Abstract. This investigation aims to propose an attenuation rate for range normalization of echo amplitudes recorded by an acoustic backscattering instrument working at a frequency of 1.0 MHz. The intention of the use of such an attenuation rate is to obtain equal echo levels when using a device from the same family of products with a different working frequency, i.e. a 0.6 MHz instrument, at an identical site. This work is based on a field experiment with a 1.0 MHz Acoustic Wave and Current (AWAC) profiler and a 0.6 MHz Aquadopp profiler. Both profilers were deployed upward, side-by-side in the Semak Daun reef lagoon, Seribu Islands, Java Sea, Indonesia. It was found that the proposed attenuation rate for the 1.0 MHz instrument was one-order magnitude higher with respect to the one used for the 0.6 MHz instrument, and logarithmically depth dependent. The proposed attenuation rate for the 1.0 MHz AWAC is -7.925log(R) + 8.551, with R is the slant range from the transducers to the measured layer. Accordingly, the overall agreement between the 1.0 MHz AWAC echo amplitude and the one recorded by the 0.6 MHz Aquadopp was improved by 18dB, which is quite significant considering that the average echo amplitude discrepancy recorded by each transducer was 2.4dB.

The coastal area in Balikpapan Bay and its surrounding area has been devastated after the burst of an underwater oil pipe at the bay on March 31st, 2018, and the crude oil still continues spreading for a few days later. A three-dimensional hydrodynamic model is used to simulate the currents dynamic and investigate the influence of the current circulation on the spreading of the oil spill in Balikpapan Bay from March 31th to April 15th, 2018, to cover the event i.e. several weeks after the oil spill incident. Model results are validated by calculating the RMSE, MAPE and model skill using water level between available observation data at Semayang Port, Balikpapan station and numerical model from October 1st, 2012 to January 1st, 2013. Verification result of tidal elevation data from observation and model prediction shows a good agreement with RMSE = 7.8 cm, MAPE = 14.3% and model skill = 0.995. Surface currents circulation in Balikpapan Bay can be distinguished by the currents pattern on the spring tide and neap tide condition. During the spring tide condition, the surface currents mostly move to the east after coming out from the bay. However, the surface currents are strongly going southward after come out from the bay on the neap tide condition. Based on the satellite images captured for the next days after the event, the spreading pattern of the oil spill seems to be matched to the pattern of surface currents circulation on the spring tide condition. From the analysis of the model result, it shows that the currents circulation playing the main role to disperse the oil spill in Balikpapan Bay towards the Makassar Strait.

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The Indonesia Coral Reef Garden (ICRG) program is announced as a coral reef restoration program which can support the marine tourism sector since the Covid-19 pandemic hit Indonesia, particularly in Bali. A comprehensive survey and preliminary study are necessary to be conducted to decide a suitable point or to avoid a premature choice for the restoration location. Field survey in Nusa Dua, Bali was carried out on November-December 2020 to determine physical and chemical characteristics of seawater which appropriate for coral life. The bathymetry result at Nusa Dua, Bali varied from shallow to middle water depth. Area covered with coral, soft coral, coral and sand, sand, and seaweed on the seabed are found over study area. In the depth close to the seabed, the sea condition of temperature, salinity, pH, turbidity, and DO is 26.04 - 28.48 °C, 33.95 - 34.29 PSU, 7.933 - 7.982, 0.81 - 2.44 FTU, and 4.40 - 4.93 mg/L, respectively. Based on the conformity of water quality, the middle depth region has sufficient condition for coral growth. Simple Addition Weighting method is used for determining potential location. The potential coral implementation is located 3-5 km from Tanjung Benoa and in south of Nusa Dua around 1-3 km from coast.