First of all, you would be most likely working with a geologist so they would determine the locations to be monitored. The survey team would set the permanent monuments in these locations, allow for these to settle and become stable ( 3 months??). After that you as the surveyor must determine the best method of collecting movement data. As I see it, leveling would provide the least value here since it will only reveal vertical movement/deformation. If you are monitoring on a hillside, you could easily miss sliding or slippage movement. If you are trying to monitor the movement on the dome itself, well the obvious safety concerns cannot be ignored. For Total Station work, the benefit here is the ability to measure a remote target has significant merit. A single trip into an unstable area, such as the dome, to set the monuments and targets would allow monitoring of the most active and dangerous locations at a much reduced risk to personnel. The downside to both leveling and Total Station work are the man hours (days) required to collect a single set of measurements. It is also possible that, over the course of collecting this single data set, that ground movement may occur during the work time. Trying to factor this possibility into the data analysis makes my heads spin. With GPS you would have the most reliable and repeatable system of covering large areas of concern - think in terms of several square miles. Also, depending on the budget, several ( 4 to 6 maybe) semi-permanent GPS stations could be setup and monitored continuously and remotely. Simultaneous readings at each monitoring point can be done daily by remote access and minimal risk to life. Hope this helps.
Thanks Kevin I appreciate your comments and thought on my subject matter . This will help me alot .
Nabil , the accuracies here are in the mm . In levelling is less than or equal to 3mm .
I agree with the reply of Kevin.
It depends from many factors, and the geologist has to evaluate the risk level and the best equipment for the monitoring.
A basic question is: how is the position sample rate (real time, hourly, daily, weekly ...)?
Topography can give a strong contribute, but a great improvment could come from geophysical sensor (seismic).
In many cases, better results can be reached with integration of different techniques.
Be carefull with the tree canopies. If You use an UAV, could be very difficult to observe the ground surface and, consequently, your DTM could be inaccurate.
If You use prisms and total station, the trees growing could hide the target.
And if You put a stationary GNSS receiver with a radiomodem and a solar panel, this must be located in a "naked" site: otherwise, due the tree canpoies the receiver could track satellites partially and the solar panel could give few energy.
thanks Carlo .
We have 17 stations around the caldera and we have been them with GPS monthly , levelled them after every 3 months . Levelling accuracies are less than 3mm .this is how we have been monitoring deformation .