Quantification and Classification of Coral Based on Backscattering Strength Using Single Beam Acoustics Method

Abstract

Hydroacoustic technology has been widely used to mapping and classify of the seabed, types of substrate and benthic biota. Several techniques of backscattering strength measurements using a single beam echosounder, as a CruzPro PcFF80 has been used to distinguish energy backscatter of bottom sediments such as sand, silt and clay. The objectives of this research are to quantify the value of surface backscattering strength (SS) and volume backscattering strength (SV) of several types of coral using single beam echosounder CruzPro PcFF80 and classify based on SV value of the first echo (E1) and second echo (E2). Collection of field data was conducted on May 2013, which located in the Seribu Islands. Recording of acoustic data done stationary, time for recording data is about 10 up to 15 minutes for each type of coral by using a frequency of 200 and 50 kHz. An underwater camera was used to validation of the acoustic recording data. The results of this research show frequency of 200 kHz to experience greater absorption in the water column and therefore does not send a lot of energy to the seabed so that the penetration is reduced, while the frequency of 50 kHz shows a small absorption, transmitting more energy into the seabed, causing the signal to penetrate deeper into the seabed and carry more information to the transducer. Average value of surface backscattering strength (SS) at 200 kHz varied between -17.99 dB up to -14.65 dB. The average value of E1 varied between -21.54 dB up to -18.24 dB, while E2 varied between -46.91 dB up to -32.78 dB. At 50 kHz, surface backscattering strength (SS) varied between -13.13 dB up to -8.41 dB. The average value of E1 varied between -16.68 dB up to -11.96 dB, while E2 varied between -32.92 dB up to -22.60 dB. Classification show there are three classes of category (soft-smooth, soft-rough and hard-rough). At 200 kHz, soft-smooth category consist of Acropora branching, soft-rough category consist of Coral massive, dead Coral massive, Coral mushroom, rubble, sand, and hard-rough category consist of Acropora tabulate. At 50 kHz, soft-smooth category consist of Acropora branching, soft-rough category consist of Coral massive, dead Coral massive, and hard-rough category consist of Acropora tabulate, Coral mushroom, rubble, sand. Overall, the results of this research indicate that SBES CruzPro PcFF80 can be used to distinguish of acoustic backscattering strength from several types of coral and sand.