Categories

Search

The accuracy of a electronic tracker

Декабрь 30th, 2015 by homesecuirtycameras and tagged , ,

GPS Sources of accuracy

With satellites, the electronic signals travel about 300,000,000 meters per second (the speed of light). So the errors in the satellite clock and the receiver clock contribute profoundly to errors in distance measurements. One billionth of a second (one nanosecond) of inaccuracy in a satellite clock results in about 30 centimeters (one foot) of error in measuring the distance to that satellite. For this reason, the satellites are equipped with very accurate (Cesium) atomic clocks. Even these very accurate clocks accumulate an error of 1 billionth of a second every three hours. To resolve the satellite clock drifts, they are continuously monitored by ground stations and compared with the master control clock systems that are combinations of more than 10 very accurate atomic clocks. The errors and drifts of the satellites’ clock are calculated and included in the messages that are transmitted by the satellites. In computing the distance to the satellites, GPS 3G receivers subtract the satellite clock errors from the reported transmit time to come up with the true signal travel time. Even with the best efforts of the control centers in monitoring the behavior of each satellite clock, their errors cannot be precisely determined. Any remaining satellite clock errors accumulate typically to about a few nanoseconds, which cause a distance error of about one meter.

the accuracy of our computed position also depends on how accurately we know the location of the satellites (the points of references). The orbits of satellites are monitored continuously from several monitoring stations around the earth and their predicted orbital information is transmitted to the satellites, which they in turn transmit to the receivers. The history of GPS has shown, thus far, that the accuracy of the orbital prediction is in the order of a few meters. This will create about a few meters of error in computing our position.

GPS receiver

A fair number of geocachers use only their GPS tracking device for cars to get them to a cache, but a good local map of the area can be very helpful. Although a receiver can lead you directly in a straight line to cache, it’s probably not going to tell you about the river, deep canyon, or cliffs between you and the cache. Even GPS receivers that display topographic maps often won’t show enough detail that can help or hinder you on your way to a cache. Additionally, a map and compass serve as a backup just in case something goes wrong with your GPS.

You can certainly find caches by using only a map and compass (my adventure racing team does this to practice our navigation skills), but it’s sure a lot easier when using a GPS receiver. You don’t need an expensive GPS unit with lots of whistles and bells to geocache; a basic model around or under $100 will work just fine; receivers that support WAAS (Wide Area Augmentation Service) usually are more accurate than those that don’t. Don’t forget to bring the GPS receiver user manual, especially if you just purchased your receiver and are still trying to figure out how to use it.

More GPS tracking solutions at http://www.jimilab.com/ .

Posted in General |



Leave a Reply