Low-altitude Sensing of Urban Atmospheric Turbulence with UAV

The capabilities of a quadcopter in the hover mode for low-altitude sensing of atmospheric turbulence with high spatial resolution in urban areas characterized by complex orography are investigated. The studies were carried out in different seasons (winter, spring, summer, and fall), and the quadcopter hovered in the immediate vicinity of ultrasonic weather stations. The DJI Phantom 4 Pro quadcopter and AMK-03 ultrasonic weather stations installed in different places of the studied territory were used in the experiment. The smoothing procedure was used to main regularities in the behavior of the longitudinal and lateral spectra of turbulence in the inertial and energy production ranges. The longitudinal and lateral turbulence scales were estimated by the least-square fit method with the von Karman model as a regression curve. It is shown that the turbulence spectra obtained with DJI Phantom 4 Pro and AMK-03 generally coincide with minor differences observed in the high-frequency region of the spectrum. In the inertial range, the behavior of the turbulence spectra shows that they obey the Kolmogorov-Obukhov “5/3” law. In the energy production range, the longitudinal and lateral turbulence scales and their ratio measured by DJI Phantom 4 Pro and AMK-03 agree to a good accuracy. Discrepancies in the data obtained with the quadcopter and the ultrasonic weather stations at the territory with complex orography are explained by the partial correlation of the wind velocity series at different measurement points and the influence of the inhomogeneous surface.

Mechanical and Thermomechanical Properties of Clay-Cowpea (Vigna Unguiculata Walp.) Husks Polyester Bio-Composite for Building Applications

This study investigates the feasibility of creating a clay polymer-based composite using cowpea husk (CPH) as filler for production of roof tiles. Polymeric composites were fabricated by mixing unsaturated polyester (UPT) resin with cowpea husk at different filler weights and curing. A hybrid composite was produced with the addition of 3 wt.% clay and all samples produced were subjected to flexural, hardness and dynamic mechanical analysis (DMA) tests. The effect of clay addition on the mechanical and thermo-mechanical behaviour of formulated composites was investigated. The morphological analysis of the mono and hybrid system shows a rough and coarse inhomogeneous surface with voids created due to the addition of CPH filler for the mono reinforced and clay uniformly filling the voids that were created by the CPH in the hybrid composite. It is observed that hardness, tensile modulus and flexural modulus of hybrid composites increase with an increase in the CPH contents, while the strength and flexural strength all decrease with filler content. The optimal composition was obtained using Grey relational analysis (GRA) at 18% CPH for both mono and hybrid composite. The results imply that the composite combination can be used in making rooftiles and/or also in applications where low strength is required.

Preparation of spheres based on NiO using cation with gel and macroporous structure

The article discusses the production of materials based on nickel oxide in the form of spherical granules ranging in size from 300 to 700 nm, by the method of thermal destruction of cation exchangers with gel (TOKEM-100)and macroporous (TOKEM-250) structures saturated with nickel (II) ions. Thermal analysis was used to establish the temperature regimes of annealing of Ni2+–ТОКЕМ-250 и Ni2+–ТОКЕМ-100 samples. The prepared materials were investigated by XRD and SEM. The use of TOKEM-100 cation exchanger makes it possible to obtain samples with spherical granules based on trigonal nickel (II) oxide, characterized by a sintered surface morphology. The use of TOKEM-250 cation exchanger leads to the formation of spheres based on NiO cubic modification with an inhomogeneous surface morphology.

Airborne measurements of directional reflectivity over the marginal sea ice zone

The directional reflection of solar radiation by the Arctic Ocean is dominated by two main surface types: sea ice (often snow-covered) and ice-free (open) ocean. However, in the transitional marginal sea ice zone (MIZ), the reflection properties of both surface types are mixed, which might cause uncertainties in the results of retrieval methods of atmospheric parameters over the MIZ using airborne and satellite measurements. To quantify these uncertainties, respective measurements of reflection properties of the MIZ are needed. Therefore, in this study, an averaged hemispherical-directional reflectance factor (HDRF) of the inhomogeneous surface (mixture of sea ice and open ocean surfaces) in the MIZ is derived using airborne measurements collected with a digital fish-eye camera. For this purpose, a sea ice mask was constructed to separate the reflectivity measurements from sea ice and open ocean pixels. The separated data sets were accumulated and averaged to provide separate HDRFs for sea ice and open ocean surfaces. The respective results were compared with simulations and independent measurements available from the literature. Using the sea ice fraction derived in parallel from the digital camera images, the mixed HDRF describing the directional reflectivity of the inhomogeneous surface of the MIZ was reconstructed by a linear weighting procedure. The result was compared with the original measurements of directional reflectivity over the MIZ. It is concluded that the HDRF of the MIZ can be well reconstructed by linear combination of the HDRFs of homogeneous sea ice and open ocean surfaces, accounting for the special conditions present in the MIZ compared to homogeneous surfaces.

Inversion for Inhomogeneous Surface Duct without a Base Layer Based on Ocean-Scattered Low-Elevation BDS Signals

The anomalous propagation conditions, particularly the tropospheric ducts, severely impact the regular operation and performance evaluation of radio devices in the atmospheric boundary layer. Therefore, it is necessary to provide the regional distribution of tropospheric ducts for utilizing or avoiding these abnormal propagation phenomena. As significant uncooperative signal sources, the global navigation satellite systems (GNSS) have been widely applied in the remote sensing of the ocean and atmosphere due to the greater convenience and lower cost. With the completed deployment of the BeiDou Navigation Satellite System (BDS) in 2020, an additional source can be chosen in the relevant studies. Taking the BDS as an example, since the scattered signals from the ocean surface at low satellite elevation angles can be effectively trapped by tropospheric ducts, we propose a method to invert for the regional distribution of tropospheric ducts using the received power of ocean-scattered signals in this paper. Firstly, the propagation model was built to calculate the received power, and a suite of simulations was made in various atmospheric environments. The results suggested that the received power is more sensitive to the surface duct without a base layer. Then, we made a preliminary estimation of the tropospheric ducts on the ocean nearby Qingdao utilizing the Weather Research and Forecasting (WRF) model as well as the echo data measured by a Doppler weather radar. Before the inversion, the actual satellite azimuth and elevation angles should be obtained to evaluate the bistatic scattering coefficients and the received powers of the selected satellite signals. Finally, we presented an inversion example using the proposed method. In absence of the actual measurements, the received powers pre-estimated at different SNRs served as the inputs of the inversion process and the estimated duct parameters were used to verify the validity of the proposed inversion method. For both the received power and modified refractivity profile, the fitness between the values pre-estimated using the estimated duct parameters and calculated by the inverted duct parameters gets better as the elevation angle decreases and the SNR increases. The variation of the fitness between the estimated and inverted values is slightly different for each duct parameter. Moreover, the calculation of inversion errors further explained the above behaviors, including the mean absolute error (MAE) and the root mean square error (RMSE). Despite some certain errors, the inversion results maintain the overall tendencies and most characteristics of the estimated values, thus proving the validity of the inversion method.

Electrically Tuneable Optical Diffraction Gratings Based on a Polymer Scaffold Filled with a Nematic Liquid Crystal

We present an experimental and theoretical investigation of the optical diffractive properties of electrically tuneable optical transmission gratings assembled as stacks of periodic slices from a conventional nematic liquid crystal (E7) and a standard photoresist polymer (SU-8). The external electric field causes a twist-type reorientation of the LC molecules toward a perpendicular direction with respect to initial orientation. The associated field-induced modification of the director field is determined numerically and analytically by minimization of the Landau–de Gennes free energy. The optical diffraction properties of the associated periodically modulated structure are calculated numerically on the basis of rigorous coupled-wave analysis (RCWA). A comparison of experimental and theoretical results suggests that polymer slices provoke planar surface anchoring of the LC molecules with the inhomogeneous surface anchoring energy varying in the range 5–20 μJ/m2. The investigated structures provide a versatile approach to fabricating LC-polymer-based electrically tuneable diffractive optical elements (DOEs).

A New Linear Relation for Estimating Surface Broadband Emissivity in Arid Regions Based on FTIR and MODIS Products

Broadband emissivity is a crucial parameter for calculating the radiation budget, still, it adopts a constant value in land surface models due to a lack of adequate observations. Arid regions have complex underlying surfaces and estimations of the broadband emissivity in such areas suffer from high spatial variation and uncertainty. Here, we propose a novel method for estimating broadband emissivity in the 8–14 µm range based on Fourier-transform infrared spectroscopy (FTIR) observations, moderate resolution imaging spectrometer (MODIS) emissivity, the leaf area index (LAI) and reflectance products. The proposed method exploits FTIR observations, MODIS single-channel emissivity, reflectance and the LAI to fit a linear regression of the broadband emissivity, so the optimal equation includes emissivity, reflectance and the LAI, with an R2 and root-mean-squared error of 0.942 and 0.08. Then we used the proposed method to generate a broadband emissivity map of Northwest of China, the broadband emissivity estimated by the method showed higher variations and finer distribution in arid areas and sparsely vegetated regions compared to data from the global land surface satellite and land model. An analysis of the relationship between the broadband emissivity, land-use type and soil moisture found an existing but not linear relationship, which indicated that the relationship was complicated under the inhomogeneous surface of wetness and vegetation. In conclusion, our results suggest that the proposed method can accurately estimate the broadband emissivity in arid regions. In future research, we will test the data in a land model.

On the question of using solid electrodes in the electrolysis of cryolite-alumina melts. Part 2. The mechanism of passivation and conditions of stable electrolysis

The aim was to investigate the mechanism of passivation of polycrystalline cathodes and to justify experimentally the possibility of stable electrolysis when using solid electrodes. Under laboratory conditions, the mechanism of electrode passivation and the conditions for stable electrolysis were experimentally studied. To this end, the methods of X-ray phase analysis and electron-microscopic examination of the spent electrodes were employed. A study of the electrolysis of cryolite-alumina melts showed that, in the presence of surface micro- and microdefects on a solid cathode, a precipitate consisting of impurities and electrolyte components was gradually formed. Under the selected experimental conditions, the surface of carbon cathodes was passivated with a dense double-layer precipitate of CaB6 and electrolyte components. Using the example of a carbon cathode containing both metallic titanium and titanium oxides, a method for eliminating surface microdefects is presented. This method consists in electrochemical borating of a carbon-titanium cathode. The conducted spectral electron microscopic and energy-dispersive analysis found that, during a 45-hour laboratory experiment at 980 °C and under a current density of 0.7 A/cm2, the inhomogeneous surface of the cathode was homogenized with a titanium diboride layer. At stable electrolysis parameters, an aluminum layer is electrodeposited on the cathode. A complex analysis of the electrolysis conditions, the appearance of the initial and spent carbon cathodes, and the data of analytical studies confirmed that micro- and macrodefects of the electrode cause the formation of a dense layer of deposits on the cathode. The established mechanism of passivation of a carbon cathode as a polycrystalline product can be applied to all composite electrodes, including those based on titanium diboride. A logical condition for the practical application of solid cathodes is the development of an electrolysis process with continuous surface reconditioning to decrease the chemical inhomogeneity and microdefects of the surface across the entire technological sequence.

Inhomogeneous surface of West Siberian peatland diagnosed by skin temperature distribution

<p>Skin temperature (Ts) plays a central role in shaping the land surface energy balance and is also widely available from remote sensing for model evaluation and data assimilation. Both offline land models and land–atmosphere coupled models still have difficulty in realistically simulating or predicting Ts. In the case of an inhomogeneous surface, under the same atmospheric conditions, there are patches of different skin temperature and different daily variability. This observational study reports variations of surface fluxes (turbulent, radiative, and soil heat) and ancillary atmospheric/surface/soil data based on in-situ measurements conducted at Mukhrino field station located in the middle taiga zone of the West Siberian Lowland. To measure the surface temperature, we used an infrared camera (TIR, ~8–14 mkm wavelength range) based on an unmanned aerial vehicle. This UAV-based system provides high-resolution multi-sensors data acquisition. It also provides maximal flexibility for data collection at low cost with minimal atmospheric influence, minimal site disturbance, flexibility in measurement planning, and ease of access to study sites (e.g., peatlands) in contrast with traditional data collection methods. e demonstrate that the temperature of the boggy surface has significant variability: depending on the time of day, temperature contrasts can reach more than 10 degrees, which is associated with different surface moisture and albedo. A technique has been developed for restoring the surface albedo from the data of IR measurements. Ground measurements have shown that the variations of temperature and humidity across the subsurface layer can be very large. Furthermore, these variations are directly related to the concept of a difference between the roughness length for momentum versus that for heat. Information about the ratio of z<sub>0</sub>/z<sub>0h</sub> is necessary in order to be able to use surface skin temperature from satellite remote sensing for the computation of surface fluxes. The relationship between the difference in skin temperature and soil contact temperature with the heat balance, especially with sensible heat fluxes and heat flux through the soil, is considered. The parametrizations obtained in this work can be used in Earth System models to represent wetland ecosystems.</p><p>The work was supported by RFBR grant 18-05-60126, by the Moscow Center for Fundamental and Applied Mathematics and within the grant of the Tyumen region Government in accordance with the Program of the World-Class West Siberian Interregional Scientific and Educational Center (National Project "Nauka").</p>