A Practical Approach to Wreck Assessment Using 3D Sidescan

In underwater archaeology, the constraint is rarely detection. It is interpretation.

Most sites of interest can be located with relative ease using conventional side scan sonar. The difficulty begins once a target is identified. At that point, the question is no longer where is it, but rather:

• What exactly is it?

• What is its geometry?

• Does it warrant further intervention?

  
  

These questions are not trivial. They directly influence whether a site progresses to ROV inspection, diver investigation, or remains undisturbed.

The Differences Between 2D and 3D Interpretation

2D side scan remains a highly effective tool for detection and general characterisation. However, it is fundamentally an intensity-based imaging method.

What is presented is:

• Backscatter strength

• Acoustic shadows

From this, the operator infers shape. This works well for experienced interpreters, but it introduces ambiguity:

• Vertical structure must be inferred from shadow length

• Object height is estimated, not measured

• Complex geometries can be misinterpreted

  
  

In archaeological contexts, where site integrity and structure matter, these limitations become significant.

3D sidescan, as implemented in Ping DSP’s system, extends the same acquisition principle but incorporates multiple simultaneous angle-of-arrival measurements for each return.

The result is a geometrically correct point cloud, generated in real time, rather than a 2D projection.

Practically, this means:

• Each return has spatial position, not just intensity

• Structures can be viewed from multiple perspectives

• The dataset behaves more like bathymetry combined with imagery

  
  

This is not simply “enhanced visualisation.” It is a shift from interpretive imaging to measurable geometry.

Why 3D Measurement Matters in Archaeological Workflow

In many cases, the decision to escalate a site depends on scale and condition. For example, a low-relief anomaly may not justify intervention, whereas a structurally intact wreck of significant dimensions likely will. Also, Evidence of collapse or debris fields may indicate site instability. With 2D data, these assessments are often approximate. With 3D sidescan:

• Height, length, and orientation can be measured directly

• Structural features can be examined in context

• The dataset supports quantitative assessment before physical access

This is particularly relevant where:

• Dive operations are costly or risky

• ROV deployment is limited by logistics

• Cultural heritage considerations require minimal disturbance

  
  

The ability to make informed decisions prior to intervention is not just efficient, it is often necessary.

Documented wrecks such as the J.E. Boyden demonstrate how 3D sidescan can capture hull geometry, orientation on the seabed, and structural preservation. Similarly, smaller, locally known sites such as submerged barges or infrastructure remnants can be resolved in a single pass, with vertical elements clearly distinguishable in the 3D dataset.

These are features that would typically require either multiple passes with 2D side scan or follow-up inspection using ROVs or divers.

J.E. Boyden Wreck

The Nadir Gap Issue

Another practical consideration is coverage. Conventional side scan suffers from a nadir gap, where data directly beneath the sonar is absent. In shallow water, this gap can be substantial relative to the target size. From the system specifications:

• The nadir gap in 2D side scan is approximately equal to water depth

• 3D sidescan and integrated bathymetry remove this gap entirely

  
  

For archaeological sites, especially those that are small or exhibit vertical complexity, this increases confidence that key features are resolved and that the site’s full extent is captured in a single pass.

What Data is Produced?

A notable advantage of the system is that it produces:

• 2D sidescan

• 3D sidescan

• Wide swath bathymetry

simultaneously.

This has 3 methodological implications:

1. Fewer survey lines are required

2. Targets do not need to be revisited for different data types

3. Spatial alignment between datasets is inherent

   
   

In practice, this reduces both survey time and post-processing complexity, while improving dataset coherence.

Why not just Multibeam?

Multibeam echo sounders remain the benchmark for high-accuracy bathymetry and are indispensable in many archaeological and survey contexts. However, they are not always the most practical first tool for site investigation, particularly in shallow or resource-constrained projects. 3D sidescan occupies an intermediate space.

For shallow water environments, especially those under ~30 m, systems like the 3DSS-iDX are specifically optimised for this operating range. In these conditions, it can represent a balanced approach between data richness, operational simplicity, and cost.

The Ping DSP 3D Sidescan

Concluding Perspective

For underwater archaeology, the primary value of 3D sidescan lies not in improved imagery, but in its capacity to support direct measurement, reduce uncertainty prior to intervention, and produce spatially coherent datasets within a single acquisition.

In environments where depth is limited, access is constrained, and decisions carry logistical or cultural weight, this capability is particularly relevant. It does not replace multibeam, nor does it render traditional side scan obsolete. But it does offer a compelling methodological step between the two.

For anyone considering the use of 3D sidescan in archaeological or wreck assessment work, the Seismic Asia Pacific team are available to discuss applications and share practical guidance.