GPS accuracy

[+zippes]

The documentation seems to indicate that on a good day with a good signal you might expect a level of 3 meter accuracy from your hand-held unit. How does that compare to the level of accuracy of the hand-helds the military are issued? I understand they have more/different satellites to play with but 3 meters ain’t bad in the resolution department. Also… do you feel the limiting factor in accuracy is in the ‘hand-helds’ or the ‘satellite’?

 

(enquiring minds and all that ya know…)

 

"Remember... nothing is completly worthless...

it can always be used as a bad example"!

[+Wadcutter]

When we were doing desert training one of the night exercises was to simulate finding a cached resupply location and also keep brushed up on land nav. One night we could only use map and compass to hike out thru the desert to various caches located 2 to 7 kilometers away. No locate the cache, no resupply of food and ammo. Can be pretty tough on moonless nights in rough desert terrain with mountains and waddies while maintaining tactical light discipline. The next night they let us use the mil GPS. The mil GPS has 2 modes. In the uncoded mode they are a bit more accurate than the civilian handhelds. However, in the coded mode they are really accurate. The 2nd night out we were to locate a .30 cal ammo can hidden in the desert that had a message in it. The purpose was to simulate hooking up with a covert agent who had left us instructions. Again, moonless night, we were moving tactically which means absolutely no lights, and it was a 7+ kilometer hike thru some pretty tough ground. Using the mil GPS in the coded mode I stepped on the can. That's how close it could get me.

This was several years ago before I retired. I have no idea what kind of improvements have been made.

[+GEO*Trailblazer 1]

4 one thousandths of a percent in the center of the Bullseye is all I will say.If you don't believe it just FOLLOW ME.....The math is all the same...The computer is only as good as the programmer...Why do you think they call them control points.I don't wanna give away all the secrets.

 

WHEN ALL ELSE FAILS *GEOTRYAGAIN* http://www.msnusers.com/MissouriTrails

[+Poindexter]

quote:

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Originally posted by zippes:

The documentation seems to indicate that on a good day with a good signal you might expect a level of 3 meter accuracy from your hand-held unit. How does that compare to the level of accuracy of the hand-helds the military are issued? I understand they have more/different satellites to play with but 3 meters ain’t bad in the resolution department. Also… do you feel the limiting factor in accuracy is in the ‘hand-helds’ or the ‘satellite’?

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What documentation are you speaking of? You can expect 3 meters (95% probability) with WAAS corrections and good satellite geometry. Without WAAS you can expect about 7 meters (95% probability) and again with good satellite geometry. Military units using the precise dual frequency code can also expect 3 meters without differential corrections. The major contributing factor to errors are ionospheric conditions (single frequency). Poor satellite geometry can greatly increase the error. Other sources contributing to errors are ephemeris data, satellite clock, tropospheric, multipath, receiver (which is very small, about .5 meter. About same as tropospheric), your current latitude, number of satellites/signal strength, current status of the satellite constellation and antenna orientation (improperly holding the receiver contributes to poor satellite geometry). The military uses the same satellites but have access to the precision code in dual frequency mode.

 

Lots of variables involved, the main one that you have some control over is satellite geometry. Learn about DOP and how to interpret the "satellite screen" on your receiver and you can improve your accuracy. EPE is NOT an absolute accuracy indication. Use it as a rough guide only.

[Kerry.]

3 metres but there can be different types of 3 metres. Like 3 metres RMS, 3 metres CEP, 3 metres average, 3 metres @ 95% etc etc. All are 3 metres but they are all "different".

 

SPS (Standard Positioning Service) accuracy is a function of the system that all receivers rely on.

 

Effectively now that Selective Availability is set to zero the accuracy difference between military and civil units isn't all that great. About the only main difference is the L2 capability which handles some of the atmospheric issues as corrections and not predictions. Timing capability is also a little better.

 

The system accuracy spec is based on a 24 satellite constellation and basically guarantees 13m @95% world average. That is also Signal-In-Space (SIS) as one hasn't any control of the user's situation.

 

Worst case scenario accuracy spec is 39m @95%.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go