Time-tagging electronic distance measurement instrument measurements to serve as legal evidence of calibration

摘要

A combined satellite positioning and electro-optical total station system including a satellite navigation receiver and a reference oscillator with a reference frequency output that can be related to precision time standards obtained from orbiting navigation-satellite transmissions. Such time standards are output by the satellite navigation receiver and are highly precise. An electronic distance meter (EDM) is included and has an EDM-transmitter for launching an out-bound signal to a distant target, and an EDM-receiver for receiving a reflected signal from the distant target. A phase measurement device is connected to the reference oscillator, and also to both the EDM- transmitter and EDM- receiver. It provides for a measurement of the difference in the number of cycles of the reference frequency between the out-bound signal and the reflected signal. A post-processor is connected, such as by radio link or floppy disk, to receive the measurement of the difference in the number of cycles of the reference frequency and the precision time standards obtained from orbiting navigation-satellite transmissions. Post- processing is then able to relate the corresponding measurements and time standards such that a distance-to-target measurement can ultimately be computed. Therefore routine calibration of the EDM is unnecessary. The measurement of the difference in the number of cycles of the reference frequency is time- tagged and stored for later retrieval to construct a time-ordered log. The precision time standards obtained from the orbiting navigation- satellite transmissions are similarly time-tagged and stored. Thus a series of distance-to-target measurement can be computed according to the order they were originally collected in the field by the EDM, as might be necessary in a legal inquiry.