Underwater Imagery Surveys

An underwater survey involves collecting data beneath the water’s surface to understand seabed conditions, underwater assets or the surrounding marine environment. Depending on the objective, surveys may use visual imagery, sonar or other remote sensing techniques.

Underwater imagery surveys focus specifically on capturing high-quality images and video, providing clear visual evidence to support inspection, assessment and environmental understanding.

A subsea survey is a type of underwater survey that concentrates on features located on or just above the seabed. This typically includes pipelines, cables, outfalls, foundations and other subsea infrastructure.

Underwater imagery plays a key role in subsea surveys by providing close-range visual confirmation of asset condition and identifying scouring, damage or debris that may not be fully apparent in acoustic data alone.

Underwater features can be surveyed using a range of methods, selected according to water depth, visibility, access and survey objectives. Within underwater imagery surveys, common methods include:

• ROV-mounted cameras for flexible, close-range inspection
• Tripod-mounted or fixed camera systems for repeat or longer-term monitoring
• Side-scan sonar to produce mosaic images highlighting seabed features and objects

These approaches allow imagery to be reviewed in real time, enabling survey teams to adapt works efficiently and focus on areas of interest.

IWS refers to Imagery and Visual Surveys, describing underwater surveys that rely on video and still imagery rather than intrusive inspection methods.

Underwater imagery surveys form a core part of this approach, providing reliable visual records of seabed conditions, underwater assets and environmental features without the need for routine diver entry.

Underwater photogrammetry creates precise, measurable 3D models and digital replicas of submerged objects or terrain by processing multiple, overlapping 2D images captured by ROVs. This non-invasive technique is used for high-accuracy inspections of underwater structures, archaeological surveys of shipwrecks, marine habitat monitoring and object identification. Photos (often with 60%+ overlap) are taken of a target and processed in specialised software (Agisoft Metashape), where images are aligned along with camera positions to generate dense and textured 3D point clouds.

ROV-mounted video and still imagery

ROV-mounted systems provide flexible, close-range visual inspection of the seabed and underwater assets. Video footage is typically supplied with professional narration describing seabed composition, pipeline routes, outfall locations and any significant findings such as scouring or damage. Accurate Positioning of the ROV is achieved by combining surface GNSS/GPS with subsea acoustic, inertial, and velocity sensors.

Tripod-mounted and fixed camera systems

Tripod-mounted cameras are well suited to longer-duration monitoring or repeat surveys in defined locations. These systems allow consistent positioning, supporting direct comparison of seabed conditions over time.

Side-scan sonar imagery

Side-scan sonar data can be supplied as mosaic images to highlight seabed features, objects and anomalies. This approach is particularly effective for wider-area seabed assessment and object detection.

Environmental and seabed characterisation

From an environmental perspective, underwater imagery is used to ground-truth multibeam backscatter data and support seabed characterisation. Imagery also contributes to habitat identification and environmental baseline studies.

Survey deliverables are tailored to project requirements and may include:

• High-resolution underwater digital stills
• Photogrammetry
• Georeferenced mosaic images
• ROV or fixed-camera video footage
• Side-scan sonar mosaic images
• Clear reporting suitable for technical and environmental review

Underwater imagery surveys are commonly used for:

• Pipeline and underwater cable inspections
• Bridge pier, pontoon and dock wall condition assessments
• Water, sewer and outfall inspections
• Seabed habitat monitoring and assessment
• Debris, wreck, pUXO and object detection
• Search and recovery of missing assets