Automatic coarse co-registration of point clouds from diverse scan geometries: a test of detectors and descriptors

Point clouds are collected nowadays from a plethora of sensors, some having higher accuracies and higher costs, some having lower accuracies but also lower costs. Not only there is a large choice for different sensors, but also these can be transported by different platforms, which can provide different scan geometries. In this work we test the extraction of four different keypoint detectors and three feature descriptors. We benchmark performance in terms of calculation time and we assess their performance in terms of accuracy in their ability in coarse automatic co-registration of two clouds that are collected with different sensors, platforms and scan geometries. One, which we define as having the higher accuracy, and thus will be used as reference, was surveyed via a UAV flight with a Riegl MiniVUX-3, the other on a bicycle with a Livox Horizon over a walking path with un-even ground.The novelty in this work consists in comparing several strategies for fast alignment of point clouds from very different surveying geometries, as the drone has a bird's eye view and the bicycle a ground-based view. An added challenge is related to the lower cost of the bicycle sensor ensemble that, together with the rough terrain, reasonably results in lower accuracy of the survey. The main idea is to use range images to capture a simplified version of the geometry of the surveyed area and then find the best features to match keypoints. Results show that NARF features detected more keypoints and resulted in a faster co-registration procedure in this scenariowhereas the accuracy of the co-registration is similar to all the combinations of keypoint detectors and features

EXPERIMENTAL VALIDATION OF A DEPLOYMENT MECHANISM FOR TAPE-TETHERED SATELLITES

The number of space debris orbiting our Earth has been continuously increasing since the beginning of the space era. The space community is converging on responsible conducts and self-regulations to address this serious problem that is degrading the near-Earth environment. In this context, green deorbiting technologies and strategies alternative to the traditional chemical propulsion are under investigation, including Electrodynamic Tethers (EDTs) because they are a promising option. To increase EDT technology maturity level, some critical points shall be addressed and experimentally evaluated, including the deployment of tape tethers, to demonstrate their reliability. This paper presents results of an experimental validation of the Deployment Mechanism (DM) proposed for the H2020 FET OPEN Project E.T.PACK \u2013 Electrodynamic Tether Technology for Passive Consumable-less Deorbit Kit. We developed a mockup that hosts the DM and other elements that are on board the tip mass of a tethered system, using off-the-shelf components. The DM is tested for the first part of the tether deployment maneuver employing the SPARTANS facility of the University of Padova. This facility includes a Testing Table where the mock-up can move with almost no friction and a Motion Capture system that provides an accurate estimation of the mock-up motion during this first part of the tether deployment maneuver

Observing Mercury: from Galileo to the stereo camera on the BepiColombo mission

AbstractAfter having observed the planets from his house in Padova using his telescope, in January 1611 Galileo wrote to Giuliano de Medici that Venus is moving around the Sun as Mercury. Forty years ago, Giuseppe Colombo, professor of Celestial Mechanics in Padova, made a decisive step to clarify the rotational period of Mercury. Today, scientists and engineers of the Astronomical Observatory of Padova and of the University of Padova, reunited in the Center for Space Studies and Activities (CISAS) named after Giuseppe Colombo, are busy to realize a stereo camera (STC) that will be on board the European (ESA) and Japanese (JAXA) space mission BepiColombo, devoted to the observation and exploration of the innermost planet. This paper will describe the stereo camera, which is one of the channels of the SIMBIOSYS instrument, aiming to produce the global mapping of the surface with 3D images

In-lab characterization of HYPSOS, a novel stereo hyperspectral observing system: first results

HYPSOS (HYPerspectral Stereo Observing System, patented) is a novel remote sensing instrument able to extract the spectral information from the two channels of a pushbroom stereo camera; thus it simultaneously provides 4D information, spatial and spectral, of the observed features. HYPSOS has been designed to be a compact instrument, compatible with small satellite applications, to be suitable both for planetary exploration as well for terrestrial environmental monitoring. An instrument with such global capabilities, both in terms of scientific return and needed resources, is optimal for fully characterizing the observed surface of investigation. HYPSOS optical design couples a pair of folding mirrors to a modified three mirror anastigmat telescope for collecting the light beams from the optical paths of the two stereo channels; then, on the telescope focal plane, there is the entrance slit of an imaging spectrograph, which selects and disperses the light from the two stereo channels on a bidimensional detector. With this optical design, the two stereo channels share the large majority of the optical elements: this allowed to realize a very compact instrument, which needs much less resources than an equivalent system composed by a stereo camera and a spectrometer. To check HYPSOS actual performance, we realized an instrument prototype to be operated in a laboratory environment. The laboratory setup is representative of a possible flight configuration: the light diffused by a surface target is collimated on the HYPSOS channel entrance apertures, and the target is moved with respect to the instrument to reproduce the in- flight pushbroom acquisition mode. Here we describe HYPSOS and the ground support equipment used to characterize the instrument, and show the preliminary results of the instrument alignment activities

Preliminary observation of Marmolada glacier collapse of July 2022 with space-based cameras

On 3 July 2022, a section of the Marmolada glacier (Marmolada Group, Fassa Dolomites, Southern Limestone Alps) collapsed, causing an ice avalanche resulting in the death of 11 alpinists. Before the event, there were no clear signs of any potential collapse, and no warning notices were broadcasted; due to the velocity of the avalanche, no escape was possible for the involved persons. In this work, a preliminary analysis of the Marmolada glacier collapse is performed with four optical channels space imaging provided by Planet Labs, with resolution of 3 m per pixel. Pre- and post-event satellite observations are employed to assess the areas involved in the event: multispectral images can be compared to identify the collapse area and the debris conoid. A first estimation suggests a collapse area of about 4800 m2 and a collapse volume of about 96,000 m3. In addition, historical data from the Planet Labs optical pictures database can be employed to compare the status of the detached glacier and the evolution of the crevasses on its surface

DESIGN OF A SMALL AXIAL-FLOW FAN WITH 0.2 HUB-TO-TIP RATIO

This paper presents the design of a 315mm axial fan obtained using the practical design approach recently proposed by the authors. Aim of the work is to explore the capability of the suggested method when a design with minimum hub-to-tip ratio is pursued. To this end, a 0.2 hub-to-tip ratio fan has been designed for the same dimensionless duty as an existing 1845mm propeller fan, whose shape and performance are known from the literature. In the paper, the ISO-5801 aerodynamic performance are compared with those measured for the reference fan and its scaled model. The results demonstrate the effectiveness of the design approach and quantify the combined effect of size and Reynolds number on the fan performance

Design of a Small Axial-Flow Fan with 0.2 Hub-to-tip Ratio

This paper presents the arbitrary vortex design of a 315 mm industrial fan prototype obtained by using a practical design approach recently proposed by the authors. Aim of the paper is to explore the capability of the suggested design method in a 0.2 hub-to-tip ratio application. This very low hub-to-tip ratio has been chosen because design examples with such a small hub-to-tip are rather rare in the literature. In fact, common design approaches relying on the cylindrical surfaces flow approximation are conceptually not suited to machines which design point operation features a strong flow recirculation in the innermost region of the blade span and a marked radial shift of the meridional flow in the remaining part of the blade span. Although there are examples of industrial fans with hub-to-tip ratio even lower that 0.2, the value of 0.2 should be considered as practical effective lower bound. In fact, existing applications with hub-to-tip ratio lower than 0.2 are usually coupled with hub disk solution and with a non-aerofoil inner part of the blades. Thus, it is expected that the aerodynamic performance of these fans is almost not dependent on the design of the blade portion close to the hub zone. In the paper, the presentation of the new 0.2 fan prototype is followed by the report of the fan aerodynamic performance, measured on an ISO 5801 test rig. These data are compared with the corresponding data of a 0.14 hub-to-tip ratio which incorporates aerofoil blades only in outer part of the span (radial coordinate - made dimensionless with the hub radius - higher than 0.2). Since the data available for the 0.14 hub-to-tip ratio have been measured for a 1845 mm industrial fan, a 315 mm scaled version, in which the hub has been enlarged to incorporate the non-aerofoil part of the blade, has been printed by rapid prototyping to estimate the decrease of aerodynamic performance due to the smaller size of the prototypes and to predict the aerodynamic performance achievable from the design obtained using the design approach proposed by the authors whether the machine is manufactured in large size. The results demonstrate the effectiveness of the design approach and quantify the combined effect of size and Reynolds number on the fan performance