High satellite rejection on PPP

Hello everyone!

I was checking some infomations from the summary of some PPP processess and found out that PPP is rejecting a lot of satellites.

Looking at two samples, one has almost 20 and another is almost at 15.

I have the two files here with me. Unfortunetaly they are in portuguese, i couldn’t translate them easily.

PPP Summary.zip (14.6 KB)

Any ideias what it could be?

It’s really hard to anything qualified without the Raw-files. Can you post them here, or a link to download from i.e. WeTransfer?

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Hi @tec.adriano.menezes,

The geometric positioning of satellites, their location above the horizon, and signal strength can influence the choice of satellites for position calculation.

15-20 satellites are usually enough to calculate the exact position. Some of them can be rejected since they have a noisy signal. So, the number of satellites may differ from time to time.

If you are concerned about the accuracy of the results, please could you send us the raw files? In case these files contain some sensitive info, you can send them to support@emlid.com. We’ll take a look at them and figure out what might be wrong.

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Unfortunately i’ve confused things, the file with higher discarted satellite are from another GPS brand.

The RS2 unit has 3 discarded GPS less than the other and in a different day, i will be sending the files from it.

raw_202103221318.zip (4.3 MB)

Do you still see it as a problem, or?

That’s what i was hoping to check in here, from an average of the satellites available for the receiver, 16 of them are getting rejected by the PPP.
Only using 16 for the PPP process

Landmark Name: Base
Start: 2021/03/22 13: 19: 16.99
End: 2021/03/22 14:01: 20.99
Observation interval (sec): 1.00
Processing interval (sec): 1.00
Number of times processed: 2525
Number of rejected seasons: 0
Number of processed satellites: 16
Number of processed observations: 7840 GPS
Number of rejected observations: 9131 GPS
Number of weighted observations: 0 GPS
Pseudodistance residuals (m): 2.46 GPS
Carrier phase residues (cm): 1.37 GPS
Number of observations processed: 10528 GLONASS
Number of rejected observations: 4780 GLONASS
Number of weighted observations: 0 GLONASS
Residues of pseudodistance (m): 3.72 GLONASS
Carrier phase residues (cm): 1.41 GLONASS

Hi @tec.adriano.menezes,

I checked the files that you shared. Indeed, there are many signals in your logs that have an unstable signal-to-noise ratio (SNR).

The GNSS signals are quite weak. If the receiver stands close to trees, the foliage can block a signal from satellites. Also, power lines generate an electromagnetic field that can affect signal stability. I’d recommend locating the receiver under the clear sky view 30 degrees above the horizon without any obstacles.

I guess this causes PPP to reject many satellites with a poor signal. However, a minimum of 4 satellites with stable SNR allows the receiver to calculate the precise position. That’s why 16 satellites should be enough.

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Well that’s the thing, if you check the coordinates inside the file, the point is in an open field.

So there is few to none obstacles inside the mask, we always work with the recommended Emlid settings for the masks.

Hi Adriano,

You have good enough data for PPP to accurately calculate the position. In this case, I just explained that it’s normal that the PPP service can reject some satellite signals with unstable SNR.

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