The accuracy of satellite derived bathymetry in coastal and shallow water zone

Precise and accurate bathymetric measurements are conventionally acquired by means of ship-based acoustic equipment. Nevertheless, recent multispectral satellite imagery has been utilised as a substitute source to map the seabed topography which indicates new revolution in hydrographic surveying. This study assesses the satellite bathymetric depth’s accuracy based on the vertical uncertainty as stated in the Standards for Hydrographic Surveys issued by the International Hydrographic Organization. Two empirical algorithms, namely, Dierssen’s and Stumpf’s approaches have been adopted to model the seafloor topography over the coastal and shallow water at Tanjung Kupang, Malaysia. The outcomes demonstrate a decent correlation between the derived water depths and the sounding values acquired from a ship-based acoustic survey. For instance, a total of 1,215 out of the 1,367 generated water depths by Stumpf’s model have hit the minimum standard of survey in S-44. Similarly, out of the 1,367 samples from Diessen’s model, 1,211 samples have met the minimum requirement listed in the survey standard. The results demonstrate both imageries derived bathymetry models convey promising results which can be ultilised for bathymetric mapping application. Therefore, this imagery derived bathymetry can be considered as an alternative bathymetric surveying technique to supply cost-effective solution and survey data to support the Blue Economy and Sustainable Development Goals 14

An Appraisal of Multibeam Echosounder Calibration

One of the most impressive hydrographic technique developed over the past few decade is multibeam sonar systems. Sounding data from these systems is a result of processing information from several data sources. Among them, positional data from Global Positioning System (GPS), vessels heading and attitude data from gyrocompass and motion sensor systems, vertical reference data from tide gauge and sound speed data, in addition to the multibeam data itself. There must be a good coordination between these systems in order to obtain reliable data. To determine this, a proper and thorough field calibration procedure has to be carried out on the system as a whole. This process begins with measurement of static offsets between each sensor system with reference to a fixed point on the vessel. Preferably, the point of centre of gravity (COG). Then the patch test is carried out to determine the mounting offsets and GPS latency and lastly a performance test to verify whether the data meet the accuracy requirements for the survey. This is achieved through a comparison of data with a reference surface. This paper discusses the theoretical aspects, steps involved and results of the calibration procedures for multibeam sonars, using RESON SeaBat 8124 multibeam system. Finally, a summary of multibeam sonar calibration criteria is also presented showing the methodology involve which include when to perform each test and applying corrections

A review of water level fluctuation models and modelling initiatives

In recent times, lakes have been essentially influenced by global warming and environmental dynamic, and this has been worsened via land cover changes, thereby raising the rate of their shrinkage and numerous models were proposed. The vast majority of these models have similar objectives, however they vary in terms of application, hypotheses assumptions. Water level fluctuation modelling project, globally has been revised in this study so as to provide evidence for further water level fluctuation modelling improvement. The scientific ideas of the modelling approaches were fundamentally observed for proper understanding of their main aspects and furthermore to provide a comprehensive depiction of the existing water level fluctuation modelling work, which has mostly overlooked in the previous studies

Presentation of a wavelet-based harmonic model for tidal level forecasting at Sabah and Sarawak

The world’s tides are a result of the combined forces of celestial forces and centrifugal force exerted by the Earth-Moon and the Sun acting on the water body, earth tides and the atmospheric tides. Harmonic analysis is the most popular and widely accepted method used for the processing and expression of tidal behavior as well as its characteristics. Despite its strengths, harmonic analysis has a few drawbacks when short data are involved for long term-prediction. However, to enhance the accuracy of the popular methodology of harmonic analysis (HA), this study presents a wavelet-based harmonic model for tidal analysis and prediction. Six months of water level heights at four tide gauge stations in Sabah and Sarawak of Malaysia were employed. The results obtained agrees with the original data when a comparison was made. The root mean square error (RMSE) and Pearson correlation coefficient (r) are the statistical index tools applied to test the functioning of the model. The residual error is the deviation between the original data and the predicted data which was also computed in this study. The new wavelet-based harmonic model improves the accuracy of prediction. Moreover, the model is efficient and feasible for tidal analysis and prediction