Joint force logistics: understanding location basics: in the January-February issue, the author discussed how military logistics management information systems often do not provide visibility of equipment in shipment. In this article, he shows how the basic concepts of latitude and longitude are helping to solve this problem.
In 1492, when "Columbus sailed the ocean blue," the use of geometry and observation of the position of the Sun and the stars were the primary methods of navigation. Like other learned people of his day, Columbus believed the Earth was round. This meant that he could use the geometry associated with a circle (360 degrees) and the Sun's position on the horizon to navigate. Although he sailed over 500 years ago, Columbus was able to estimate his latitude through the use of a quadrant and navigational charts. Unfortunately, since the chronometer had not yet been invented, the same could not be said for his longitude. So, during his first voyage to the new world, Columbus and his sailors could only guess how many miles they were from home once they left the familiar waters around the Canary Islands and sailed westward.
Before the global positioning system (GPS) was invented, the sextant was the primary tool used for navigation. It measures the degree of angle between the horizon and the noonday sun. By comparing the angle to published tables, the user of the sextant can determine latitude. Latitude has been a lifeline for mariners for several hundred years.
After the mutiny aboard his vessel, the H.M.S. Bounty, Captain William Bligh was placed aboard a lifeboat, and, in one of the greatest feats of navigation ever accomplished, he and his 18 crewmembers sailed the open boat 3,600 miles to the Dutch colony of Timor using a sextant as their primary navigational tool.
Early navigation at sea was a problem because of the difficulty in calculating longitudinal position. Although navigators could determine their latitude by measuring the Sun's angle at noon, they had no means of estimating longitude. They lacked a portable method of determining time of day that would function on a ship. The clocks available at the time were pendulum clocks, which were useless on a rolling ship at sea. In 1763, John Harrison, a carpenter from Yorkshire, England, perfected a clock (chronometer) that was not affected by gravity or the motion of a ship.
Once the chronometer was invented, a mariner had to know only the time of day at his location and the time of day in Greenwich, England, to determine his longitude. At the Equator, if Greenwich time was 1200 and local time was 1600, a mariner knew that he was 4,200 miles west of Greenwich, England (each hour representing about 1,050 miles, or 15 degrees of longitude).
The concepts of latitude and longitude, premised on the fact that the Earth is nearly round and has a magnetic north, are not only one of the oldest means of identifying location but also one of the best.
World Geodetic System
Emerging technology holds the promise to simplify location identification. Satellite-based GPSs and digitized maps frequently express physical locations using the conventions of the World Geodetic System (WGS), which was developed in 1960. Latitude and longitude are essential components of the GPS, so it is important to understand these concepts.
Latitude. The Earth has a circumference of about 25,000 miles at the Equator and a slightly smaller circumference around the poles. Since the Earth is nearly round, it can be divided into 360 degrees. Therefore, we can express location by using the angles of arc between two reference points. Latitudes are horizontal lines that are parallel to the Equator, which is used as one of two reference points; it is designated as 0 degrees latitude.
In the WGS, minutes and seconds are not expressions of time but the amount of arc in the circular Earth. There are 60 minutes (of arc) in a degree and 60 seconds (of arc) in a minute. Therefore, each degree of latitude represents about 69 miles (the Earth's 25,000-mile circumference divided by 360 degrees equals 69 miles). A location with latitude of 45 degrees north is halfway between the Equator (0 degrees latitude) and the North Pole (90 degrees latitude north). A location with latitude of 45 degrees south is halfway between the Equator (0 degrees latitude) and the South Pole (90 degrees latitude south). In the WGS, it is not possible to exceed 90 degrees latitude.
Longitude. Longitude lines (also called meridians) are vertical lines that connect at the poles. Longitude represents location as an angle between a line running north and south through Greenwich, England (called the Prime Meridian), and a vertical location point. The Prime Meridian is the other reference point; it is designated as 0 degrees longitude. Moving west from the Prime Meridian, one would pass the east coast of the United States, the west coast, and Hawaii to a maximum longitude of 180 degrees west. This is the location of the international dateline, which is on the opposite side of the world from the Prime Meridian. Heading east from the Prime Meridian, one would pass through France and Russia to a maximum longitude of 180 degrees east. This would again be the international dateline.
Converting angles of arc into distance for longitude is much different than for latitude. While lines of latitude are parallel and remain at a constant distance from one another, lines of longitude converge at the poles. The distance between degrees of longitude at the Equator is 69 miles; the distance between degrees of longitude at either of the poles is 0. Typically, the latitude and longitude grid lines shown on world maps are 15 degrees apart. Locations are pinpointed using degrees, minutes, and seconds of latitude and longitude. The latitude and longitude for San Diego, California, for example, are latitude 32 degrees, 51 minutes, and 9.36 seconds north and longitude 117 degrees, 6 minutes, and 36 seconds west.
GPSs are helping to transform logistics. Twenty-four solar-powered satellites that are 12,000 miles above the Earth serve as the foundation of the GPS. To determine their current location, military personnel can use GPS receivers to retrieve radio signals from the satellites. If they are able to receive signals from three different satellites, the GPS receiver can display location to within plus or minus 10 meters. If the GPS receiver can pick up signals from four or more of the satellites, military users also can determine altitude.
With GPS information--expressed in latitude and longitude and accurate to within 100 feet or better--deployed forces can easily determine their current locations. These could be established sites such as aerial ports of debarkation, shallow-draft seaports, highway intersections, container consolidation points, or supply points. Deployed forces also can use a GPS to determine temporary sites, such as supply storage areas hastily assembled in forests or deserts, helicopter landing zones, tactical assembly areas, container-handling areas, and ammunition transfer points. Once this location information is loaded into a computer network, joint logisticians worldwide can use a variety of software programs to view the locations and surrounding areas on digitized maps. For example, if a Soldier located in a forest on the island of Sumatra needs ammunition and provides the latitude and longitude of his location to a logistician in Australia, the logistician can access a digitized map database, analyze the surrounding area, determine the best route of resupply, and program a Joint Precision Airdrop System, loaded with ammunition, to land within 100 feet of the desired drop location.
With the dramatic advancements that have been made in GPS technology, telecommunications, automatic identification technology, data processing, and advanced software systems such as those that digitize maps, photographs, and images, there soon will be no need to truncate word-related data fields or encode location data for the Joint Operations Planning and Execution System, the Global Transportation Network, or the Defense Transportation Regulation. Since current computers and telecommunications systems can readily store, process, and transmit a tremendous amount of data, it is no longer necessary to encode location information. Whenever possible, the Department of Defense should express locations as mailing addresses (currently used in direction-finding software such as MapQuest) and cite latitude and longitude. Because of the enormous quantity of logistics data that must be processed to attain asset visibility of items in shipment, military shipment labels and transportation control movement documents should be redesigned to minimize the number of data elements that must be captured at transshipment points.
Locating items in shipment and determining their final destinations is complex, but continuous advancements in technology are significantly improving the process. Many streets in countries around the world will remain unnamed; however, modern technology will enable us at least to determine the latitudes and longitudes of equipment traversing them.
LIEUTENANT COLONEL JAMES C. BATES, USA (RET.), WORKS FOR ALION SCIENCE AND TECHNOLOGY AND SERVES AS A SUSTAINMENT PLANNER FOR THE U.S. JOINT FORCES COMMAND, STANDING JOINT FORCE HEADQUARTERS (STANDARDS AND TRAINING), AT NORFOLK NAVAL BASE, VIRGINIA. HE IS A CERTIFIED PROFESSIONAL LOGISTICIAN AND A GRADUATE OF THE ARMY COMMAND AND GENERAL STAFF COLLEGE AND HOLDS AN M.B.A. DEGREE FROM THE UNIVERSITY OF HAWAII. HE CAN BE CONTACTED BY EMAIL AT JAMES.BATES@JFCOM.MIL.
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|Author:||Bates, James C.|
|Date:||Mar 1, 2006|
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