Airborne Depth Sounder Research Articles

Towards a regional high-resolution bathymetry of the North West Shelf of Australia based on Sentinel-2 satellite images, 3D seismic surveys, and historical datasets

Abstract. High-resolution bathymetry forms critical datasets for marine geoscientists. It can be used to characterize the seafloor and its marine habitats, to understand past sedimentary records, and even to support the development of offshore engineering projects. Most methods to acquire bathymetry data are costly and can only be practically deployed in relatively small areas. It is therefore critical to develop cost-effective and advanced techniques to produce regional-scale bathymetry datasets. This paper presents an integrated workflow that builds on satellites images and 3D seismic surveys, integrated with historical depth soundings, to generate regional high-resolution digital elevation models (DEMs). The method was applied to the southern half of Australia's North West Shelf and led to the creation of new high-resolution bathymetry grids, with a resolution of 10 × 10 m in nearshore areas and 30 × 30 m elsewhere. The vertical and spatial accuracy of the datasets have been assessed using open-source Laser Airborne Depth Sounder (LADS) and multibeam echosounder (MBES) surveys as a reference. The comparison of the datasets indicates that the seismic-derived bathymetry has a vertical accuracy better than 1 m + 2 % of the absolute water depth, while the satellite-derived bathymetry has a depth accuracy better than 1 m + 5 % of the absolute water depth. This 30 × 30 m dataset constitutes a significant improvement of the pre-existing regional 250 × 250 m grid and will support the onset of research projects on coastal morphologies, marine habitats, archaeology, and sedimentology. All source datasets are publicly available, and the methods are fully integrated into Python scripts, making them readily applicable elsewhere in Australia and around the world. The regional digital elevation model and the underlying datasets can be accessed at https://doi.org/10.26186/144600 (Lebrec et al., 2021).

Airborne GPS kinematic positioning and its application to oceanographic mapping

Precise, long-range, airborne GPS kinematic positioning requires the use of carrier phase measurements, the data processing of which suffers from the technical challenges of “on-the-fly” ambiguity resolution and cycle slip repair. In this paper the authors describe how the combination of an ‘ambiguity recovery’ technique and a ‘linear bias correction’ method has been used to support oceanographic mapping in Australian waters, together with the augmentation from the Laser Airborne Depth Sounder (LADS) system. Two experiments, carried out on the 4th December 1997 in the Torres Strait between Papua New Guinea and Australia, and on the 20 May 1998 at Lake Argyle in Australia, were analysed. The results indicate that the topography of the water surface can be obtained with sub-decimetre accuracy, with a spatial resolution of a few metres. The main errors are attributable to multipath interference of the GPS signals at the antennas from the aircraft surface.

Sea Surface Determination Using Long-Range Kinematic GPS Positioning and Laser Airborne Depth Sounder Techniques

Precise long-range kinematic GPS positioning requires the use of carrier phase measurements, the data processing of which suffers from the technical challenges of ambiguity resolution and cycle slip repair. In this paper, the combination of an ambiguity recovery technique and a linear bias correction method has been used to overcome such problems. An experiment was conducted to test the utility of this technique to determine aircraft height to high accuracy, over very long baselines (of the order of one thousand kilometres), in support of the Laser Airborne Depth Sounder (LADS). From a comparison of four independently derived trajectories, this airborne GPS kinematic positioning experiment has confirmed that the sea surface can be determined to centimetre accuracy. The sea surface profiles thus obtained can be used to correct the errors introduced by long period ocean swells.

Final design and testing of the laser airborne depth sounder filter

The final design and testing of a filter for the Australian Navy’s Laser Airborne Depth Sounder is reported. This filter is a six-stage, actively tuned, Lyot birefringent filter with approximately 10 times better signal-to-noise performance than the narrow-band filter currently in use. It is expected that this filter will improve the available flying time by up to 6 h/day.

Royal Australian navy laser airborne depth sounder project status brief—May 1992

Royal Australian navy laser airborne depth sounder project status brief—May 1992

LADS—the Australian Laser Airborne Depth Sounder

Abstract The Australian Laser Airborne Depth Sounder (LADS) represents a major technical transition in shallow water hydro-graphic survey that can be compared with the change from the lead line to acoustic sounder. LADS offers a substantially increased rate of data acquisition, a demonstrated accuracy which meets international hydrographic standards and a total area cover capability. The system generates discrete depth measurements in a rectangular grid pattern with 10m spacing between measurements. The concepts, methods and processing algorithms used in the design of LADS are based on an extensive research and development programme which has been widely reported in the technical literature. The LADS system has a depth capability of 50 m with depth errors less than 0.28 m (one standard deviation) over the depth range 2–30 m. LADS, installed in a Fokker F27 aircraft, is designed for operational use with the Royal Australian Navy Hydrographic Service. The project has Department of Defence approval and tenders for the manufacture and commissioning of the system are currently being sought.

Laser Airborne Depth Sounder Update

Laser airborne hydrography is one area of marine high technology where Australian scientists are making a significant contribution. The LADS (Laser Airborne Depth Sounder) system currently being developed by Navy will play an important part in the survey of Australian coastal waters with benefits to Defence and Shipping interests. There is considerable overseas marketing potential in the system.

Rogue point elimination in airborne laser hydrography

Elimination of rogue points from data gathered by an airborne laser depth sounding system is a vital part of the processing of such data for hydrographic purposes. Application of the probabilistic data association filter is made to achieve this function with extensions to 2-D operation and the inclusion of smoothing. The algorithms are shown to perform well on data gathered by the airborne depth sounder (WRELADS II). They are successful both in eliminating false detections of the sea bottom and in retaining a single true shallower depth surrounded by deeper water.

Airborne laser hydrography in Australia

The Australian laser airborne depth sounder WRELADS II was developed to demonstrate the feasibility of using airborne laser techniques for hydrographic survey. This paper describes the system, the experimental program used for its evaluation, and some results obtained by it. Development of the system over a five-year period involved 550 h of airborne evaluation, including the collection of data during 22 sorties over a calibrated test range. Analysis of these data has permitted development of an empirical depth bias model. It is shown that the system meets the requirements of the Royal Australian Navy Hydrographic Service for depth accuracy and provides an adequate data yield.

Estimation of a mean sea surface reference in the wrelads airborne depth sounder

The determination of an accurate mean sea surface reference is an essential step in any system seeking to provide accurate measurements of sea depth. Algorithms developed to achieve this for the laser-based airborne depth sounder wrelads are presented, and their performance under extensive testing of that system is assessed. They are shown to generate successfully an accurate mean sea surface reference under a wide range of conditions that might be expected operationally. Use of this analysis as a diagnostic tool in monitoring other aspects of the performance of the depth sounding hardware is also discussed.

Airborne estimation of sea turbidity parameters from the WRELADS laser airborne depth sounder

Techniques are presented for the estimation of the optical attenuation coefficient and a backscatter parameter that is proportional to the optical backscatter coefficient from data collected from a laser-based airborne hydrographic system. The validity of two such techniques is discussed in light of substantial amounts of data that have been collected using the WRELADS airborne depth sounder. The data collected demonstrate a number of different functional relationships linking attenuation to backscatter in adjacent bodies of water. It also demonstrates the capability of using such airborne techniques for detection, mapping, and monitoring of unusual turbidity features within the ocean.

Sea surface and depth detection in the WRELADS airborne depth sounder

Algorithms are presented which have been developed for the WRELADS airborne depth sounder for the detection and location of sea surface and sea bottom reflections within the waveform of 256 consecutive 2-ns samples of received green light energy. The algorithms must be flexible to cater to the wide range of sea conditions encountered operationally in the WRELADS testing program and simple to cater to the computational intensiveness of this portion of the overall WRELADS data processing and yet have quantifiable reliability and accuracy. A concept of pulse confidence (related to SNR) is developed and shown to be related to the probability that a pulse detected as a sea bottom reflection is valid.