I have a Topcon Hiper Pro, that I use on the FDOT Network. The satellites used always seems low. I'm in an area that doesn't have Glonass on the network, yet. So, I often see, Tracking 18-24 sats, but only using 4-8 sats. I don't think I've ever seen 9 sats being used. When I look at the satellite info, I see about half the sats being tracked are Glonass (so those don't count), and about 1/3 the GPS sats being tracks are below the elevation mask ... hence, I only get to use about 1/3 of the sats I'm tracking. That all makes sense to me. I know why all those satellites are not being used, but these days, I'm surprised to see that sometimes I'm only showing 4 usable sats.
So, I'm wondering, are there GPS sats up there, that due to the age of my equipment, and the firmware capabilities, that these units are not able to track? For example, if at the time of the last firmware update, there were 30 GPS sats #1-30, but since then, they've launched 10 more GPS sats, #31-40, would this equipment even know that #31-40 exist, and be able to use them?
Yes Older GPS Units Track Newer Satellites
I have several Ashtech Z-12s, and you don't get much older than that. I can get up to 9 satellites, old or new. Because I am limited to 9 channels and the searching in the last 3 takes a while to run through the available list, I seldom get 10. I could speed up the search by telling the unit not to look for certain satellites but it is not worth the bother. Two weekends ago I replaced the internal memory batteries in one unit and set it up as a test. Once it was warmed up it tracked 8 satellites.
For half of the observation it locked on the newest GPS 2F and tracked it. Because that satellite is not yet fully turned on, my receiver did not record any data but it kept a channel busy. I stay with a 10° horizon and during that observation only the following 9 satellites were above the horizon: 3, 7, 8, 13, 16, 19, 23, 27 & 30.
That means I had 100% of the available satellites. 7 is a 2R-M and 27 & 30 are 2Fs. Earlier last month I checked an observation that used 7 satellites and 4 of which were the newer and newest 2R-M or 2F. Here is the result of my OPUS-Rs submission:
SOFTWARE: rsgps 1.37 RS83.prl 1.99.2 START: 2014/04/27 21:08:00
EPHEMERIS: igr17900.eph [rapid] STOP: 2014/04/27 21:25:10
NAV FILE: brdc1170.14n OBS USED: 1836 / 1854 : 99%
ANT NAME: LEIAT502 NONE QUALITY IND. 32.28/ 6.09
ARP HEIGHT: 0.000 NORMALIZED RMS: 0.387
REF FRAME: NAD_83(2011)(EPOCH:2010.0000) IGS08 (EPOCH:2014.32024)
X: 1234138.307(m) 0.011(m) 1234137.476(m) 0.011(m)
Y: -4683916.254(m) 0.037(m) -4683914.819(m) 0.037(m)
Z: 4135721.332(m) 0.032(m) 4135721.282(m) 0.032(m)
LAT: 40 40 53.62281 0.007(m) 40 40 53.65538 0.007(m)
E LON: 284 45 39.78294 0.004(m) 284 45 39.76429 0.004(m)
W LON: 75 14 20.21706 0.004(m) 75 14 20.23571 0.004(m)
EL HGT: 78.423(m) 0.049(m) 77.178(m) 0.049(m)
ORTHO HGT: 112.567(m) 0.051(m) [NAVD88 (Computed using GEOID12A)]
So the answer is definitely yes.
I highlighted the observations used, since I do not recall ever seeing such a high percentage before.
There are 32 PRN numbers in use, 31 currently set active. The satellite SVN number is unimportant since the receiver looks for the PRN number.
Paul in PA
Yes Older GPS Units Track Newer Satellites
Thanks, Paul. I pulled up my receiver settings with the Topcon utilities program, and it shows PRN 1-32 are available. I also checked the GPS website for satellite health, and it shows PRN 1-32 in use, so I guess I'm getting everything I can get.
On A Network Only Common Satellites Are Used
How close are the network receivers?
What elevation mask are they using?
Are your network solutions restricted to only satellites that are common to every
receiver?
Can you also record observations for post processing to see how many satellites are actually being observed?
I would be looking for a 6 satellite minimum.
Paul in PA
On A Network Only Common Satellites Are Used
> How close are the network receivers?
>
> What elevation mask are they using?
>
> Are your network solutions restricted to only satellites that are common to every
> receiver?
>
> Can you also record observations for post processing to see how many satellites are actually being observed?
>
> I would be looking for a 6 satellite minimum.
>
> Paul in PA
There is a pretty good cluster of Network CORS in this area. 10 CORS within 40 miles from my office. But only one of those CORS is within 15 miles (4 miles away), the other 9 are 15-40 miles away, so I think the solution may be heavily weighted towards the nearest one. I did experiment a little tonight and I found that I can get 2-3 more sats into the solution if I use nearest single baseline instead of a network solution, so there may be a problem with the RTN only using sats that all receivers in the cluster have in common, as you pointed out. I'm really not sure how that works.
I know how many sats are being observed. There are normally 8 to 10 GPS sats in view, it just seems that the DC is only able to use 5-8.
I Thought You Chose Your Own Set Of Bases
At least that is what I recall from demonstrations I attended. Typically the 3 nearest or 3 that put you inside the triangle.
By being inside the triangle the software can average the atmospheric corrections of the three and use that value for the rover site.
Are RINEX files available from the base stations? I would suggest for your next project you also save some static files at the beginning and end. Send those files to OPUS-RS and compare positions with your RTK results. Then download the base's RINEX and compare with your RINEX as to quantity and quality of observations.
Is your software or network administrator under the mistaken impression that only 4 satellites are needed for a good solution? 4 are required for a solution. A good solution requires 6 or more depending on constellation geometry. I have seen poor static solutions with up to 8 satellites because 5 or 6 of them were strung out in a line over only area of the sky. When it comes to short time solutions and RTK is indeed short, satellite geometry can change from good to bad to good within a 1/2 hour period sometimes as a result of only 1 additional or less satellite. Your receiver software may be looking at your minimum 4 satellites and taking that position instead of waiting to see if additional satellites are locked in and resolved. A locked in satellite is not necessarily instantly resolved when you start to collect a position. Try double tapping your RTK, after saving a positions, save it again without moving and see if the second results are generally better.
Use your planning software and take a look at the times of your poor positioning.
Paul in PA
I Thought You Chose Your Own Set Of Bases
With this RTN set-up, I can't choose the bases. In fact, I don't even know what bases are being use, except for the nearest base which the software automatically picks as the main reference point and stores coordinates for. I think the Master Auxiliary Concept (MAC) type RTN just automatically picks the nearest bases. I know the DOT uses the Lieca "SpiderNet" software to run their RTN, and it's a pretty good network when you have enough sats.
I think my issue is really just bad timing. When I went out last night in my back yard for a test I had 8 sats being used and the solution kicked right in. It seems like during normal working hours the satellites are just not there or lack good geometry. I'm sure that will change over the coming weeks...
I Thought You Chose Your Own Set Of Bases
I just ran the mission planning software from Trimble - online.
http://www.trimble.com/gnssplanningonline/#/NumSats
It pretty much confirms that I'm looking at 5-7 sats on average from about 6AM to 3:30 PM .... then after 3:30 PM it jumps to 8-11 until about 9PM.
That's not good for working hours. I know the constellation slowly changes through the year. Looks like it's a bad time of the year for me.
Since When Are You Surveying At The Equator ?
How about your actual location, Pseudo and we'll try Planning over.
Paul in PA
Since When Are You Surveying At The Equator ?
I did put my location in, but I'm sure that the link I posted did not pass that information along to the next user. I was just posting the link because I thought it was a nice online tool.
