Echo signal analysis for underwater sediment classification in tropical regions

Abstract

Fresh water, sediment classification is increasingly becoming critical for numerous water resource management initiatives with growing depletion of natural resources andincreasing human population. The tropical regions with their concentration of monsoons into few months in a year, experience heavy flow and subsequent siltation of water reservoirs, rivers, dams, etc. Heavy siltation depletes the storage capacities, impacting the sustainability during thedry seasons. Acoustic techniques can potentially provide efficient and cost effective assessment for planning of long term utilization in irrigation, power generation, industry, and urban power supply and flood moderation. Analysis of underwater sediment using single-beam and multi-beam echo sounders has been recognized as an effective tool in sea/river floor classification. Empirical method of sea/river floorclassification relies on features extracted from the backscatter signal such as maximum amplitude, echo duration, energy and higher order moments. These features are highly dependent on the medium properties, bottom properties and specifications of the sonar like frequency, beam width, incident angle, and etc.Received signal characteristics are sensitive to physical properties of medium such as sound speed and sediment reflectivity. This paper discusses the significance of grazing angle, transmission loss and seasonal variation in the Sound Velocity Profile (SVP) for the application of sediment classification. Khadakwasala Lake (latitude 18.340 and longitude 73.760) in central India has been chosen as an experimental site to undertake the simulation study for a tropical shallow fresh water reservoir. The effect of sound speed on backscatter strength is analyzed using Kirchhoff's model by considering seasonal variation of realistic SVP.The bellhop ray tracing model is used for computation of transmission loss and the channel impulse response. Linear Frequency Modulated (LFM) signal the spectral band 50 to 100 kHz has been used as a probing signal for sediment types of sand, fine sand, mud and mixed sediment.