Factors Affecting Quality of Topographic Survey
Topographic surveyors perform most of their operational duties away from the parent unit. Topographic surveying involves fieldwork over a project area. Survey fieldwork consists of making observations and measurements; recording data; and returning the data to a computer and/or draftsman for computation, compilation, and dissemination. Surveyors must overcome many factors that combine to affect working conditions. They must be constantly alert to various factors such the following:
1. Weather and Terrain
Weather and terrain can adversely affect field surveys. The effectiveness of optical and electro-optical instruments can be severely reduced by fog, mist, smog, or ground haze. Swamp sand flood plains under high water can impede leveling operations.
Signals from the GPS constellation generally require a clear line of sight to the sky. Urban and forested areas can mask or deflect the direct signal that is needed for accurate measurements. Good recon and proper planning can alert the field parties of the best times and methods to use.
The rate of progress often varies in direct proportion to the training and experience level of the assigned personnel. The most effective method of training personnel is under conditions where their actions have real consequence as opposed to mere practice. On-the-job training produces a measurable product but frequently results in lost work due to correcting mistakes.
Equipment reliability must be considered when setting completion dates. Modern, well-maintained equipment can often increase the rate of progress. Older equipment, if properly maintained or adjusted, will yield accurate results. Repairing or replacing broken instruments or parts will sometimes slow down or stop a field survey.
Equipment must be calibrated as part of combat checks before the survey mission begins.
The purpose and the type of survey will determine the accuracy requirements. Control networks are established by using high-accuracy GPS, triangulation, traverse, or leveling procedures. At the other extreme, cuts and fills for a highway have much lower standards. In some surveys, distances to inaccessible points must be determined. High-accuracy distance and angle measurements are required so that these values, when used in trigonometric formulas, will yield acceptable results. This type of survey is directly dependent on the clearness of the atmosphere. Observing measurements for a single position can be delayed for days while waiting on good weather.
Accuracy requirements will dictate the equipment and techniques selected. For instance, comparatively rough techniques can be used for elevations in site surveys, but control-network leveling requires much more precise and expensive equipment and extensive, time-consuming techniques.
All measurements contain some amount of error. Errors classified as systematic and accidental are the most common uncontrollable errors. Besides errors, measurements are susceptible to mistakes or blunders that arise from misunderstanding the problem, poor judgment, confusion, or carelessness. The overall effect of mistakes and blunders can be greatly reduced by following a pre-established systematic procedure. This procedure will be advantageous in all phases of a survey.
7. Progress Rates
Rates of progress vary, depending on experience and repetition. As skill and confidence increase, so does speed. Proper preparation and planning reduce duplication of effort and increase efficiency.