Seabed identification from digital echogram of 24 khz and 200 khz single beam echo sounder in shallow coastal environment of Panggang Cay, Seribu Islands, Indonesia

In this study, digital echogram from dual-frequency echo sounder are compared with seabed samples from survey area of 2 m to 8 m depths around Panggang cay, Seribu islands, Indonesia. Echo sounder's digital echogram refers to normalized envelope of discrete returning echoes on average basis. It is recorded using dual-frequency echosounder operated at 24 kHz and 200 kHz. Measure of digital signature is proposed here to be characterized according to the lengths of normalized echo amplitudes at 95% confidence level throughout a burst of multiple pings. It is expected that specific type of seabed reflector appears as unique numbers of echo markers. An echo marker indicates the 95% confidence level of echo in an individual length of returning signal. Seabed samples were collected from six
different types of benthic covers of mainly biogenic sediments, as well as corals and artificials. It is found that mixture of silt and sand sediments had Dso grain size
ranging between 0.07 mm and 0.37 mm, with the corresponding density varied from 1640 kg/m³ to 1960 kg/m³. Yellow leather coral (Sarcophyton elegans) dominates seabed cover on coral sampling site while the artificial cover of seabed is metal
wreck. The results reveal that echo lengths indicate significant dissimilarity due to the different type of seabed. This is seen from the properties of descriptive statistics of each of group of echogram reading and the results from two samples procedure. Echograms from higher frequency channel indicate better uniformity of echo
lengths indicating a better precision of measure. However, correlation between echograms and the physical properties of seabed are less evidence.

Key words: Single beam echo sounder, digital echogram, seabed samples, and D50 grain size