A surveying device consisting of reflective material used to mark points and reflect light back to measuring instruments.

Reflective Target

Definition and Purpose

A reflective target is a fundamental surveying accessory consisting of reflective material arranged in specific patterns, primarily designed to work with electronic distance measurement (EDM) instruments and total stations. These targets serve as focal points for laser or infrared beams, allowing precise measurement of distances and angles between survey points.

Types and Configurations

Prism Targets

The most common type of reflective target is the corner cube prism, which consists of three mutually perpendicular reflective surfaces. This configuration returns light directly back to its source, regardless of minor angular variations. Corner cube prisms are typically mounted on adjustable poles or tripods and come in various sizes, from single prisms to arrays containing multiple prisms for enhanced reflection.

Tape Targets

Reflective tape targets are adhesive-backed materials applied directly to surfaces. These are useful for marking survey points on buildings, walls, or existing structures where traditional prism poles cannot be installed.

Mini-Prisms

Small prism targets are designed for measuring to inaccessible areas or for applications requiring minimal visibility. These are often used in specialized surveying applications such as structural monitoring.

Material Properties

Reflective targets are manufactured using materials with high refractive indices and reflective coatings. Modern targets utilize corner cube prism technology fabricated from glass or specialized optical plastics. The reflective quality ensures maximum return of incident light to the survey instrument, enabling accurate measurements across considerable distances.

Applications in Surveying

Distance Measurement

Reflective targets enable electronic distance measurement instruments to accurately calculate horizontal and slope distances by measuring the time required for light to travel to the target and return.

Traverse Surveys

In traverse surveying, reflective targets mark stations, allowing surveyors to establish control networks with precise horizontal and vertical positioning.

Setting Out

During construction projects, reflective targets guide the placement of structural elements, ensuring alignment according to design specifications.

Monitoring and Deformation

Permanently installed reflective targets enable ongoing structural monitoring, detecting movement or deformation in buildings and infrastructure.

Advantages

Accuracy: Corner cube prisms provide excellent return signal quality, improving measurement precision

Distance Capability: Enable measurements over considerable distances, often exceeding 1,000 meters

Reliability: Perform consistently in varying light conditions

Durability: Modern targets withstand harsh environmental conditions

Versatility: Compatible with most EDM and total station instruments

Limitations and Considerations

Reflective targets require direct line of sight between the instrument and target. Atmospheric conditions, particularly fog or heavy rain, can reduce effective range. Weather protection and proper maintenance of target surfaces are essential for optimal performance. Users must ensure targets remain clean and undamaged, as dirt or scratches significantly reduce reflective efficiency.

Selection Criteria

Choosing appropriate reflective targets depends on several factors: measurement distance requirements, environmental conditions, mounting surfaces, and instrument specifications. Single prisms suffice for short-range work, while longer distances or adverse conditions benefit from multi-prism arrays.

Maintenance

Regular cleaning of target surfaces using soft cloths preserves reflective efficiency. Proper storage protects targets from damage, and periodic inspection identifies coating degradation requiring replacement.

Reflective targets remain indispensable tools in modern surveying practice, providing the essential link between field instruments and measurable survey points.