Being a former Rockwell employee I am very familiar with what today is referred to simply as GPS. The Global Positioning System (GPS) was built by Rockwell International
(Block I and Block II) and later by General Electric/Lockheed Martin (Block IIR) and is overseen by the United States Air Force Space Command. Boeing, formerly Rockwell, just won the follow on contract to Block IIF and will hopefully be building another 24 satellites over the next twelve years or so.
GPS is basically a constellation of 24 semi-synchronous orbiting satellites
each containing its own atomic clocks and identification codes. Each satellite continuously sends a stream of encoded information down to the Earth which is received by ground stations, aircraft, ships, field personnel, surveyors, etc.. whom have special GPS receivers. These receivers have sophisticated electronic engines/computers coupled with special antennas which can receive multiple signals. Several points in space can be used for triangulation which allows the user to determine with a high degree of accuracy their latitude, longitude, altitude, speed, and direction.
The Air Force has the ability to control the quality of the signal by electronic
means but there are ways around the degraded signal. For example, one could
have several receivers on the ground to provide a baseline error measurement,
or offset, which can be used to correct any gathered data. This is extremely
important when performing critical functions such as ground surveying.
A basic methodology for using GPS to find old collecting localities is as
follows:
- a) Research the mine or site you want to visit. Check several sources.
- b) Buy one or more topographic map(s) for the area in question.
- c) Use a ruler and convert the mine location, if shown, into an approximate
lat / longitude.
- d) Program the latitude and longitude into the GPS unit as a waypoint.
- e) Put the GPS receiver into tracking mode. As you approach the mine site
the display should indicate your direction of travel and your straight line
distance to the target.
- f) Some of the receivers will provide an audible tone when you are very
near the target.
- g) Others will give you data that correlate directly with topographic maps.
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There is one problem with GPS and that is Selective Availability. This is a mechanism by which the Department of Defense can selectively degrade the signal accuracy of the GPS satellite positioning data. When this mode is engaged the altitude, latitude, and longitude can all be off by as much as 100 feet or more. When trying to layout claims or other property boundaries this can be very disappointing. The only way around this is thru LORAN, compass bearings to known geographic points (as long as the ground is not too heavily concentrated with iron or other metals which will cause errors), or the preferred method with a topographic map and a level transit. Fortunately in the year 2000 the government had the common sense to turn off the error signals so that the true commercial uses of GPS could benefit once and for all.
As a part time exploration entity I own several pieces of equipment including three GPS receivers, one LORAN receiver and a Bushnell laser rangefinder. The three GPS units vary in vintage but all serve their purpose: one is a TRAXAR GPS unit which was made by Motorola; the second one is an Eagle Accunav Sport which is very nice and has a large screen and also allows me to interface it to StreetAtlas USA via an RS232 interface to my portable Macintosh computer; and third my latest acquisition a Lowrance GlobalMap 100 which has downloadable maps, on-screen maps for some geographic features like rivers, lakes, major roads and also interfaces directly to my portable Macintosh.
I use a software program called Gypsy which can translate and display any coordinate system from the GPS output data. It is really a useful program.
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