High-Resolution Digital Photography for Offshore Aerial Bird Surveys
As a result of the rapid growth in the offshore wind sector, the demand for spatial environmental data is constantly increasing. Traditional visual aerial survey methods suffer from reliability, safety and data quality drawbacks. These can be overcome by new digital methods, and in this article we discuss the application of these new technologies to offshore aerial bird and mammal surveys.
By Stuart C. Clough, Director of Remote Sensing, APEM, UK
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}Bespoke surveys collect a series of ultra-high-resolution digital still images which are captured using state-of-the-art, aircraft-mounted camera equipment, typically forming a grid of images across the survey area. This technique has been applied successfully to generate statistically robust population estimates and to describe distribution for offshore wind farm sites around the UK. Obtaining accurate and precise estimates of bird and mammal abundance is crucial to quantifying the effects of offshore wind farm construction and operation, while exact geo-referenced locations of birds can inform decisions on turbine placement. This technology can help answer essential questions about the potential impact of offshore development, and ensure developments are optimally sited It is neither appropriate nor safe to carry out low-level visual aerial surveys after the construction of a wind farm, and the data collected is inherently biased by the presence of the turbines. Therefore, APEM has developed a very high-resolution digital aerial photography technique to determine animal density and distribution based on scientifically sound principles, which can be used before and after construction.
Background
Birds are among the most protected classes of fauna in both the UK and Europe, with government bodies, local authorities, pressure groups and the general public taking great interest in their protection. To satisfy stringent regulator requirements and ornithological focus groups, any data on breeding, passage or wintering birds needs to be robust, defensible and reliable. To this end, APEM has developed high-resolution digital aerial imaging techniques, designed to provide statistically sound results with the quickest possible turnaround. APEM have been conducting ultra-high-resolution aerial surveys since 2006 to provide expertise in a business area that continues to thrive and develop, and is currently engaged in aerial ornithological surveys for a number of marine renewable energy projects, including Round 1, 2 and 3 offshore wind farms and at sites proposed for wave and tidal energy generation.
Aerial Survey Methods
Ornithological surveys have traditionally been carried out by boat or low-level aerial-based bird spotters. However, such techniques can often be costly and/or unreliable, and pose greater risk to both participants and wildlife. Modern aerial surveys are undertaken in twin-engine aircraft fitted with state-of-the-art cameras and bespoke flight management systems (Figure 1). These systems, controlled by comprehensively trained staff, produce digital still imagery at resolutions as high as 2 centimetres (Figure 2). Such images are used to identify birds (and marine mammals) from a safe altitude, thus minimising ecological disturbance. An aircraft can safely cover huge areas in a single day and collect large datasets quickly and efficiently. Data is often collected in a grid pattern, each image being equidistant from its counterparts on the x and y axes. Survey design is defined prior to the start of monitoring and therefore the amount of data collected is dependent on the size of the area and the spacing between image nodes.
Analysis of Imagery
While the collection of large datasets has clear advantages it has also presented the industry with a need to develop innovative ways to handle and analyse data. Bespoke bird identification software has been developed in-house using novel object recognition algorithms. This has been linked to a tailored graphical user interface (GUI), which automates the geo-location of birds and facilitates the measurement of wing-span, length and flight height and direction (Figure 3), thus speeding up the bird identification process prior to analysis by APEM’s specialist ornithologists. Automated analysis tools have also been developed in-house to differentiate between species where similarities in colour and plumage are not distinguishable by eye. Developers often require a rapid turnaround between survey and data delivery; therefore maximising automation at this stage of the process – without reduction in output quality – is key to meeting industry requirements. Such datasets can be stored permanently and revisited when required.
Population Estimates and Statistical Analysis
APEM routinely uses a systematic grid-based approach to data collection, collecting a representative sample of the birds present at the time of survey. Each sample can be considered an independent estimate of population. This survey approach is conducive to spatial statistical analysis, which regulators deem increasingly reliable for bird population assessment. Non-parametric bootstrap methods are used to provide confidence limits and contribute to the high degree of statistical robustness. Precision calculations are used to obtain a ‘coefficient of variation’ (CV), which can be used before or after survey to determine the ideal number of image samples to detect a change in the population of a particular species. For a species of interest, a CV of <0.16 is targeted, enough to be able to detect a doubling or halving of a population.
Model-Based Spatial Distribution Estimates
Using relevant covariate data, model-based statistical approaches such as General Additive Models (GAMs) can be used to produce density surface maps over the study area (Figure 4). These display areas of lesser and greater density, based on model predictions and including environmental parameters such as bathymetry, geological substrate, distance to shoreline and distance to relevant Special Protection Areas (SPAs). As an equal number of images are collected on the x and y axes in a gridded survey, coverage of the survey area is evenly spread, meaning that models including environmental variables are not biased by disproportionate coverage of relatively more (or less) important habitat. Pre- and post-construction geospatial comparisons can be performed to illustrate the changes in bird densities across the survey area resulting from wind farm development. This analysis will detect and pinpoint where these changes are the most important, and will reveal whether these changes are statistically significant.
The Future of High-Resolution Aerial Photography
The scientifically robust nature of the survey design, and the significant cost savings compared to other techniques, has led to a huge increase in the demand for high-resolution aerial photographic surveys. For this reason, it is expected that this survey technique will quickly become an industry standard. Increasingly, developers are seeing the merits of high-resolution still photography for other aspects of offshore wind farm development. For example, identifying and selecting the most appropriate route for the cable which brings the energy ashore is a complex process, which can be informed by high-resolution still photography. The images can be used to underpin a range of studies including archaeology, ornithology and terrestrial habitats without setting a foot on the ground. Remote sensing techniques are becoming increasingly mainstream for environmental assessments, and with much impact assessment work still to be done for many offshore renewable projects, the future for specialist environmental consultancies looks bright.
Summary
High-resolution aerial photographic surveys provide a modern, viable and safer alternative method to traditional data collection and handling for the offshore wind industry. The high-resolution data outputs obtained from high-resolution aerial photographic surveys of proposed and operational offshore wind farm sites have generated robust datasets on which critical planning and implementation decisions can be based and which can be revisited many times. The data outputs are of a very high standard, enabling quality assurance and detailed statistical analysis to examine avian population densities and abundance in the offshore environment. Confidence in the implementation of the data collection, handling and statistical analysis methodologies is ever increasing, as methodologies are refined and uncertainty is reduced through improved survey design and modelling techniques.
Biography of the Author
Dr Stuart C. Clough, BSc (Hons), FIFM, is Director of Remote Sensing at APEM, having previously held the positions of Technical Director at Jacobs and Director of Fawley Aquatic Research. As Director at APEM he is a leading specialist on aerial bird and marine mammal surveying for environmental assessments for the offshore energy sector.{/access}
As a result of the rapid growth in the offshore wind sector, the demand for spatial environmental data is constantly increasing. Traditional visual aerial survey methods suffer from reliability, safety and data quality drawbacks. These can be overcome by new digital methods, and in this article we discuss the application of these new technologies to offshore aerial bird and mammal surveys.By Stuart C. Clough, Director of Remote Sensing, APEM, UK
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}Bespoke surveys collect a series of ultra-high-resolution digital still images which are captured using state-of-the-art, aircraft-mounted camera equipment, typically forming a grid of images across the survey area. This technique has been applied successfully to generate statistically robust population estimates and to describe distribution for offshore wind farm sites around the UK. Obtaining accurate and precise estimates of bird and mammal abundance is crucial to quantifying the effects of offshore wind farm construction and operation, while exact geo-referenced locations of birds can inform decisions on turbine placement. This technology can help answer essential questions about the potential impact of offshore development, and ensure developments are optimally sited It is neither appropriate nor safe to carry out low-level visual aerial surveys after the construction of a wind farm, and the data collected is inherently biased by the presence of the turbines. Therefore, APEM has developed a very high-resolution digital aerial photography technique to determine animal density and distribution based on scientifically sound principles, which can be used before and after construction.
Background
Birds are among the most protected classes of fauna in both the UK and Europe, with government bodies, local authorities, pressure groups and the general public taking great interest in their protection. To satisfy stringent regulator requirements and ornithological focus groups, any data on breeding, passage or wintering birds needs to be robust, defensible and reliable. To this end, APEM has developed high-resolution digital aerial imaging techniques, designed to provide statistically sound results with the quickest possible turnaround. APEM have been conducting ultra-high-resolution aerial surveys since 2006 to provide expertise in a business area that continues to thrive and develop, and is currently engaged in aerial ornithological surveys for a number of marine renewable energy projects, including Round 1, 2 and 3 offshore wind farms and at sites proposed for wave and tidal energy generation.
Aerial Survey Methods
Ornithological surveys have traditionally been carried out by boat or low-level aerial-based bird spotters. However, such techniques can often be costly and/or unreliable, and pose greater risk to both participants and wildlife. Modern aerial surveys are undertaken in twin-engine aircraft fitted with state-of-the-art cameras and bespoke flight management systems (Figure 1). These systems, controlled by comprehensively trained staff, produce digital still imagery at resolutions as high as 2 centimetres (Figure 2). Such images are used to identify birds (and marine mammals) from a safe altitude, thus minimising ecological disturbance. An aircraft can safely cover huge areas in a single day and collect large datasets quickly and efficiently. Data is often collected in a grid pattern, each image being equidistant from its counterparts on the x and y axes. Survey design is defined prior to the start of monitoring and therefore the amount of data collected is dependent on the size of the area and the spacing between image nodes.
Analysis of Imagery
While the collection of large datasets has clear advantages it has also presented the industry with a need to develop innovative ways to handle and analyse data. Bespoke bird identification software has been developed in-house using novel object recognition algorithms. This has been linked to a tailored graphical user interface (GUI), which automates the geo-location of birds and facilitates the measurement of wing-span, length and flight height and direction (Figure 3), thus speeding up the bird identification process prior to analysis by APEM’s specialist ornithologists. Automated analysis tools have also been developed in-house to differentiate between species where similarities in colour and plumage are not distinguishable by eye. Developers often require a rapid turnaround between survey and data delivery; therefore maximising automation at this stage of the process – without reduction in output quality – is key to meeting industry requirements. Such datasets can be stored permanently and revisited when required.
Population Estimates and Statistical Analysis
APEM routinely uses a systematic grid-based approach to data collection, collecting a representative sample of the birds present at the time of survey. Each sample can be considered an independent estimate of population. This survey approach is conducive to spatial statistical analysis, which regulators deem increasingly reliable for bird population assessment. Non-parametric bootstrap methods are used to provide confidence limits and contribute to the high degree of statistical robustness. Precision calculations are used to obtain a ‘coefficient of variation’ (CV), which can be used before or after survey to determine the ideal number of image samples to detect a change in the population of a particular species. For a species of interest, a CV of <0.16 is targeted, enough to be able to detect a doubling or halving of a population.
Model-Based Spatial Distribution Estimates
Using relevant covariate data, model-based statistical approaches such as General Additive Models (GAMs) can be used to produce density surface maps over the study area (Figure 4). These display areas of lesser and greater density, based on model predictions and including environmental parameters such as bathymetry, geological substrate, distance to shoreline and distance to relevant Special Protection Areas (SPAs). As an equal number of images are collected on the x and y axes in a gridded survey, coverage of the survey area is evenly spread, meaning that models including environmental variables are not biased by disproportionate coverage of relatively more (or less) important habitat. Pre- and post-construction geospatial comparisons can be performed to illustrate the changes in bird densities across the survey area resulting from wind farm development. This analysis will detect and pinpoint where these changes are the most important, and will reveal whether these changes are statistically significant.
The Future of High-Resolution Aerial Photography
The scientifically robust nature of the survey design, and the significant cost savings compared to other techniques, has led to a huge increase in the demand for high-resolution aerial photographic surveys. For this reason, it is expected that this survey technique will quickly become an industry standard. Increasingly, developers are seeing the merits of high-resolution still photography for other aspects of offshore wind farm development. For example, identifying and selecting the most appropriate route for the cable which brings the energy ashore is a complex process, which can be informed by high-resolution still photography. The images can be used to underpin a range of studies including archaeology, ornithology and terrestrial habitats without setting a foot on the ground. Remote sensing techniques are becoming increasingly mainstream for environmental assessments, and with much impact assessment work still to be done for many offshore renewable projects, the future for specialist environmental consultancies looks bright.
Summary
High-resolution aerial photographic surveys provide a modern, viable and safer alternative method to traditional data collection and handling for the offshore wind industry. The high-resolution data outputs obtained from high-resolution aerial photographic surveys of proposed and operational offshore wind farm sites have generated robust datasets on which critical planning and implementation decisions can be based and which can be revisited many times. The data outputs are of a very high standard, enabling quality assurance and detailed statistical analysis to examine avian population densities and abundance in the offshore environment. Confidence in the implementation of the data collection, handling and statistical analysis methodologies is ever increasing, as methodologies are refined and uncertainty is reduced through improved survey design and modelling techniques.
Biography of the Author
Dr Stuart C. Clough, BSc (Hons), FIFM, is Director of Remote Sensing at APEM, having previously held the positions of Technical Director at Jacobs and Director of Fawley Aquatic Research. As Director at APEM he is a leading specialist on aerial bird and marine mammal surveying for environmental assessments for the offshore energy sector.{/access}
