Help in selecting GPS

I am a seismologist. My need is to find a a GPS with a good precision (not accuracy) at the lowest possible cost. What I need is to put the instrument on the ground and leave it there for the next few years. If the instrument has a high precision, let us say less than 1 cm, the averaging out of thousands of measurements with the typical 2.5 m accuracy will allow me to figure out the exact position with the centimetrical precision that I need.
Any suggestions?
Thanking you in advance
Paolo

 

You aren't going to find a gps that can measure in the inches without paying serious money.

Period.

 

High precision GPS?

Dear Paolo,

I somehow disagree with Phantom.
Let us look at the possible sources of error in the GPS UERE:
edu-observatory.org/gps/gps_accuracy.html

Multipath can be very high (e.g. urban environment) and will be hard to beat.
But if this is not your case then the main errors left are atmospheric errors and ephemeris/clock errors. To estimate the atmospheric errors normally there are three options:
- using dual frequency receivers (real time),
- use the ionospheric grid information carried by SBAS (in Europe EGNOS) messages (real-time)
- use the meteorologic information from the ground segment of GPS (post-processing, see IGS IONEX)
While dual frequency receivers are very expensive, most receivers receive SBAS and apply its ionospheric corrections.

The ephemeris/clock contribute can be mitigated by using precise products (quasi real-time, e.g. from IGS) or implementing some sort of PPP (Precise Point Positioning) which will have long convergence time (2-3 hours) but you can afford that.
There is free software supporting PPP (see RTKLIB) both in real-time and post-processing and a recent uBlox module (NEO-6P, 40EUR/piece) also implements "in hardware" a "light" version of it.

In my opinion if you want low cost cm accuracy you must look at L1 only receivers which are low cost and output raw measurements, so you can post-process them with ionospheric grids and ephemeris/clock precise products ...effectively mitigating the major contributors to an error that does not average out.
The lowest cost receivers I know are the Skytraq S1315F-RAW, followed by the NVS NV08C-CSM (GPS/Glonass) and the uBlox NEO-6P/T (embedded PPP/timing). They respectively come at _about_ 20EUR and 30EUR/piece in quantities.

Hope this helps!

Best regards,
Michele

 

Thanks

You gave me exactly the kind of answer I was looking for.
I am used to build my own instruments and I have realized that as long as you really know how they works, you can get 90% of the optimal performance at 5% of the cost.
Since I want to associate the monitoring of crustal deformation to sismicity, I need a low cost instrument to deploy in a dense grid, that just tell me if there is on-going deformation or not.
Sincerely,
Paolo

 

I do apologize, I was under the impression you were looking for an in-tact off the shelf unit.

 

Please let me know your budget which is affordable for you. It could be easy for me to suggest you some device which fulfills your criteria.

 

Go to Gpsgate to find many of the devices you are looking for. They offer free software or the SDK if you would rather have that at a fraction of the cost of a gps company.