Now showing items 1-11 of 11

    • Classification of acoustically stable areas using empirical orthogonal functions - examination of stability methods 

      Østenstad, Petter; Hjelmervik, Karl Thomas (2011-11-08)
      Overview and control of the oceanographic and acoustic variations are very important in underwater warfare. We have developed a method for dividing an area into smaller subareas that can be represented by a single vertical ...
    • 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 ...
    • LYBIN 6.0 - user manual 

      Dombestein, Elin; Gjersøe, Amund; Hjelmervik, Karl Thomas; Kloster, Morten (2011-07-18)
      The acoustic ray trace model LYBIN uses a broad set of parameters to accurately calculate the probability of detecting objects in a given area under water with the use of sonar technology. As this probability changes with ...
    • Proposed use of Lybin in project Simson 

      Tveit, Elling; Hjelmervik, Karl Thomas; Dombestein, Elin (2003)
      Previous and present versions of the acoustic ray trace model Lybin are described briefly. The use of Lybin in FFI project Simson can be divided into three categories: simulation of submarine detection coverage, simulation ...
    • Sensitivity of LYBINs transmission loss due to variations in sound speed 

      Hjelmervik, Karl Thomas (2006)
      This study is motivated by the Sea Acceptance Test 2 (SAT2) to be made sometime in 2006. The testing of the new Norwegian Frigates sonar system will involve use of the acoustic ray trace model, LYBIN. The study reveals ...
    • 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 ...
    • Sonar simulation for the Action Speed Tactical Trainer at KNM Tordenskjold 

      Hjelmervik, Karl Thomas; Gjersøe, Amund; Alsterberg, Svein (2008)
      This report describes a sonar simulation module planned implemented into Kongsberg Defence and Aerospace’s Action Speed Tactical Trainer. A land-based and modular training facility for frigate crew members. The sonar ...
    • Undersøkelse av sonarsimulatoralgoritme i PROTEUS 

      Hjelmervik, Karl Thomas (2014-05-09)
      KDA har utviklet en sonarsimulator som er basert på en metode utviklet av FFI [1]. Sonarsimulatoren brukes i dag i den KDA-utviklede treneren, PROTEUS. Sjøforsvaret har rapportert manglende realisme i simuleringene og ...