Aeromagnetic compensation, elimination of magnetic interferences produced by the aircraft platform, plays a vital role in aeromagnetic applications. Conventional compensation methods are based on the Tolles–Lawson (T–L) model, which accounts for only the manoeuvring interferences. However, magnetic interferences due to other factors, such as currents from electrical systems and movable parts, are found significant in practice. In this study, the authors take these interference factors into consideration, including the strobe light and beacon light, the rudder and elevator. The magnetic interference from constant current is equivalent to the ‘permanent magnetisation’ and has been contained in the T–L model. The interferences due to the strobe and beacon lights are modelled to be proportional to the currents and their temporal variations. The model coefficients can be estimated in advance in a ground experiment. The interferences by the pivoting rudder and elevator are still characterised by the T–L model but in the local rudder or elevator coordinate systems, and the compensated coefficients can be obtained on the ground or in the sky. Onsite experiments both on the ground and in the sky are conducted to illustrate the proposed modelling, and improved compensation results are obtained.

Magneto-optical double-resonance magnetometers are attractive candidates for sensitive measurements of magnetic fields but suffer from a fundamental problem known as the “dead zone”: certain magnetic field directions where the magnetometer loses its sensitivity. We present a dead-zone-free double-resonance magnetometer with a single linearly polarized laser, which keeps uniform signal amplitude and isotropic sensitivity among varying magnetic field directions. The isotropic magnetometer can be switched between two modes, i.e., $M_z$ mode insensitive to phase shifts and $M_x$ mode with a higher upper bound of bandwidth. The dead-zone-free magnetometer exhibits a magnetic field noise floor of $0.9\mathrm{pT}/\sqrt{\mathrm{Hz}}$ and $1.2\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in $M_z$ and $M_x$ modes, respectively. The proposed double-resonance magnetometer, benefiting from its compact single-beam structure, isotropic sensitivity, and capability of dual modes, would be useful for high-sensitivity magnetic field measurements in mobile applications.

Aeromagnetic surveys play an important role in geophysical exploration and many other fields. In many applications, magnetometers are installed aboard an aircraft to survey large areas. Due to its composition, an aircraft has its own magnetic field, which degrades the reliability of the measurements, and thus a technique (named aeromagnetic compensation) that reduces the magnetic interference field effect is required. Commonly, based on the Tolles–Lawson model, this issue is solved as a linear regression problem. However, multicollinearity, which refers to the case when more than two model variables are highly linearly related, creates accuracy problems when estimating the model coefficients. The analysis in this study indicates that the variables that cause multicollinearity are related to the flight heading. To take this point into account, a multimodel compensation method is proposed. By selecting the variables that contribute less to the multicollinearity, different sub-models are built to describe the magnetic interference of the aircraft when flying in different orientations. This method restricts the impact of multicollinearity and improves the reliability of the measurements. Compared with the existing methods, the proposed method reduces the interference field more effectively, which is verified by a set of airborne tests.

Scalar atomic magnetometer (SAM) with high sensitivity is designed to measure the total magnetic field and has been widely applied in aeromagnetic surveys. However, the measured total magnetic field of SAM is influenced by the magnetic disturbances due to the permanent, induced and eddy-current fields of the aircraft and heading errors of SAM. To reduce the magnetic disturbances caused by the aircraft maneuvers, a model was proposed by Tolles and Lawson and has been used in aeromagnetic compensation. However, the heading error of SAM deviates the compensation coefficients estimated by the Tolles-Lawson model. In this letter, we propose a linear model of heading error for multi-cell SAMs and analyze the new aeromagnetic compensation model in which the geomagnetic gradient and heading error are both taken into account. With using a ⁴He magnetometer consisting of three orthogonal cells, the experimental results show that our proposed model has better performances than the previous model in terms of the figure of merit (FOM) and standard deviation (STD).

We present both a theoretical and experimental study of the magneto-optical spectra induced with intensity-modulated resonant laser light that synchronously pumps and detects the metastable ${}^4\mathrm{He}$ atoms in the presence of a quasistatic magnetic field. We extend previous work and derive complete analytical expressions for the resonance signals by taking into account arbitrary magnetic-field directions and arbitrary light polarizations. The analytical results are derived by solving the Liouville equation using the irreducible tensor formalism on the assumption of low light power. We discuss the potential application of the derived analytical results in constructing and optimizing a dead-zone-free all-optical atomic magnetometer.

Differential single-beam saturated-absorption spectroscopy (DSSAS) is proposed to stabilize lasing frequency and suppress Doppler-broadened background and common-mode optical noise. The spectral first-derivative demodulated signal of metastable ${}^4\mathrm{H}\mathrm{e}$ atoms is used as an error signal to stabilize a fiber laser around 1083 nm. Experimental results show that, compared with existing non-DSSAS frequency stabilization, DSSAS stabilization produces better stability and lower fluctuations, especially for frequency-noise-corrupted lasers. In DSSAS stabilization, for data acquired over 7000 s, the root mean square frequency fluctuation of the fiber laser is 16.4 kHz, and the frequency stability described by the modified Allan deviation is 4.1 × 10⁻¹² at 100 s. Even for a defective laser with poor frequency stability, the proposed scheme demonstrates experimentally high capability of noise suppression and reduces the frequency fluctuations by two orders of magnitude. Given its simplicity and compact design, frequency stabilization by DSSAS is promising for quantum-sensor applications, such as atomic magnetometers, atomic gyroscopes, and atomic clocks.