Lowrance lms-522c igps 操作指南

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The system requires signal reception from three satellites in order to 

determine a position. This is called a 2D fix. It takes four satellites to 

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, the 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 it to de-

termine direction of travel, you must be moving and the faster, the bet-

ter. This is not to say that it won’t work at walking 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. So, the FAA has developed a program to boost GPS 

performance with its Wide Area Augmentation System, or WAAS. The 

FAA commissioned the system on July 11, 2003. 

WAAS is designed to  increase GPS accuracy to within 7.6 meters vertically 

and horizontally, but it consistently delivers accuracies within 1-2 meters 

horizontal and 2-3 meters vertical, according to the FAA. It does this by 

broadcasting correction signals on GPS frequencies. Your unit automati-

cally receives both GPS and WAAS signals.