Design of a Low-Cost Small-Size Fluxgate Sensor

Traditional fluxgate sensors used in geomagnetic field observations are large, costly, power-consuming and often limited in their use. Although the size of the micro-fluxgate sensors has been significantly reduced, their performance, including indicators such as accuracy and signal-to-noise, does not meet observational requirements. To address these problems, a new race-track type probe is designed based on a magnetic core made of a Co-based amorphous ribbon. The size of this single-component probe is only Φ10 mm × 30 mm. The signal processing circuit is also optimized. The whole size of the sensor integrated with probes and data acquisition module is Φ70 mm × 100 mm. Compared with traditional fluxgate and micro-fluxgate sensors, the designed sensor is compact and provides excellent performance equal to traditional fluxgate sensors with good linearity and RMS noise of less than 0.1 nT. From operational tests, the results are in good agreement with those from a standard fluxgate magnetometer. Being more suitable for modern dense deployment of geomagnetic observations, this small-size fluxgate sensor offers promising research applications at lower costs.

The fluxgate magnetometer of the Low Orbit Pearl Satellites (LOPS): overview of in-flight performance and initial results

The Low Orbit Pearl Satellite series consists of six constellations, with each constellation consisting of three identical microsatellites that line up just like a string of pearls. The first constellation of three satellites were launched on 29 September 2017, with an inclination of ∼ 35.5∘ and ∼ 600 km altitude. Each satellite is equipped with three identical fluxgate magnetometers that measure the in situ magnetic field and its low-frequency fluctuations in the Earth's low-altitude orbit. The triple sensor configuration enables separation of stray field effects generated by the spacecraft from the ambient magnetic field (e.g., Zhang et al., 2006). This paper gives a general description of the magnetometer including the instrument design, calibration before launch, in-flight calibration, in-flight performance, and initial results. Unprecedented spatial coverage resolution of the magnetic field measurements allow for the investigation of the dynamic processes and electric currents of the ionosphere and magnetosphere, especially for the ring current and equatorial electrojet during both quiet geomagnetic conditions and storms. Magnetic field measurements from LOPS could be important for studying the method to separate their contributions of the Magnetosphere-Ionosphere (M-I) current system.

Science Missions of the Korean Lunar Exploration Program

The Korea Pathfinder Lunar Orbiter (KPLO), which is the Korean first lunar and space exploration spacecraft, will be launched in August 2022 and arrive in a lunar orbit in December 2022. The KPLO will carry out nominal missions while in a lunar polar orbit an ~100-km altitude for one year. The KPLO has five lunar science mission payloads and one technology demonstration payload in order to achieve their own science and technology goals. The science payloads consist of four Korean domestic instruments and one internationally collaborated science instrument for scientific investigations on the lunar surface and in a space environment. The Korean dometstic science instruments are the gamma-ray spectrometer named KGRS, the wide-angle polarimetric camera named PolCam, the fluxgate magnetometer named KMAG, and the high resolution camera named LUTI. The name of the internationally collaborated science instrument is ShandowCam, which was developed by Arizona State University, U.S., and funded and managed by NASA. The science data acquired by the science payloads will be released to the public in order to enhance scientific and educational achievements. The science data acquired by each science instrument will be archived and released through the web sites of the KPDS (KARI Planetary Data System) for the Korean science instruments and the NASA PDS (Planetary Data System) for the internationally collaborated science instrument.

Chitosan-Derived Magnetic Nanomaterials: Synthesis, Characterization, and Nitrite Adsorption in Water

Nitrite is one of the main pollutants in the water worldwide. In this study, we have applied the reverse suspension crosslinking methodology based on chitosan (CS) and Fe3O4 (FeO) to synthesize the novel magnetic nanomaterial of chitosan (CS-FeO). The physical and chemical properties of CS-FeO were further characterized by scanning electron microscopy, particle size distribution, thermogravimetry, fluxgate magnetometer, Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, and energy dispersive spectroscopy. Results revealed that CS-FeO showed high thermal stability in the temperature ranging from 50 to 200°C. CS-FeO showed high crystallinity and magnetism and was easily and quickly separated from aqueous solution in the presence of an external magnetic field. The molecular structure of CS-FeO showed that the core-shell structure of CS-FeO was established with FeO as the core and CS as the shell. Furthermore, the adsorption rate of nitrite by CS-FeO reached 65.83 ± 0.76 % under optimal conditions. Moreover, CS-FeO showed high regeneration capability with Na2SO4 used as the eluent. Our study demonstrated evidently that CS-FeO can be potentially used to remove nitrite from drinking water sources and industrial wastewater, suggesting the promising future of the application of CS-derived magnetic nanomaterials in the areas of environmental protections.

Automatic calculation of the magnetometer zero offset using the interplanetary magnetic field based on the Wang-Pan method

The space-borne fluxgate magnetometer (FGM) needs regular in-flight calibration to obtain its zero offset. Recently, a new method based on the properties of Alfvén waves for the zero offset calibration was developed by Wang and Pan (2021). They found that there exists an optimal offset line (OOL) in the offset cube for a pure Alfvén wave, and the zero offset can be determined by the intersection of at least two non-parallel OOLs. Since no pure Alfvén waves exist in the interplanetary magnetic field, the calculation of the zero offset relies on the selection of the highly Alfvénic fluctuation event. Here, we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset. This procedure includes three parts: (1) selection of highly Alfvénic fluctuation events, (2) evaluation of the OOL of the selected fluctuation events, and (3) determination of the zero offset. We test our automatic procedure by applying it to the magnetic field data measured by the FGM onboard Venus Express. The tests reveal that our automatic procedure is able to achieve as good results as the Davis-Smith method. One advantage of our procedure is that the selection criteria and process for the highly Alfvénic fluctuation event are simpler. Our automatic procedure might also be applied to find fluctuation events for the Davis-Smith method after proper modification.

The sporadic sodium layer: a possible tracer for the conjunction between the upper and lower atmospheres

In this research, we reveal the inter-connection between lightning strokes, reversal of the electric field, ionospheric disturbances, and a sodium layer (NaS), based on the joint observations by a temperature/wind (T/W, where the slash means “and”) lidar, an ionosonde, an atmospheric electric mill, a fluxgate magnetometer, and the World Wide Lightning Location Network (WWLLN). Our results suggest that lightning strokes could trigger or amplify the formation of an NaS layer in a descending sporadic E layer (ES), through a mechanism that involves the overturning of the electric field. A conjunction between the lower and upper atmospheres could be established as follows by these inter-connected phenomena, and the key processes could be suggested to be: lightning strokes → overturning of the electric field → ES generating NaS.

MagneToRE: Mapping the 3-D Magnetic Structure of the Solar Wind Using a Large Constellation of Nanosatellites

Unlike the vast majority of astrophysical plasmas, the solar wind is accessible to spacecraft, which for decades have carried in-situ instruments for directly measuring its particles and fields. Though such measurements provide precise and detailed information, a single spacecraft on its own cannot disentangle spatial and temporal fluctuations. Even a modest constellation of in-situ spacecraft, though capable of characterizing fluctuations at one or more scales, cannot fully determine the plasma’s 3-D structure. We describe here a concept for a new mission, the Magnetic Topology Reconstruction Explorer (MagneToRE), that would comprise a large constellation of in-situ spacecraft and would, for the first time, enable 3-D maps to be reconstructed of the solar wind’s dynamic magnetic structure. Each of these nanosatellites would be based on the CubeSat form-factor and carry a compact fluxgate magnetometer. A larger spacecraft would deploy these smaller ones and also serve as their telemetry link to the ground and as a host for ancillary scientific instruments. Such an ambitious mission would be feasible under typical funding constraints thanks to advances in the miniaturization of spacecraft and instruments and breakthroughs in data science and machine learning.

Characterizing Electromagnetic Interference Signals for Unmanned Aerial Vehicle Geophysical Surveys

The development of a functional Unmanned Aerial Vehicle (UAV) mounted aeromagnetic system requires integrating a magnetometer payload onboard a UAV platform in a manner that preserves the integrity of the total magnetic field measurements. One challenge when developing these systems is accounting for the sources of in-flight magnetic and electromagnetic interference signals that are greater than the resolvability threshold of the magnetometer. Electromagnetic interference generated by the platform has the potential to be mitigated using several techniques such as magnetic shielding, filtering, or compensation; and can be attenuated by strategically positioning the magnetometer at a distance from the UAV. The integration procedure and selection of a mitigation strategy can be informed by characterizing the electromagnetic interference generated by the platform. Scalogram analysis was employed to characterize the high-frequency electromagnetic signals generated by a multi-rotor UAV’s electromagnetic motors. A low sensitivity (7 nT) vector, fluxgate magnetometer was used to measure the electromagnetic interference generated by two unique multi-rotor UAVs in a controlled lab setting. Results demonstrated three spectrally distinct electromagnetic signals, each with unique frequency and amplitude, generated by each UAV platform. The frequency of these electromagnetic interference signals was found to be directly proportional to the applied rotation frequency of the electromagnetic motor. The aforementioned knowledge was applied to UAV field surveys to assess the high-frequency electromagnetic interference signals experienced. This was achieved by using a high sensitivity (0.01 nT), scalar optically pumped magnetometer with a 1000 Hz sampling frequency. The results show that adequate sensor placement and pre-flight evaluation of the platform-sensor interactions provide useful mitigation strategies, which can compensate for electromagnetic interference signals generated by the UAV platform during aeromagnetic surveys.