GNSS for monitoring

John Hamilton should be along shortly. This is his bread and butter. You could also contact Steve Martin at the East Bay Municipal Utility District in Oakland California. They use fixed GNSS receivers (Leica, I believe) to monitor the deformation on their dams.

Unsolicited comments (worth what you paid for it).

Monitoring a structure, I would argue, is significantly different from monitoring ƒ??...changes in land level.ƒ? Setting up a receiver, like the Leica GR10, on a permanent site can yield excellent results (look at the plots for any NCN aka CORS site) IF the site is stable. Monumentation is critical in my opinion.

A critical question for me is you intend to monitor land levels and your sites with respect to what? If you monitor the land level with respect to your continuous sites, how do you insure that the continuous sites arenƒ??t deforming??ÿ

What type of changes do you intend to monitor? Land subsidence or similar geophysical phenomena?

For me, I have seen some impressive results based on InSAR and similar techniques. See: https://earthsciences.osu.edu/sites/earthsciences.osu.edu/files/report-503.pdf ?ÿ

There is a lot of academic literature on the subject including free articles in journals like the Journal of Applied Geodesy and Journal of Geodetic Science. ?ÿCheck out the UNAVCO and FIG sites for information about setting up and running a monitor network and for presentations on deformation modeling surveys.

BTW, a stable permanent GNSS site can achieve NCN site accuracies IF you do your data reductions using precise orbits, account for GPS antenna model differences, apply the right tropo models, etc.

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Posted by: @geeoddmike

A critical question for me is you intend to monitor land levels and your sites with respect to what? If you monitor the land level with respect to your continuous sites, how do you insure that the continuous sites arenƒ??t deforming??ÿ

Teasing all this out at the moment. I believe it is to be tied to 3 CORS stations closest one being 25km.

You should be able to get several mm accuracy from continuous receivers. But, as others said, against what reference? CORS are subject to possible movements as well, and coordinate updates.?ÿ

I wonder what the long term repeatability of PPP is? Just for testing I sometimes set my Alloy (RTX) to output NMEA strings, and there is repeatability at the several mm level over days. But, if Trimble were to change their software that creates the corrections, I could see the possibility of a jump in the results. RTX uses ITRF at a fixed epoch or the current epoch, you would want to make sure it is using the fixed epoch as ITRF has velocities.?ÿ

We monitor an area on Lake Erie for mm level subsidence (from a deep salt mine) by doing second order levels once a year. We run from an area that is apparently stable. There is a CORS and a lake water level station in the area that we monitor, but they are in an area that is less affected.?ÿ?ÿ

It would seem important to maintain comparisons against multiple reference points, so if one turns out to be not stable it can be identified.?ÿ What if your favorite CORS has an equipment failure or is damaged by a storm?

Many CORS stations are placed for the express purpose of monitoring crustal movement.?ÿ

I suggest the following book and articles for insights into monitoring and deformation surveys:

ƒ??Geodetic Network Analysis and Optimal Design: Concepts and Applications,ƒ? by Kuang, Shanlong (1996). I have a hardcover copy but believe there is a softcover version.

My copy has: ISBN 1-57504-044-1. Published by Ann Arbor Press, 121 South Main St, Chelsea, MI 48118.

Checking Amazon, they link to used bookseller offering ƒ??very goodƒ? copies at around $115 + P&H. Did not do any further searches. I have my copy.

He has entire chapter on deformation monitoring network design. I highly recommend this book as it provides good detail on error sources in observations, statistical testing, adjustments and their analysis. He emphasizes the importance of designing the network for not only geometric strength but also to interpret the results of the surveys to prove your hypothesis. He discusses issues like precision, reliability and sensitivity.?ÿ

Given the ability of many adjustment software packages to perform simulations, I wonder why most donƒ??t use this to test whether their design will satisfy their requirements.

https://www.researchgate.net/publication/237551439_Use_of_Geodetic_Monitoring_Measurements_in_Solving_Geomechanical_Problems_in_Structural_and_Mining_Engineering

https://www.researchgate.net/publication/264536634_Anthropogenic_land_subsidence_in_the_Perth_Basin_challenges_for_its_detection_and_monitoring

Lots of good material available on the web. Most anything on the subject by Adam Chrzanowski of UNB is recommended.

HTH,

DMM

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