Mapping Finland’s ocean floor

Author: Penny Boviatsou

Accurate nautical charts ensure safe navigation and better voyage planning. These are graphic representations of a maritime area and coastal regions, showing depths of water and heights of land, details of the seabed and the coastline, navigational threats, and structures, such as harbours.

Nautical charts are essential tools for marine navigation, Meritaito Ltd, a leading Finnish marine survey service and infrastructure management company, produces official nautical charts for safe navigation in Finnish waters. The company has decades of experience in a comprehensive range of services in:

1. Maintenance of waterways
2. Use and maintenance of canals
3. Hydrographic surveying services
4. Hydraulic engineering
5. Waterways design and manufacturing of aids to navigation
6. Oil spill response services.

Meritaito was founded in 2010 when the waterways functions of the Finnish Maritime Administration, the Finnish Rail Administration and the Finnish Road Administration merged into the Finnish Transport Agency (FTA). The FTA is a government agency operating under the authority of the Ministry of Transport and Communications; its main responsibility is the maintenance and development of the transport system overseen by the government.

Organising the mission

Depths are measured in a variety of ways. Historically, the sounding line was used. In modern times, echo sounding, and LiDAR are used for measuring the seabed in the open sea. The FTA had tested bathymetric LiDAR in Finland in the past but with rather poor success. In 2015, Meritaito organised a pilot program after FTA’s request, and this time new technology was used including the Leica Chiroptera II, a coastal survey LiDAR sensor. The results of the pilot program were satisfactory, and FTA requested two more hydrographic surveys, these took place in 2016 and 2017.

The data obtained from the surveys was used to produce up-to-date, large-scale nautical charts. Three different technologies were used for the data acquisition:

1. Singlebeam echosounding (SBES)
2. Multibeam echosounding (MBES)
3. Bathymetric LiDAR.

These surveys worked as a guide for Meritaito for managing hydrographic surveys and improving the execution of a project containing bathymetric information from different data collection methods.

Gaining the knowledge

For the first survey, Meritaito used different bathymetric sensors – among them was the Chiroptera II. The LiDAR data was requested separately, and, consequently, the surveys took place in different times.

“For the shallow areas, we used single-beam echosounders and the Leica Chiroptera II, and for the deeper areas multibeam echosounders,” said Aaro Nurmiainen, Meritaito LiDAR expert.

Once completed the data evaluation, Meritaito created a report for the FTA. After the analysis of the report, FTA concluded the Chiroptera II coastal survey LiDAR technology could be used to replace the singlebeam echosounders in the coastal areas.

“The LiDAR technology opened the way for other applications,” said Nurmiainen. “Considering the long coastline and big number of lakes in Finland, this is the ideal tool for shallow water surveys.”

Leading with vast experience

In the second project, FTA excluded all other methods and only kept LiDAR data for the shallow water areas. Meritaito used multi beam echosounders for the deeper parts.

“The Chiroptera II sensor allowed for rapid and accurate mapping, replacing the far less efficient single-beam mapping tool,” explained Nurmiainen.

Meritaito used the Leica LiDAR Survey Studio (Leica LSS) and Terrasolid software suite to create a fast and automated workflow. After the processing and evaluation, FTA received the final product ready for the agency’s mapping projects.

“The Chiroptera II captured the full waveform in both the 35 kHz bathymetric channel and the 500 kHz topographic channel and gave us seamless coastal and land surveying results,” explained Nurmiainen. “The results after the data processing in the second survey were not comparable with any other method previously used.”