With the requirement of safe navigation in South China Sea, airborne laser bathymetry technique becomes attractive in China recently. A prototype of laser airborne depth mapping (LADM-I) system was developed. System included a diode laser pumped solid-state laser with a repetition rate of 200 Hz and the peak power of 2 Mw, a 15°nadir quasi-elliptical scanner, a combination unit of DGPS and an electronics compass, and a post-flight data processor. System has been demonstrated in South China Sea during last two years. In order to improve sounding density, survey productivity, maximum penetrable depth and accuracy of depth, a new generation of LADM-II is under developed. System will be constituted of a 1 kHz diode pumped laser, INS and KGPS. The performance will also upgrade to meet the higher requirement. In this paper, the detail parameters and specifications of LADM-I, and the experimental result will be reported. The protocol of LADM-II system will be also present.
A laser airborne depth mapping (LADM) for the topography of coastal water was developed in China. System was implemented in South China Sea between 2001 and 2002. Data processing subsystem is introduced in this paper. Three automated waveform processing algorithms have been developed around several sets of heuristic rules to extract reliably accurate depths with a low false alarm rate. The position, pulse width and ratio of signal to noise are obtained by the low-pass differentiator algorithm (LD). The floor reflecting is determined by the signal above some thresholds in LD method. According to the characteristics of water attenuation, the received signal is revised by the inverse of the water attenuation coefficient (here after, RA method). The bottom is easier to distinguished from the enhanced contrast between the floor reflecting and water scattering. The LD and RA algorithms show a consist results in the post-flight data processing. A more simple and fast algorithms of delayed signal subtracter (DS) is used on flight as a real time data processing, in which the signal is delayed some time abd subtracted by the original signal. The three methods are analyzed in details. The result of data processing isalso presented.