OPUS and L1 Antenna

OPUS does NOT process single-frequency data. There is talk of future L-1 only capability. It is not in place now. Maybe someone has heard of the timeline for deployment, I have not.

If you want to try an automated processor using L-1only data, try http://www.nrcan.gc.ca/earth-sciences/products-services/land-geodetic-survey/gps-processing/online-global-gps-processing/5415. You will need to register to use the site. The L1 capability is mentioned on their site. I have not checked it myself.

Be advised that you need to be aware of the difference between the US and Canadian versions of NAD 83 as well as differences in geoid models.

You can always use the ITRF coordinates from the CSRS-PPP tool in HTDP at the NGS site. Once you have NAD 83(2011) coordinates you can use GEOID 2012 to compute an NAVD 88 compatible height. Keep track of epoch dates.

Check out my web site and look at the file: http://geodesyattamucc.pbworks.com/w/file/64369423/GPSsolutionsCompared_2013.pdf that addresses some of the issues with respect to comparing results from different automated processing tools.

In closing, there are good reasons to use dual (or more) frequency data to generate GPS solutions. I would not trust L1 solutions for long baselines.

Cheers,

DMM

I think it would be nice for GIS mapping if OPUS had an L1 only flavor.

For a while some time back there was some thoughts at NGS about L1 only OPUS. I'm pretty sure that's very much on hold until OPUS-PROJECTS is finally released. Given the state of resources at NGS I would be very surprised if they take this up any time soon. The list of antennas accessed by OPUS is the general list of antennas that NGS has modeled over many years, which does include some L1 only units.

That is what I have heard and read in various NGS presentations.

Is it true that PAGES is capable of processing L1 observations?

I am hoping to attend OPUS Projects training in my area.

Howdy,

The PAGES tool requires dual frequency data as it solves each frequency's integer bias ambiguity separately. It does so through the use of both the wide and narrow lane frequency combinations. You CAN and DO generate L1 only baselines ONLY after determining the integer unknowns using the frequency combinations described above.

The L1-only baselines are appropriate for short baselines where the additional noise resulting from the ion-free solution degrades the solution.
This process is much more robust than any single frequency solution would be.

That said, I have been retired for a while things could have changed. I don't think so however. I imagine that some significant rethinking of the entire process of GNSS data reduction is underway given the significant hurdles dealing with GLONASS integer fixing and remaining interoperability issues. PAGES also does not solve for clock errors as parameters.

As base9geodesy states an L1 processor was planned for mapping grade accuracy positions. It appears in a number of NGS presentations on their site.

HTH,

DMM

OPUS-RS L1 Data

I have an OPUS-RS solution using a ProMark 2 L1 receiver.

If you understand your GPS data, you can calculate bogus L2 & P2 data from L1 and C1 data. I did that manually a few years ago and submitted and received an OPUS-RS solution. Since I did it manually I limited myself to 15+ minutes of data. Since OPUS-RS is more particular with it's needed observation quality I assume it would work with OPUS. I intended to write a routine for the data creation but never got around to it. Creating that file was trial and error manually, but a written program could be adjusted to get somewhat close to L1/L2 standards.

I also observed an L1 file simultaneously with an L1/L2 using a GPS antenna signal splitter. The problem is my Ashtech Z-12s use Z-Tracking which creates L2 data in a different format than other L2 receivers. Other receivers give L1 and L2 data that is esaier to mathematically compare. Since I do not understand how the atmospheric correction is calculating I had to approximate it from actual data.

Since that effort I have discover VRS solutions. In a Virtual Reference Station solution the software downloads 3 surrounding CORS station data, calculates the atmospheric correction at the point of interest, then creates an L1/L2 observation file out of thin air using a "none" antenna value. The L1 only observations are then processed on short baseline vectors. I have done several VRS solutions and submitted my created file to OPUS-RS and gotten good results. It is a good check on your work.

Since RSGPS, the software used by OPUS-RS, creates the atmospheric correction for the point of interest prior to solving vectors to the L1/L2 rover data, it could easily include code to simulate an L1/L2 rover observation then do an almost zero baseline solution to the actual L1 rover observation.

Were Charlie Schwarz still at NGS it would have been working years ago.

Paul in PA

OPUS-RS L1 Data

I have just downloaded CORS from three surrounding stations and processed independently to each station and saved the results. These three solutions usually agree +- 1 foot, a simple average works for my purposes.

I am usually pretty far from the CORS stations so this isn't too alarming for me and these positions are used for GIS mapping, not survey control.

This allows me to get great results from low cost L1 receivers for GIS mapping.

I have also used the L1 units for survey work, but the workflow and survey methods are different.

I have to admit that my desire for an OPUS L1 processor is motivated by efficiency and to help reduce chances for human error introduced by me when procssessing.

L1 Data

After meaning your 3 L1 positions hold that fixed in your software and compare the fixed and solved positions of your CORS stations.

Using more that 1 L1 receiver also helps. I began my GPS carrer using 3 L1 receivers. By solving to all 3 from each CORS I could hold my best mean L1 position and let the rest float. Generally I was in the +/- 0.5' area.

I use VRS in GNSS Solutions, but I do not know what Spectra Precision holds in the future for me.

Paul in PA