ALBERT

Description: Aeromagnetic exploration is an important method of geophysical exploration. We study the compensation method of the towed bird system and establish the towed bird interference model. Due to the geomagnetic gradient changing greatly, the geomagnetic gradient is considered in the towed bird interference model. In this paper, we model the geomagnetic field gradient and analyze the influence of the towed bird system on the aeromagnetic compensation results. Finally, we apply the ridge regression method to solve the problem. We verify the feasibility of this compensation method through actual flight tests and further improve the data quality of the towed bird interference.

Description: The study of aerosol optical properties is essential to understand its impact on the global climate. In our recent field measurement carried out in the Gehu area of southwest Changzhou City, a photoacoustic extinctiometer (PAX) and a cavity attenuated phase shift albedo monitor (CAPS-ALB) were used for online aerosol optical properties measurement. Laboratory calibration with gas and particle samples were carried out to correct disagreements of field measurements. During particle calibration, we adopted ammonium sulfate (AS) samples for scattering calibration of nephelometer parts of both the instruments, then combined these with number-size distribution measurements in the MIE model for calculating the value of the total scattering (extinction) coefficient. During gas calibration, we employed high concentrations of NO2 for absorption calibration of the PAX resonator and then further intercompared the extinction coefficient of CAPS-ALB with a cavity-enhanced spectrometer. The correction coefficient obtained from the laboratory calibration experiments was employed on the optical properties observed in the field measurements correspondingly and showed good results in comparison with reconstructed extinction from the IMPROVE model. The intercomparison of the calibrated optical properties of PAX and CAPS-ALB in field measurements was in good agreement with slopes of 1.052, 1.024 and 1.046 for extinction, scattering and absorption respectively, which shows the reliability of measurement results and verifies the correlation between the photoacoustic and the cavity attenuated phase shift instruments.

Description: This paper describes a newly designed, experimental, and affordable rock slope monitoring system. This system is being used to monitor three rock slopes in Czechia for a period of up to 2 years. The instrumented rock slopes have different lithology (sandstone, limestone, and granite), aspect, and structural and mechanical properties. Induction crackmeters monitor the dynamic of joints, which separate unstable rock blocks from the rock face. This setup works with a repeatability of measurements of 0.05 mm. External destabilising factors (air temperature, precipitation, incoming and outgoing radiation, etc.) are measured by a weather station placed directly within the rock slope. Thermal behaviour in the rock slope surface zone is monitored using a compound temperature probe, placed inside a 3 m deep subhorizontal borehole, which is insulated from external air temperature. Additionally, one thermocouple is placed directly on the rock slope surface. From the time series measured to date (the longest since autumn 2018), we are able to distinguish differences between the annual and diurnal temperature cycles of the monitored sites. From the first data, a greater annual joint dynamic is measured in the case of larger blocks; however, smaller blocks are more responsive to short-term diurnal temperature cycles. Differences in the thermal regime between the sites are also recognisable and are caused mainly by different slope aspect, rock mass thermal conductivity, and colour. These differences will be explained by the statistical analysis of longer time series in the future.

Description: The paper presents information about the seismic experiment “AniMaLS” which aims to provide a new insight into the crust and upper mantle structure beneath the Polish Sudetes (NE margin of the Variscan orogen). The seismic network composed of 23 temporary broadband stations was operated continuously for about 2 years (October 2017 to October 2019). The dataset was complemented by records from eight permanent stations located in the study area and in the vicinity. The stations were deployed with an inter-station spacing of approximately 25–30 km. As a result, recordings of local, regional and teleseismic events were obtained. We describe the aims and motivation of the project, the station deployment procedure, as well as the characteristics of the temporary seismic network and of the permanent stations. Furthermore, this paper includes a description of important issues like data transmission setup, status monitoring systems, data quality control, near-surface geological structure beneath stations and related site effects, etc. Special attention was paid to verification of correct orientation of the sensors. The obtained dataset will be analysed using several seismic interpretation methods, including analysis of seismic anisotropy parameters, with the objective of extending knowledge about the lithospheric and sublithospheric structure and the tectonic evolution of the study area.

Description: New energy acquisition devices are urgently required to address the increasing global energy consumption and increasing difficulty of energy exploitation. Devices for seismic exploration appear to be small in size, wireless and rapidly becoming more intelligent; hence, a traditional operating platform can no longer satisfy the demand of portable exploration device usage. This study investigates and develops hardware for a wireless microseismic acquisition station and then uses this hardware as a platform to address the distribution of wireless microseismic acquisition stations and deliver monitoring software based on the Android platform, which is portable, popular and has a large number of users. In large-scale field constructions, software can provide operators with visualised station layouts throughout the process, including positioning, ranging, angle measuring and network monitoring. It also offers a real-time network for monitoring small- and medium-sized microseismic acquisition station arrays under construction as well as other functions, such as intelligent control and real-time data monitoring of the status of the acquisition station. A drainage blast monitoring test is conducted on the system, showing positively monitored data and accurate results in the inverse operation. Moreover, the software and hardware are proven to be highly stable and portable through a post-construction test, which can help enhance the field construction efficiency.

Description: The transient electromagnetic method (TEM) is widely used for mapping subsurface resistivity structures, but data are inevitably contaminated by noise from various sources. It is common practice to gate signals from TEM systems to reduce the amount of data and improve the signal-to-noise ratio (SNR). Gating acts as a filter, and optimum gating will pass the TEM signal un-attenuated while suppressing noise. In systems based on analog boxcar integrators, the gating corresponds to filtering with a square window. The frequency response of this window shape has large side lobes, which are often insufficient in attenuating noise, e.g., from radio signals in the very low frequency (VLF) 3–30 kHz band. Tapered gates have better side lobe suppression and attenuate noise better, but tapering with analog boxcar integrators is difficult. We propose using many short boxcar gates, denoted sub-gates, and combine the sub-gates into semi-tapered gates to improve noise rejection at late gates where low signal normally leads to poor SNR. The semi-tapering approach is analyzed and tested experimentally on data from a roving TEM system. We quantify the effect of semi-tapered gates by computing an improvement factor as the ratio between the standard error of data measured with boxcar gates and the standard error of data measured with semi-tapered gates. Data from a test survey in Gedved, Denmark, with 1825 measurements gave mean improvement factors between 1.04 and 2.22 for the 10 late-time gates centered between 78.7 and 978.1 µs. After inversion of the data, we find that semi-tapering increases the depth of investigation by about 20 % for this specific survey. We conclude that the semi-tapered approach is a viable path towards increasing SNR in TEM systems based on analog boxcar integrators.

Description: Quantum gravimeters are a promising new development allowing for continuous absolute gravity monitoring while remaining user-friendly and transportable. In this study, we present experiments carried out to assess the capacity of the AQG#B01 in view of future deployment as a field gravimeter for hydrogeophysical applications. The AQG#B01 is the field version follow-up of the AQG#A01 portable absolute quantum gravimeter developed by the French quantum sensor company Muquans. We assess the instrument's performance in terms of stability (absence of instrumental drift) and sensitivity in relation to other gravimeters. No significant instrumental drift was observed over several weeks of measurement. We discuss the observations concerning the accuracy of the AQG#B01 in comparison with a state-of-the-art absolute gravimeter (Micro-g-LaCoste, FG5#228). We report the repeatability to be better than 50 nm s−2. This study furthermore investigates whether changes in instrument tilt and external temperature and a combination of both, which are likely to occur during field campaigns, influence the measurement of gravitational attraction. We repeatedly tested external temperatures between 20 and 30 ∘C and did not find any significant effect. As an example of a geophysical signal, a 100 nm s−2 gravity change is detected with the AQG#B01 after a rainfall event at the Larzac geodetic observatory (southern France). The data agreed with the gravity changes measured with a superconducting relative gravimeter (GWR, iGrav#002) and the expected gravity change simulated as an infinite Bouguer slab approximation. We report 2 weeks of stable operation under semi-terrain conditions in a garage without temperature-control. We close with operational recommendations for potential users and discuss specific possible future field applications. While not claiming completeness, we nevertheless present the first characterization of a quantum gravimeter carried out by future users. Selected criteria for the assessment of its suitability in field applications have been investigated and are complemented with a discussion of further necessary experiments.

Description: Conventional surface electromagnetic methods have limitations of a shallow detection depth and low resolution. To increase the detection depth and resolution, borehole–surface electromagnetic methods for electromagnetic three-dimensional observations of the ground, tunnels, and boreholes have been developed. Current borehole receivers only measure a single parameter of the magnetic field component, which does not meet the special requirements of controlled-source electromagnetic (CSEM) methods. This study proposes a borehole electromagnetic receiver that realizes synchronous acquisition of the vertical electric field component in the borehole and the three-axis orthogonal magnetic field components. This receiver uses Ti electrodes and fluxgate magnetometers (fluxgates) as sensors to acquire electric and magnetic field components. Multi-component comprehensive observation methods that add the electric field component can effectively support the CSEM method, improve detection accuracy, and exhibit a strong potential for detecting deep ore bodies. We conducted laboratory and field experiments to verify the performance of our new borehole electromagnetic receiver. The receiver achieved a magnetic field noise of less than 6 pTHz-1/2 at 1 kHz, and the electric field noise floor was approximately 20 nVm-1Hz-1/2 at 1 kHz. The −3 dB electric field bandwidth can reach DC −10 kHz. The results of our experiments prove that high-quality CSEM signals can be obtained using this new borehole electromagnetic receiver and that the electric field component exhibits sufficient advantages for measuring the vertical component of the electric field.

Description: Climate change raises important issues concerning hydrological engineering. The impact of climate change on important river basins should be investigated rigorously. Extreme temperature variability has a direct impact on the hydrological cycle, especially the evaporation component. In this paper, spatial and temporal patterns of changes in extreme temperatures were investigated using 10 meteorological stations' data for the period 1950–2018 in the Blue Nile Basin. Long-term trends in the Blue Nile Basin annual and monthly temperatures were investigated. The statistical significance of the trend was calculated by applying the Mann–Kendall (MK) test. The analysis of data was performed using the coefficient of variance and anomaly index. The results showed that the annual maximum and minimum temperatures were increasing significantly with a magnitude of 0.037 and 0.025 ∘C per decade respectively in the period from 1950 to 2018. The result of the Mann–Kendall analysis test revealed a marked increase in the mean maximum and minimum temperature trends over time during the study period (the minimum temperature rate is more evident than the maximum). The long-term anomalies of mean annual minimum temperature revealed the interannual variability while the trend after 1977 was higher than the long-term average, which is proof of the warming trend's existence during the last two decades of the 20th century.

Description: Marine self-potential (SP) investigation is an effective method to study deep-sea hydrothermal vents and seafloor sulfide deposits. At present, one of the commonly used marine self-potential systems is a towed array of electrodes. Large noises are recorded when great changes in electrode distance and array attitude occur due to the complex seafloor topography. In this paper, a new multicomponent electrical field observation system based on an autonomous underwater vehicle (AUV) was introduced for the measurement of seafloor self-potential signals. The system was tested in a lake, and the multicomponent self-potential data were collected from there. Observed data involve the navigational information of the AUV, which could be corrected using a rotation transform. After navigational correction, measured data can recover the location of the artificial source using self-potential tomography. The experimental results showed that the new SP system can be applied to marine SP observations, providing an efficient and low-noise SP acquisition method for marine resources and environmental investigations.