Standard Atmospheric Model Research Articles

A Tale of Two Molecules: The Underprediction of CO2 and Overprediction of PH3 in Late T and Y Dwarf Atmospheric Models

The sensitivity and spectral coverage of JWST are enabling us to test our assumptions of ultracool dwarf atmospheric chemistry, especially with regards to the abundances of phosphine (PH3) and carbon dioxide (CO2). In this paper, we use Near Infrared Spectrograph PRISM spectra (∼0.8−5.5 μm, R ∼ 100) of four late T and Y dwarfs to show that standard substellar atmosphere models have difficulty replicating the 4.1−4.4 μm wavelength range, as they predict an overabundance of phosphine and an underabundance of carbon dioxide. To help quantify this discrepancy, we generate a grid of models using PICASO, based on the Elf Owl chemical and temperature profiles, where we include the abundances of these two molecules as parameters. The fits to these PICASO models show a consistent preference for orders-of-magnitude higher CO2 abundances and a reduction in PH3 abundance as compared to the nominal models. This tendency means that the claimed phosphine detection in UNCOVER−BD−3 could instead be explained by a CO2 abundance in excess of standard atmospheric model predictions; however, the signal-to-noise ratio of the spectrum is not high enough to discriminate between these cases. We discuss atmospheric mechanisms that could explain the observed underabundance of PH3 and overabundance of CO2, including a vertical eddy diffusion coefficient (K zz) that varies with altitude, incorrect chemical pathways, or elements condensing out in forms such as NH4H2PO4. However, our favored explanation for the required CO2 enhancement is that the quench approximation does not accurately predict the CO2 abundance, as CO2 remains in chemical equilibrium with CO after CO quenches.

Geometric Factor Correction Algorithm Based on Temperature and Humidity Profile Lidar

Due to the influence of geometric factors, the temperature and humidity profile of lidar’s near-field signal was warped when sensing the air environment. In order to perform geometric factor correction on near-field signals, this article proposes different correction solutions for the Mie and Raman scattering channels. Here, the Mie scattering channel used the Raman method to invert the aerosol backscatter coefficient and correct the extinction coefficient in the transition zone. The geometric factor was the ratio of the measured signal to the forward-computed vibration Raman scattering signal. The aerosol optical characteristics were reversed using the corrected echo signal, and the US standard atmospheric model was added to the missing signal in the blind zone, reflecting the aerosol evolution process. The stability and dependability of the proposed algorithm were validated by the consistency between the visibility provided by the Environmental Protection Agency and the visibility acquired via lidar retrieval data. The near-field humidity data were supplemented by the interpolation method in the Raman scattering channel to reflect the water vapor transfer process in the temporal dimension. The measured transmittance curve of the filter, the theoretical normalized spectrum, and the sounding data were used to compute the delay geometric factor. The temperature was retrieved and the near-field signal distortion issue was resolved by applying the corrected quotient of the temperature channel. The proposed algorithm exhibited robustness and universality, enhancing the system’s detection accuracy compared to the temperature and humidity data constantly recorded by the probes in the meteorological gradient tower, which have a high correlation with the lidar observation data. The comparison between lidar data and instrument monitoring data showed that the proposed algorithm could effectively correct distorted echo signals in the transition zone, which was of great value for promoting the application of lidar in the meteorological monitoring of the urban canopy layer.

Simulation and analysis of the CO2 range-resolved differential absorption lidar system at 2 μm

The range-resolved differential absorption lidar is a high-precision device to measure the concentration of carbon dioxide. This paper provides a system-wide theoretical analysis method for the performance analysis and parameter optimization of the lidar system using the given parameter range. The scattered echo signal, signal-to-noise ratio, and detection sensitivity were simulated by setting assumed parameters with the HITRAN 2020 database and the US 1976 standard atmosphere model to analyze the detection distance and concentration resolution of the lidar system. The effects of the laser energy, repetition frequency, and photodetector noise were also discussed. The wavelength selection near the absorption line is critical because it controls the height region of the highest sensitivity and the demands on frequency stability. Recommendations for the selection of absorption lines are provided in this paper. A quantitative analysis of each error source provided reasonable error ranges.

Titanium abundances in late-type stars

Context. Rapidly growing datasets from stellar spectroscopic surveys are providing unprecedented opportunities to analyse the chemical evolution history of our Galaxy. However, spectral analysis requires accurate modelling of synthetic stellar spectra for late-type stars, for which the assumption of local thermodynamic equilibrium (LTE) has been shown to be insufficient in many cases. Errors associated with LTE can be particularly large for Ti I, which is susceptible to over-ionisation, particularly in metal-poor stars. Aims. The aims of this work are to study and quantify the 1D non-LTE effects on titanium abundances across the Hertzsprung-Russell diagram for a large sample of stars. Methods. A large grid of departure coefficients, βν, were computed on standard MARCS model atmospheres. The grid extends from 3000 K to 8000 K in Teff, −0.5 dex to +5.5 dex in log g, and −5.0 to +1.0 in [Fe/H], with non-LTE effects in this grid reaching up to 0.4 dex. This was used to compute abundance corrections that were subsequently applied to the LTE abundances of over 70 000 stars selected from the GALAH survey in addition to a smaller sample of literature Keck data for metal-poor dwarfs. Results. The non-LTE effects grow towards lower [Fe/H], lower log g, and higher Teff, with a minimum and maximum ΔA(Ti)Ti I of 0.02 and 0.19 in the GALAH sample. For metal-poor giants, the non-LTE modelling reduces the average ionisation imbalance (ΔI−II) from −0.11 dex to −0.01 dex at [Fe/H] = −1.7, and the enhancement in titanium abundances from Ti I lines results in a [Ti/Fe] versus [Fe/H] trend that more closely resembles the behaviour of Ti II at low metallicities. At higher metallicities, the results are limited by the precision of the GALAH DR3 LTE abundances and the effects are within the errors. For the most metal-poor dwarfs from the Keck sample, the average ionisation imbalance increases from −0.1 dex to +0.2 dex, a shortcoming that is consistent with previous 1D non-LTE studies and which we speculate could be related to 3D effects. Conclusions. Non-LTE effects on titanium abundances are significant. Neglecting them may alter our understanding of Galactic chemical evolution. We have made our grid of departure coefficients publicly available, with the caveat that the Ti abundances of metal-poor dwarfs need further study in 3D non-LTE.

Improvement of the spaceborne synthetic aperture radar stereo positioning accuracy without ground control points

AbstractCompared with optical remote sensing satellites, the geometric positioning accuracy of synthetic aperture radar (SAR) satellite is not affected by satellite attitude or weather conditions. SAR satellites can achieve relatively high positioning accuracy without ground control points, which is particularly important in global surveying and mapping. However, the stereo positioning accuracy of SAR satellites is mainly affected by the SAR systematic delay and the atmospheric propagation delay of radar signals. An iterative compensation method for the SAR systematic time delay is proposed based on digital elevation model to improve the stereo positioning accuracy of SAR satellites without control points. In addition, to address the non‐real‐time updates of external reference atmospheric param, an iterative compensation method to estimate the atmospheric propagation delay of radar signals is proposed based on standard atmospheric models. In this study, SAR images from the Gaofen‐3 (GF‐3) satellite with 5 m resolutions were used as experimental data to verify the effectiveness of our proposed method. Simultaneously, the 2D positioning accuracy was better than 3 m and increased by 42.9%, and the elevation positioning accuracy was better than 3 m and increased by 90.2%.

Study of Atmospheric Depth Profiles at LHAASO Using the MSISE-90 Model

High Altitude Cosmic Ray Observatory (LHAASO) is located at Haizi Mountain in Daocheng County, Sichuan Province. Its Wide Field of view Cherenkov Telescope Array (WFCTA) primarily studies cosmic rays by observing the Cherenkov light signals produced during extensive air showers. Calibration, simulation, and reconstruction of WFCTA are all related to atmospheric depth. The currently used atmospheric depth model is the US Standard Atmosphere Depth Profile Model. In this study, the US Standard Atmosphere Depth Profile Model is compared with the atmospheric depth profile recorded by the infrared radiometer SABER carried by the satellite TIMED at LHAASO from 14 km to 50 km, as well as with the atmospheric depth recorded by the ground meteorological station at LHAASO. The atmospheric depth obtained from the US Standard Atmosphere Model is consistently smaller. The MSISE-90 atmospheric model describes the neutral temperature and density from the Earth's surface to the thermosphere. Further research shows good consistency between the MSISE-90 atmospheric model and the atmospheric depth recorded by TIMED/SABER and the ground standard meteorological station at LHAASO. According to the MSISE-90 atmospheric model, the mean atmospheric depth profile at LHAASO is lowest in January, followed by February, March, April, November, and December, which are also the optimal observation months for WFCTA operation. The atmospheric boundary layer is highest in April, and there is about 2% diurnal variation in atmospheric depth. Using the functional form of the US Standard Atmosphere Model, the atmospheric depth profiles from 4.4 to 100 kilometers were fitted for each month, obtaining monthly atmospheric depth profile models at the LHAASO site. And compared the lateral distribution of the Cherenkov photons produced by 100 TeV cosmic-ray protons incident at a zenith angle of 30° in the MSISE-90 atmospheric model and the US Standard Atmosphere Model,with the maximum difference reaching approximately 20%.

Model sensitivity of Tibetan Plateau surface potential vorticity and the Asian summer monsoon system to Asian orographic perturbation in FGOALS-f2

The thermodynamic forcing of the Tibetan Plateau (TP) is important for the regulation of the Asian summer monsoon (ASM). However, the monsoon responses to orographic perturbation simulations show controversial results in previously published literature. One reason for this is that the monsoon responses to orographic forcing differ among climate models. Another reason is that the quantitative changes in the TP thermodynamic forcing remain unknown when the orography is modified. Therefore, the relationship between the TP forcing and the ASM may be different among climate models. In this paper, the surface potential vorticity (SPV) is used to quantify the surface thermodynamic forcing on the TP in the FGOALS-f2 climate model for both the standard Atmospheric Model Intercomparison Project (AMIP) and Coupled Model Intercomparison Project (CMIP) experiments with a modified orography, and various aspects of the ASM responses are also examined. Finally, their relationships with TP-SPV changes are quantitively estimated. The results indicate that the intensity of TP-SPV is reduced by nearly 100% in the AMIP runs, while it is reduced by 68% in the CMIP runs when the Asian mountains are removed. Overall, the responses of the monsoon system are more sensitive when air-sea interactions are considered. When the mountains are removed, the precipitation over the southern slope of the TP decreases by 73% and increases by nearly 30% over the tropical Indian Ocean in the CMIP runs. Moreover, the precipitation responses exhibit the largest difference between the AMIP and CMIP runs over the East Asian and Western Pacific regions. The precipitation over the Western Pacific remains almost unchanged when the orography is removed in the AMIP runs but is reduced by 20% in the CMIP runs. We propose that the calculation of SPV over the TP is helpful for understanding the TP orographic forcing and monsoon dynamics in the future.

Chemical abundance analysis of symbiotic giants. Metallicity and CNO abundance patterns in 14 northern S-type systems

ABSTRACT In previous works, we computed abundances for the red giant in nearly four dozen S-type symbiotic systems (SySt). The abundances provide information about metallicity, evolutionary status, and possible memberships in Galactic stellar populations. Here, we extend our studies with a northern hemisphere sample of SySt. This northern sample is dominated by Galactic disc/halo objects, whereas our previous southern sample is heavily biased toward the bulge population. Spectrum synthesis of high-resolution (R ∼ 50 000), near-IR spectra using standard LTE analysis and atmospheric models have been used to measure abundances of CNO and elements around the iron peak (Fe, Ti, Ni, and Sc) in the atmospheres of the red giant component. The SySt sample shows generally slightly sub-solar metallicity, as expected for an older disc population, with a median at [Fe/H] ∼ −0.2 dex. Enhanced 14N, depleted 12C, and decreased 12C/13C, indicate that all these giants have experienced the first dredge-up. Comparison with theoretical predictions indicates that additional mixing processes had to occur to explain the observed C and N abundances. Relative O and Fe abundances agree with those represented by Galactic disc and bulge giant populations in the APOGEE data, with a few cases that can be attributed to membership in the extended thick-disc/halo. As an interesting byproduct of this study, we observed a blue-shifted additional component on the wings of absorption lines in the spectra of AG Peg, which could be connected with accretion on to the hot component.

Simulation and Error Analysis of Methane Detection Globally Using Spaceborne IPDA Lidar

Methane (CH4) is recognized as the second most important greenhouse gas. An accurate and precise monitoring of methane gas globally has a vital role in studying the carbon cycle and global warming. The spaceborne integrated path differential absorption (IPDA) lidar is one of the most effective payload for methane detection. The simulation and optimization of the lidar system parameters can create an important base for the development of spaceborne payloads. However, previous IPDA lidar simulations have mostly used standard atmospheric models at simulation conditions, and to the best of our knowledge, there is no literature yet which applies a wavelength optimization to the IPDA system. In this study, we have investigated the relationship between the IPDA lidar system, based on wavelength optimization, and error measurement for CH4 column-averaged concentration. By selecting the wavelengths with the lowest comprehensive error as on-line and off-line, the error has been minimized by 10 ppb approximately relative to before optimization. We have proposed an IPDA simulation model at real atmospheric conditions, combining with ERA-5 reanalysis data, to simulate methane concentration globally, and present the distribution of errors. Finally, after the optimization of the lidar system parameters, we have ensured that the maximum inversion error for CH4 measurement is less than 10 ppb, to provide a reference for designing spaceborne IPDA lidar systems for high-precision CH4 column-averaged concentration detection.

Estimating the Radiance in Atmosphere-Ocean Systems With Different Atmosphere Models by Discrete Spherical Harmonics Method

Abstract The radiative transfer in atmosphere-ocean systems with different atmosphere models is evaluated by the discrete spherical harmonics method. Four standard atmosphere models, namely, Tropical, Mid-Latitude Summer, Mid-Latitude Winter, and U.S. Standard (1976) limited to a height of 16 km are considered above an ocean. Two monochromatic radiations are considered according to the preponderance of the interaction they present with the participating medium, namely, λ=0.55 μm for scattering by particles and λ=16.8 μm for absorption and emission by water vapor and carbon dioxide. The absorption by the atmospheric gases considered is analyzed by the statistical narrow-band correlated-k method. The optical properties of aerosols and water clouds considered are calculated by Lorenz-Mie theory. The results obtained by the proposed discrete spherical harmonics method are in agreement with those of the literature and demonstrate the efficiency and accuracy of the developed radiative transfer code. The effects of the governing parameters of the system are investigated and show that the presence of the ocean contributes to increasing the upward radiation fluxes in the atmosphere. The presence of aerosols in the atmosphere leads to downward radiance curves at ground level that show significant peaks around the zenith angle of observation θ=0 deg. Additionally, the presence of the cloud in the atmosphere creates a discontinuity in the radiation flux curves at the height of the cloud.

The SPHINX M-dwarf Spectral Grid. I. Benchmarking New Model Atmospheres to Derive Fundamental M-dwarf Properties

About 70%–80% of stars in our solar and Galactic neighborhood are M dwarfs. They span a range of low masses and temperatures relative to solar-type stars, facilitating molecule formation throughout their atmospheres. Standard stellar atmosphere models primarily designed for FGK stars face challenges when characterizing broadband molecular features in spectra of cool stars. Here, we introduce SPHINX—a new 1D self-consistent radiative–convective thermochemical equilibrium chemistry model grid of atmospheres and spectra for M dwarfs in low resolution (R ∼ 250). We incorporate the latest precomputed absorption cross sections with pressure broadening for key molecules dominant in late-K, early/main-sequence-M stars. We then validate our grid models by determining fundamental properties (T eff, log g, [M/H], radius, and C/O) for 10 benchmark M+G binary stars with known host metallicities and 10 M dwarfs with interferometrically measured angular diameters. Incorporating the Gaussian process inference tool Starfish, we account for correlated and systematic noise in low-resolution (spectral stitching of SpeX, SNIFS, and STIS) observations and derive robust estimates of fundamental M-dwarf atmospheric parameters. Additionally, we assess the influence of photospheric heterogeneity on inferred [M/H] and find that it could explain some deviations from observations. We also probe whether the adopted convective mixing length parameter influences inferred radii, effective temperature, and [M/H] and again find that may explain discrepancies between interferometric observations and model-derived parameters for cooler M dwarfs. Mainly, we show the unique strength in leveraging broadband molecular absorption features occurring in low-resolution M dwarf spectra and demonstrate the ability to improve constraints on fundamental properties of exoplanet hosts and brown-dwarf companions.

Effect of flight level to maximum power utilization for PEMFC/supercapacitor hybrid uav with switched reluctance motor thruster

In this study, the performance of a fixed-wing PEMFC/SC hybrid UAV with an SRM thruster is investigated by different flight levels. Flight levels negatively affect the PEMFC due to changing ambient conditions such as air temperature and pressure. Hence, the international standard atmosphere (ISA) model for PEMFC voltage-current-power ratings is derived with 100 m intervals for 0–7500 m. The demanded electrical power by UAV increases at high altitudes due to the compressor used for air pressurization of PEMFC. Therefore, a maximum power point tracking (MPPT) model of PEMFC should be utilized in case of overshooting the maximum power level that can be provided. While the main power source of the UAV is PEMFC, the auxiliary power source is SC. The SC is preferred for DC bus voltage stabilization, avoiding maximum power point overshoot, and preventing high instantaneous current that shortens the lifespan of PEMFC. The proposed UAV model is verified at MATLAB/Simulink and the results prove that the system is satisfying.

Estimation and characterization of the refractive index structure constant within the marine atmospheric boundary layer.

We verified the feasibility of an alternative solution to generate temperature and pressure profiles with the U.S. standard atmosphere model (USSA-76). We simultaneously integrated this model with conventional meteorological parameters measured by a weather station in the course of estimating the refractive index structure constant (C n2). Moreover, a continuous-time-series estimation method of the refractive index structure constant was established within the marine atmospheric boundary layer (ABL) based on wind data obtained from a coherent Doppler wind lidar (CDWL). We also analyzed the optical turbulence characteristics induced by wind shear during the conducted experiment. Laminated and patchy stratified turbulences, which affect the performance of imaging and light transmission systems, were found within the marine ABL. Additionally, the relationship between the ABL and all atmospheric optical turbulence factors shows that the ratio of marine ABL in the entire layer differs from that reported in previous studies. Moreover, the influence of thermal turbulence factors within the marine ABL was less than that of the entire layer in our case. We report a real-time C n2 estimation method based on a CDWL. The characteristics of the marine ABL C n2 constitute a reference for optoelectronic applications.

THE MEMS-BASED BAROMETRIC ALTIMETER INACCURACY AND DRIFT PHENOMENON

MEMS technology has made sensors for measuring barometric pressure and altitude above sea level very cheap and widely used in many consumer electronic devices. This paper presents a theoretical analysis of the sources and types of errors in the barometric altimeter using the standard atmosphere model (ISA). Methods for correcting principal errors caused by non-standard sea level conditions are described and compared. A method of correcting errors in the case of altimeter horizontal movement to the air column and total pressure measurement was proposed. It was compared with another method known from the literature. In the numerical experiment, data recorded by a bicycle computer equipped with a MEMS-based barometric altimeter was analyzed. As the GPS data of the route covered was also known, it was possible to compare the recorded altimeter data with the heights determined from the digital terrain model (DTM), which in this case were considered accurate. The error of the measured altitude calculated in this way was tried to be divided into the principal error, the external error caused by the sensor movement, and the barometer drift. Hence, a numerical experiment was carried out in which, based on the recorded data, an attempt was made to reconstruct non-standard sea level conditions and the impact of speed on the sensor measurements. Furthermore, a method of solving such a reverse problem was proposed. The results of the presented studies can be used in the design of systems correcting the indications of barometric altimeters. The accuracy of the altitude measurement is especially important for small controlled flying objects (UAH) and when recording the route of vehicles moving on the ground.

Novel Inversion Algorithm for the Atmospheric Aerosol Extinction Coefficient Based on an Improved Genetic Algorithm

As an important atmospheric component, aerosols play a very important role in the radiation budget balance of the earth–atmosphere system. To study the optical characteristics of aerosols, it is necessary to use an inversion algorithm to process the lidar return signal to obtain both the aerosol extinction coefficient and the backscattering coefficient. However, the lidar return power equation is ill-conditioned and contains two unknown parameters, meaning that traditional inversion algorithms must be solved by adopting certain assumptions (e.g., a uniform atmosphere and the lidar ratio), which to a certain extent can seriously affect the inversion accuracy. Here, to improve the accuracy of the aerosol extinction coefficient inversion, an inversion method based on an improved genetic algorithm is proposed. Using the U.S. Standard Atmosphere model and the return power equation, the aerosol extinction coefficient and the backscattering coefficient are independent variables that randomly provide initial values to simulate the theoretical lidar power. Then, the genetic algorithm is used to approximate the theoretical lidar power to the measured lidar return power with height; when the two are infinitely close, the values of the corresponding two independent variables (i.e., the extinction and backscattering coefficients) are inverted. Experiments performed to compare the different effects between a simple genetic algorithm and the improved genetic algorithm showed the proposed method capable of inverting the aerosol extinction coefficient without reliance on traditional inversion methods, representing a novel approach to the inversion of the aerosol extinction coefficient and the backscattering coefficient.

High altitude balloon testing of Arduino and environmental sensors for CubeSat prototype

CubeSats were conceived with an aim to provide students with hands-on, design, build, and test experiences on spacecraft. Many education-class CubeSats keep the cost of the projects low with the use of commercial off-the-shelf (COTS) products. But using parts not designed for space missions often means a compromise in performance (e.g., low sensor accuracy, low power efficiency) and reliability, which makes component testing a necessary part of the development process. Unfortunately, there is no single lab equipment that can test the integrated features of CubeSats, including the radio communication over ranges of altitudes and distances. It has been pointed out that a high altitude reached by a weather balloon offers an environment similar to the space environment. This paper describes a balloon flight testing of Arduino and sensors for a CubeSat “prototype”—a preliminary mock-up model used for hardware selection and validation during the initial building phase. Atmospheric pressures and temperatures were measured throughout the balloon flight. The measured pressures were validated by comparing Arduino’s pressure altitudes against the GPS altitudes, and the measured temperatures were assessed against the standard atmosphere model.

A Genetic Algorithm to Model Solar Radio Active Regions From 3D Magnetic Field Extrapolations

In recent decades our understanding of solar active regions (ARs) has improved substantially due to observations made with better angular resolution and wider spectral coverage. While prior AR observations have shown that these structures were always brighter than the quiet Sun at centimeter wavelengths, recent observations at millimeter and submillimeter wavelengths have shown ARs with well defined dark umbrae. Given this new information, it is now necessary to update our understanding and models of the solar atmosphere in active regions. In this work, we present a data-constrained model of the AR solar atmosphere, in which we use brightness temperature measurements of NOAA 12470 at three radio frequencies: 17, 100 and 230 GHz. The observations at 17 GHz were made by the Nobeyama Radioheliograph (NoRH), while the observations at 100 and 230 GHz were obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Based on our model, which assumes that the radio emission originates from thermal free-free and gyroresonance processes, we calculate radio brightness temperature maps that can be compared with the observations. The magnetic field at distinct atmospheric heights was determined in our modelling process by force-free field extrapolation using photospheric magnetograms taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). In order to determine the best plasma temperature and density height profiles necessary to match the observations, the model uses a genetic algorithm that modifies a standard quiet Sun atmospheric model. Our results show that the height of the transition region (TR) of the modelled atmosphere varies with the type of region being modelled: for umbrae the TR is located at 1080 ± 20 km above the solar surface; for penumbrae, the TR is located at 1800 ± 50 km; and for bright regions outside sunspots, the TR is located at 2000 ± 100 km. With these results, we find good agreement with the observed AR brightness temperature maps. Our modelled AR can be used to estimate the emission at frequencies without observational coverage.

An Accurate Calculation of the Atmospheric Refraction Error of Optical Remote Sensing Images Based on the Fine-Layered Light Vector Method

Atmospheric refraction is an important factor that affects the positioning accuracy of optical high-resolution satellite imaging. Current calculation methods do not consider regional change characteristics in the atmosphere; the atmospheric division model is rough and does not conform to reality. This article studies atmospheric refraction in optical remote sensing satellite observations, provides a formula for calculating the strict refraction of a multilayer atmosphere, and shows a new method for calculating atmospheric refraction error. We use a ray-tracing method to calculate the light propagation path in the atmosphere and continuously layer the atmosphere according to the height difference of 100 m. Different from general calculation methods, we prove that a regional atmospheric model can calculate the atmospheric refraction index more accurately than using the empirical model. As the off-nadir angle gradually increases, the calculation results in this article are better than the current commonly used methods. We use WorldView-2 images of the Qinghai–Tibet Plateau region in China for the experiments. When the off-nadir angle is less than 32°, the positioning accuracy improves by 6–47%. Compared with the standard atmospheric model, the regional atmospheric model improves positioning accuracy by 2–18%. This method reflects the continuous variation in the atmospheric refractive index with the vertical distribution of the atmosphere and amended regional meteorological conditions. Model errors caused by overly simple atmospheric division are avoided, andthe positioning accuracy of optical remote sensing images is increased.

Учет свойств атмосферы при сравнении математических моделей аэродинамических коэффициентов с данными летных испытаний

Methodological approaches to the calculation of atmospheric parameters, primarily air density and velocity head, in the task of comparing flight data with the results of mathematical modeling of the aircraft motion are proposed. Models with different degrees of using onboard measurements and standard atmosphere models are considered. The models are compared according to the data of flight experiments performed on a modern aircraft for such flight modes as horizontal platform, turn, climb, descentin, and acceleration. The comparison results are given the form of absolute and relative discrepancies in temperature, static pressure and air density. It is shown that the difference between the properties of the real atmosphere and the standard atmosphere is the main source of mismatches, compared to which the influence of the type of flight modes, altitude, speed is insignificant. In addition, a comparison of the standard atmosphere model with the data of atmospheric meteorological sounding is made, which gave similar results. It is concluded that the calculation of air density and velocity head through the standard atmosphere, widespread in practice, in the general case creates a significant error, which may lead to erroneous conclusions in assessing the correspondence of the aircraft mathematical model and the real object

Evaluation of a small drone performance using fuel cell and battery; Constraint and mission analyzes

Drones have important uses such as relief, photography, military purposes. However, designing an efficient propulsion system for the drone that can ensure its reliability and flight endurance is a major challenge. Relying on an all-electric propulsion system can enhance flight endurance and improve drone performance. In this article, two types of fuel cells, proton-exchange membrane fuel cell and solid oxide fuel cell have been considered (individually) to supply the power consumption of the drone. In addition, a battery is embedded in parallel with the fuel cell in the propulsion system. To evaluate the performance of the drone, two constraint and mission analyzes have been established to determine the power consumption of the drone during various flight modes and weight distribution of the drone. Then a comparison on the drone’s performance with respect to the electrochemical behavior of both fuel cells is provided. Finally, the performance of fuel cells in propulsion system based on the International Standard Atmosphere model is discussed. Results revealed that the solid oxide fuel cell and proton-exchange membrane fuel cell can generate 82.1 and 162.7 W of electrical power respectively. In addition, drone needs about 1.46 kW of electrical power. The flight endurance and total weight of the drone are equal to 6.8 h and 6.3 kg, respectively. It was also found that the required area of the solid oxide fuel cell is approximately 98% less than the proton-exchange membrane fuel cell to provide the total electricity consumption of the drone. Furthermore, the effect of increasing cruise speed on drone’s net weight is more remarkable compared to power consumption.