arXiv subjects

David Čapek

Publications and source records attributed to David Čapek.

9 recordsLinked to original sources

arXiv2026

Kilometer-Scale GNSS-Denied UAV Navigation via Heightmap Gradients: A Winning System from the SPRIN-D Challenge

Reliable long-range flight of unmanned aerial vehicles (UAVs) in GNSS-denied environments is challenging: integrating odometry leads to drift, loop closures are unavailable in previously unseen areas and embedded platforms provide limited computational power. We present a fully onboard UAV system developed for the SPRIN-D Funke Fully Autonomous Flight Challenge, which required 9 km long-range waypoint navigation below 25 m AGL (Above Ground Level) without GNSS or prior dense mapping. The system integrates perception, mapping, planning, and control with a lightweight drift-correction method that matches LiDAR-derived local heightmaps to a prior geo-data heightmap via gradient-template matching and fuses the evidence with odometry in a clustered particle filter. Deployed during the competition, the system executed kilometer-scale flights across urban, forest, and open-field terrain and reduced drift substantially relative to raw odometry, while running in real time on CPU-only hardware. We describe the system architecture, the localization pipeline, and the competition evaluation, and we report practical insights from field deployment that inform the design of GNSS-denied UAV autonomy.

cs.RO↗

arXiv2026

Meteor clusters: tracing meteoroid fragmentation in near-Earth space

Meteor clusters are typically defined as groups of meteors that appear close together in both space and time. To date, only a handful of such events have been recorded instrumentally and analysed in detail. In many documented cases, thermal stress has been identified as the most likely cause of meteoroid fragmentation near Earth. This paper documents two further cases and provides a summary of all currently known clusters. The two clusters that were recorded over Hawaii Island in 2023 and 2024 represent two distinct scenarios. The 2024 meteor cluster was characterised by a dominant mass body and, with the fragments arranged along the antisolar direction according to their mass. Such cases enable us to reliably determine the age of the cluster and identify the most likely formation scenario. This cluster was around three days old, and the thermal stress was the most likely mechanism of its formation. The 2023 cluster was not such a case. It does not contain a mass dominant body, nor are its fragments arranged by their mass. Therefore, it was only possible to estimate its age to be no more than four days. Furthermore, other potential formation mechanisms besides thermal stress cannot be ruled out. This fact was observed in all analysed clusters. All clusters known up to date were formed in close proximity to Earth. The volume of a cluster increases with its age. This means that older clusters, formed by the fragmentation far away from Earth may remain undetected, as their fragments are also dispersed too widely to be observed by local experiment. However, global networks can detect such dispersed clusters.

astro-ph.EP↗

arXiv2025

Geminids are initially cracked by atmospheric thermal stress

Geminids have the highest bulk density of all major meteor showers and their mechanical strength appears to depend on their mass. They are also the most active annual shower, enabling detailed studies of the dependence of their physical and mechanical properties on mass. We calculated the fragmentation cascades of 39 bright Geminid fireballs, as well as faint video meteors, to derive fragmentation pressures and other physical properties characterizing the meteoroids, such as their bulk densities. Our goal is to describe the mechanical properties across a broad range of initial masses and explain the cause of the observed behavior. We used a physical fragmentation model with a semiautomatic method based on parallel genetic algorithms to fit the radiometric and regular light curve and dynamics data. We also calculated the thermal stress of model bodies with the type of physical properties and trajectories as the observed Geminids. Then, we compared the outcomes of these simulations to our observations. We find that the Geminids are probably cracked by thermal stress in the atmosphere first and then eroded by mechanical forces. The most compact Geminids are in the 20-200 g mass range. The largest observed meteoroids have a wide range of grain sizes, from about 20 um to large, non-fragmenting parts of 1-20 mm in size. The derived bulk densities range from about 1400 to 2800 kg/m3 for smaller meteoroids and approach the assumed grain density of 3000 kg/m3 for larger Geminids.

astro-ph.EP↗

arXiv2025

A very young tau-Herculid meteor cluster observed during a 2022 shower outburst

To date only very few meteor clusters have been instrumentally recorded. This means that every new detection is an important contribution to the understanding of these phenomena, which are thought to be evidence of the meteoroid fragmentation in the Solar System. On 31 May 2022, at 6:48:55 UT, a cluster consisting of 52 meteors was detected within 8.5 seconds during a predicted outburst of the tau-Herculid meteor shower. The aim of this paper is to reconstruct the atmospheric trajectories of the meteors and use the collected information to deduce the origin of the cluster. The meteors were recorded by two video cameras during an airborne campaign. Due to only the single station observation, their trajectories were estimated under the assumption that they belonged to the meteor shower. The mutual positions of the fragments, together with their photometric masses, was used to model the processes leading to the formation of the cluster. The physical properties of the cluster meteors are very similar to the properties of the tau-Herculids. This finding confirms the assumption of the shower membership used for the computation of atmospheric trajectories. This was the third cluster that we have studied in detail, but the first one where we do not see the mass separation of the particles. The cluster is probably less than 2.5 days old, which is too short for such a complete mass separation. Such an age would imply disintegration due to thermal stress. However, we cannot rule out an age of only a few hours, which would allow for other fragmentation mechanisms.

astro-ph.EP↗

arXiv2025

FlightForge: Advancing UAV Research with Procedural Generation of High-Fidelity Simulation and Integrated Autonomy

Robotic simulators play a crucial role in the development and testing of autonomous systems, particularly in the realm of Uncrewed Aerial Vehicles (UAV). However, existing simulators often lack high-level autonomy, hindering their immediate applicability to complex tasks such as autonomous navigation in unknown environments. This limitation stems from the challenge of integrating realistic physics, photorealistic rendering, and diverse sensor modalities into a single simulation environment. At the same time, the existing photorealistic UAV simulators use mostly hand-crafted environments with limited environment sizes, which prevents the testing of long-range missions. This restricts the usage of existing simulators to only low-level tasks such as control and collision avoidance. To this end, we propose the novel FlightForge UAV open-source simulator. FlightForge offers advanced rendering capabilities, diverse control modalities, and, foremost, procedural generation of environments. Moreover, the simulator is already integrated with a fully autonomous UAV system capable of long-range flights in cluttered unknown environments. The key innovation lies in novel procedural environment generation and seamless integration of high-level autonomy into the simulation environment. Experimental results demonstrate superior sensor rendering capability compared to existing simulators, and also the ability of autonomous navigation in almost infinite environments.

cs.RO↗

arXiv2024

Properties, age, and origin of a huge meteor cluster observed over Scandinavia on 30 October 2022

A meteor outburst consisting of at least 22 meteors above the Baltic sea and southern Scandinavia that occurred on 30 October 2022 was recorded using multiple cameras. A bright fireball was followed by fainter meteors over a 10 second period. All the meteors were travelling on parallel trajectories. The goal of this study is to determine the atmospheric trajectories and photometric masses of meteors and to use these data to determine the specifics of the progenitor meteoroid break-up and cluster formation. Double and triple-station observations using video cameras were used for the calculation of the atmospheric trajectories and photometric masses of the meteors. Their relative positions and mass distribution were then used to determine the time and cause of the meteoroid fragmentation. The relative position of the cluster particles in the atmosphere and the distribution of their masses best correspond to the separation of the smaller fragments from the mass-dominant fragment 10.6$\pm$1.7 days before the collision with Earth, assuming a meteoroid bulk density of 1000 kg.m$^{-3}$. The ejection velocities are in the range 0.16-0.61 m.s$^{-1}$. The directions of the ejection velocities are bounded by a cone with an apex angle of $43^\circ$. The axis of this cone has ecliptic coordinates of $l=154^\circ$ and $b=26^\circ$ and is $66^\circ$ away from the direction to the Sun. Thermal stresses appear to be the most likely cause of such meteor cluster formation.

astro-ph.EP↗

arXiv2022

Ejection velocities, age, and formation process of SPE meteoroid cluster

We follow our previous work about the September epsilon Perseid (SPE) meteoroid cluster from 2016. We assumed that the mass-dominated meteoroid is the parent body of the cluster and that the observed positions of meteoroids are controlled by the ejection velocities and the action of solar radiation pressure. A formula for the dependence of meteoroid ejection velocities on the mutual positions, masses, and cluster age was derived. Knowing values and directions of ejection velocities together with meteoroid masses then allowed us to determine the most likely process of cluster formation. The meteoroids occupy a volume of 66$\times$67$\times$50 km and are shifted in the antisolar direction by 27 km relative to the parent meteoroid. The age of the cluster is 2.28$\pm$0.44 days. The ejection velocities range from 0.13$\pm$0.05 m/s to 0.77$\pm$0.34 m/s with a mean value of 0.35 m/s. The ejection velocity directions are inside the cone with an apex angle of 101$\pm$5$^\circ$. The axis of the cone is $\sim$45$^\circ$ away from the solar direction and $\sim$34$^\circ$ away from the mean direction of the flux of small meteoroids' incident on the parent meteoroid. Formation due to the separation of part of the surface due to very fast rotation is the least likely thing to occur. We estimate the rotation frequency to be about 2 Hz and the corresponding stress is several orders of magnitude lower than the predicted strength limit. It is also difficult to explain the formation of the cluster by an impact of a small meteoroid on the parent body. However, this possibility, although not very likely, cannot be completely ruled out. The most probable process is the exfoliation due to thermal stresses. Their estimated magnitude is sufficient and the derived ejection velocities are consistent with this process of formation.

astro-ph.EP↗

arXiv2021

Search for pairs and groups in the 2006 Geminid meteor shower

The question of the existence of pairs and groups among the meteor showers is opened for a long time. The double station video observation of the 2006 Geminid meteor shower, one of the most active annual showers, is used for the search of such events. The atmospheric trajectories of the observed meteors, photometric masses, and both time and spatial distances of meteoroids in the atmosphere were determined using a double station video observation. Time gaps among them were analysed statistically. The Monte Carlo simulation was used for the determination of the probability of random pairings. Higher than expected number of candidates for pairs was found among 2006 Geminids. Evaluation of Poisson distribution shows that a significant fraction of them may be real cases. However, the Monte Carlo simulation did not confirm this result and provided a different view. Analysis of geometrical positions of candidate pairs also did not support the presence of real pairs and groups. Although we cannot exclude that some of them may be physically connected pairs, all the observed cases can be explained as the coincidental appearance of unrelated meteors.

astro-ph.EP↗

arXiv2014

Density, porosity and magnetic susceptibility of the Košice meteorite shower and homogeneity of its parent meteoroid

Bulk and grain density, porosity, and magnetic susceptibility of 67 individuals of Košice H chondrite fall were measured. The mean bulk and grain densities were determined to be 3.43 g/cm$^\text{3}$ with standard deviation (s.d.) of 0.11 g/cm$^\text{3}$ and 3.79 g/cm$^\text{3}$ with s.d. 0.07 g/cm$^\text{3}$, respectively. Porosity is in the range from 4.2 to 16.1%. The logarithm of the apparent magnetic susceptibility (in 10$^\text{-9}$ m$^\text{3}$/kg) shows narrow distribution from 5.17 to 5.49 with mean value at 5.35 with s.d. 0.08. These results indicate that all studied Košice meteorites are of the same composition down to ~g scale without presence of foreign (non-H) clasts and are similar to other H chondrites. Košice is thus a homogeneous meteorite fall derived from a homogeneous meteoroid.

astro-ph.EP↗