Project Background& Details
To determine kelp bed dispersal and extent together with density and biomass calculations along the South African West Coast, multiple stakeholders initiated a project to gather more precise orthorectified aerial imagery as the current National Biodiversity maps were found to be largely inaccurate. These stakeholders included the University of the Western Cape (UWC), the Department of Fisheries, Forestry, and Environment (DFFE) Seaweed Unit, the kelp industry, and two conservation organizations, SANParks, and CapeNature.
The intention was to survey the 32 km coastline near Gansbaai, a coastal town 160 km south of Cape Town. The area covered started approximately 4 km north of the Gansbaaiharbour in the east, continuing around the Gansbaai peninsula, and ending short of the Pearly Beach residential area in the west.To capture the extent of the kelp, about 75% of the nearshore ocean had to be included in the survey swathe. The Dyer Island survey area included the kelp beds surrounding the island as well as the kelp beds between the island and the closest shore, resulting in an area of roughly 6.5 km².
Kelp (lat. Ecklonia maxima and Laminaria pallida) is a vital component of marine ecosystems, providing numerous ecological, commercial, and environmental benefits. Its rapid growth and ability to form dense underwater forests make it an important species for marine biodiversity and coastal health. Kelp can help improve water quality by absorbing excess nutrients and pollutants from the water whilst also absorbing carbon dioxide from the atmosphere. Efforts to map and to study kelp are crucial for understanding and preserving these valuable underwater forests.
Project Requirements
12.4 & 1.3 pts/ m2 Point Density
32 Km Coastline & 6.5 Km² for Dyer Island
Data to be delivered as soon as possible.
Orthophotos required as an option.
Project Delivery
SAEON, the South African Environmental Observation Network (SAEON) was commissioned for project delivery. SAEON is a science network of people, organisations and, most importantly observation platforms, that perform Long-Term Ecological Research in South Africa and its surrounding oceans. With its headquarters in Pretoria and network of six local research offices (nodes) throughout South Africa, SAEON’s Elwandle Coastal Node, based in Port Elizabeth at the Ocean Sciences Campus of the Nelson Mandela University – and focusing on long-term monitoring and research on South Africa’s coastal zone – was the ideal partner with local knowledge and expertise to deliver this project in the short timeframe required.
Data collection and reasons for choosing LiDAR and GeoLas ELMAP
Why SAEON scientists chose the GeoLas ELMAP sensor for this project.
The GeoLas Elmap system was chosen for its compatibility with the specific requirements of the project
The ELMAP system allowed for efficient data collection and
processing, meeting the high standards needed for accurate kelp mapping.
LiDAR, combined with DTM-derived imagery, overcomes the limitation of image only triangulation over water, resulting in high-quality
LiDAR provides highly accurate data, which is essential for precise mapping of kelp extents and densities.
The GeoLas ELMAP Series
The ELMAP LiDAR systems are state-of-the-art mid- to high-range LiDAR sensors designed for integration in manned fixed-wing and helicopter aircraft, gyrocopters, ultralight aircraft, and heavy-lift drones. They are built to withstand the harshest environments and offer unparalleled performance and ease of use.
Highlights:
- Compact all-in-one mapping systems
- Huge 80° field-of-view
- Linear uniform scan pattern with parallel scan lines
- Integrated removable data storage on standard SSDs
- Waveform digitization for every pulse
“Our ELMAP-V lidar is a perfect fit for our Glasair Sportsman aircraft. We have performed several projects with it and are very impressed with its performance, reliability, ease of use, and data quality”, summarizes Sean Bailey, Airborne Remote Sensing Platform Coordinator at SAEON.
Data Collection
The data captured included detailed imagery and LiDAR data to produce high-resolution orthophotos in GeoTiff format. The data collection flights were meticulously planned to cover the specified areas and achieve the required point densities.
Location (160 miles from Cape Town)
Flight Plan (Part)
Glasair GS2
1900ft & 5000ft AGL
3:34h flying time
425 Images captured
The project was flown with a Glasair Sportsman GS-2 aircraft with a speed of 100 knots GS and was delivered with short flight times of only 2:25 hrs for the coastline survey with 25 strips and 1:09hrs, 3 strips for the Dyer Island survey.
Due to the project parameters and required point densities the flying altitude for the coastal project was 1900 ft, and 5000 ft for Dyer Island.
A total of 282 images for the coastal survey and 143 images for Dyer Island were captured during the flight.
Glasair Sportsman GS-2
Challenges
The flights were supposed to happen over the spring low tide;however, spring low tide is difficult to coordinate because the challenging weather conditions. The flight over Dyer Island was particularly challenging since SAEON had to stay within gliding distance of the shore due to their single-engine aircraft. This required SAEON to fly at 5000 feet ASL, where winds were over 35 knots. Additionally, SAEON could only fly in one direction to keep the ground speed under 100 knots, which affected the lidar resolution but still allowed them to produce a sufficient DTM. Adding to the challenges, theyhad to be based about a 50-minute flight away in Swellendam, as they couldn’t find avgas or hangarage closer to the project site, so the flight time had to be coordinated with the tide.
Data Processing
The LiDAR data was used to generate DTMs, which were then used to create orthophotos.
The high-resolution imagery was processed to accurately determine the extents, densities, and biomass of the kelp beds.
The project successfully delivered the required orthophotos and LiDAR data within the specified timeframe. The high-resolution images and accurate mapping provided by the ELMAPdata met the needs of all stakeholders, enabling more precise and reliable kelp bed management and conservation efforts.
RGB Ortho Image
LiDAR DTM
LiDAR DTM and Intensity Data
Main take-aways – recap
Technology Selection: Choosing the right technology (LiDAR over photogrammetry) is crucial for accurate data collection in challenging environments and terrains.
Stakeholder Collaboration: Close collaboration between stakeholders and project delivery teams ensures that the data collected meets their specific needs.
Efficiency in Data Processing: Using advanced data processing techniques, such as integrating LiDAR-derived DTMs with imagery, enhances data quality, accuracy, and reliability, which are crucial for conservation and management efforts.
The successful execution of this study demonstrates the efficacy of LiDAR technology in coastal and marine applications, particularly in environments where traditional photogrammetry falls short.
The GeoLas ELMAP system proved to be an excellent choice for this project, providing the accuracy and efficiency needed to meet the diverse requirements of the stakeholders involved.
RGB Ortho Image Dyer Island
