An important consideration in selecting a site for a permanent GPS station is a clear view of the sky with no obstructions above an inclination angle of 10-15 degrees. Keep in mind that tall, dense trees and foliage near the site can contribute to intermittent signal loss, just as buildings do. Be aware of the impact of foliage when reconnaissance is conducted during the cold season. If small trees are present but do not block the sky appreciably, assess their rate of growth if the station is to be occupied for several years. Flat surfaces (vertical or horizontal) near the antenna can cause serious multipath interference. As a rule of thumb, a one-story building should be at least 50 feet away while taller buildings need to be farther away.

Other potential fixed reflectors include chain-link fences, metal objects located in the vicinity, and time-varying reflectors such as parked cars, moving vehicles, scaffolding, etc. A station obstruction diagram should be sketched to identify the approximate distance and bearing to the nearest obstacles. Include potential sources of radio interference such as high-power television or microwave transmission towers. Ideally, the site should be kept at least 1 km away from such structures.

Weather conditions are not normally a factor for permanent site selection since automation is a primary goal and maintenance visits can be arranged during period of good weather. The local climate will mainly dictate the choice of equipment and standards that must be met. For instance, in a cold climate, snow accumulation on the antenna may become a factor, and an antenna radome should be considered.

During the initial visit to the proposed site, try to collect data for at least 24 hours (preferably 48 hours) to assess the quality of the site. Consider also ease of access and proper authorization from private property owners. For example, permission to build a station may be granted by the owner, but access may have to be negotiated with landowners whose properties are adjacent to the site in question. Names and numbers of site contacts should be well documented.

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Last modified Thursday, 17-Nov-2005 03:57:00 UTC

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