Multi-frequency backscatter data collected from multibeam echosounders (MBESs) is increasingly becoming available. The ability to collect data at multiple frequencies at the same time is expected to allow for better discrimination between seabed sediments. We propose an extension of the Bayesian method for seabed classification to multi-frequency backscatter. By combining the information retrieved at single frequencies we produce a multispectral acoustic classification map, which allows us to distinguish more seabed environments. In this study we use three triple-frequency (100, 200, and 400 kHz) backscatter datasets acquired with an R2Sonic 2026 in the Bedford Basin, Canada in 2016 and 2017 and in the Patricia Bay, Canada in 2016. The results are threefold: (1) combining 100 and 400 kHz, in general, reveals the most additional information about the seabed; (2) the use of multiple frequencies allows for a better acoustic discrimination of seabed sediments than single-frequency data; and (3) the optimal frequency selection for acoustic sediment classification depends on the local seabed. However, a quantification of the benefit using multiple frequencies cannot clearly be determined based on the existing ground-truth data. Still, a qualitative comparison and a geological interpretation indicate an improved discrimination between different seabed environments using multi-frequency backscatter.

The sea surface circulation pattern over the Strait of Malacca during Northeast Monsoon (NE) and Southwest Monsoon (SW) were derived using multi-year averaged sea level anomaly from altimetric data. This altimetric data has been derived using multi-mission satellite altimeter TOPEX, ERS-1, ERS-2, JASON-1, ENVISAT, JASON-2, CryoSAT-2 and SARAL for the period of twenty-three years (1993 to 2015). In general, the surface current pattern during Northeast Monsoon and Southwest Monsoon are rather complex than inter-monsoon. Number of eddies were found in seasonal surface circulation of the studied region. During the first inter-monsoon (April), there was an anti-cyclonic eddy formed near the northern part of Sumatra centered at (~ 6N, 97.5 E). Meanwhile, a cyclonic eddy formed at the central region of Malacca Strait centered at (~ 5.5N, 99.5 E) during SW Monsoon and the eddy still existed during second inter-monsoon (October) but weaker than previous monsoon. The pattern of the surface current during April was almost consistent with the trajectories of surface drifter developed in this study.

Real Time Kinematic become a popular high precision technique in Malaysia. However, limitation of the distance for base station to rover station, this technique still difficult to implement. Virtual Reference Station (VRS) is a new concept developed by Trimble Terrasat is efficient method to overcome the limitation of classical RTK. The Malaysian Real-Time Kinematic Network (MyRTKnet) has been developed to facilitate RTK positioning in Malaysia. MyRTKnet consists 78 reference stations located at Peninsular Malaysia, Sabah and Sarawak. The most Northern reference station in Peninsular Malaysia located at Arau, Perlis. The gap distance from the Arau station to the Malaysia - Thailand border is around 35 km. This paper will discuss the practical accuracy of the RTK positioning using VRS generated by MyRTKnet outside the network. In this study, four points outside the MyRTKnet network were observed continuously in VRS RTK mode. Distances between rover station and the nearest physical reference station are 1 km, 10 km, 20 km and 30 km. It was found that the VRS generated using MyRTKnet can be achieved up to 6 cm in horizontal component and up to 8 m in vertical component even the positions of the rover stations are outside the MyRTKnet.

Unmanned aerial vehicles (UAVs) have recently been suggested as a swift, simple to replicate, and economical way to monitor macro litter. High-resolution UAV im

International Journal of GEOINFORMATICS

In hydrographic uncertainty and acoustic seabed characterization, the depth residuals used as roughness descriptors carry two superimposed contributions: true small-scale seabed roughness and beam-...