RIEGL streamlines hydrographical scanning
During the Oceanology International in London this March, RIEGL invited visitors on board a surveying vessel on the Thames for a special cruise that could be described as "cool" in more than one sense. What was demonstrated there in typical London springtime weather was nothing less than a hydrographic surveying system capable of capturing data both below and above the water surface simultaneously and put out data ready for post-processing
Keeping waterways navigable
Like roads or railroads, shipping channels need to be maintained, too so that ships can pass them safely without running aground. Therefore, waterways must be surveyed periodically in order to find out where channels may have to be dredged, whether any breakwaters or other protective structures need repair, or whether existing charts may need updating.
The conventional approach
The conventional approach to surveying waterways is to use multibeam echo sounders to scan the seabed and standard surveying methods like, e.g. DGPS, total stations or land based laser scanners, to map near-shore and coastline features, breakwaters, dockside structures, etc. from on-shore.
Combining of conventionally surveyed on-shore features with seabed data is not only time consuming but also full of gaps and incomplete because it is impossible to scan the seaward-facing sides of objects with on-shore surveying methods.
The innovative way
Today, there is an easier way. A total of at least one hundred visitors boarded the Freedom, a survey vessel Braveheart Shipping had moored on the Thames, for a series of demonstrations by RIEGL and the Dutch software house QPS specializing in hydrographic and maritime applications. What RIEGL and QPS had installed on the boat was the first "turnkey" solution allowing simultaneous online surveying below and above the water surface in real time.
The demonstration system comprised the following components:
- A Reson 8101 multibeam echo sounder with a coverage angle of about 210 degrees scanned the riverbed.
- A RIEGL VQ-250 laser scanner captured the topography above the water surface. The important point is that the VQ-250 is a full-circle scanner that can capture data over a 360-degree angle. This means that it can acquire data from port and starboard, above and down the boat in a single pass. Rotating at a rate of 100 revolutions per second, the scanner can produce an extremely dense point cloud as long as the boat is running at moderate speed.
- An RTK GPS system with an on-shore base station as a reference point for correcting the inaccuracy of GPS data was used to log the true position of the survey vessel at any time.
- An IXSEA Octans IMU provided data to compensate for ship motion and prevent image distortion due to the pitching, rolling and heaving of the boat.
- QINSy, a special software from QPS, acquired and merged the data from the multibeam sonar and laser scanner and made all necessary corrections in real time.
The result was a georeferenced point cloud of the riverbed and (almost) everything above the water surface that the VQ-250 laser scanner can cover. Whenever the demonstrator pressed the stop button, the passengers on board the Freedom could see the surveying results on the computer screen and thus watch how the environment changed as the boat progressed. At one point, the screen even showed one or more airplanes as the survey vessel passed under the approach to London City Airport. Of course, the sonar and laser data could also be viewed separately.
QPS implemented the RIEGL RiVLib library that is available for each RIEGL scanner in QINSy. This library allows all QINSy users worldwide to add a RIEGL scanner to their surveying system at any time. All they need to do is upgrade their QINSy software to the latest version.
Another significant benefit of the new system is that any existing tool for calibrating an echo sounder can be used to calibrate the laser scanner data as well. This makes it extremely easy to add a RIEGL scanner to any survey vessel with a multibeam echo sounder, QINSy software, and IMU.
The Freedom cruises on the Thames demonstrated how a RIEGL VQ-250 laser scanner in combination with QPS QINSy software can make marine surveying easier, faster, more efficient, and ultimately less costly than conventional methods. And it can even warn you of approaching airplanes on a cool and windy day in London.