Abstrakt

The paper presents the partial work done within the framework of the EDA Siramis II project focused on magnetic signature reproduction of ships. Reproduction is understood here as the ability to determine the magnetic anomaly of the local Earth magnetic field in any direction and at any measurement depth due to the presence of the analysed object. The B-91 type hydrographic ship Zodiak was selected as the real case study. The work was divided into two main stages: the development of a measurement campaign taking into account physical measurements, and the development of a mathematical model on the basis of the measured values. The measurement campaign included: preparation of the measuring range, selection of equipment for the measurement of magnetic quantities and geographical location, and data recording while the ship passes the measuring point according to the designated course. As a result of the measurement campaign, magnetic flux density components were collected in different positions in relation to the measuring instruments and the ship's heading. A multi-dipole model was used to build the mathematical model in accordance with the idea of inverse modelling. The effectiveness of this model was previously checked on synthetic data of virtual ships generated using the finite element method. Experiments performed with simulation models were helpful in determining the structure of the model, the nature of the data, and the number of samples needed to properly determine the multi-dipole model parameters. The parameters were determined using the nonlinear least squares method according to the idea of data fitting. The classical Ridge and Lasso regularization methods were applied to prevent the developed multi-dipole model from overfitting. Other regularization methods based on GPS accuracy marks and modification of fitness functions were also considered. The verification was done using real data: the data generated by the model was compared with patterns recorded during the Zodiak measurement campaign. High degree of conformity of the shape of characteristics was obtained. Moreover, the correctness of model execution was confirmed by low values of quantitative indices such as RMSE and MAE representing modelling errors. The methodology presented in the paper is quite universal and can be used to determine the signatures of other ferromagnetic objects.

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