Abstract
To reduce the size and cost of an integrated infrared (IR) and green airborne LiDAR bathymetry (ALB) system, and improve the accuracy of the green ALB system, this study proposes a method to accurately determine water surface and water bottom heights using a single green laser corrected by the near water surface penetration (NWSP) model. The factors that influence the NWSP of green laser are likewise analyzed. In addition, an NWSP modeling method is proposed to determine the relationship between NWSP and the suspended sediment concentration (SSC) of the surface layer, scanning angle of a laser beam and sensor height. The water surface and water bottom height models are deduced by considering NWSP and using only green laser based on the measurement principle of the IR laser and green laser, as well as employing the relationship between NWSP and the time delay of the surface return of the green laser. Lastly, these methods and models are applied to a practical ALB measurement. Standard deviations of 3.0, 5.3, and 1.3 cm are obtained by the NWSP, water-surface height, and water-bottom height models, respectively. Several beneficial conclusions and recommendations are drawn through the experiments and discussions.
Highlights
Airborne LiDAR bathymetry (ALB) is an accurate, cost-effective, and rapid technique for shallow water measurements [1]
In the waveform of green lasers, the surface return is a linear superposition of the energy that is reflected from the actual air–water interface, as well as the energy backscattered from particulate materials in the water volume just under the interface [1]
∆d0 = hs − h0s where hg s is the water surface height derived from the pulse waveforms of the green laser. h0 s is the known water surface height, which can be obtained using an IR laser scanner mounted on the same platform as the green laser scanner; this setup is called the Mandlburger’s calibration scheme [5]
Summary
Airborne LiDAR bathymetry (ALB) is an accurate, cost-effective, and rapid technique for shallow water measurements [1]. Due to the existence of the surface uncertainty, an additional IR laser is used in the integrated IR and green ALB systems to determine the actual water surface height and accurate water depth [2]. LADS-MK3, Optech Aquarius, USGS Experimental Advanced Airborne Research LiDAR (EAARL) and EAARL-B, and RIEGL VQ-820-G [6,7,8,9,10,11,12,13,14,15] As they ignore the water surface uncertainly, the simplified systems conduct the measurements despite the loss of accuracy [5,16], and cannot comply with the requirements of highly accurate applications. The statistical analysis method is simple and efficient in calm and clear rivers and lakes, and can accurately reflect the spatial distribution of NWSP This method may be affected by the undulating water surface and turbid coastal waters.
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