Surface surveys for suspected explosive ordnance

Historical aerial photographs, archive information, former military or industrial uses, known finds and existing statements determine which object types and patterns of ordnance presence are plausible. General suspicion for a property is insufficient where only a subarea or particular intervention is to be investigated.

The basis for suspicion is referenced to the site plan, construction site, route or section. This establishes which areas need complete, section-based or point-specific work and whether a technical surface survey is the next appropriate step.

The survey task depends on whether larger ferromagnetic objects, smaller munitions, conductive non-ferrous metals, buried infrastructure or structural ground changes are relevant. Object size, shape, position and material properties affect which measurement principle can produce a usable signal.

The proposed intervention matters equally. A utility trench, area-wide topsoil removal, demolition, breaking out a road or foundation works affect different depths and working envelopes. The investigation area must cover this geometry rather than follow property boundaries alone.

Open ground, vegetation, ballast, paving, asphalt, concrete, track areas and indoor spaces place different demands on sensor movement, survey height and line positioning. Uneven ground, vegetation, obstacles and changing surfaces may affect coverage and comparability between lines.

Before execution, establish whether the site can be accessed on foot or by vehicle, which areas can be made accessible by removing obstacles or cutting vegetation, and where deviations from the planned grid are unavoidable. Inaccessible zones are identified clearly in the survey plan and subsequent report.

Utilities, rails, fences, sheet piles, reinforced concrete, vehicles, containers, scrap and former structures can generate magnetic or electromagnetic signals. Their location and extent determine whether a method needs local restrictions, a different configuration or supplementation by another measurement principle.

As-built plans are not always sufficient because their positional accuracy and currency may vary. Known interfering objects are therefore checked against field conditions. Subsequent interpretation distinguishes measurable anomalies from areas where interference prevents reliable individual-object assessment.

Line spacing, sensor arrangement, survey height, acquisition speed, coordinate system and positioning method follow the target and required conclusions. A high point count alone does not guarantee quality if survey lines are inconsistent, areas are omitted or coordinates cannot be assigned reliably.

Suitable quality checks are defined beforehand. These may include trial surveys, control lines, plausibility checks, coverage checks and comparison with known reference objects or interference sources. Quality control must be traceable in the report.

Before work begins, establish how the result will be used: design, tendering, selection of further surveys, target investigation, excavation supervision or documentation of a defined working area. The report addresses that decision and must not exceed the work scope.

The result may show that an area is technically interpretable, individual anomalies require further investigation or particular zones remain unresolved because of interference, depth or access. A technically suitable next step is identified for each category.