## 1 Introduction  
Compared with the scalar magnetic survey, three-component magnetic survey can obtain richer magnetic information, facilitate making quantitative interpretation of magnetic anomaly and enhance the resolution of magnetic target positioning, which plays an important role in geological survey, mineral exploration and earth science research [1; 2; 3; 4; 5]. However, the magnetic survey accuracy is inevitably decreased by diurnal variation, thus making it of great importance to develop an effective method for interference compensation.  
The magnetic field measured by tri-axial magnetometer can be modeled as the sum of three components  
\[\mathbf{h}_{m}=\mathbf{h}_{g}+\mathbf{h}_{i}+\mathbf{h}_{o}\]  
Where \(\mathbf{h}_{m}\) denotes the measured data, \(\mathbf{h}_{g}\) denotes the geomagnetic field, \(\mathbf{h}_{i}\) denotes the magnetic interference field, and \(\mathbf{h}_{o}\) denotes the diurnal variation interference.  
In practice of three-component magnetic survey, the first component is considered as a valuable element while the other two components are as magnetic interference. The magnetic interference field is mainly generated by ferromagnetic material and the maneuvers of carrier [6; 7]. Different from the magnetic interference field, diurnal variation represents drift of the geomagnetic field with time. As a matter of fact, diurnal variation can be compensated by simultaneously recording the geomagnetic field variation and then directly subtracting these variation data from the magnetic survey data. Although the established geomagnetic stations can provide accessible diurnal variation information for certain magnetic survey work, the diurnal variation accuracy of magnetic survey area far from the fixed stations will be decreased to a large extent. At present, some researchers have been trying to compensate the diurnal variation by modeling. For instance, [PERSON] [8] regards the diurnal variation as a function of magnetic survey time and compensates it by utilizing a neural network. However, this method can merely estimate the expectation of diurnal variation.  
Addressing the deficiencies of the above methods, a novel compensation method is proposed in the paper. Considering that the diurnal variation is the vector data, the prerequisite for compensating diurnal variation is to unify it into a coordinate system with the three-component magnetic survey data. With the proposed method, the diurnal variation is accurately observed in the geographic coordinate system, based on which, the interference can be effectively compensated. In addition, this method enables us to establish movable diurnal observation station in magnetic survey area, thus ensuring the compensation accuracy of diurnal variation to the largest extent. The proposed method is composed of three main procedures: (1) calibrating the magnetometer error; (2) calibrating the misalignment error between the magnetometer and theodolite; (3) aligning the magnetometer's axial direction and true north.  
The rest of the paper is organized as follows. Section 2 includes measurement error analysis and introduction on the corresponding calibration method. Section 3 describes the experimental setup and presents the experimental results. Section 4 presents the conclusion.