Browsing Articles by Author "Hjelmervik, Karl Thomas"
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Demonstration of Comparison Methods for Ocean Model Validation
Hjelmervik, Karina Bakkeløkken; Hjelmervik, Karl Thomas (2012)In recent years an increasing amount of oceanographic data has become available. This includes observations as well as data from hydrodynamic ocean models. Validation is required for establishing the necessary confidence ... -
Estimating temperature and salinity profiles using empiricalorthogonal functions and clusteringon historical measurements
Hjelmervik, Karl Thomas; Hjelmervik, Karina Bakkeløkken (2013)Oceanographic climatology is normally estimated by dividing the world’s oceans into geographical boxes of fixed shape and size, where each box is represented by a climatological salinity and temperature profile. The ... -
A hybrid recorded-synthetic sonar data set for validation of ASW classification algorithms
Hjelmervik, Karl Thomas; Berg, Henrik; Sekse, Dan Henrik; Solberg, Tale (2015)Modern anti-submarine warfare sonars are often designed with narrow beamwidths and wide frequency bandwidths in order to maximize spatial resolution and sonar performance. A known issue for high-resolution sonars in littoral ... -
Improved estimation of oceanographic climatology using empirical orthogonal functions and clustering
Hjelmervik, Karl Thomas; Hjelmervik, Karina Bakkeløkken (2013)Vertical profiles of temperature, salinity, and sound speed velocity are used in numerous applications where accurate vertical profiles are crucial. Conventional climatological representations of vertical oceanographic ... -
Modelled sonar and target depth distributions for active sonar operations in realistic environments
Andreassen, Kristoffer Engedal; Hjelmervik, Karl Thomas (2022-09-08)Target detection performance of mid-frequency active sonars depends heavily on both sonar and target depth. For a given target depth, a sonar performance model may help predict a sonar depth that maximizes the detection ... -
Optimization of active sonar parameters in a measured environment
Hjelmervik, Karl Thomas; Dombestein, Elin Margrethe Bøhler (2021-09-13)ABSTRACT Sonar operation in coastal waters is challenging due to high false alarm rates and strongly varying sonar conditions. Optimal choices for sonar design and pulse characteristics depend strongly on target location ... -
Predicting False Alarm Rates for High-Resolution Antisubmarine Warfare Sonars in a Cluttering Environment Prone to False Alarm Rate Inflation
Hjelmervik, Karl Thomas; Berg, Henrik; Såstad, Tale Solberg (2019-09-13)Operation of high-resolution, broadband, antisubmarine warfare sonars in littoral waters is challenging, since the presence of sea mounts, underwater ridges, and other topographic features causes increased false alarm ... -
Sonar scattering from the sea bottom near the Norwegian coast
Vestgården, Jørn Inge; Hjelmervik, Karl Thomas; Stender, Dan Henrik Sekse; Berg, Henrik (2017)High false alarm rates on active sonar systems in shallow waters is a well known problem which may be a limiting factor for the sonar performance. One way to reduce the false alarm rate is through supervised learning and ...