In the field of ocean technology, ocean exploration technology is a key means to break down the barrier between humans and the ocean. Advanced LiDAR systems and algorithms are of great significance for underwater tasks, including underwater positioning, target search, and rescue. Distance information, as the most basic physical parameter, can be regarded as the basis for many target characterization parameters and plays a crucial role in applications such as remote sensing and terrain detection.
The sound and light detection team of the School of Oceanography at Tianjin University has proposed a laser radar system based on dual comb interference to achieve accurate underwater absolute distance measurement. In order to eliminate non blurry distance in pulse laser measurement, a designed pulse encoding strategy was adopted, which utilizes an acousto-optic modulator to achieve switch modulation of the optical signal, thereby encoding the dual comb signal and greatly expanding the non blurry range of underwater measurement.This combination significantly expands the non blurry range of the dual comb LiDAR without sacrificing sampling rate or measurement accuracy. With a repetition frequency difference of 2 kHz, it can be increased to about 55 km, achieving one-time accurate long-distance detection.
The team proposes an improved Variational Mode Decomposition (VMD) scheme for the problem of dual comb LiDAR signals being affected by environmental interference and system noise in complex underwater environments, which is applicable to underwater dual comb ranging systems. By considering the Gaussian like shape and high signal-to-noise ratio of the ideal dual comb interference signal, the Grey Wolf Optimization (GWO) algorithm was introduced into VMD for parameter optimization, and a special design was made for the fitness function of GWO.By optimizing the VMD algorithm, the distorted noise interference signal is decomposed into a series of high-quality sub signals, and the best fitness sub signal is ultimately selected for signal reconstruction. The experimental results on dual comb signals under different conditions show that this method can not only improve the signal-to-noise ratio of interferograms, but also simultaneously restore the Gaussian shape of interferograms, expand the working range of dual comb LiDAR, and improve its robustness to non ideal environments.
Overall, this work utilizes the precise measurement characteristics of optical frequency combs to improve the accuracy and distance of underwater optical detection, achieving high-precision and large-scale ocean exploration. At the same time, it can denoise and optimize the detection signal, further improving the environmental adaptability and robustness of the measurement. This study has broad application prospects in the field of underwater LiDAR, which will contribute to the development and implementation of high-precision 3D reconstruction of ocean morphology.
Source: Sensor Expert Network