Innovations For Submarine Cable Planning: An Optical Survey Toolbox
By Robert van de Poll, Sandeep Narayan Kundu and René d’Avezac de Moran
October 1, 2021
As pressure mounts to reduce our carbon footprint, the impetus is on harvesting renewable energy. Offshore wind farms (OWFs) and floating solar farms (FSFs) are therefore the new resources to feed our hunger for energy. The frequency and density of these developments are exponential and techniques for surveying and characterising the seabed need to evolve and keep pace. During this era of pandemic-related restrictions, projects are taking longer. At Fugro, we have found out innovative ways to characterise the seabed using optical observations from high and very high-resolution satellite imagery. This technology has greatly enhanced planning for submarine cables and executing bathymetric and topographic surveys arrays for many recent projects. Adopting satellite technology has not only kept projects on schedule but also has other benefits: it poses few health and safety risks and is environmentally friendly too. Below is a visual summary of optical survey methods organised from left to right, from the fastest and least precise to the slowest and most precise end of the spectrum.
In order to detail the optical surveys, we shall touch upon how satellite images are sourced, how they are processed and most importantly how they are interpreted to transform the signals into relevant information which we then use to decipher the nature of the seabed on the area we are planning to lay a submarine cable. It is also important to understand how we can glean information from these images to mitigate risks to the cable.
Efficiency, accuracy, detail, and capability are the fundamental factors that need to be evaluated when selecting an appropriate remote sensing technology for shallow water surveys. Complex coastal environments typically require more than one technology to achieve the optimum mapping solution. Fugro’s integrated approach to shallow water surveying, utilising satellite-derived bathymetry (SDB) and airborne LiDAR bathymetry (ALB) enable us to deliver quality Geo-data within shorter project windows.
Fugro SatRecon produces 4DSSM imagery, which is a visualisation tool that takes advantage of the human brain’s ability to rapidly sort through information to determine similarity, difference, and relative changes in optical reflectivity. Images are rendered in CARIS LOTS (Law of the Sea) software to make the information visually intuitive to a human observer.
Fugro SatRecon (4DSSM imagery) may contain general bathymetric information, but it is not a bathymetric product. The visualisation complements a bathymetric chart in understanding the seabed. Bathymetric (or nautical) charts are not generally updated fast but satellite imageries do have a repeat image over the same area on a weekly or fortnightly temporal basis. Hence SatRecon helps in fast visualisation of the recent changes that a bathymetric chart is unable to provide which makes it an indispensable tool to monitor recent changes and plan cable routes and inshore surveys without having to visit anywhere.