Increasing Angle Of Incidence Research Articles

Preparation of ring-shaped frequency selective fabrics and analysis of electromagnetic transmission characteristics

In order to explore the feasibility of preparing frequency selective fabrics by computer embroidery technology, two complementary ring-shaped structures were selected for design in this paper. Several samples with different size parameters were prepared by the computer embroidery process, and the electromagnetic transmission characteristics were systematically tested using the free-space method. The effects of unit type, electromagnetic wave polarization mode, incident angle, unit size parameters and processing methods on different samples were analyzed in depth. The results show the aperture-type and patch-type samples have obvious band-pass and band-stop characteristics in the test frequency range, respectively, but there are some differences in the resonance frequency and peak of the complementary structure samples of the same size. Different parameters have dissimilar influences on the electromagnetic transmission characteristics. With the increase in incident angle, the frequency selective characteristics of two complementary structures are gradually weakened, and the aperture structure has higher angular stability. Under the conditions of different electromagnetic wave polarization modes and incident angles, the computer embroidery samples have good frequency selective characteristics, which demonstrates the effectiveness of computer embroidery processing technology. However, compared with the ideal computer-based carving sample, there is a certain gap in the resonance peak, and the electromagnetic loss is large. The processing accuracy of the computer embroidery technology needs to be explored further.

Propagation Characteristics of Obliquely Incident Terahertz Waves in High-Temperature Magnetized Plasma

Propagation characteristics of obliquely incident terahertz waves in high-temperature magnetized plasma are studied by the scattering matrix method (SMM) and Wentzel–Kramers–Brillouin (WKB) method. Three cases of electron density distribution (uniform, double exponential, and Epstein distributions) are considered. Numerical simulation exhibits that the SMM can give out the nearly same results with the WKB method, which indicates that these two methods work very well for solving this problem. Through the analysis of the incident angle, we found that as the incident angle increases, it is not conducive to the transmission of left-handed circularly polarized (LCP) waves and right-handed circularly polarized (RCP) waves. When the incident angle increases to a certain value, the phenomenon of “total reflection” will appear. We also systematically calculated the influence of physical parameters such as electron density, collision frequency, plasma thickness, magnetic field strength, and electron temperature on the transmission characteristics. These theoretical results are helpful to alleviate “blackout” problem and improve communication quality.

A Study on the Electromagnetic-Thermal Coupling Effect of Cross-Slot Frequency Selective Surface.

In high-power microwave applications, the electromagnetic-thermal effect of frequency selective surface (FSS) cannot be ignored. In this paper, the electromagnetic-thermal coupling effects of cross-slot FSS were studied. We used an equivalent circuit method and CST software to analyze the electromagnetic characteristics of cross-slot FSS. Then, we used multi-field simulation software COMSOL Multiphysics to study the thermal effect of the FSSs. To verify the simulation results, we used a horn antenna with a power of 20 W to radiate the FSSs and obtain the stable temperature distribution of the FSSs. By using simulations and experiments, it is found that the maximum temperature of the cross-slot FSS appears in the middle of the cross slot. It is also found that the FSS with a narrow slot has severer thermal effect than that with a wide slot. In addition, the effects of different incident angles on the temperature variation of FSS under TE and TM polarization were also studied. It is found that in TE polarization, with the increase in incident angle, the maximum stable temperature of FSS increases gradually. In TM polarization, with the increase in incident angle, the maximum stable temperature of FSS decreases gradually.

Investigating the PS seismic imaging of faults using seismic modelling and data from the Snøhvit field, Barents Sea

PS seismic data from the Snøhvit field are compared with seismic modelling to understand the effect of azimuthal separation and incidence angle on the imaging of faults and associated horizon discontinuities. In addition, the frequency content of seismic waves backscattered from faults is analysed. The study area consists of a horst structure delimited by a northern fault dipping NW and oblique to the east–west survey orientation, and a southern fault dipping SSW and subparallel to the survey. Due to the raypath asymmetry of PS reflections, the northern fault is imaged better by azimuthally partitioned W data that include receivers downdip of the fault, relative to the sources, than by E data where the receivers are updip from the sources. Partial stack data show a systematic increase in the PS fault-reflected amplitude and therefore quality of fault imaging with increasing incidence angle. Fault images are dominated by internal low-medium frequency shadows surrounded by medium-high frequencies haloes. Synthetic experiments suggest that this is due to the interaction of specular waves and diffractions, and the spectral contribution from the fault signal, which increases with fault zone complexity. These results highlight the impact of survey geometry and processing workflows on fault imaging. Supplementary material: model description, processed sections and videos are available at https://doi.org/10.6084/m9.figshare.c.5727552

Vortex dynamics and entropy generation in separated transitional flow over a compressor blade at various incidence angles

The transition process within a Laminar Separation Bubble (LSB) that formed on a compressor blade surface was investigated using Large Eddy Simulations (LESs) at a Reynolds number of 1.5 × 105 and incidence angles of 0°, +3°, and +5°. The vortex dynamics in the separated shear layers were compared at various incidence angles and its effects on the loss generation were clarified through entropy analysis. Results showed that transition onset, which was accurately identified by the Linear Stability Theory (LST), was significantly promoted at the increased incidence angle. As such, the development of LSB was suppressed and the relative role of viscous instability played in the transition process was weakened. At the incidence angle of 0°, two-dimensional spanwise vortices detached from the blade surface and rolled up periodically, which were further stretched and eventually evolved into large-scale hairpin vortices. As time passed, the fully developed hairpin vortices broke down into small-scale eddies. Meanwhile, the flow near the wall reversely ejected into the outer separated shear layers and a sweeping process happened subsequently, forcing the separated shear layers to reattach and accelerating the generation of turbulent fluctuations. By comparison, the strength of vortex rolling-up was weakened at higher incidence angles, and the vortex pairing and breakdown of large-scale vortices were less pronounced. Therefore, the level of turbulent fluctuations that generated in the separated shear layers was reduced. Detailed entropy analysis showed that the turbulent dissipation effect related to the Reynolds shear stresses determined the largest amount of positive entropy generation, which declined to a lower level as the incidence angle increased from 0° to +5°. Correspondingly, the profile loss was reduced by 50.4%.

Dual-band metamaterial absorber with a low-coherence composite cross structure in mid-wave and long-wave infrared bands.

The atmospheric window in the infrared (IR) band primarily consists of mid-wave (MWIR, 3-5 μm) and long-wave IR (LWIR, 8-12 μm) bands, also known as the working bands in most of the IR devices. The main factor affecting the device capability includes the absorption efficiency, hence, the absorption material. Herein, a dual-band absorber based on the composite cross structure (CCS) in both MWIR and LWIR bands was proposed, with absorption peaks of 4.28 μm and 8.23 μm. The obtained absorber is with high scalability in the MWIR and LWIR region respectively by tuning the structural parameters. A quadrupole polarization model is proposed for further understanding of the uneven distribution of electromagnetic field that was caused by the change of the center spacing of the embedded structure. Meanwhile, it was shown that the two absorption peaks exhibited good incident angle stability. In addition, as the incident angle of the TM mode increases, a waveguide is formed between the embedded structure and the surface structure, leading to another strong absorption in the LWIR band. The results showed that absorption increases as the incident angle increases. The proposed absorber can be a good candidate for applications in thermal emission, detection and solar energy harvesting.

Energy Loss and Radial Force Variation Caused by Impeller Trimming in a Double-Suction Centrifugal Pump.

Impeller trimming is an economical method for broadening the range of application of a given pump, but it can destroy operational stability and efficiency. In this study, entropy production theory was utilized to analyze the variation of energy loss caused by impeller trimming based on computational fluid dynamics. Experiments and numerical simulations were conducted to investigate the energy loss and fluid-induced radial forces. The pump’s performance seriously deteriorated after impeller trimming, especially under overload conditions. Energy loss in the volute decreased after trimming under part-load conditions but increased under overload conditions, and this phenomenon made the pump head unable to be accurately predicted by empirical equations. With the help of entropy production theory, high-energy dissipation regions were mainly located in the volute discharge diffuser under overload conditions because of the flow separation and the mixing of the main flow and the stalled fluid. The increased incidence angle at the volute’s tongue after impeller trimming resulted in more serious flow separation and higher energy loss. Furthermore, the radial forces and their fluctuation amplitudes decreased under all the investigated conditions. The horizontal components of the radial forces in all cases were much higher than the vertical components.

A Sensor Based on One-Dimensional Cylindrical Photonic Crystals and Graphene Elements With a Higher Quality Factor and a Wider Measurement Range

In this paper, a new structure for the sensing and detection of refractive index (RI) based on the one-dimensional cylindrical photonic crystals containing the graphene elements with a higher quality factor (QF) and a wider measurement range are theoretically investigated by the transfer matrix method. The sensing function of the presented structure is that, under impedance matching conditions, the defect cavity captures the tunnel optical Tamm state, and then generates high absorption through electromagnetic resonance. The obtained results show that it is almost unaffected for the sensor in measuring by minor chemical potential, core radius, loss tangent value, and smaller manufacturing roughness. Consequently, it is very tolerant of the working environment and the production industry. However, it is angle-sensitive. As the incident angle ( θ) increases, the sensitivity (S) is enlarged obviously, but the linear area of the sensor shrinks by a large margin. So, the choice of θ should be considered comprehensively. The proposed sensor provides relatively higher performance, ranging from 1.0 ~ 2.8, the S is equivalent to 117.639 nm/RIU, and the average figure of merit is 2707.804. In addition, the average QF arrives at 29906.059. The average detection limit (DL) is 0.0001688 nm, and the lowest DL reaches 0.000006715 nm. In overall sensors, owing to the much-needed to identify substances in the fields of biology, chemistry, environmental monitoring, food safety biological analysis, engineering, and military, the RI sensors are demanded desperately, and it is so far more than other sensor types to research.

Improving the Specular Point Positioning Accuracy of Ship-Borne GNSS-R Observations in China Seas Based on Comprehensive Geophysical Correction

The accurate modeled GNSS-R reflection delay, which is indispensable for the quantification, modeling, and correction of the GNSS-R altimetry sea-state bias, can be obtained based on the accurate modeled position of the specular point. At present, the reflection surface model of the specular point positioning still has the mean dynamic topography (MDT) error and the deviation of the vertical (DOV) error relative to the instantaneous sea surface. In this study, the following studies have been carried out. Based on the ship-borne GNSS-R observations in China seas, we introduced various elevation parameters including the MDT to correct the elevation error of the reflection surface. We introduced the DOV based on the elevation correction, and the DOV correction positioning method was proposed to correct the slope error of the reflection surface. The specular point was positioned on the instantaneous sea reflection surface. We verified the instantaneous sea reflection surface model and the specular point positioning results, analyzed the relationship between the position correction distance and the reflection incident angle, and discussed the spatial distribution characteristics of the MDT correction distance. The results showed that the reflection surface modeling and the specular point positioning were accurate. The positioning error increased to varying degrees with the increase of the reflection incident angle. The MDT correction improved the positioning by 0.91 m, and the DOV correction further improved the positioning by 0.12 m. Based on the combined application of the two kinds of correction positioning, the positioning was comprehensively improved by 0.99 m. The MDT correction of China seas gradually increased from the north to south. While in the regional sea areas, it gradually decreased from the north to south and showed randomness. The relative position between the antennas and their random changes introduced uncertainty, which can be reduced by integration. The new instantaneous sea reflection surface model and the corresponding specular point positioning method can provide accurate modeled reflection delay for the sea-state bias correction of ship-borne GNSS-R observations, and they can be extended to satellite-borne global observations.

The Critical Capture Velocity of Coal Ash Particles Oblique Impact on a Stainless Steel Surface

In this paper, the rebound characteristics of coal ash particles impacting on a stainless steel surface are studied experimentally with the background of ash deposition on the heating surface of the boiler. The impact processes of coal ash particles with different incident angles were recorded by high-speed digital camera technology. The evolution of the normal restitution coefficient with incident normal velocity was obtained. Three different static contact theories are used to establish the equations of motion to predict the critical capture velocity of particles. The results show that the normal restitution coefficient first increases and then decreases with the increase of incident normal velocity. The critical capture velocity of particles under the three models was predicted. It is found that the prediction results of the Brach and Dunn (BD) model for the critical capture velocity are close to the experimental results. Taking the particle of size 23 μm as an example, the maximum critical capture velocity predicted by BD model is 1.0611 m/s at 0° incident angle. The minimum value is 0.7940 m/s when the incident angle is 45°.The critical capture velocity of particles decreases with the increase of incident angle and with the increase of particle diameter.

Automated Rain Detection by Dual-Polarization Sentinel-1 Data

Rain Signatures on C-band Synthetic Aperture Radar (SAR) images acquired over ocean are common and can dominate the backscattered signal from the ocean surface. In many cases, the inability to decipher between ocean and rain signatures can disturb the analysis of SAR scenes for maritime applications. This study relies on Sentinel-1 SAR acquisitions in the Interferometric Wide swath mode and high-resolution measurements from ground-based weather radar to document the rain impact on the radar backscattered signal in both co- and cross-polarization channels. The dark and bright rain signatures are found in connection with the timeliness of the rain cells. In particular, the bright patches are demonstrated by the hydrometeors (graupels, hails) in the melting layer. In general, the radar backscatter under rain increases with rain rate for a given sea state and decreases when the sea state strengthens. The rain also has a stronger impact on the radar signal in both polarizations when the incidence angle increases. The complementary sensitivity of the SAR signal of rain in both channels is then used to derive a filter to locate the areas in SAR scenes where the signal is not dominated by rain. The filter optimized to match the rain observed by the ground-based weather radar is more efficient when both polarization channels are considered. Case studies are presented to discuss the advantages and limitations of such a filtering approach.

Broadband wide-angle multilayer absorber based on a broadband omnidirectional optical Tamm state.

Recently, broadband optical Tamm states (OTSs) in heterostructures composed of highly lossy metal layers and all-dielectric one-dimensional (1D) photonic crystals (PhCs) have been utilized to realize broadband absorption. However, as the incident angle increases, the broadband OTSs in such heterostructures shift towards shorter wavelengths along the PBGs in all-dielectric 1D PhCs, which strongly limits the bandwidths of wide-angle absorption. In this paper, we realize a broadband omnidirectional OTS in a heterostructure composed of a Cr layer and a 1D PhC containing layered hyperbolic metamaterials with an angle-insensitive photonic band gap. Assisted by the broadband omnidirectional OTS, broadband wide-angle absorption can be achieved. High absorptance (A > 0.85) can be remained when the wavelength ranges from 1612 nm to 2335 nm and the incident angle ranges from 0° to 70°. The bandwidth of wide-angle absorption (0°-70°) reaches 723 nm. The designed absorber is a lithography-free 1D structure, which can be easily fabricated under the current magnetron sputtering or electron-beam vacuum deposition technique. This broadband, wide-angle, and lithography-free absorber would possess potential applications in the design of photodetectors, solar thermophotovoltaic devices, gas analyzers, and cloaking devices.

The broadband and omnidirectional antireflective performance of perovskite solar cells with curved nanostructures

Various shaped nanostructures have been continually used in the antireflection of organic-inorganic hybrid perovskite solar cells. A full understanding of the shape-dependent light trapping behavior is the basis for finding the excellent broadband and omnidirectional photovoltaic performance. Hence, three-dimensional models of silica sphere, hemisphere, moth-eye and cone nanostructured perovskite solar cells were performed at omnidirectional angle in this work. We proposed electric field intensity per volume as a key parameter, verifying the transition of light trapping modes of several curved nanostructures from normal incidence to oblique incidence. As the incident angle increases, the antireflection effect of four curved structures becomes increasingly crucial, and the differences among them are also greater. Consequently, the moth-eye nanostructured perovskite solar cell has achieved the best photovoltaic performance considering omnidirectional incidence. The short-circuit current density is increased by 8.4% at normal incidence and increased by 36.4% at 60° incidence compared to the planar reference. Our work offers the theoretical analysis for omnidirectional antireflection structure optimization, and provides guidance for the experimental research and production of potential antireflection structures of solar cell.

Exploring the heat transfer for spherical nanoparticles under electron irradiation

To explore the thermal effect of an electron beam irradiation during a scanning electron microscope (SEM) imaging process, a Monte Carlo (MC) method has been used to calculate the spatial distributions of local temperature rise in a spherical gold (Au) nanoparticle (i.e. Au Nano sphere (Au-NS)). The influencesofthe size of the nanoparticle, incident angle of the primary electron (PE) beam, PE energy and the PE beam size on the heat generation were systematically investigated. First of all, this work verified that Au-NSs with various sizes present different heat capacities under the same condition of the electron irradiation. The smaller the sphere, the less heat is accumulated. Besides, the heat in the periphery of a relatively large Au-NS is less than that inside. As the incident angle increases, the distribution regions of the temperature rise gradually expand from the contact surface deep into the interior and its amount rises proportionately. This rule is the same for an Au-NS with the diameter of 40 nm under various PE energies, but is quite opposite for the case of an Au-NS with the diameter of 5 nm. This study next presents that the PE beam size affects the heat generation in a spherical Au nanoparticle significantly. The distribution of temperature rise specifically shows a gradually reduced intensity towards the larger PE beam size. In addition, this work found that the total electron (TE) line-scan profile inversely relates the temperature contour map. The underlying mechanisms of these results were explained in detail primarily with the analysis of the trajectory of electrons as well as the interaction of electron-solid. This work, on the one side, greatly benefits the study of the relationship between the sample structures and the local thermal effect under the electron irradiation. On the other side, this work provides a further understanding and elucidation of the mechanism of electron-beam-induced deposition, compared to those earlier reports only focusing on plane bulks. It is believed that the proceeding of the semiconductor industry would be significantly promoted by this study.

Comparison of a standard elliptical Bessel beam and a refracted circular Bessel beam at oblique incidence

An analytical expression of an elliptical Bessel beam (EBB) is deduced on the basis of the angular spectrum decomposition (ASD) method, starting from an elliptical Bessel-like profile in the initial transverse plane. The angular spectrum representation is also obtained for another approximate EBB that is produced by the refraction of a circular Bessel beam at an interface in oblique incidence. The expressions are further expanded into a series of vector spherical harmonic functions for describing the scattering of the beams by a spherical particle. Numerical calculations are implemented with different parameters and the results are discussed. A length parameter is obtained for evaluating the variation of the EBB along the propagation. It is confirmed that the refracted CBB at small incident angle behaves in a similar way to the EBB. When the incident angle increases, the asymmetry of the transverse beam profile becomes serious and the propagation of the beam deviates gradually from the predicted direction.

Prediction of submarine pipeline equilibrium scour depth based on machine learning applications considering the flow incident angle

Scouring below submarine pipelines, due to fluid, structure and soil material interaction, is a complex phenomenon involving numerous effective parameters. In this research, machine learning methods, such as the GA-BP (Genetic Algorithm based Back Propagation) neural network, RBF (Radial Basis Function) and SVM (Support Vector Machine) are presented and prediction models are built for forecasting pipeline equilibrium scour depth. The results of the prediction models are compared with observed data, which shows that the GA-BP model provides the best predictive performance for scour depth exhibiting highest correlation coefficient and lowest Root Mean Square Error as compared with RBF, SVM in live-bed conditions. Results of the sensitivity analysis indicate that Froude number (Fr) is the most effective parameter for predicting the scouring depth below the pipeline. With the increase of flow incident angle, its influence on the predicted scour depth results becomes more obvious.

Atomistic-scale investigations of hyperthermal oxygen–graphene interactions via reactive molecular dynamics simulation: The gas effect

Hyperthermal atomic oxygen (AO) bombardment to thermal protection system surface has been identified to impact the aerodynamic heating significantly, due to complex chemical reactions at the gas–solid interface, e.g., surface catalysis recombination, oxidation, and ablation. Previous investigations have focused on the surface effects of the AO collision process, while the influence of impacting gas characteristics remains unclear under various non-equilibrium aerodynamic conditions. This work conducts a reactive molecular dynamics (RMD) study of AO collisions over graphene surface, by considering the incoming gas at different translational energies (0.1 ≤ Ek ≤ 10 eV), incident angles (θ = 15°, 30°, 45°, 60°, 75°, and 90°), and O/O2 ratios (χO2 = 0.00, 0.25, 0.50, 0.75, and 1.00). The RMD results indicate that for AO normal incidence, the predominant reactive products of O2, CO, and CO2 molecules are produced due to the synergistic catalytic recombination and surface ablation reaction effects. A maximum recombination performance is identified around 5-eV AO incidence. For off-normal AO incidence, the recombination coefficient increases with the increase in incidence angle from 15° to 60° due to the larger perpendicular components of translational energy and then decreases smoothly. With the increase in O2 mole fraction, the surface reflection probabilities increase, which result in the decrease in both catalytic recombination and ablation activities. Via revealing the atomistic-scale mechanism of gas effects on the surface under hypersonic non-equilibrium conditions, this work sheds light for the future design and optimization of thermal protection materials.

Single-Mode Lasing in Polymer Circular Gratings.

In recent years, conjugated polymers have become the materials of choice to fabricate optoelectronic devices, owing to their properties of high absorbance, high quantum efficiency, and wide luminescence tuning ranges. The efficient feedback mechanism in the concentric ring resonator and its circularly symmetric periodic geometry combined with the broadband photoluminescence spectrum of the conjugated polymer can generate a highly coherent output beam. Here, the detailed design of the ultralow-threshold single-mode circular distributed feedback polymer laser is presented with combined fabrication processes such as electron beam lithography and the spin-coating technique. We observe from the extinction spectra of the circular gratings that the transverse electric mode shows no change with the increase of incident beam angle. The strong enhancement of the conjugated polymer photoluminescence spectra with the circular periodic resonator can reduce the lasing threshold about 19 µJ/cm2. A very thin polymer film of about 110 nm is achieved with the spin-coating technique. The thickness of the gain medium can support only the zero-order transverse electric lasing mode. We expect that such a low threshold lasing device can find application in optoelectronic devices.

Investigation on the Damage Mode and Anti-penetration Performance of B4C/UHMWPE Composite Targets for Different Incident Velocities and Angles

To found out the effects of incident velocity and incident angle on the damage mode and anti-penetration performance of ceramic composite targets, and provide a certain basis for optimizing the structural design of ceramic composite armor. The penetration of 7.62 mm bullet into oblique boron carbide (B4C)/UHMWPE composite target was investigated by ballistic testing and numerical simulation. The effects of incident velocity and incident angle on the fragmentation degree of bullet and ceramic panel were analyzed, also the damage mode of bullet penetrating ceramic composite target was developed preliminarily to estimate the anti-penetration performance of ceramic composite targets. Based on the testing and simulation results, it was found that the fragmentation degree of bullet and ceramic panel increases gradually with the increase of incident velocity and incident angle, but the fragmentation degree of bullet and ceramic panel decreases obviously when the incident velocity exceeds the ballistic limit; the damage mode of UHMWPE laminate is mainly tensile failure when the bullet’s incident velocity is lower than the ballistic limit, and the increase of incident velocity or incident angle makes UHMWPE laminate more prone to shear failure and delamination failure. With the increase of incident angle, the ballistic limit of B4C/UHMWPE composite target increases significantly, the deflection angle of bullet increases similarly, and the optimal thickness ratio of ceramic panel and backplate tends to decrease with the increase of incident angle.

Retrievals of soil moisture and vegetation optical depth using a multi-channel collaborative algorithm

Due to the success of the SMOS (Soil Moisture and Ocean Salinity) and SMAP (Soil Moisture Active Passive) missions, new satellite missions are on the horizon. The current and future missions can benefit from investigations that seek to improve retrieval algorithms that quantitatively map global soil moisture and vegetation optical depth (tau) from Earth's microwave emissions. In this study, we explore multi-angular and multi-frequency approaches for the retrieval of soil moisture and vegetation tau, considering the payload configurations of current and future satellite missions (such as the Copernicus Imaging Microwave Radiometer, the Water Cycle Observation Mission, and the Terrestrial Water Resources Satellite) using a new set of ground observations. Two ground-based microwave radiometry datasets collected in Inner Mongolia during the Soil Moisture Experiment in the Luan River from July to August 2017 (cropland) and August to September 2018 (grassland) are used for this study. The corn field, which covers an entire growth period, indicated that the degree of information increases linearly as the number of channels (in terms of the incidence angle and frequency) increases, and that the multi-frequency observations contain slightly more independent information than do the multi-angular observations under the same number of channels. The polarization difference in brightness temperature is sensitive to both soil moisture and vegetation water content, especially at L-band due to its penetrating ability. Soil moisture explains most of the variance in frequency differences of brightness temperature at adjacent frequencies (L- & C-bands, C- & X-bands), while the variance in incidence-angle differences of brightness temperature is mostly associated with the vegetation water content. A multi-channel collaborative algorithm (MCCA) is developed based on the two-component version of the omega-tau model, which utilizes information from collaborative channels expressed as an analytical form of brightness temperature at the core channel to rule out the parameters to be retrieved. Results of soil moisture retrieval show that the multi-angular approach used by the MCCA generally has a better performance, unbiased root mean square difference (ubRMSD) varying from 0.028 cm3/cm3 to 0.037 cm3/cm3, than the multi-frequency approach (ubRMSD from 0.028 cm3/cm3 to 0.089 cm3/cm3) for the corn field. This is attributed to the dependence of vegetation tau on the frequency being more significant than that on the incidence angle. Except for in the C- & X-band combination, the multi-frequency approach used by the MCCA performs better (ubRMSD from 0.018 cm3/cm3 to 0.023 cm3/cm3) than the multi-angular version (ubRMSD from 0.026 cm3/cm3 to 0.034 cm3/cm3) for the grass field due to reduced vegetation effects for this type of cover. It is affirmed that increasing the number of observation channels could make the soil moisture retrieval more robust, but might also limit the retrieval performance, as the probability that the model estimations will not match the observations is increased. This study provides new insights into the design of potential satellite missions to improve soil moisture retrieval. A satellite with simultaneous multi-angular and multi-frequency observation capabilities is highly recommended.