Low-flying Vehicle Research Articles

Altitude minimization of a group of unmanned low-flying vehicles without use of a priori information about the physical fields of the Earth

The article proposes a method for minimizing the altitued of a group of unmanned low-flying vehicles formed mainly over the lowest parts of the terrain. The input information is point slant ranges, the current parameters of the motion of the unmanned aerial vehicle and the specified end point of the route. As a result of the work, by means of computer simulation of Unmanned Arial Vehicle (UAV) motion in mountainous areas, the effectiveness of the proposed method for minimizing the altitude was evaluated. Computer simulation has shown that depending on the location of the start and end points of the trajectory, the terrain, the size of the permitted motion sector and the characteristics of the UAV, the average altitude of the trajectories of a group of low-flying vehicles decreases by approximately 150–540 m, which allows motion significantly below the tops of the terrain.

Optimization of 3D Trajectory of the Vehicle with Dynamic Principle of Maintaining According to the Criterion of Minimum Average True Geometric Altitude

The paper proposes to minimize the altitude of a low-flying vehicle near the waved sea surface due to the desire to lay a trajectory in smooth maneuvers mainly over the troughs of sea waves. The approach to the wave hollow is carried out by comparing the measurements of two radar altimeters and deviating the course by a certain amount in the direction of the altimeter, which showed higher altitude. The change in altitude is due to the property of self-stabilization of the vehicle and vertical maneuvers. The effectiveness of the proposed algorithm was evaluated by computer simulation of the movement of a light highly maneuverable vehicle under conditions of 6 sea state number. The simulation results showed the possibility of reducing the altitude from 3.0 to 2.35 meters and increasing the aerodynamic quality (lift-to-drag ratio) of the winged vehicle by 20%. It was also found that the greatest efficiency of minimizing altitude is achieved with the reference heading of the vehicle perpendicular to the general direction of sea wave’s propagation. The modeling did not take into account the influence of wind disturbances and accidental touches of the sea surface by the vehicle body, as well as the punching of the sea surface by air cushion. Consideration of these factors will be the direction of further research.

Minimizing the absolute height of a low-flying vehicle due to vertical tracking of long-period sea waves

Minimizing the absolute height of a low-flying vehicle due to vertical tracking of long-period sea waves

Minimization of the absolute altitude of a low-flying vehicle due to the desire to smoothly bend around the low-frequency components of the sea waves ordinate

The method for minimizing the altitude of a low-flying vehicle moving near the disturbed sea surface is proposed. The altitude is minimized due to the desire to go around the low-frequency components of sea waves, primarily due to the natural property of self-stabilization inherent in non-displacement vessels and wing in ground effect vehicles (WIGs). It is possible to increase the efficiency of minimizing the altitude using the elevator and flaps. It is shown in the work that this control method is quite effective for small maneuverable vehicles at a see wave intensity score above 4 points. In relation to WIGs, this method of movement allows to save fuel by increasing the aerodynamic quality of vehicles with the decrease in altitude.

СИНТЕЗ И АНАЛИЗ ТОЧНОСТИ СИСТЕМЫ ИЗМЕРЕНИЯ ПАРАМЕТРОВ МОРСКОГО ВОЛНЕНИЯ, ИСПОЛЬЗУЕМОЙ НА НИЗКОЛЕТЯЩЕМ АППАРАТЕ

СИНТЕЗ И АНАЛИЗ ТОЧНОСТИ СИСТЕМЫ ИЗМЕРЕНИЯ ПАРАМЕТРОВ МОРСКОГО ВОЛНЕНИЯ, ИСПОЛЬЗУЕМОЙ НА НИЗКОЛЕТЯЩЕМ АППАРАТЕ

Control of a group of low-flying vehicles near the waved sea surface in order to minimize their average altitude

The paper deals with a method of control over a group of flying vehicles to minimize their mean altitudes when in motion near the surface of rough sea. Using a method of mathematical simulation, effectiveness of minimizing these altitudes is defined, and, when surface-effects vehicles are controlled, fuel consumption is specified. This control method involves laying out vehicles’ trajectories along wave troughs so as to avoid their being bumped into each other. The results of simulation have demonstrated rationales for using this method in real control systems by low flying vehicles. At last, flying vehicles are simulated in a collaborative mission to join a rendezvous point by taking into account constraints on the flight altitude control and their respective maximum turn rates.

Evaluation of satellite remote sensing albedo retrievals over the ablation area of the southwestern Greenland ice sheet

MODerate resolution Imaging Spectroradiometer (MODIS) albedo products have been validated over spatially uniform, snow-covered areas of the Greenland ice sheet (GrIS) using the so-called single ‘point-to-pixel’ method. This study expands on this methodology by applying a ‘multiple-point-to-pixel’ method and examination of spatial autocorrelation (here using semivariogram analysis) by using in situ observations, high-resolution WorldView-2 (WV-2) surface reflectances, and MODIS Collection V006 daily blue-sky albedo over a spatially heterogeneous surfaces in the lower ablation zone in southwest Greenland. Our results using 232 ground-based samples within two MODIS pixels, one being more spatial heterogeneous than the other, show little difference in accuracy among narrow and broad band albedos (except for Band 2). Within the more homogenous pixel area, in situ and MODIS albedos were very close (error varied from −4% to +7%) and within the range of ASD standard errors. The semivariogram analysis revealed that the minimum observational footprint needed for a spatially representative sample is 30m. In contrast, over the more spatially heterogeneous surface pixel, a minimum footprint size was not quantifiable due to spatial autocorrelation, and far exceeds the effective resolution of the MODIS retrievals. Over the high spatial heterogeneity surface pixel, MODIS is lower than ground measurements by 4–7%, partly due to a known in situ undersampling of darker surfaces that often are impassable by foot (e.g., meltwater features and shadowing effects over crevasses). Despite the sampling issue, our analysis errors are very close to the stated general accuracy of the MODIS product of 5%. Thus, our study suggests that the MODIS albedo product performs well in a very heterogeneous, low-albedo, area of the ice sheet ablation zone.Furthermore, we demonstrate that single ‘point-to-pixel’ methods alone are insufficient in characterizing and validating the variation of surface albedo displayed in the lower ablation area. This is true because the distribution of in situ data deviations from MODIS albedo show a substantial range, with the average values for the 10th and 90th percentiles being −0.30 and 0.43 across all bands. Thus, if only single point is taken for ground validation, and is randomly selected from either distribution tails, the error would appear to be considerable. Given the need for multiple in-situ points, concurrent albedo measurements derived from existing AWSs, (low-flying vehicles (airborne or unmanned) and high-resolution imagery (WV-2)) are needed to resolve high sub-pixel variability in the ablation zone, and thus, further improve our characterization of Greenland's surface albedo.

Adaptive-Repetitive Visual-Servo Control of Low-Flying Aerial Robots via Uncalibrated High-Flying Cameras

This paper presents the design and implementation of an adaptive-repetitive visual-servo control system for a moving high-flying vehicle (HFV) with an uncalibrated camera to monitor, track, and precisely control the movements of a low-flying vehicle (LFV) or mobile ground robot. Applications of this control strategy include the use of high-flying unmanned aerial vehicles (UAVs) with computer vision for monitoring, controlling, and coordinating the movements of lower altitude agents in areas, for example, where GPS signals may be unreliable or nonexistent. When deployed, a remote operator of the HFV defines the desired trajectory for the LFV in the HFV’s camera frame. Due to the circular motion of the HFV, the resulting motion trajectory of the LFV in the image frame can be periodic in time, thus an adaptive-repetitive control system is exploited for regulation and/or trajectory tracking. The adaptive control law is able to handle uncertainties in the camera’s intrinsic and extrinsic parameters. The design and stability analysis of the closed-loop control system is presented, where Lyapunov stability is shown. Simulation and experimental results are presented to demonstrate the effectiveness of the method for controlling the movement of a low-flying quadcopter, demonstrating the capabilities of the visual-servo control system for localization (i.e.,, motion capturing) and trajectory tracking control. In fact, results show that the LFV can be commanded to hover in place as well as track a user-defined flower-shaped closed trajectory, while the HFV and camera system circulates above with constant angular velocity. On average, the proposed adaptive-repetitive visual-servo control system reduces the average RMS tracking error by over 77% in the image plane and over 71% in the world frame compared to using just the adaptive visual-servo control law.