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msar-riders - Re: [MSAR] GPS and field navigation

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  • From: T'mi Fi <tfinkle@erols.com>
  • To: Mounted search and rescue <msar-riders@lists.ibiblio.org>
  • Subject: Re: [MSAR] GPS and field navigation
  • Date: Tue, 04 Jul 2006 11:11:56 -0400

When we have roads, power lines, heights of land, mountains, rivers and lakes, these are often sufficient along with the map and compass for us to establish with a reasonable degree of accuracy, where we are on the map. In those featureless areas however, where all looks the same for miles and miles of slowly rolling bushland, grassland, dessert, tundra, swamp etc., the GPS takes over and will give a definitive location which then may be plotted on a map (please note that "map" remains an important tool).

One thing that we all must keep in mind is the use of GPS units are an enhancement tool for field navigation and not a replacement tool. Technology is no where near the point for GPS units to replace the map and compass. Because of satellite coverage, unit placement and blocked signals there will connectivity flaws with reception and in many situations a person may simply need to move several meters to restore satellite signals. The major down side to GPS Units is the need for a power source, but that can be corrected by carrying a few extra batteries (generally AA or AAA), which will extend the units operations for another 12 to 24 hours. Even a week's worth of batteries can be easily carried in something that takes up less space than a pack of cigarettes.

The Global Positioning System is composed of twenty-four satellites 20,200 km (12,500 miles or 10,900 nautical miles) above the earth. The satellites are spaced in orbit so that at any time a minimum of six satellites will be in view to users anywhere in the world. The satellites continuously broadcast position and time data to users throughout the world.

Using a portable or handheld receiver unit that receives data from the closest satellites, the GPS unit triangulates the data to determine the unit's exact location (typically in latitude and longitude), elevation, speed, and time. This information is available around-the-clock anywhere in the world and is not dependent on weather. The "Selective Availability," which made the public GPS less accurate than the military GPS, was turned off on May 1, 2000. Thus, the GPS unit you can buy over the counter at many retailers is as accurate as those used by the military today.

Many over-the-counter handheld GPS units contain base maps of a region of the earth but most can be hooked up to a computer to download additional data for specific locales, which is a feature quickly is becoming a valuable tool to planning section personnel when developing incident action plans. UTM is becoming the standard with most search operations in the United States, however, since UTM deals with meters many americans do not understand the mathematical conversions required for field application. On the newest 1:25,000 US topos, 1 mm. would represent 25 meters on the ground. Even the most common Silva compasses have a mm. scale on one side and this may be used to measure east from a grid line and north from the E-W grid lines.

Map and compass skills will and must always be a part of field navigation for SAR personnel. However, the use of GPS units have quickly become equally important and with basic GIS functionality software programs, these systems being integrated into search planning, high-tech downloadable data is of utmost importance to enhance POD efforts. If you remember, it just a few years ago when laptop computers began to make an appearance at ICP's and have now become the norm for progressive and/or highly skilled SAR teams.
Tomi`
TROTSAR Mounted Team
Maryland





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