Bathymetry and Hydrographic Data Processing

Next is **Bathymetry & Hydrographic Data Processing**.

What issues are involved in Bathymetry & Hydrographic Data Processing?

• How are the depth and shape of the seabed measured and mapped?
• What measurement methods and sensors are used for bathymetric surveys?
• Relative to which reference plane are water depths and seabed elevations recorded?
• How do water level, sound speed, and the position and movement of a survey vessel affect the measurements?
• How are large volumes of hydrographic measurement data checked, corrected, and processed?
• How are bathymetric data converted into reliable depth models, profiles, and maps?

During this Blended Learning course, you’ll be introduced to bathymetry: the measurement and mapping of the depth and shape of the seabed. You’ll discover how hydrographic surveys are conducted and what data is needed to derive a reliable position and seabed elevation from a measured depth.

The focus is not only on collecting measurement data, but primarily on its processing and quality control. You’ll learn what corrections are needed and how bathymetric data is ultimately used in waterway management, water management, dredging operations, offshore projects, and other Geo-ICT applications.

Measuring the Underwater Seabed

Underwater, the seabed cannot be surveyed in the same way as land above water. That is why various acoustic and other measurement methods are used in hydrography.

You’ll be introduced to techniques such as single-beam echo sounders, multibeam echo sounders, and other sonar techniques. You’ll learn the basics of how sound waves are transmitted, reflected by the seabed, and received again by a sensor.

The distance to the seabed can be determined from the measured transit time of the sound signal. In doing so, you’ll discover why knowledge of the speed of sound in water is essential for reliable depth measurement.

The goal of this Blended Learning course is not to become a specialist in a single specific measurement system. Rather, it is to help you understand how bathymetric measurements are made and what data is needed to reliably map the seafloor.

Positioning and Movement of the Survey Vessel

A measured depth is only meaningful if the exact location where the measurement was taken is also known. GNSS therefore plays an important role in modern hydrographic surveys.

You will learn how the position of a survey vessel is determined and how this position is linked to the measured depths. This connects to the topic of GNSS & Satellite Positioning.

Furthermore, a survey vessel is constantly in motion. Waves and currents cause movements such as roll, pitch, and heave. You’ll be introduced to the sensors used to record these movements and learn why corrections are necessary.

This makes it clear that a bathymetric measurement point is the result of multiple sensors that must work together precisely.

Water Level, Reference Surfaces, and Corrections

Water level changes constantly due to factors such as tides, wind, and river discharge. A distance measured directly between the survey vessel and the seabed cannot therefore simply be used as seabed elevation.

You’ll learn why bathymetric measurements must be tied to a fixed vertical reference plane. You’ll also explore the relationship between water depth, water level, seabed elevation, and vertical references.

You will also examine various corrections that may be necessary during the processing of hydrographic data. These include corrections for water level, sound velocity, sensor position, and the movement of the survey vessel.

You’ll discover why proper management of references, sensors, and corrections is essential for correctly processing and comparing measurement data later on.

From Raw Measurements to Reliable Bathymetric Data

During a hydrographic survey, large amounts of measurement data can be collected. In addition to reliable measurements, this raw data also contains anomalies, noise, and sometimes erroneous measurement points.

You’ll learn how hydrographic data is checked and cleaned before it can be used further. In doing so, you’ll examine anomalous depths, missing data, overlaps between survey lines, and the consistency between different measurements.

You’ll also learn about the importance of metadata and quality information. After all, an end user must be able to assess when, how, and with what level of accuracy a dataset was acquired.

This will teach you not only to visualize bathymetric data but also to critically assess its reliability and suitability for a specific application.

From Measurement Points to Depth Models and Maps

After processing and quality control, bathymetric measurement points can be used to model the seabed.

You’ll learn how measurement points can be converted into profiles, raster models, contour lines, and digital elevation models of the seabed. You’ll also explore how different choices regarding interpolation and resolution affect the final representation of the seabed.

This connects to GIS. Bathymetric datasets can be combined with, for example, waterways, shorelines, structures, dredging areas, and other geographic data.

This illustrates how hydrographic measurement data is ultimately converted into usable Geo-ICT information for analysis, management, and decision-making.

Bathymetry & Hydrographic Data Processing in Practice

During the Blended Learning program, you’ll work with provided hydrographic measurement data to walk through the various steps from measurement to final product. You’ll analyze and visualize bathymetric data and investigate which corrections and quality controls are necessary.

You’ll work on assignments such as:

• Investigate how an echo sounder determines the distance between a survey vessel and the seabed.
• Analyze how the speed of sound, water level, and the movement of the survey vessel affect a depth measurement.
• Investigate how GNSS positions and bathymetric measurements are combined.
• Check a supplied bathymetric dataset for anomalous or unreliable measurement points.
• Create a profile or digital model of the seabed based on bathymetric measurement data.
• Process and visualize bathymetric data in QGIS and combine it with other geographic data.

By the end of the course, you will understand how bathymetric surveys are conducted and the roles that positioning, water level, sound velocity, and the movement of the survey vessel play in the process. You will be able to explain how raw hydrographic survey data is checked, corrected, and processed into reliable depth data, and how this data can be used within GIS and other Geo-ICT applications.