John
I was lucky to have been given the opportunity in 2005 to redesign all of the monitoring schemes. Same points, but the old methods were obsolete. Prior to 2005 it was done by Corps in-house personnel. They used an optical instrument (T2) and a movable target with a micrometer. The T2 was set at one end of the line, and a fixed target at the other. They would set the moveable target up over each pin, and using the T2 would have the target operator move the target until it was online, then they would read the offset from the line on the micrometer.
In fact, I did this on all of these dams when I worked on a Corps crew in the early-mid 80's, so I was quite familiar with it. But, as you can imagine, heat waves wreak havoc with this method. Two of the dams are more than 1 mile long along the crest. Even at 750' it is difficult. They tried to do it at night, didn't help much.
The first thing I did in 2005 was to go to each project and prepare a proposed monitoring plan. Many of the off structure pedestals were blocked by vegetation. The first year we did a combination of total station and GPS on the earthen dams, but then decided that GPS alone was sufficently accurate (and much easier). The plans were modified slightly in 2005 and 2006 as we gained experience at each project. Least Squares simulation mode was used to make sure we were meeting the required accuracies.
By the way, here is a link to some papers given at the last deformation conference, in Lisbon, Portugal in 2008:
http://www.fig.net/commission6/lisbon_2008/index.htm.
I did not attend that one, but I was at the previous conference in 2006 in Baden, Austria, I don't have a link for any proceedings from the 2006 conference.
There is an upcoming deformation conference in Hong Kong in November, which I intend to attend and present a paper: http://dma.lsgi.polyu.edu.hk/
John
John
To your credit, you are always looking for ways to improve your technique and results. Thanks for the links. Who knows, I like to travel, maybe I'll get the chance to hear you deliver your paper in Hong Kong.
John & John
Great post,
thanks to John H. for the clear explanation of how you deal with this kind of surveys.
John M. success with the processing of your data, keep me posted about how you'll handle this in TGO, I will learn something new.
chr.
John
This is an interesting discussion and I enjoyed reading it. Always learning.
I'd also like to call your attention to a recent joint NGS/ASCE publication "CORS and OPUS for Engineers." Of course, one does not need to be an engineer to read the book and/or learn more about working with 3-D digital spatial data.
To find a web page for the book quickly, google "American Surveyor ASCE" or see a recent post by Dave Wahlstrom on "CORS and OPUS." The book contains a compilation of recent authorative information.
CORS and OPUS for Engineers
I am currently doing a book review of that for ASCE. Should be finished soon. Excellent resource.