6. Reflectorless Total Stations

The past decade has seen the introduction and maturation of reflectorless total stations. Their inherent advantage is the ability to measure distances to points not accessible with a prism. Their biggest drawback is their generally (much) shorter range. This is in large part dependent on surface reflectivity. However, most reflectorless instruments can also use a prism as a conventional TSI giving them greater flexibility.

A reflectorless TSI uses short pulses of high energy laser light. This energy is considerably higher than that used by phase shift TSIs in order to get a return signal off low reflection surfaces. The instrument measures travel times of the laser pulses and from that can determine the total instrument-surface-instrument distance.

Because the laser pulses reflect off different surfaces, care must be exercised when pointing the instrument. This is especially critical when there are multiple surfaces at various orientations near the measurement point. Many instruments feature a built-in laser pointer which provides the operator a visual indication of where the measurement will be made.