Non-intrusive soil carbon content quantification methods using machine learning algorithms:A comparison of microwave and millimeter wave radar sensors

Agricultural and forestry biomass can be converted to biochar through pyrolysis gasification,making it a significant carbon source for soil.Applying biochar to soil is a carbon-negative process that helps combat climate change,sustain soil biodiversity,and regulate water cycling.However,quantifying soil carbon content conventionally is time-consuming,labor-intensive,imprecise,and expensive,making it difficult to accurately measure in-field soil carbon’s effect on storage water and nutrients.To address this challenge,this paper for the first time,reports on extensive lab tests demonstrating non-intrusive methods for sensing soil carbon and related smart biochar applications,such as differentiating between biochar types from various biomass feedstock species,monitoring soil moisture,and biochar water retention capacity using portable microwave and millimeter wave sensors,and machine learning.These methods can be scaled up by deploying the sensor in-field on a mobility platform,either ground or aerial.The paper provides details on the materials,methods,machine learning workflow,and results of our investigations.The significance of this work lays the foundation for assessing carbon-negative technology applications,such as soil carbon content accounting.We validated our quantification method using supervised machine learning algorithms by collecting real soil mixed with known biochar contents in the field.The results show that the millimeter wave sensor achieves high sensing accuracy(up to 100%)with proper classifiers selected and outperforms the microwave sensor by approximately 10%–15%accuracy in sensing soil carbon content.

0-10 KM TEMPERATURE AND HUMIDITY PROFILES RETRIEVAL FROM GROUND-BASED MICROWAVE RADIOMETER

Deviation exists between measured and simulated microwave radiometer sounding data. The bias results in low-accuracy atmospheric temperature and humidity profiles simulated by Back Propagation artificial neural network models. This paper evaluated a retrieving atmospheric temperature and humidity profiles method by adopting an input data adjustment-based Back Propagation artificial neural networks model. First, the sounding data acquired at a Nanjing meteorological site in June 2014 were inputted into the Mono RTM Radiative transfer model to simulate atmospheric downwelling radiance at the 22 spectral channels from 22.234 GHz to 58.8 GHz, and we performed a comparison and analysis of the real observed data; an adjustment model for the measured microwave radiometer sounding data was built. Second, we simulated the sounding data of the 22 channels using the sounding data acquired at the site from 2011 to 2013. Based on the simulated rightness temperature data and the sounding data, BP neural network-based models were trained for the retrieval of atmospheric temperature, water vapor density and relative humidity profiles. Finally, we applied the adjustment model to the microwave radiometer sounding data collected in July 2014, generating the corrected data. After that, we inputted the corrected data into the BP neural network regression model to predict the atmospheric temperature, vapor density and relative humidity profile at 58 high levels from 0 to 10 km. We evaluated our model's effect by comparing its output with the real measured data and the microwave radiometer's own second-level product. The experiments showed that the inversion model improves atmospheric temperature and humidity profile retrieval accuracy; the atmospheric temperature RMS error is between 1 K and 2.0 K; the water vapor density's RMS error is between 0.2 g/m^3 and 1.93 g/m3; and the relative humidity's RMS error is between 2.5% and 18.6%.

Primary Analysis of Sounding Data from a Multi-channel Parallel Ground-based Microwave Radiometer

The sounding data of a multi-channel parallel ground-based microwave radiometer （MWR） in Fuzhou station in July and August in 2016 were compared with the sounding data of a radiosonde in the same position in the same period. The results showed that the correlations between the two types of temperature or humidity detected by the microwave radiometer and the radiosonde were significant at 0.05 level, indicating that the overall changing trends of temperature or humidity detected by the two devices were similar. The temperature detected by the microwave radiometer and the radiosonde decreased with the increase of height. The difference between the changes in the height of the zero layer detected by the micro- wave radiometer and the radiosonde was not significant, and their trends were basically the same.

Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides(MXene)have emerged as promising candidates for microwave absorption(MA)materials.However,they also have some drawbacks,such as poor impedance matching,high self-stacking tendency,and high density.To tackle these challenges,MXene nanosheets were incorporated into polyacrylonitrile(PAN)nanofibers and subsequently assembled into a three-dimensional(3D)network structure through PAN carbonization,yielding MXene/C aerogels.The 3D network effectively extends the path of microcurrent transmission,leading to enhanced conductive loss of electromagnetic(EM)waves.Moreover,the aerogel’s rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXenebased absorbers.EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss(RL_(min))value of−53.02 dB(f=4.44 GHz,t=3.8 mm),and an effective absorption bandwidth(EAB)of 5.3 GHz(t=2.4 mm,7.44–12.72 GHz).Radar cross-sectional(RCS)simulations were employed to assess the radar stealth effect of the aerogels,revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m^(2).In addition to the MA performance,the MXene/C aerogel also demonstrates good thermal insulation performance,and a 5-mm-thick aerogel can generate a temperature gradient of over 30℃ at 82℃.This study provides a feasible design approach for creating lightweight,efficient,and multifunctional MXene-based MA materials.

Microwave Photonics for Modern Radar Systems

The emerging new concepts and technologies based on microwave photonics have led to an ever-increasing interest in developing innovative radar systems with a net gain in functionality,bandwidth /resolution,size,mass,complexity and cost when compared with the traditional implementations. This paper describes the techniques developed in the last few years in microwave photonics that might revolutionize the way to design multifunction radar systems,with an emphasis on the recent advances in optoelectronic oscillators( OEOs),arbitrary waveform generation,photonic mixing,phase coding,filtering,beamforming,analog-to-digital conversion,and stable radio-frequency signal transfer. Challenges in implementation of these components and subsystems for meeting the technique requirements of the multifunction radar applications are discussed.

Numerical simulation and inversion of offshore area depth based on x-band microwave radar

A detection method of offshore area depth utilizing the x-band microwave radar is proposed. The method is based on the sea clutter imaging mechanism of microwave radar, and combined with dispersion equation of the liner wave theorem and least square method （LSM）, consequently get the inversion results of water depth in the detected region. The wave monitoring system OSMAR-X exploited by the Ocean State Laborato-ry, Wuhan University, based on a microwave radar has proven to be a powerful tool to monitor ocean waves in time and space. Numerical simulation and inversion of offshore area depth are carried out here; since JONSWAP model can give description of stormy waves in different growth phase, it is suitable for simulation. Besides, some results from measured data detected by OSMAR-X x-band radar located at Longhai of Fujian Province, China, validates this method. The tendency of the average water depths inferred from the radar images is in good agreement with the tide level detected by Xiamen tide station. These promising results suggest the possibility of using OSMAR-X to monitor operationally morphodynamics in coastal zones. This method can be applied to both shore-based and shipborne x-band microwave radar.

An approach to a non-contact vital sign monitoring using dual-frequency microwave radars for elderly care

This study aimed to produce a prototype system for non-contact vital sign monitoring of the elderly using microwave radar with the intention of reducing the burdens on monitored individuals and nursing caregivers. In addition, we tested the ability of the proposed prototype system to measure the respiratory and heart rates of the elderly in a nursing home and discussed the systems effectiveness and problems by examining results of real-time monitoring. The prototype system consisted of two 24-GHz microwave radar antennas and an analysis system. The antennas were positioned below a mattress to monitor motion on the body surface for measuring cardiac and respiratory rates from the dorsal side of the subjects (23.3 ± 1.2 years) who would be lying on the mattress. The heart rates determined by the prototype system correlated significantly with those measured by electrocardiography (r = 0.92). Similarly, the respiratory rates determined by the prototype correlated with those obtained from respiration curves (r = 0.94). Next, we investigated the effectiveness of the prototype system with 7 elderly patients (93.3 ± 10.56 years) at a nursing home. The proposed system appears to be a promising tool for monitoring the vital signs of the elderly in a way that alleviates the need to attach electrodes overnight to confirm patient safety.

Time-varying baseline error correction method for ground-based micro-deformation monitoring radar

In recent years, ground-based micro-deformation monitoring radar has attracted much attention due to its excellent monitoring capability. By controlling the repeated campaigns of the radar antenna on a fixed track, ground-based micro-deformation monitoring radar can accomplish repeat-pass interferometry without a space baseline and thus obtain highprecision deformation data of a large scene at one time. However, it is difficult to guarantee absolute stable installation position in every campaign. If the installation position is unstable, the stability of the radar track will be affected randomly, resulting in time-varying baseline error. In this study, a correction method for this error is developed by analyzing the error distribution law while the spatial baseline is unknown. In practice, the error data are first identified by frequency components, then the data of each one-dimensional array(in azimuth direction or range direction) are grouped based on numerical distribution period, and finally the error is corrected by the nonlinear model established with each group.This method is verified with measured data from a slope in southern China, and the results show that the method can effectively correct the time-varying baseline error caused by rail instability and effectively improve the monitoring data accuracy of groundbased micro-deformation radar in short term and long term.

Constrained geometry analysis to resolve 3-D deformations from three ground-based radars

When multiple ground-based radars(GB-rads)are utilized together to resolve three-dimensional(3-D)deformations,the resolving accuracy is related with the measurement geometry constructed by these radars.This paper focuses on constrained geometry analysis to resolve 3-D deformations from three GB-rads.The geometric dilution of precision(GDOP)is utilized to evaluate 3-D deformation accuracy of a single target,and its theoretical equation is derived by building a simplified 3-D coordinate system.Then for a 3-D scene,its optimal accuracy problem is converted into determining the minimum value of an objective function with a boundary constraint.The genetic algorithm is utilized to solve this constrained optimization problem.Numerical simulations are made to validate the correctness of the theoretical analysis results.

Noncontact Monitoring of Relative Changes in Blood Pressure Using Microwave Radar Sensors

This study aims to confirm whether noncontact monitoring of relative changes in blood pressure can be estimated using microwave radar sensors. First, an equation to estimate blood pressure was derived, after which, the effectiveness of the estimation equation was confirmed using data obtained by a noncontact method while inducing variations in blood pressure. We considered that the Bramwell-Hill equation, which contains some parameters that directly indicate changes in blood pressure, would be an appropriate reference to construct an estimation equation for the noncontact method, because measurements using microwave radar sensors can measure minute scale motion on the skin surface induced by the pulsation of blood vessels. In order to estimate relative changes in blood pressure, we considered a simple equation including the pulse transit time (PTT), amplitude of signals and body dimensions as parameters. To verify the effectiveness of the equation for estimating changes in blood pressure, two experiments were conducted: a cycling task using an ergometer, which induces blood pressure fluctuations because of changes in cardiac output, and a task using the Valsalva maneuver, which induces blood pressure fluctuations because of changes in vascular resistance. The results obtained from the two experiments suggested that the proposed equation using microwave radar sensors can accurately estimate relative changes of blood pressure. In particular, relatively favorable results were obtained for the changes in blood pressure induced by the changes in cardiac volume. Although many issues remain, this method could be expected to contribute to the continuous evaluation of cardiac function while reducing the burden on patients.

Environmentally Friendly and Multifunctional Shaddock Peel-Based Carbon Aerogel for Thermal-Insulation and Microwave Absorption

Eco-friendly electromagnetic wave absorbing materials with excellent thermal infrared stealth property,heat-insulating ability and compression resistance are highly attractive in practical applications.Meeting the aforesaid requirements simultaneously is a formidable challenge.Herein,ultra-light carbon aerogels were fabricated via fresh shaddock peel by facile freeze-drying method and calcination process,forming porous network architecture.With the heating platform temperature of 70℃,the upper surface temperatures of the as-prepared carbon aerogel present a slow upward trend.The color of the sample surface in thermal infrared images is similar to that of the surroundings.With the maximum compressive stress of 2.435 kPa,the carbon aerogels can provide favorable endurance.The shaddock peel-based carbon aerogels possess the minimum reflection loss value(RLmin)of−29.50 dB in X band.Meanwhile,the effective absorption bandwidth covers 5.80 GHz at a relatively thin thickness of only 1.7 mm.With the detection theta of 0°,the maximum radar cross-sectional(RCS)reduction values of 16.28 dB m^(2) can be achieved.Theoretical simulations of RCS have aroused extensive interest owing to their ingenious design and time-saving feature.This work paves the way for preparing multi-functional microwave absorbers derived from biomass raw materials under the guidance of RCS simulations.

Ultrabroad Microwave Absorption Ability and Infrared Stealth Property of Nano-Micro CuS@rGO Lightweight Aerogels

Developing ultrabroad radar-infrared compatible stealth materials has turned into a research hotspot,which is still a problem to be solved.Herein,the copper sulfide wrapped by reduced graphene oxide to obtain three-dimensional(3D)porous network composite aerogels(CuS@rGO)were synthesized via thermal reduction ways(hydrothermal,ascorbic acid reduction)and freeze-drying strategy.It was discovered that the phase components(rGO and CuS phases)and micro/nano structure(microporous and nanosheet)were well-modified by modulating the additive amounts of CuS and changing the reduction ways,which resulted in the variation of the pore structure,defects,complex permittivity,microwave absorption,radar cross section(RCS)reduction value and infrared(IR)emissivity.Notably,the obtained CuS@rGO aerogels with a single dielectric loss type can achieve an ultrabroad bandwidth of 8.44 GHz at 2.8 mm with the low filler content of 6 wt%by a hydrothermal method.Besides,the composite aerogel via the ascorbic acid reduction realizes the minimum reflection loss(RL_(min))of−60.3 dB with the lower filler content of 2 wt%.The RCS reduction value can reach 53.3 dB m^(2),which effectively reduces the probability of the target being detected by the radar detector.Furthermore,the laminated porous architecture and multicomponent endowed composite aerogels with thermal insulation and IR stealth versatility.Thus,this work offers a facile method to design and develop porous rGO-based composite aerogel absorbers with radar-IR compatible stealth.

Ultralight Magnetic and Dielectric Aerogels Achieved by Metal-Organic Framework Initiated Gelation of Graphene Oxide for Enhanced Microwave Absorption

The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks(MOFs)and graphene oxide(GO)building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications.Herein,we report a facile route for synthesizing MOF/reduced GO(rGO)aerogels based on the gelation of GO,which is directly initiated using MOF crystals.Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal–oxygen covalent or electrostatic interactions.The MOF/rGOderived magnetic and dielectric aerogels Fe_(3)O_(4)@C/rGO and Ni-doped Fe_(3)O_(4)@C/rGO show notable microwave absorption(MA)performance,simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5(-58.1 dB and 6.48 GHz)and 2.8 mm(-46.2 dB and 7.92 GHz)with ultralow filling contents of 0.7 and 0.6 wt%,respectively.The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation,which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering.This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.

An approach to wide-field imaging of linear rail ground-based SAR in high squint multi-angle mode

Ground-based synthetic aperture radar(GB-SAR) has been successfully applied to the ground deformation monitoring.However, due to the short length of the GB-SAR platform, the scope of observation is largely limited. The practical applications drive us to make improvements on the conventional linear rail GB-SAR system in order to achieve larger field imaging. First, a turntable is utilized to support the rotational movement of the radar.Next, a series of high-squint scanning is performed with multiple squint angles. Further, the high squint modulation phase of the echo data is eliminated. Then, a new multi-angle imaging method is performed in the wave number domain to expand the field of view. Simulation and real experiments verify the effectiveness of this method.

An Overview of Active Microwave Imaging for Early Breast Cancer Detection

First,this article reviews the background of microwave imaging for early breast cancer detection,with a focus on active methods.Then active approaches,namely microwave tomography and radar-based microwave imaging,to microwave breast cancer detection are overviewed briefly,where there are recent developments in imaging algorithms as well as antennas,models,phantom and experimental systems.Lastly,we give concluding remarks and future research.In a word,the main objective of this article is to provide an overview of the principles,development,and current research status of these approaches.

Microwave characteristic simulation research for a kind of novel electromagnetic structure

A kind of novel electromagnetic structure of Cassini cross section is proposed and simulation is implemented with business microwave soft CST based on finite integral technique （FIT）. The electromagnetic field mode type of Cassini wave-guide belongs to TE, and the electromagnetic field intensity is stronger near the neck region than at other areas. For Cassini electromagnetic patches and lumped elements, the radar cross section （RCS） is smaller around 7 GHz with -30.85 dBsm, and the absorbing property is better around 13 GHz with 4.56 dBsm difference of RCS from comparing of pure medium. For novel radiation structure of Cassini cross-section patches, the electromagnetic field value is larger in the neck areas of two half patches. At last, the potential application and development of Cassini oval structure are put forward in the electromagnetic stealth technology and antennae design.

MICROWAVE SENSOR DEVELOPMENT IN RECENT TWO YEARS IN CHINA

The development of microwave sensors in recent two years in China are in troduced with an emphasis on spaceborne sensors without the applications in cluded. The microwave sensors as the main payloads to be boarded on the future operational satellites, such as FY-3 meteorological satellites and HY-2 marine satellite are introduced with much in detail. Besides these, four new sensors are outlined, i.e. the imaging radar altimeter,synthetic aperture radiometer, and polarimetric radiometer. Two recently conducted flight experiment campaigns are also introduced with results shown.

Assessment of Non-Contact Measurement Using a Microwave Sensor to Jugular Venous Pulse Monitoring

The jugular venous pulse (JVP) waveform provides an insight into right heart function, and its assessment is important in patients with heart failure. However, the conventional pulse-transducer (contact) method for monitoring this waveform is not frequently used because it requires a high degree of skill. The aim of this study was to confirm the effectiveness of a prototype non-contact system that employs microwave radar (24 GHz, 7 mW;non-contact system) for JVP measurement. Experiments were conducted on eight healthy male volunteers (21.88 ± 0.99 years). JVP measurements were compared between the conventional contact method and the proposed non-contact method. Change in JVP waveform was measured in response to an angle of reclining in five steps from the supine position to 75° of elevation. The obtained JVP measurements were similar between the two methods. Because in the non-contact method the faint pulsation of the JVP is not suppressed by the pressure of a sensor placed on the skin, the prototype microwave radar system is particularly suitable for evaluating the JVP waveform.

微波视觉与SAR图像智能解译

高分辨率雷达成像技术和人工智能、大数据技术的快速发展,有力促进了雷达图像智能解译技术的进步。由于雷达传感器本身的特殊性和电磁散射成像物理的复杂性,雷达图像的解译缺乏光学图像的直观性,准确迅速识别分类的需求对雷达图像解译提出了迫切的挑战。在借鉴人脑光视觉感知机理和计算机视觉图像处理相关技术基础上,进一步融合电磁散射物理规律及其雷达成像机理,我们提出发展微波域雷达图像解译的“微波视觉”的新交叉领域研究。该文介绍微波视觉的概念与内涵,提出微波视觉认知模型,阐述其基础理论问题与技术路线,最后介绍了作者团队在相关问题上的初步研究进展。

雷达抗前门耦合攻击防护能力对比分析

针对雷达遭受高功率微波武器攻击时容易损伤的问题,理论分析了雷达最远防护边界和雷达天线增益及接收机限幅器能力的关系,从空间滤波的角度,对比了反射面雷达和有源相控阵雷达抗前门耦合攻击的能力。分析得出只有高功率微波武器处于反射面雷达天线的主瓣范围附近时,对其前门耦合攻击效果才强于有源相控阵雷达;反之,要弱于有源相控阵雷达。由于反射面天线雷达主波束很窄,造成攻击的时机很短,所以反射面雷达在面对高功率微波武器时防护能力更强。