A Range-Based Algorithm for Autonomous Navigation of an Aerial Drone to Approach and Follow a Herd of Cattle

This paper proposes an algorithm that will allow an autonomous aerial drone to approach and follow a steady or moving herd of cattle using only range measurements. The algorithm is also insensitive to the complexity of the herd’s movement and the measurement noise. Once arrived at the herd of cattle, the aerial drone can follow it to a desired destination. The primary motivation for the development of this algorithm is to use simple, inexpensive and robust sensing hence range sensors. The algorithm does not depend on the accuracy of the range measurements, rather the rate of change of range measurements. The proposed method is based on sliding mode control which provides robustness. A mathematical analysis, simulations and experimental results with a real aerial drone are presented to demonstrate the effectiveness of the proposed method.

LIDAR altimeter conception for HERA spacecraft

Purpose This paper aims to report the first iteration on the Light Detection and Ranging (LIDAR) Engineering Model altimeter named HELENA. HELENA is a Time of Flight (TOF) altimeter that provides time-tagged distances and velocity measurements. The LIDAR can be used for support near asteroid navigation and provides scientific information. The HELENA design comprises two types of technologies: a microchip laser and low noise sensor. The synergies between these two technologies enable developing a compact instrument for range measurements of up to 14 km. Thermal-mechanical and radiometric simulations of the HELENA telescope are reported in this paper. The design is subjected to vibrational, static and thermal conditions, and it was possible to conclude by the results that the telescope is compliant with the random vibration levels, the static load and the operating temperatures. Design/methodology/approach The Asteroid Impact & Deflection Assessment (AIDA) is a collaboration between the NASA DART mission and ESA Hera mission. The aim scope is to study the asteroid deflection through a kinetic collision. DART spacecraft will collide with Didymos-B, while ground stations monitor the orbit change. HERA spacecraft will study the post-impact scenario. The HERA spacecraft is composed by a main spacecraft and two small CubeSats. HERA will monitor the asteroid through cameras, radar, satellite-to-satellite doppler tracking, LIDAR, seismometry and gravimetry. Findings The HELENA design comprises two types of technologies: a microchip laser and low noise sensor. The synergies between these two technologies enable developing a compact instrument for range measurements of up to 14 km. Originality/value In this paper is reported the first iteration on the LIDAR Engineering Model altimeter named HELENA. HELENA is a TOF altimeter that provides time-tagged distances and velocity measurements. The LIDAR can be used for support near asteroid navigation and provides scientific information. The HELENA design comprises two types of technologies: a microchip laser and low noise sensor. The synergies between these two technologies enable developing a compact instrument for range measurements of up to 14 km.

Inter-Vehicle Position Estimation For NLOS Condition In The Persistence Of GPS Outages

The main focus of thesis work addresses one of the functional key points of Cooperative Collision Warning application which is an accurate estimation of the range data of neighboring vehicles during persistent GPS outages under both line-of-sight (LOS) and non-line-of-sight (NLOS) situations. Cooperative Collision Warning, based on vehicle-to-vehicle radio communications and GPS systems, is one promising active safety application that has attracted considerable research interest. One of the severe estimation error is due to NLOS that can be mitigated by applying biased Kalman filter on range measurements. For our algorithm these inter-vehicle distances are measured from using one of the radio-based ranging techniques. Main objective is to establish an accurate map of positions for neighboring vehicles in the persistance of GPS outages. GPS outages can be possible in multipath environments where NLOS component is introduced to the true range measurements. These position estimates mainly depend on two factors: (i) Preprocessed inter-vehicle distances (range data is processed from biased Kalman filter); (ii) Road constraints (the vehicle uncertainty is more in the direction of road than the uncertainty in the direction opposite the road); This thesis suggests smoothing and mitigating the NLOS for radio-based ranging measurements under multipath conditions. In order to find accurate positions of neighboring vehicles an extended Kalman filter is implemented along with road constraints. Unbiased Kalman filter, biased Kalman filter and extended Kalman filter performances are experimentally verified using Matlab simulation tool with random number of vehicles at unknown random distinct positions in some physical region along a section of road for vehicular environment.

Inter-Vehicle Position Estimation For NLOS Condition In The Persistence Of GPS Outages

The main focus of thesis work addresses one of the functional key points of Cooperative Collision Warning application which is an accurate estimation of the range data of neighboring vehicles during persistent GPS outages under both line-of-sight (LOS) and non-line-of-sight (NLOS) situations. Cooperative Collision Warning, based on vehicle-to-vehicle radio communications and GPS systems, is one promising active safety application that has attracted considerable research interest. One of the severe estimation error is due to NLOS that can be mitigated by applying biased Kalman filter on range measurements. For our algorithm these inter-vehicle distances are measured from using one of the radio-based ranging techniques. Main objective is to establish an accurate map of positions for neighboring vehicles in the persistance of GPS outages. GPS outages can be possible in multipath environments where NLOS component is introduced to the true range measurements. These position estimates mainly depend on two factors: (i) Preprocessed inter-vehicle distances (range data is processed from biased Kalman filter); (ii) Road constraints (the vehicle uncertainty is more in the direction of road than the uncertainty in the direction opposite the road); This thesis suggests smoothing and mitigating the NLOS for radio-based ranging measurements under multipath conditions. In order to find accurate positions of neighboring vehicles an extended Kalman filter is implemented along with road constraints. Unbiased Kalman filter, biased Kalman filter and extended Kalman filter performances are experimentally verified using Matlab simulation tool with random number of vehicles at unknown random distinct positions in some physical region along a section of road for vehicular environment.

Complexity and Limitations of GNSS Signal Reception in Highly Obstructed Enviroments

Multipath (MP) and/or Non Line-Of-Sight (NLOS) reception remains a potential vulnerability to satellite-based positioning and navigation systems in high multipath environments, such as an urban canyon. In such an environment, satellite signals are reflected, scattered or faded, and sometimes completely blocked by roofs and walls of high-rise buildings, fly-over bridges, complex road structures, etc. making positioning and navigation information inaccurate, unreliable, and largely unavailable. The magnitude of the positioning error depends on the satellite visibility, geometric distribution of satellites in the sky, and received signal quality and characteristics. The quality of the received signal (i.e. its statistical characteristics) can significantly vary in different environments and these variations can reflect in signal strength or power, range measurements (i.e. path delay and phase difference), and frequency, all of which distort the correlation curve between the received signal and receiver-generated replicas, resulting in range errors of tens of meters. Therefore, in order to meet stringent requirements defined for the Standard Positioning Service (SPS), the characterization of distortions that could significantly affect a Global Navigation Satellite System (GNSS) signal is essentially important. The scope of this paper is to detect possible imperfections/deviations in the GNSS signal characteristics that can occur due to MP or NLOS reception and analyze its effects. For this purpose, analysis of fading patterns in received signal strength (i.e. Carrier-to-Noise Ratio and strength fluctuations) is carried out in both clear LOS and high MP environment and then its impact on satellite lock state (i.e. tracking) is assessed. Furthermore, phase fluctuations and range residuals are computed to analyze the effects of path delays. The results show that significant variations can occur in GNSS signal characteristics in the MP environment that may result in loss of lock event and inaccurate/faulty range measurements.

Inflight performance of the state-of-the-art BepiColombo MORE radio-tracking system

<p>The ESA/JAXA mission BepiColombo, launched on 20 October 2018 is in cruise towards Mercury and will arrive at Mercury in 2025 to investigate its surface, interior structure and magnetosphere. The Mercury Orbiter Radio-science Experiment (MORE) onboard the Mercury Planetary Orbiter (MPO) aims at determining the gravity field, the rotational state and librations of the planet, using precise tracking of the spacecraft during its orbital phase around Mercury. Range and range-rate measurements collected during the cruise phase will be used to test the theory of general relativity starting in March 2021. The MORE experiment exploits two-way multifrequency microwave links from ESA and NASA: two downlinks in X- and Ka-band coherent with the X-band uplink and one Ka-band downlink coherent with the Ka-band uplink. The range-rate and range measurements accurately BepiColombo’s line-of-sight velocity and the round-trip light-time of the signal, respectively. The calibration of the dispersive plasma noise component through the combination of the X/X, X/Ka and Ka/Ka links and the use of water vapor radiometers to correct for the path delay due to Earth’s troposphere will result in an accuracy of ~3 µm/sec (at 1000-s integration time) on the Doppler and centimeter-level range accuracies. We report on the analysis of dedicated tests executed on range and Doppler data collected by ESA and NASA stations at X and Ka-band. The comparison of the observed noise with the predictions shows results exceeding the expectations. In particular, the 24 Mcps pseudo-noise modulation of the Ka-band carrier, enabled by MORE’s KaT transponder built by Thales Alenia Space Italia, provided two-way range measurements accurate to ~3 cm with just 4 s integration time, at a distance of 0.7 AU, September 2021, and 1.3 AU, November 2021. Under favorable weather conditions, the range rate has shown an accuracy of 25 µm/s at 10 s integration time, in line with the expected end-to-end performance. Under unfavorable weather conditions the performance was slightly over the requirements. We must remark that calibrations from water vapor radiometers were not available during these tests and only GNSS calibration were applied.</p>