Which Bathymetric Surveying (Hydrographic Surveying) Method Fits My Project? A Practical Guide for Offshore Services in the Philippines
- Clinton Bravo
- Aug 5
- 5 min read
Updated: Aug 13
The Philippines is booming its blue economy and building offshore infrastructure, and selecting the appropriate bathymetric surveying method for your next project is crucial. Whether you’re building ports, laying underwater cables, conducting environmental assessments, or mapping for offshore wind farms, choosing the right tool ensures accuracy, efficiency, and cost-effectiveness. This guide provides an overview of the main offshore bathymetric methods offered by
AB Surveying and Development (ABSD) and assists you in determining the most suitable method for your project.
What Is Bathymetric Surveying?
Bathymetric surveying is the science of measuring water body depths and mapping underwater features. It provides essential data for engineering, environmental, and marine applications. In the Philippine context, bathymetric data is vital due to the country’s archipelagic geography and growing demand for coastal infrastructure and renewable energy projects.
Method 1: Using Single Beam Echosounder (SBES)
Best for: Narrow water bodies, preliminary reconnaissance, rivers, and port dredging feasibility.
Use Case: For example, in Pasig River dredging projects or small port maintenance surveys in Cagayan or Batangas, SBES is often sufficient.
How It Works: A single transducer mounted beneath a survey boat emits a narrow acoustic (sonar) pulse directly downward toward the seafloor. The system measures the time it takes for the pulse to reflect back from the bottom surface to the receiver. As the vessel moves along a transect line, the echo sounder continuously records these depth points to produce a 2D profile of the seabed directly beneath the vessel path. GPS integration ensures each depth point is geo-referenced.
Equipment used by ABSD: Sonarmite Echosounder
Advantages:
Cost-effective for small-scale projects
Simple to deploy with a small team
Quick data collection in shallow waters
Limitations:
Captures data only along a single transect line
Limited spatial resolution
Method 2: Using Multibeam Echosounder (MBES)
Best for: Large-scale marine infrastructure, offshore wind farm development, navigational safety studies, and port expansion in deep waters.
Use Case: MBES is used to survey potential construction sites for offshore wind farms, pipelines, and other infrastructure. It helps in planning safe placement of structures and identifying potential risks like unstable seabed conditions.
How It Works: MBES systems emit multiple sound beams in a fan-shaped pattern that spans across the seafloor perpendicular to the vessel's track. This wide swath enables the system to collect hundreds of depth measurements with each ping, capturing detailed 3D topography in a single pass. Each beam's return time and angle are used to calculate precise bathymetric data. The system continuously adjusts for vessel motion, water depth, and sound velocity to ensure accuracy. The deeper the water, the wider the swath coverage becomes making MBES especially ideal for deepwater surveys.
Equipment used by ABSD: SeaBat T50-R
Advantages:
Full seafloor coverage
High-resolution topographic data (comparable to onshore LiDAR data)
Ideal for deep or complex seabed terrain
Limitations:
Requires specialized equipment and trained personnel
Higher cost compared to SBES
Method 3: Aerial Bathymetric LiDAR
Best for: Coastal zone mapping, coral reef studies, environmental assessments, and island baseline surveys in shallow waters.
Use Case: Mapping coral reefs in Tubbataha Reefs Natural Park or baseline surveys in Palawan for maritime territorial claims.
How It Works: This method uses a specialized airborne laser scanning technology where aircraft-mounted sensors emit green-wavelength laser pulses capable of penetrating water. A portion of the laser reflects off the water surface, while the rest penetrates and reflects off the seabed. The difference in return times allows for precise depth calculations. Aerial LiDAR systems scan large areas quickly, and GPS/IMU systems onboard ensure accurate spatial positioning. Offers rapid data collection and highly detailed mapping of underwater terrain, achieving up to 200,000 measurements per second with an accuracy of about 2 centimeters.
Note: The maximum laser penetration is 30 meters, depending on water clarity. This is typically estimated as 2.5 times the Secchi disk depth, which varies based on water turbidity and water.
Equipment used by ABSD: Riegl VQ-840-G
Advantages:
Rapid large-area coverage
Minimal on-water logistics
Effective in clear shallow waters
Limitations:
Reduced accuracy in turbid or deep waters
Weather and water clarity dependent
For shallow waters
Other Hydrographic Surveying Capabilities:
Note: The additional hydrographic services listed below are optional and may be deployed depending on your project’s specific requirements. While they can be conducted independently of bathymetric surveying, they are most effective when integrated with it to provide a more comprehensive understanding of the marine environment.
Method 4: Subbottom Profiling
Best for: Mapping sediment layers, distinguishing between soft and hard geological strata, archaeological studies, and planning routes for subsea cables and pipelines.
Use Case: Ideal for cable landing site studies or sediment layer analysis for reclamation.
How It Works: Low-frequency acoustic pulses penetrate the seafloor and reflect back from subsurface layers, showing stratigraphy.
Equipment used by ABSD: Innomar SES 2000
Method 5: Marine Magnetometer Profiling
Best for: Detecting ferrous objects like shipwrecks, unexploded ordnance (UXO), and buried infrastructure
Use Case: Locating buried pipelines or cables to prevent damage during construction or dredging or detecting UXO (unexploded ordnance) detection for safety in offshore construction zones.
How It Works: Detects variations in the Earth's magnetic field caused by metallic objects beneath the seafloor.
Equipment used by ABSD: Innomar SES 2000
Method 6: Side Scan Sonar Profiling
Best for: Seabed characterization, habitat mapping, locating submerged objects
Use Case: Ideal for marine habitat monitoring or locating underwater obstructions near shipping routes.
How It Works: Emits fan-shaped sonar pulses perpendicular to the survey path to generate detailed imagery of the seafloor texture.
Equipment used by ABSD: Klein 4900 Towfish
Method 7: Sound Velocity Profiling (SVP)
Best for: Calibrating echo-sounding data for accurate depth and positioning
Use Case: Required in any MBES or SBES survey in the Philippines where salinity, temperature, and pressure gradients vary drastically.
How It Works: SVP sensors measure the speed of sound in water, which affects sonar accuracy. Profiles are integrated into sonar processing.
Equipment used by ABSD: Klein 4900 Towfish
Method 8: Geophysical Analysis
Best for: Subsurface hazard detection, foundation site characterization, mineral and gas exploration
Use Case: Suitable for identifying fault lines near offshore infrastructure zones or analyzing sedimentary basins for resource potential.
How It Works: Geophysical analysis methods such as seismic reflection and resistivity profiling involve sending energy waves (acoustic or electrical) into the seabed. This method provides deeper geological context for engineering, drilling, and environmental projects.
Equipment used by ABSD: This project will be carried out with our geo-professional partners .
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