Were up in Prescott, Arizona and are using Spectra SP 80's

from what i understand they can mix and match satellites from any constellation, and this is why they are always locked onto and using so many satellites.  They work way way WAY better in the heavy tree cover than any other system i have seen.  

My question is, does any other system on the market do this? does the Spectra epoch 50 do this? 

i know that other systems use multiple constellations, but they can only use one constellation at a time. 

and cant for instance use glonass and US satellite at the same time.  

any one have any knowledge they can share on this?  

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Adam, 

what do You mean when say " ...but they can only use one constellation at a time."?

The GNSS receivers work, in RTK, using all common satellites tracked by rover and base. If You have a full GNSS system, it works with four constellations simultaneously (Navstar-GPS, Glonass, Beidou and Galileo) when the base receiver (or CORS network) is sending correction data of each sat "family" to the rover.

E.g., if You are working in N-RTK and the CORS network has only GG receivers, Your rover will use only Navstar-GPS and Glonass satellites, even if it can track Beidou and Galileo.

Regarding the performance under trees canopy, many factors can determine the RTK accuracy (DOP, multipath) and the only valid comparison is a test with different receivers in the same site and at the same day/time.

Bye

Carlo Alberto

Hey Adam,

To add to Carlo Alberto’s comments (thank you Carlo Alberto), another factor in positioning under canopy with GNSS receivers is the SNR thresholds over which a receiver will compute/report a position solution. My following comments generally refer to RTK, but can apply to other modes of GNSS surveying.

Many GIS-grade receivers have a user-configurable SNR threshold. GISers are often quite happy with meter-level precision.

Conversely, I have never seen, read of, or used a Survey-grade receiver with a user-configurable SNR threshold. Can you imagine the pin-cushion corners caused by each surveyor using different SNR thresholds in tough conditions and, thus, using varying position solutions to mark a corner?

Generally, SNR thresholds are hard-coded in the Survey-grade receivers’ firmware. Survey-grade receivers which appear to “work way way WAY better in the heavy tree cover”… likely use a lower (read: noisier) SNR threshold to compute and report a position solution. A position solution using noisy data is a less accurate (and less repeatable) solution.

A GNSS receiver simply reporting a position fix is not necessarily a guarantee that the fix is accurate enough for the type of work being done. I’ve spent plenty of time trying to “break” GNSS kit in tough conditions (various canopies, high-multipath, canyons) by checking GNSS-derived positions against positions computed using conventional methods and kit.

Cheers,

Kev

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