Measuring by Light Wave DevicesThe light wave measuring device (fig. 12-25)uses electro-optical instruments to measuredistances accurately. The device consists basicallyof two units: the measuring unit (transmitter/receiver) and the reflector unit (fig. 12-26). Thedistance is measured by precise electronic timingof a modulated LIGHT WAVE after it travels to,and when it returns from, a reflector at the otherend of a course (fig. 12-27). When the instrumentreceives the reflected light flash, it registersreadings that can be converted into the lineardistance between the instrument and the reflector(with corrections made for atmospheric condi-tions).Like their microwave counterparts, the lightwave distance-measuring devices are capable offirst order base lines in triangulation and all ordersof traverse distance measurements. Most of theseinstruments have a rated range of 200 to 50,000meters.These instruments, as all delicate scientificequipment, are to be treated with proper care andoperator maintenance so that they may continueto be available for use. Refer to the instrumentmanufacturer’s manual for instructions on basicoperation, care, adjustments, calibrations, andother details of the system.FIELD PARTY SAFETYA surveying field party is frequently workingits way through rugged terrain a long distanceaway from any professional medical assistance.Working through brush, felling trees, scalingbluffs, and crossing streams are all hazardous.Also, the use of such sharp-edged tools asmachetes, brush hooks, axes, and hatchets isequally hazardous. Besides those dangers that areinherent in the work itself, a party may be exposedto a variety of natural dangers, such as thosecreated by weather conditions, by reptiles, byinsects, and by poisonous plants. Occasionally,in some areas, there may be dangerous wildanimals or even dangerous domestic animals, suchas vicious dogs or angry bulls. When a party isworking along a thoroughfare on which vehicularFigure 12-25.-A light wave distance-measuring device (Geodimeter, Model 2A).12-26
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