Tip:
Highlight text to annotate it
X
Survey boat is held steady so the total station can lock onto prism.
4Site uses a combination of power search and ATR to find and lock onto the prism.
So that we pick up enough data the tracking interval is set to one second.
The Total station will now track the boat and return the raw angles and distances back to 4Site at the required time interval.
4Site’s graphical display updates the position live on screen with every successful tracking reading.
Thereby allowing the user to ensure sufficient coverage of the required survey area. Optional background mapping can also be displayed.
Sonar depth and quality information is transmitted back to shore via long range bluetooth.
This allows the boat to be 250m+ away from the tablet running 4Site, which can then in turn be a similar distance away from the total station.
The dual hull design of the catamaran helps steady the boat even in fast flowing, turbulent, water.
The on-board camera streams its data directly back to shore to further aid the surveyor control and drive the boat.
Having conducted the survey, 4Site is then used in its desktop mode to synchronise and edit out any lag in the system.
We will first preview the raw sonar log and edit out any extraneous sonar readings.
The time interval can be changed to show a larger slice of the raw data.
When then apply a filter drawn through extraneous values to try and extrapolate the raw bed profile.
Filtered readings are just ignored but can be recovered at any time.
When saved, no data is lost and the original sonar log is still easily recoverable.
4Site then uses the edited log to begin the compensation process.
Any sonar readings with low quality are removed to further aid the validity of the compensation.
An inward and outbound section in the same place must be chosen to provide the source data to tune the adjustment.
We can then dial out the lag by adding an offset to each individual reading in the section, based on each readings' particular velocity at that time.
This compensation is in seconds, per/m/s the boat is travelling. Hence when the boat is stationary at the ends, the readings tally.
As the slider is moved the readings are corrected dynamically to adjust for the lag, until the two profiles are in agreement.
Once the section has been suitably corrected the same correction is applied to the rest of the survey and exported for modelling purposes.
The data is then imported into n4ce for modelling
The raw coordinates are imported directly into a model in n4ce.
The sonar depths are stored as attributes on the points.
This attribute is then taken off the height of the point to give us the corrected depth.
The point data is then modelled to form a DTM which we can use for section and volume purposes.
Which can be viewed in 3D.
For more in-depth checks we can use the live section tool to better interrogateand edit the ground profile.