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NIST Construction Automation Program Report No. 1: Non-Line-of-Sight (NLS) Construction Metrology.

pdf icon NIST Construction Automation Program Report No. 1: Non-Line-of-Sight (NLS) Construction Metrology. (15878 K)
Stone, W. C.

NISTIR 5825; 217 p. February 1996.

Available from:

National Technical Information Service


construction automation; dielectric constant; diffraction; metrology; multipath; NLS; non-line-of-sight; penetration capacity; positioning system; propagation delay; spread spectrum radar; surveying


This paper addresses the subject of automated metrology (surveying) for use on construction sites. Specifically, the research is directed to the development of a novel Non-Line-of-Sight (NLS) system with which the real-time position and orientation (attitude) of any object on a construction jobsite may be determined, irrespective of the presence of intervening obstacles that would otherwise render optical and/or electro-optical techniques useless. Tests were conducted using a specially configured broad-band, low-frequency spread-spectrum radar. The transmission and receiving antennae, which in normal radar are typically one and the same, were physically separated so as to create a system with a fixed broadcast unit and a "roving" receiver, whose range was to be determined relative to the transmission antenna by means of time-of-arrival measurements. Time domain response was synthesized by means of fourier theory from a broad spectrum of data sampled in the frequency domain. Numerous field experiments were performed in which typical construction site obstacles were placed between the transmitter and receiver with separation distances of up to 80 meters. The obstacles included a half-meter thick, heavily reinforced concrete wall, varying combinations of masonry block and brick up to more than a meter in thickness, and metal pre-fabricated wall panels. In all but the latter case, repeatable distances were obtained. Range detection was lost in the presence of extensive metal panels that contained no windows. However, the presence of even small openings permitted range acquisition. Sources of error, limits of resolution and accuracy, and factors affecting time of flight measurement are discussed.