1 Method of identifying and eliminating magnetic compass deviation V.V.Meleshko, S.L. Lakoza, S.A.Sharov Aerospace & Navigation Instruments Dept. National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute» Kiev, Ukraine mvv44@mail.ru, hakserg@rambler.ru Abstract — It is considered method of identifying and eliminating deviation of any type magnetic compass. It is used Poisson model for describing object’s magnetic field. This approach allows to describe magnetic deviation more precise in compare with Archibald Smith technique that uses magnetic deviations model in the form of a Fourier series with an approximate calculation of the Fourier coefficients. In a short time the method allows to determine the parameters of the Poisson model when object moves. It doesn’t require performing special deviation. Using these parameters you can calculate the deviation and eliminate it with power or algorithmically means. The method allows to determine both the horizontal and heeling deviation. Method is suitable for large objects such as ships and aircraft, and for the small object such as unmanned maneuverable vehicle or different navigational robots. Keywords – magnetic compass; magnetic deviation; Poisson model. I. INTRODUCTION Magnetic compass has been important navigational device for many mobile objects for many years. Its main advantage is autonomous work without electrical power often [1-3]. It is installed on ships, airplanes, cars. Magnetic compass can use the magnetic needle, and can use various types of magnetometers together with the pendulum or accelerometers. Now in compasses small-sized magnetoresistive magnetometers are widely used [6]. In complex with micromechanical gyros and accelerometers it allows build attitude and heading reference system (AHRS). It is significantly expanded the scope of such AHRS application due size miniaturization and power consumption. AHRS is used by unmanned aerial vehicles, various types of robots, medical equipment, etc. A common problem of magnetic compasses and magnetometers are errors so called magnetic deviation. There are caused by distortion of earth magnetic field from magnetic fields of the moving object. Methods for eliminating of magnetic deviation have been improved from ancient times to the present day [4, 5]. This paper shows novel promising method of identifying and eliminating magnetic compass deviation. II. MAGNETIC DEVIATION CALCULATION It is known, magnetic deviation is the difference between the compass (device) heading к K and magnetic heading м K : δ к м K K   . In the 19th century Archibald Smith introduced an approximate description of the magnetic deviation in the form of series [1, 2]  = A + B sinK K + C cosK K + D sin2K K +E cos2K K , (1) where A, B, C, D, E - deviation coefficients. According to Smith deviation coefficients are calculated after making measurements on the 8 headings. Large object alignment on to the 8 headings respectively to the ground reference or accurate gyrocompass is highly difficult process. Coefficients of semicircular deviation are [2] 90 270 (δ δ )/2 B   ; 0 180 (δ δ )/2 С   , (2) where the deviation index corresponds to the heading at which the measurement is carried out. Coefficients’ calculating using the Fourier series has the following equation: 90 270 45 315 225 135 1 δ δ sin(4η )(δ δ δ δ ) 4 o B           ; (3) 0 180 45 315 225 135 1 δ δ cos(4η )(δ δ δ δ ) 4 o C           .