I read somewhere that in RTK only the L1 signal is used by the units in determining actual position of the rover unit. Is this true?
As a followup, if above premise is true then can I use a L1 unit as 2nd base for the rover units?
What about accuracy of the rover unit's position - especially the z value?
The L1 is used once the ambiguities are fixed. The L1 is a shorter wavelength than the L2, which makes it more precise for positioning. Using ONLY L1 though, means you won't be able to fix ambiguities on the fly like you can with dual frequency receivers (or even dual constellation receivers), so you'll have to occupy points for a long enough time for the processor to fix using the L1 only signal - depending on range this could be as little as a couple of minutes on a short vector (100 feet or so) to 30+ minutes on longer vectors (over a mile) of uninterrupted data (no loss of lock). Accuracy (once fixed) will be as good as RTK.
In short, it can work, and provide very precise results, but there are caveats.
OK, What Is PPK ?
Assuming you were using an L1/L2 base, and had 1 minute of 1 second data, the L1 only second base may help. However you may need greater than 1 minute. So you are looking at short static occupations.
Paul in PA
Post Processed Kinematic, My Duh
And I have done this in the past.
Most of what I do now is static control surveys.
Paul in PA
Shawn,
You are somewhat corrrect. You are correct that you cannot fix the ambiguities on the fly with L1 only. That means you have to do a "known point initialization" before you start collecting points. If you sit on each point until the post processing software has enought data to solve for the integer ambiguities then you are doing a fast static survey and not a ppk survey. With PPK, once initialized on a known point, you only need several epochs on each point. So the time you spend on each point is more a function of your logging interval. I get three epochs per point so if I'm logging 1 second data, 3 seconds / point, 5 second epochs = 15 seconds / point. Make sure your logging intervals are the same at the base and rover. On some systems like Trimble, you can do the "known point init." at any point in the survey as long as you havent lost lock. That's a bit more advanced technique and I don't reccomend it until you really know what you are doing with PPK.
Good luck,
Bryan Baker
Frontier Precision Inc.
You can fix on the fly with L1 RTK, it just takes longer.
> Shawn,
>
> You are somewhat corrrect. You are correct that you cannot fix the ambiguities on the fly with L1 only. That means you have to do a "known point initialization" before you start collecting points. If you sit on each point until the post processing software has enought data to solve for the integer ambiguities then you are doing a fast static survey and not a ppk survey. With PPK, once initialized on a known point, you only need several epochs on each point. So the time you spend on each point is more a function of your logging interval. I get three epochs per point so if I'm logging 1 second data, 3 seconds / point, 5 second epochs = 15 seconds / point. Make sure your logging intervals are the same at the base and rover. On some systems like Trimble, you can do the "known point init." at any point in the survey as long as you havent lost lock. That's a bit more advanced technique and I don't reccomend it until you really know what you are doing with PPK.
>
> Good luck,
>
> Bryan Baker
> Frontier Precision Inc.
I agree with Al. It can be done OTF. I mentioned uniterrupted data. You can be walking around from point to point, as long as the receiver doesn't lose lock, you can locate points in seconds, just like RTK, but if lock is lost, a lead time of a couple of minutes to 30+ minutes may be necessary to get fixed again. And, you are correct, a known point initialization is always an option.
so this is a correct procedure?
i have only 3 dual frequency gps units that can record kinematic data but i have 5 L1 units lying around th office.
we have an upcoming bathymetry survey and I was planning of putting 2 dual units on the boat & 1 dual + 1 L1 on the shoreline controls.
why?
the last bathymetry survey we did, we used 1 dual unit on the boat & 2 units on the shore control points. when we downloaded the data, the boat unit was skipping data. don;t know the reason why. satellite positions, signal bouncing off nearby ships, bad sd card. never really found the reason.
so to avoid this scenario again, we plan to place to dual units on the boat for redunduncy & 2 units on the ground for reference points.
hope this works.
thank you guys.
Since You Have 3 L1
Use more than 1 on the beach. Put your L2 base nearest the survey area, and an L1 well off to either side.
Paul in PA
