Combined multibeam/laser acquisition with QINSy
Most multibeam transducers employ a swath sector of 120-150 degrees. Two transducers mounted at angles to the vertical in a dual head configuration widen the swath sector beyond 180 degrees. A few sounders offer a swath sector of 210 degrees using a single transducer. Such wide swaths permit observation of vertical underwater structures right up to the water surface. Extremely detailed 3D images of the underwater environment are routinely produced, including breakwaters, quay walls, platforms and other underwater structures with centimeter level accuracy.
Multibeam systems cannot acquire point cloud data above the water surface. Terrain models of structures are simply “cut off” above the air-water interface. In many cases we would prefer continuous terrain models that include above-water structures.
Lidar (Light Detection And Ranging) techniques have also been employed for almost two decades, mostly for topographic surveys. Airborne laser has long been efficient at mapping large land areas. For smaller areas, static Lidar techniques are commonly used to map terrain for various purposes, including land development projects. Under pressure to acquire ever more dense data, in shorter periods of time, with less manpower, terrestrial mobile laser systems have recently been introduced successfully. In combination with high-end INS systems they can produce extremely detailed 3D point clouds with centimeter level accuracy.
In 2008 QPS added support in QINSy for the MDL Dynascan, an instrument with a rotational speed of 10 Hz, an angular resolution of 0.01 degrees and a maximum distance of 150 meters. In 2009, two high resolution lasers were integrated into QINSy: the extremely accurate Leica HDS6000/6100 (50Hz, 0.009 degrees, 100 meters) and the longer range Riegl laser, also an extremely accurate laser (100Hz, 0.018 degrees, 800 meters). With a multiple target option the Riegl is even able to penetrate vegetation on breakwaters for example. Both produce huge data volumes.
As with multibeam systems, lasers suffer from physical limitations. The penetration of laser light into water is very limited. Structures like bridges are simply “cut off” at the air-water interface.
At the land-sea interface, and where structures extend above and below the waterline, it makes sense to integrate laser and multibeam into one system, acquiring above and below water data in one pass.
Continuous software refinements have kept QINSy ahead of the steep data volume curve. QINSy can handle most multibeam echosounders and laser systems simultaneously. The real-time processing capabilities of QINSy mean that point clouds for both sensor types are generated on-the-fly and combined into one homogeneous 3D terrain model. Structures extending above and below the waterline are no longer “cut-off” at the water surface. Kalman filtering in QINSy allows integration of GNSS with an INS, and even an acoustic bottom tracking system, with multibeam and laser systems, so that surveying under bridges and near gantry cranes is not interrupted.
To provide context for the 3D point clouds, QPS recently added QINSy support for the Nikon D Series digital cameras. Digital photographs, taken at regular intervals during acquisition, enhance processing and visualization of 3D point clouds for the scene above water.
QPS presented this combined, fully integrated multibeam/laser/digital photo data acquisition and processing system at the Oceanology 2010 Conference in London.