the air, particles, large insects and sea spray) is isolated, giving our image analysts the confidence that clusters of points captured are more likely to be birds than noise. Birds identified and tagged are then overlaid to the LiDAR data using GIS and further clusters are matched.
This enhanced methodology is suitable for all stages of the permitting of an offshore wind farm including targeted monitoring studies for pre-construction/operations.
Usually for offshore wind site characterisation, a survey every month, and usually for a minimum period of two years to account for annual variation, is what regulators require to record aspects of a birds abundance and distribution. This includes behaviour, how their flight heights are distributed (are they feeding and therefore flying lower, or are they migrating and therefore flying higher) as well as taking account of windspeeds*. It provides invaluable site specific data on the ornithological activity and from this wealth of robust data, our specialists are able to input with high levels of confidence and precision into collision risk modelling to reduce precautionary assessment, typically as part of a Environmental Impact Assessment (EIA) or specific monitoring objective to validate assessment predictions.
How it all comes together – delivering global best practice
APEM’s approach to best in class survey design is a four step process, and has evolved over years of delivering digital aerial surveys.
Step 1 is data acquisition. This starts with planning the survey area to ensure that the correct data is captured at the optimal condition. Each survey flown has an onboard aerial survey technician who constantly monitors the data that is captured, ensuring that any adjustments needed are made immediately, negating the need to fly a further survey.
The second step is the analysis of the data captured. This is a meticulous task undertaken by highly skilled image analysts who review the images and identify species, providing characteristic tagging to each image.
Step 3 is taking all sources of data and bringing them together. When LiDAR is used as part of the data acquisition, APEM’s remote sensing scientists overlay the outputs from the image analysts with bird location GIS and the flight heights captured with LiDAR. A classing system is then used to rate high or low confidence based on the culmination of the data.
The final step is interpretation and recommendations. Our ornithology experts provide comprehensive reporting and modelling from the data captured, providing the detail required by the regulator.
This approach is unique to APEM, who have invested in purpose built LiDAR systems that will compliment our UK and European work such as at Sofia offshore wind farm.
To find out more please contact Stephanie McGovern, Associate Director Marine Wildlife Surveys.
* Notably this LiDAR technology is not the same as those deployed routinely for metocean monitoring.