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The seakeeping test is one of the tests done in the Indonesia Hydrodynamic Laboratory (IHL) test tank on a model ship or floating unit. In the test tank, a wave can be generated by using electric and mechanic wave flaps that are pre-programmed on a certain condition of the wave, i.e. different frequencies and amplitude. To measure waves, produced by a wave generator, a wave measuring instrument is needed that can measure changes in water level in the test tank. The current wave measuring instrument is in the form of a 600 mm twin wire wave probe. This instrument is can be used to measure waves in the test tank but has limitations because it is only placed in one location without being moved. Another method is developed to be used in making alternative measuring instruments using ultrasonic sensors. In this paper, this alternative wave measuring instrument shows that measuring waves even when moving the measurement point to a new point location or following a towing carriage can be done and gives better measurement results. Based on these results, this new measuring instrument can be used in a more complex configuration test in the tank.

Understanding of channel propagation characteristics is a key to the optimal design of underwater acoustic communication. Generally, modelling of underwater acoustic channel is performed based on measurement result in certain site at certain times. Different sites might have different characteristics, each of which can generally be described by a model obtained by averaging measurement results at multiple points in the same environment. This paper describes a characterization of the underwater acoustic channel of tropical shallow water in a Mangrove estuary, which has sediment up to 60 cm at the bottom. Such a channel model is beneficial for the design of communication system in an autonomous underwater vehicle, for instance. The measurement result of delay spread parameter from three different points with the distance of 14 ~ 52 m, has various values. The root mean square (RMS) of delay spread ranges between 0.0621 ~ 0.264 ms, and the maximum delay spread varies with the value of 0.187 ~ 1.0 ms. The pdf fitting shows that Rayleigh distribution describes the fading variation more accurately than Nakagami and Ricean.

The sparse method or better known as compressed sensing (CS), is a method often used for the signal reconstruction process. This method had considered better than conventional methods because it can reconstruct a signal with a smaller amount of data. Many algorithms had used for signal reconstruction using the CS method, including l1-minimization and orthogonal matching pursuit (OMP). In this study, the two algorithms were used for signal reconstruction of underwater objects and then compared to find out which algorithm is better for the signal reconstruction of underwater objects. Comparing the two algorithms had based on parameters in the form of PSNR and RMSE against sparsity. Based on the simulations that had been doing, known that the l1-minimization algorithm can reconstruct signal up to 40% sparsity. Whereas the OMP algorithm can only reconstruct signals up to 30% sparsity. PSNR and RMSE generated from the l1-minimization algorithm show that this algorithm provides better reconstruction results than OMP for underwater object signals. The results obtained show that the best tracking process is at an angle of incidence of 90°.

Understanding the characteristics of channel propagation plays an important role in designing communication systems. Underwater acoustic channel modeling is commonly done by the direct measurement result from a specific location and time. This paper presents an evaluation of channel impulse response (CIR) and power delay profile (PDP) measurements in shallow water environment using three types of probe signals, i.e., pseudonoise (PN)-sequence, exponentially sine swept (ESS), and amplitude-modulated ESS (AM-ESS). The measurements have been carried out in a laboratory-scale towing tank. The ESS signal has been found to produce CIR and PDP that are close to those of the ray tracing model. The multipath pattern of CIR obtained from ESS signal shows an 80% similarity; it was closer to the ray tracing model compared with other results, made using PN-sequence and AM-ESS signals. The estimated value of rms delay spread obtained by the ray tracing model is 1.023 ms and that obtained by the ESS signal is 1.502 ms. Meanwhile, the values obtained by the PN-sequence and AM-ESS signals are 0.769 and 1.410 ms, respectively. In the frequency domain, the spaced-frequency correlation function, obtained using the PN-sequence and ESS signals, is more similar to the ray tracing model compared with the AM-ESS signal.

This experiment conduct in mini semi-anechoic water test tank and towing tank at IHL. The purpose is to analyse performance from ALS algorithm in dimension, salinity and temperature water environment. For this purpose we varied water salinity and temperature in mini semi-anechoic water test tank, and for different dimension we took the experiment on two different size of test tank. The results showed that ALS have consistent result at salinity and temperature variety but at large dimension test tank 200 × 10 × 5.5 m without variation on the water medium indicates an anomaly in the results of the ALS BSS technique performance.

This paper describes a brief description of Orthogonal Frequency Division Multiplexing (OFDM) waveform design and parameter for submarine radars. The radar works when the submarine is floating on the sea surface and it uses a radio frequency signal to detect multiple moving objects in the surrounding area. The OFDM parameters discussed here are including the carrier frequency, number of sub-carriers, number of OFDM symbols and the frequency spacing between subcarriers. By varying those parameters value to see how significant are their impact on radar performance, includes its maximum unambiguous range, maximum speed of the target and also its range and speed resolution. The simulation results show that there is a trade-off for frequency spacing parameter to have a good radar performance. Set the space too wide would destroy radar's speed resolution and too narrow would ruin its range resolution.

Understanding of environmental characteristic is a key factor in design of communication system. This paper describes an ambient noise characterization of measurement in the shallow water of Surabaya bay. The result showed that probability density function (pdf) of ambient noise is close to a Gaussian distribution with the mean of −2.85×10−5 V, and deviation standard of 9.87×10−4V. Validation has been done by using mean square error (MSE) and Bhattacharya distance. In the frequency domain analysis, it is showed that in the range of 0 ∲ 9 kHz has a deceasing level from −100 until −140 dB. In the frequency of 9 ∲ 13.5 kHz, the spectral is flat as like a white. It can be used as a reference in decision of range frequency of underwater acoustic communication systems that will be applied.

In this paper, we report the development of water tank for underwater acoustic communication. Compared to most of underwater test tank, the tank may be considered as mini in term of its size. However, the test tank is intended to serve as controlled environment to develop a theoretical model and its validation experimentally before full-scale test at sea. We present on how to analyze the physical characteristics of the test tank with respect to salinity and temperature affected to speed and pattern of propagation waves. We designed the test tank made of 12mm thick of glass with dimension 2 × 1 × 1 in meter, then we placed corrugated sponges inside the walls to reduce the echo from signal that we generated. The measurements were conducted by placing array of hydrophones and analyze the propagating waves in fresh water with variation temperature 15°C, 20°C, 25°C and 30°C to simulate depth. In term of salinity we fixed at room temperature 30°C and varied the salinity of 3.1%, 3.2% 3.3%, 3.4% and 3.5%, respectively. The results showed that the sound propagation characteristics are in agreement with previous studies. This may suggest that the test tank may serve as small scale underwater acoustic experiment with controlled environment.

Development of an underwater acoustic communication system is a necessity for the majority of the nation as a sea area of Indonesia. Most area s of the ocean in Indonesia is shallow, the environment has unique characteristics compared to other countries. It is a challenge in the research underwater acoustic communication system. This paper presented a preliminary study of the developing of soft acoustic modem testbed for underwater acoustic communication system with OFDM technique. Modem has been implemented on a PC with Matlab, with the objective to evaluate the algorithm development. Image file in JPEG format is encoded with a discrete cosine transform (DCT). To improve performance, information is encoded with a forward error correction, FEC-Hamming. The system uses BPSK modulation, OFDM transmission techniques, and using acoustic signal as carrier wave. In this system, the occupation bandwidth is 5.3 kHz, transmission rate of 3.7 k sps, and center frequency at 13.3 kHz. As an initial stage, the model presented in the form of simulator tesbed passband, and is treated with the propagation parameters that was obtained from measurements in a Towing Tank in previous experiment. The next stage is tesbed evaluation through experimental in a laboratory, such the effect of conversion process from electrical to audio signal at PC sound card and the capability of the receiver to recover the information.

Propeller cavitation noise analysis is necessary since this noise is one of the components of the ship noise signature that would be different for each type of the ship. Therefore, the noise can be used for detection and identification process of a ship. This noise can be simulated by doing the experiment generating one component of the ship noise signature, i.e. the propeller cavitation noise. The experiment is done in the cavitation tunnel of the Indonesian Hydrodynamic Laboratory (IHL), Surabaya, Indonesia to generate this noise. Two techniques, i.e. the Wigner-Ville distribution and the backpropagation neural network, are applied to analyse this noise. The results are compared to examine which technique shows better representation.

Acoustic cavitation noise caused by propeller is used in many underwater applications as one of the ships noise signatures. This paper reports characterization process done by measuring the cavitation noise generated by a propeller in a cavitation tunnel. The cavitation tunnel used for the measurement is of the K16B type belonging to the Indonesian Hydrodynamic Laboratory, Surabaya, Indonesia. The experiment is done using a B-series four-blade bronze propeller (diameter 23cm) using a hydrophone placed in the tunnel at window section (60x90)cm2 of the measurement section (400x85x85)cm3. Some of the solutions to get accurate and reliable measurement results include calibration measurement and minimizing acoustic noise system and environment. Preliminary process has been done to analyse the characteristics of the measurement results in the time-frequency domain, with the objective being to detect when and which type of cavitation noise occurs in any kind of condition. Measurement outcomes in the form of acou...