Lowrance 5150c 操作ガイド

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determine both position and elevation (your height above sea level — 

also called altitude). This is called a 3D fix. 
Remember, the unit must have a clear view of the satellites in order to 

receive their signals. Unlike radio or television signals, GPS works at 

very high frequencies. These signals can be easily blocked by trees, 

buildings, an automobile roof, even your body. 
Like most GPS receivers, this unit doesn’t have a compass or any other 

navigation aid built inside. It relies solely on the signals from the satel-

lites to calculate a position. Speed, direction of travel, and distance are 

all calculated from position information. Therefore, in order for the 

GlobalMap 5150c to determine direction of travel, you must be moving 

and the faster, the better. This is not to say that it won’t work at walk-

ing or trolling speeds — it will. There will simply be more "wandering" 

of the data shown on the display. 
GPS alone is plenty accurate for route navigation, but the U.S. Federal 

Aviation Administration has special aircraft navigation needs that go 

beyond basic GPS. Consequently, the FAA has developed a program to 

boost GPS performance with its Wide Area Augmentation System 

(WAAS). The FAA commissioned the system on July 11, 2003. 
WAAS is designed to increase GPS accuracy to within 7.6 meters verti-

cally and horizontally, but according to the FAA, it consistently comes 

within 1-2 meters horizontally and 2-3 meters vertically. It does this by 

broadcasting correction signals on GPS frequencies. Your unit auto-

matically receives both GPS and WAAS signals. 
There are, however, some fringe areas of the U.S., including parts of 

Alaska, that do not yet receive robust WAAS coverage. Continued 

WAAS development is planned to extend WAAS coverage in the years 

to come. 
WAAS boosts the accuracy of land GPS navigation, but the system is 

designed for aircraft. The satellites are in a fixed orbit around the 

Equator, so they appear very low in the sky to someone on the ground 

in North America. Aircraft and vessels on open water can get consis-

tently good WAAS reception, but terrain, foliage or even large man-

made structures can sometimes block the WAAS signal from ground 

receivers. 
You'll find that using your GPS receiver is both easy and amazingly 

accurate. It’s easily the most accurate method of electronic navigation 

available to the general public today. Remember that this receiver is 

only a tool. Always have another method of navigation available, such 

as a map or chart and a compass.