Single Aircraft Research Articles

A Composite Approach for Evaluating Operational Cloud Seeding Effect in Stratus Clouds

Robust water management is in intense demand in many water scarcity areas, such as arid and semi-arid regions in the world. As part of the regional water management strategy, rain enhancement is vital to replenish groundwater reservoirs, and the key challenge is how to assess its effectiveness. Some recent weather modification experiments attained cloud seeding effect through advanced in situ measurement coupled with accurate numerical simulation. However, there is still a lack of an objective and scientific approach to quantitatively evaluate the rain enhancement effect, especially for many non-randomized operational cloud seeding activities in China. In this study, we proposed a composite evaluation approach by analyzing two operational aircraft cloud seeding cases in stratus clouds in Shaanxi, China. By calculating the aircraft cloud seeding agent plumes, the target areas (as well as the control areas) of cloud seeding were dynamically and roughly determined. Physical properties, such as radar reflectivity and precipitation, were individually quantified in these areas. The cloud seeding effect was then evaluated by calculating the difference in parameter variation between target and control areas. This approach can be applied to qualitative analysis in a single aircraft cloud seeding operation and can also provide quantitative statistical results from multiple cloud seeding cases. We found that the average precipitation enhancement percentage of 18 operational aircraft cloud seeding cases is ~4.84%. Note that the homogeneity hypothesis of the seeding cloud, the error in the calculation of the target area, and the selection of control areas are the major uncertainties likely in the evaluation of the cloud seeding effect by this approach.

A New Accurate Aircraft Trajectory Prediction in Terminal Airspace Based on Spatio-Temporal Attention Mechanism

Trajectory prediction serves as a prerequisite for future trajectory-based operation, significantly reducing the uncertainty of aircraft movement information within airspace by scientifically forecasting the three-dimensional positions of aircraft over a certain period. As convergence points in the aviation network, airport terminal airspace exhibits the most complex traffic conditions in the entire air route network. It has stronger mutual influences and interactions among aircraft compared to the en-route phase. Current research typically uses the trajectory time series information of a single aircraft as input for subsequent predictions. However, it often lacks consideration of the close-range spatial interactions between multiple aircraft in the terminal airspace. This results in a gap in the study of aircraft trajectory prediction that couples spatiotemporal features. This paper aims to predict the four-dimensional trajectories of aircraft in terminal airspace, constructing a Spatio-Temporal Transformer (ST-Transformer) prediction model based on temporal and spatial attention mechanisms. Using radar aircraft trajectory data from the Guangzhou Baiyun Airport terminal airspace, the results indicate that the proposed ST-Transformer model has a smaller prediction error compared to mainstream deep learning prediction models. This demonstrates that the model can better integrate the temporal sequence correlation of trajectory features and the potential spatial interaction information among trajectories for accurate prediction.

Modular reconfigurable rotorcraft for autonomous cargo delivery

Traditional air mobility capability development consists of defining a set of requirements and subsequently designing an aircraft that satisfies these requirements. Once designed, the overall structure or topology of the aircraft is fixed. That is, the aircraft has certain fixed physical dimensions, number and sizes of rotors, engines, etc. The topology cannot be changed to accomplish missions outside of its original design envelope, and if designed for a robust mission spectrum, the aircraft may be inefficient during routine missions that do not require peak performance. The work reported here takes a different approach where a core set of components (fuselage, rotor, power plant, etc) defines the fundamental modules of the air mobility system. The modules were developed using mature and readily available technologies and designed to be quickly connected to other modules to assemble different aircraft configurations with widely varying performance characteristics. The aircraft can be reconfigured between missions to best satisfy mission requirements. Thus, the envelope of achievable performance characteristics is significantly expanded compared to a single aircraft. This concept is explored for autonomous air cargo delivery missions targeted for nominal payloads and ranges around 500 pounds and 500 nautical miles with maximum payloads up to 3500 pounds across shorter distances. Results indicate that for mission spectrums with large differences between nominal and maximum payloads and skewed towards smaller payloads, the operational cost per lb-km is significantly reduced using a modular and reconfigurable air mobility system since cargo delivery requirements can be better matched to an air vehicle system.

Space and time joint optimization for vertical takeoff and landing aircraft in dense obstacles and interference environments

ABSTRACT The Vertical Takeoff and Landing Aircraft (VTOL) is capable of both low-speed hovering and high-speed flight. This paper proposes an autonomous motion planning and anti-wind disturbance control algorithm for the VTOL, implemented spatial and temporal joint motion planning for VTOL, under the limitation of maximum flight speed of the aircraft, VTOL can achieve fully autonomous flight in complex environments, which can realize the autonomous flight of a single aircraft in a complex and dense environment, achieve real-time perception and avoidance of static and dynamic obstacles. The information generated by motion planning includes the position, velocity, and acceleration information of the aircraft, and proposes a wind disturbance estimation and active control strategy in a wind disturbance environment, accurate estimation of wind disturbance is achieved through a state observer, and the wind disturbance was suppressed through nonlinear error feedback control law, implemented wind disturbance estimation and suppression for aircraft in wind disturbance environments, and achieved complete autonomous motion planning and trajectory tracking of VTOL in a complex and wind disturbance environment. Our work can provide a basis for the collaborative control of multiple UAVs.

Fleet & tail assignment under uncertainty

Airlines solve many different optimization problems and combine the resulting solutions to ensure smooth, minimum-cost operations. Crucial problems are the Fleet Assignment, which assigns aircraft types to flights of a given schedule, and the Tail Assignment, which determines individual flight sequences to be performed by single aircraft. In order to find a cost-optimal solution, many airlines use mathematical optimization models. For these to be effective, the available data and forecasts must reflect the situation as accurately as possible. However, especially in times of a pandemic, the underlying plan is subject to severe uncertainties: Staff and demand uncertainties can even lead to flight cancellations or result in entire aircraft having to be grounded. Therefore, it is advantageous for airlines to protect their mathematical models against uncertainties in the input parameters. In this work, two computational tractable and cost-efficient robust models and solution approaches are developed: First, we set up a novel mixed integer model for the integrated fleet and tail assignment, which ensures that as few subsequent flights as possible have to be canceled in the event of initial flight cancellations. We then solve this model using a procedure that ensures that the costs of the solution remain considerably low. Our second model is an extended fleet assignment model that allows us to compensate for entire aircraft cancellations in the best possible way, taking into account rescheduling options. We demonstrate the effectiveness of both approaches by conducting an extensive computational study based on real flight schedules of a major German airline. It turns out that both models deliver stable, cost-efficient solutions within less than ten minutes, which significantly reduce follow-up costs in the case uncertainties arise.

Coupled Aerodynamics–Structure Analysis and Wind Tunnel Experiments on Passive Hinge Oscillation of Wing-Tip-Chained Airplanes

This study examines the wing hinge oscillations in an aircraft concept that employs multiple wings, or small aircraft, chained at the wing tips through freely rotatable hinges with minimal structural damping and no mechanical position-locking system. This creates a single pseudo long-span aircraft that resembles a flying chain oriented perpendicular to the flight direction. Numerical calculations were conducted using the vortex lattice method and modified equations for a multi-link rigid body pendulum. The calculations demonstrated good agreement with small-scale wind tunnel experiments, where the motion of the chained wings was tracked through color tracking, and the forces were measured using six-axis force sensors. The total CL/CD increased for the chained wings, even in the presence of hinge joint oscillations. Furthermore, numerical simulations assuming an unmanned airplane size corroborated the theoretical attainment of passive stability with high chained numbers (≥9 wings), without any structural damping and relying solely on aerodynamic forces. Guidelines for appropriate hinge axis angle δ and angle-of-attack regions for different chained wing numbers to maximize passive oscillation stability were obtained. The results showed that wing-tip-chained airplanes could successfully provide substantially large wing spans while retaining flexibility, light weight and CL/CD, without requiring active hinge rotation control.

Effects of Aircraft Noise on Sleep: Federal Aviation Administration National Sleep Study Protocol.

Aircraft noise can disrupt sleep and impair recuperation. The last U.S. investigation into the effects of aircraft noise on sleep dates back more than 20 years. Since then, traffic patterns and the noise levels produced by single aircraft have changed substantially. It is therefore important to acquire current data on sleep disturbance relative to varying degrees of aircraft noise exposure in the U.S. that can be used to check and potentially update the existing noise policy. This manuscript describes the design, procedures, and analytical approaches of the FAA's National Sleep Study. Seventy-seven U.S. airports with relevant nighttime air traffic from 39 states are included in the sampling frame. Based on simulation-based power calculations, the field study aims to recruit 400 participants from four noise strata and record an electrocardiogram (ECG), body movement, and sound pressure levels in the bedroom for five consecutive nights. The primary outcome of the study is an exposure-response function between the instantaneous, maximum A-weighted sound pressure levels (dBA) of individual aircraft measured in the bedroom and awakening probability inferred from changes in heart rate and body movement. Self-reported sleep disturbance due to aircraft noise is the secondary outcome that will be associated with long-term average noise exposure metrics such as the Day-Night Average Sound Level (DNL) and the Nighttime Equivalent Sound Level (Lnight). The effect of aircraft noise on several other physiological and self-report outcomes will also be investigated. This study will provide key insights into the effects of aircraft noise on objectively and subjectively assessed sleep disturbance.

Design and flight test of the fixed-flapping hybrid morphing wing aerial vehicle

Bionic aircrafts have become a hot topic in the research on unmanned aerial vehicles (UAVs). By mimicking the flight mechanics and wing morphology of living organisms, bionic aircraft not only improve aerodynamic performance, stealth, and convenience but also enable single aircraft to complete multiple specific tasks. To further improve the practical performance of bionic aircraft, a fixed-flapping hybrid morphing wing aerial vehicle (F-FWAV) is designed, and the aerodynamic and flight mechanics are studied. First, kinematic simulations are conducted on the designed F-FWAV, and the kinematic characteristics of the flapping wing are analyzed. Then, flight tests are conducted on the aircraft model, and time-domain and frequency-domain analyses were performed on the data of the pitch angle and roll angle during level flight, high angle of attack (AOA) maneuvering and landing, indicating that the pitch and roll angles of the F-FWAV are coupled. CFD numerical simulations are used to obtain the cruise points of the F-FWAV under different AOAs, frequencies, and freestream velocities. The results of the mutual interference between the fixed wing and flapping wing sections show that the flapping wing section provides more than 50 % of the lift of the entire flight process, and the downward flapping movement of the flapping wing section increases the edge vortex of the fixed wing section, thereby increasing the lift of the fixed wing section.

HEALTH RISK AS A CRITERION TO ESTIMATE POPULATION SAFETY IN AN AIRPORT ZONE

The paper considers and tests methodological approaches to assessing public health risks when establishing and using the sanitary (seventh) subzone in an airport zone. Testing was performed at a large civilian airport in Russia. It involved outlining noise contours in accordance with the ICAO methodology. The aviation noise contours were verified with the results produced by instrumental measurements. Acoustic exposure was calculated through assessing averaged daily equivalent noise level (LDN) that was equal to 65 dBA. Health risk assessment showed that long-term exposure primarily affected the cardiovascular system: moderate risks would occur by 23 years; high, by 55 years; and very high, by 63 years. Identified health disorders may become apparent through elevated blood pressure, heart diseases, myocardial infarctions and others.
 Background. It is quite common to locate certain objects within an AZ that are subject to sanitary-epidemiological standardization. Use of any AZ for location of such objects should be well grounded and this is a significant issue occurring when the sanitary (seventh) subzone is established. In particular, this concerns equivalent outdoor noise levels and equivalent and maximum permissible indoor noise levels.
 Purpose. Our research goal was to test the suggested approach to health risk assessment within the boundaries of an aircraft zone.
 Materials and methods. Our research object was a large civil aviation airport located in the temperate zone with an average daily number of landings and takeoffs being about 200. At the exposure assessment stage, we calculated aircraft noise contours by using a certified software package that was based on «Recommended Method for Computing Noise Contours Around Airports» (ICAO Doc 9911-2018). We took an equivalent averaged noise level (LAday, dBА) as an indicator applied to estimate population exposure to a harmful factor.
 We performed continuous AN measurements on a territory that was planned for development. This AN occurred due to AC takeoffs and landings with more than 600 AC flights detected during the measurement period. This determined effects produced by AN on the examined territory. Assessment of “exposure – response” and “exposure – effect” relationships involved using recurrent risk growth equations built on conventional pair mathematical models. This risk was measured within a range from 0 to 1 and scale was considered when giving its estimates.
 Results. This value was calculated based on maximum noise levels established during a single aircraft flight when it took off or landed along a route that was the most significant for determining exposure to aircraft noise. We also calculated equivalent noise levels at day and at night that corresponded to flight intensities typical for normal airport operations (2019). These levels were LAeq.day = 66,0 dBA (“takeoff”), LAeq.night = 52,0 dBA (“landing”).
 Health risk assessment indicated that long-term (chronic) exposure to average daily noise LАd = 65 dBA primarily produced effects on the cardiovascular system. This created moderate risks by the age of 23 years; high risks, 55 years; and extremely high risks, by 63 years.
 We established that living for more than 15 years in an airport zone with identified noise levels could result in negative health outcomes.
 Conclusion. Overall, we have confirmed that health risk assessment should be considered an important instrument for substantiating boundaries of a zone influenced by an airport. Results produced by such assessment are a key criterion in determining how to use a territory near an airport in future as regards locating capital objects there including residential areas and their exploitation.

Comparison of cabin noise of turboprop and turbofan aircrafts

Turboprop aircrafts are typically used for transporting cargos and for low-capacity short-haul air transport between regional cities. The new designs of turboprop aircrafts tend to focus on noise and comfort level of the aircrafts. Although turboprop aircrafts are known to have relatively higher cabin noise, there are limited reported studies in the open literature examining the actual cabin noise level in commercial flights. In this study, the cabin noise of the ATR 72-500 turboprop aircraft was examined and compared with that of the Bombardier CRJ 900 turbofan aircraft during actual commercial flights. Both are passenger planes which are designed to carry fewer than 100 passengers and are deemed to be a more compatible comparison. Both are single isle aircraft with two seats on each side of the isle. The Bombardier CRJ 900 is found to have a lower cabin noise in terms of both dBA and dBC for both taxing and cruising. As the average equivalent continuous sound pressure level (Leq) for cabin noise is found to be well below 85 dBA, there is no risk of exceeding the daily exposure to noise of 85 dBA for eight hours under the National Institute for Occupational Safety & Health (NIOSH) regulation. However, as many reported studies have shown that prolonged exposure to low frequency noise may lead to disorders, discomfort, sensitivity to and irritability from noise, annoyance, hearing loss, and cardiovascular diseases, there may be a need to carry out a more detailed study of the effect of low frequency noise on passengers.

Uncrewed aerial vehicle radiometric calibration: A comparison of autoexposure and fixed‐exposure images

AbstractRemote sensing with uncrewed aerial vehicles (UAVs) is increasingly being used in agriculture to provide data on the physical characteristics of plants under field conditions. Data accuracy is critical for decision making with a high degree of confidence. In this work, we compared two multispectral camera calibration methods for image data collected with a UAV: (1) an autoexposure method that relies on a single calibration panel and a post hoc calibration, and (2) a fixed‐exposure system that uses three in‐field gray calibration panels using the empirical line calibration method. Both methods were compared to reflectance data from (a) four ground calibration targets measured with a spectroradiometer and (b) a single manned aircraft image calibrated with commercial calibration tarps. In a band‐by‐band comparison, the autoexposure method produced almost twice as much radiometric error on average compared with fixed exposure. Because remote sensing data are commonly converted to spectral indices, the calibration methods were also evaluated by calculating the visible atmospherically resistant index (VARI) and comparing the resulting data to the manned aircraft image. Similarly, the autoexposure method in this case produced twice the error of the fixed‐exposure method. The effect of the error was considered in a production agriculture context by simulating a remote sensing‐based prescription map for pesticide application in a cotton (Gossypium) field and calculating the number of mislabeled management zones. The simulation showed that the autoexposure method would be more costly to the farm because of its higher error, roughly $8.00/ha based on the assumptions made.

The low latency networking method for task-driven MEC-enabled UAV swarm

Unmanned Aerial Vehicles (UAVs) are increasingly being used for special missions as Mobile Edge Computing (MEC) devices, and the utilization of multiple UAVs who are integrated into formations for collaboratively executing tasks that cannot be performed by single aircraft has also been a recent research hit. In this paper, we present a low latency networking method aims to shorten the preparation time so that MEC-enabled swarm can as quick as possible concentrate on the task execution. For reducing the time of swarm initialization, we consider applying the Leader-Follower (L-F) topology model in networking and formation control. Firstly, by combining the nature of wireless communication and correlation analysis, we improve the traditional L-F model to avoid too many nodes accessing the same node and raise the communication efficiency. Secondly, in order to choose the topology that can provide better performance in network, we adopt an improved Particle Swarm Optimization (PSO) algorithm to customize the appropriate factor coefficients during leader selection for swarms with different densities and communication initial conditions. Experiments and evaluations demonstrate that the proposed algorithm has significant effect in reducing network latency.

Swift Assessment of Flexible Elements of High Speed Flexible Couplings for Aircraft Transmission Systems

The High Speed Flexible Coupling (HSFC) known as Power Take-Off shaft (PTO) is used in combat aircraft for connecting engine gearbox with accessory gearbox to transmit power and to accommodate larger misalignments. The HSFC utilizes series of metallic contoured plates as flexible elements. The development of a HSFC shaft assembly involves high cost and time process. Any failure of the HSFC during flight operation will deprive the secondary power system mainly used for controlling the single engine fighter aircraft. To develop the reliable HSFC with minimum developmental cost and time, an innovative approach termed as Swift Assessment of Flexible Elements (SAFE) for the development of HSFC is evolved. A case study of a typical high speed flexible coupling developed using this approach is presented With the SAFE approach, sufficient level of flexibility in design modification, trim down product development cycle time and cost were realized.

Modal Analysis and Flight Validation of Compound Multi-Body Aircraft

The flight dynamics of a compound aircraft are highly coupled and significantly different from those of a single aircraft. In this paper, the characteristic flight dynamics of a three-unit connected aircraft are analyzed in detail. By distinguishing the aircraft’s modes into a symmetric mode group and an asymmetric mode group, the mechanisms by which the relative roll modes of the compound aircraft significantly impact the rigid-body modes of the vehicle become clear. The trim configuration of a compound aircraft has a profound influence on its stability and flight modes. In addition, the relative roll modes can be separated from the full-state model by appropriate simplifications, and the modal coupling mechanism and evolution law can be analytically derived. The key parameters which have a significant influence on the trim configuration and flight modes of the aircraft are pointed out in this paper. Finally, the common failure modes of compound aircraft are identified. A flight experiment with test data verifies the correctness of the above theoretical analysis.

The Lynchpin—A Novel Geometry for Modular, Tangential, Omnidirectional Flight

<div>A novel geometry for a six degrees of freedom (6DOF) unmanned aerial vehicle (UAV) rotary wing aircraft is introduced and a flight mechanical analysis is conducted for an aircraft built in accordance to the thrust vectors of the proposed geometry. Furthermore, the necessary mathematical operations and control schemes are derived to fly an aircraft with the proposed geometry. A system identification of the used propulsion system with the necessary thrust reversal in the form of bidirectional motors and propellers was conducted at a whirl tower. The design of the first prototype aircraft is presented as well as the first flight test results. It could be demonstrated that an aircraft with the thrust vectors oriented according to the proposed geometry works sufficiently and offers unique maneuvering capabilities that cannot be reached with a conventional design. The biggest limiting factor could be identified to be the latency resulting from the time needed to reverse the direction of rotation of the bidirectional propellers. Special operational handling considerations for a manually flown 6DOF vehicle are summarized, and different approaches to control such a vehicle are described. Different mission scenarios and applications for a single aircraft in this design are concluded. Due to the symmetrical properties of the proposed geometry, several aircraft can also be connected at different orientations in flight. Consequently, the possibilities of docking in midair are illustrated, and possible mission scenarios for a group of aircraft, working together collaboratively, are presented. Especially when operated autonomously in a group of aircraft, new possibilities evolve from the capability of the proposed geometry to bond in different orientations.</div>

Optimization Design and Performance Evaluation of U-Shaped Area Operation Procedures in Complex Apron

In view of the common U-shaped apron structure of large- and medium-sized airports at home and abroad, this study considered the optimization design and performance evaluation of the U-shaped apron operation procedure. First, by analyzing the physical structure characteristics and traffic operation characteristics of the U-shaped area, exclusive, partition-shared, and global-shared operation procedures of the U-shaped area were designed, and differentiated apron-operation rules and traffic models were constructed for different types of operation procedures. Then, from the perspectives of safety, efficiency, and environmental protection, a multi-dimensional evaluation index system of U-shaped area operation performance is established, and a classification measurement and comprehensive evaluation method based on critique is proposed. Finally, a traffic simulation model was established based on airport network topology modeling. We used Monte Carlo methods for the simulation in Python 3.6, and the experimental results show that, in the scenario of high-density traffic operation, compared with exclusive and partition-shared procedures, the implementation effect of the global shared procedure is very significant, and the apron operation capacity increased by 14.8% and 5.0%, respectively. The probability of aircraft conflict decreased by 32.2% and 11.8%, respectively, and the time of single conflict relief decreased by 16.1 s and 10.6 s, respectively. The average resource utilization in each U-shaped area increased by 66% and 25%, respectively, while the average daily carbon emissions of a single aircraft were reduced by 16.7 kg and 11.0 kg and the average daily fuel consumption of a single aircraft were reduced by 3.6 kg and 2.4 kg, respectively. The proposed method is scientific and effective and can provide theoretical and methodological support for optimizing the configuration of the scene operation mode of complex airports and for improving flight operation efficiency.

Process-based deep learning model: 3D prediction method for shot peen forming of an aircraft panel

Shot peen-forming is a more precise method of forming aircraft panels than conventional methods. The traditional method of acquiring the process parameters relies mainly on prior theoretical knowledge and trial-and-error. Despite the finite element method's ability to replace some experimentation, it still cannot realize the design of shot peen forming processes parameters of an aircraft panel based on a known contour. This study uses an innovative model-based deep learning approach to predict aircraft panel deformation and active design the shot peening parameters. The prediction time is less than 1 second, resulting in a significant reduction in computational time. The shot peen forming process parameters and the geometric structure characteristics of the aircraft panel are divided into independent channels to establish a high-dimensional feature map, which are used to train the deep learning model. The forming contours of the 2024-T351 high-strength aluminum alloy panel are predicted under different shot peening processes. In addition, the process parameters are designed according to the known contour of the forming process. To verify the precision of the proposed method, the designed shot peen forming process is used to manufacture a single curvature aircraft panel with a curvature radius of 3500 mm. There is good agreement between the forming contour and the theoretical design contour. The maximum deformation error is less than 1 mm and its mean error is 7.8%. The mean curvature radius error is 5.668%. The proposed method provides a new and practical reference to the precise design of the shot peen-forming process.

A review analysis of tilt rotor unmanned aerial vehicles

TRUAVs (Tilt Rotor Unmanned Aerial Vehicles) are a new technology that is becoming more and more popular in today's modern world for a range of uses, including agricultural, civil engineering, target tracking, search and salvage operations, and surveillance. Such aerial vehicles were created as a solution to a number of issues, such as the lack of runways in remote and heavily forested areas. The TRUAV is a hybrid aircraft that presents the advantages of both conventional aero plane and helicopter technology in a single aircraft. This review article is largely concerned with the design and analysis of Tilt Rotor Unmanned Aerial Vehicles (TRUAV). The flight control legislation we developed has a straightforward design and excellent technical dependability.

Snow stratigraphy observations from Operation IceBridge surveys in Alaska using S and C band airborne ultra-wideband FMCW (frequency-modulated continuous wave) radar

Abstract. During the concluding phase of the NASA Operation IceBridge (OIB), we successfully completed two airborne measurement campaigns (in 2018 and 2021, respectively) using a compact S and C band radar installed on a Single Otter aircraft and collected data over Alaskan mountains, ice fields, and glaciers. This paper reports seasonal snow depths derived from radar data. We found large variations in seasonal radar-inferred depths with multi-modal distributions assuming a constant relative permittivity for snow equal to 1.89. About 34 % of the snow depths observed in 2018 were between 3.2 and 4.2 m, and close to 30 % of the snow depths observed in 2021 were between 2.5 and 3.5 m. We observed snow strata in ice facies, combined percolation and wet-snow facies, and dry-snow facies from radar data and identified the transition areas from wet-snow facies to ice facies for multiple glaciers based on the snow strata and radar backscattering characteristics. Our analysis focuses on the measured strata of multiple years at the caldera of Mount Wrangell (K'elt'aeni) to estimate the local snow accumulation rate. We developed a method for using our radar readings of multi-year strata to constrain the uncertain parameters of interpretation models with the assumption that most of the snow layers detected by the radar at the caldera are annual accumulation layers. At a 2004 ice core and 2005 temperature sensor tower site, the locally estimated average snow accumulation rate is ∼2.89 m w.e. a−1 between the years 2003 and 2021. Our estimate of the snow accumulation rate between 2005 and 2006 is 2.82 m w.e. a−1, which matches closely to the 2.75 m w.e. a−1 inferred from independent ground-truth measurements made the same year. The snow accumulation rate between the years 2003 and 2021 also showed a linear increasing trend of 0.011 m w.e. a−2. This trend is corroborated by comparisons with the surface mass balance (SMB) derived for the same period from the regional atmospheric climate model MAR (Modèle Atmosphérique Régional). According to MAR data, which show an increase of 0.86 ∘C in this area for the period of 2003–2021, the linear upward trend is associated with the increase in snowfall and rainfall events, which may be attributed to elevated global temperatures. The findings of this study confirmed the viability of our methodology, as well as its underlying assumptions and interpretation models.

Preliminary Concept of Urban Air Mobility Traffic Rules

Driven by recent technological breakthroughs, the electric vertical take-off and landing (eVTOL) aircraft has gained considerable attention. The widespread demand for eVTOL aircraft can be attributed to their potential use in the commercialisation of urban air mobility (UAM) in low-altitude urban airspaces. However, the urban low-altitude airspace environment is complex. UAM has a high traffic density and the eVTOL aircraft specifications are not uniform. Particularly in commercial scenarios, controlling eVTOL aircraft and ensuring safety in UAMs are the two major problems that should be addressed in future studies. The design of reasonable traffic rules is a potential solution; hence, we organised a UAM traffic rule system and proposed several alternative UAM traffic rules from three perspectives: a single eVTOL aircraft, a certain route, and key control areas. In addition, we validated these traffic rules using multi-rotor and fixed-wing eVTOL aircraft. The results show that designing reasonable traffic rules can facilitate attaining the primary objectives of commercialisation of UAM.