Ultralight Radar Sensor for Autonomous Operations by Mini- and Micro-UAS

In recent years the boost in operations by mini- and micro-UAS (Unmanned Aircraft Systems, also known as Remotely Piloted Aircraft Systems - RPAS - or simply drones) and the successful miniaturization of electronic components were experienced. Radar sensors demonstrated to have favorable features for these operations. However, despite their ability to provide meaningful information for navigation, sense-and-avoid, and imaging tasks, currently very few radar sensors are exploited onboard or developed for autonomous operations with mini- and micro-UAS. Exploration of indoor complex, dangerous, and not easily accessible environments represents a possible application for mini-UAS based on radar technology. In this scenario, the objective of the thesis is to develop design strategies and processing approaches for a novel ultralight radar sensor able to provide the miniaturized platform with Simultaneous Localization and Mapping (SLAM) capabilities, mainly but not exclusively indoors. Millimeter-wave Interferometric Synthetic Aperture Radar (mmw InSAR) technology has been identified as a key asset. At the same time, testing of commercial lightweight radar is carried out to assess potentialities towards autonomous navigation, sense-and-avoid, and imaging. The two main research lines can be outlined as follows: - Long-term scenario: Development of very compact and ultralight Synthetic Aperture Radar able to provide mini- or micro-UAS with very accurate 3D awareness in indoor or GPS-denied complex and harsh environments. - Short-term scenario: Assessment of true potentialities of current commercial radar sensors in a UAS-oriented scenario. Within the framework of long-term scenario, after a review of state-of-art SAR sensors, Frequency-Modulated Continuous Wave (FMCW) SAR technology has been selected as preferred candidate. Design procedure tailored to this technology and software simulator for operations have been developed in MATLAB environment. Software simulator accounts for the analysis of ambiguous areas in a three-dimensional environment, different SAR focusing algorithms, and a Ray-Tracing algorithm specifically designed for indoor operations. The simulations provided relevant information on actual feasibility of the sensor, as well as mission design characteristics. Additionally, field tests have been carried out at Fraunhofer Institute FHR with a mmw SAR. Processing approaches developed from simulations proved to be effective when dealing with field tests. A very lightweight FMCW radar sensor manifactured by IMST GmbH has been tested for short-term scenario operations. The codes for data acquisition were developed in Python language both for Windows-based and GNU/Linux-based operative systems. The radar provided information on range and angle of targets in the scene, thus being interesting for radar-aided UAS navigation. Multiple-target tracking and radar odometry algorithms have been developed and tested on actual field data. Radar-only odometry provided to be effective under specific circumstances

NAV-Landmarks: deployable 3D infrastructures to enable CubeSats navigation near asteroids

Autonomous operations in the proximity of Near Earth Objects (NEO) are perhaps the most challenging and demanding type of mission operation currently being considered. The exceptional variability of geometric and illumination conditions, the scarcity of large scale surface features and the strong perturbations in their proximity require incredibly robust systems to be handled. Robustness is usually introduced by either increasing the number and/or the complexity of on-board sensors, or by employing algorithms capable of handling uncertainties, often computationally heavy. While for a large satellite this would be predominantly an economic issue, for small satellites these constraints might push the ability to accomplish challenging missions beyond the realm of technical possibility. The scope of this paper is to present an active approach that allows small satellites deployed by a mothership to perform robust navigation using only a monocular visible camera. In particular, the introduction of Non-cooperative Artificial Visual landmarks (NAVLandmarks) on the surface of the target object is proposed to augment the capabilities of small satellites. These external elements can be effectively regarded as an infrastructure forming an extension of the landing system. The quantitative efficiency estimation of this approach will be performed by comparing the outputs of a visual odometry algorithm, which operates on sequences of images representing ballistic descents around a small non-rotating asteroid. These sequences of virtual images will be obtained through the integration of two simulated models, both based on the Apollo asteroid 101955 Bennu. The first is a dynamical model, describing the landing trajectory, realized by integrating over time the gravitational potential around a three-axis ellipsoid. The second model is visual, generated by introducing in Unreal Engine 4 a CAD model of the asteroid (with a resolution of 75 cm) and scattering on its surface a number N of cubes with side length L. The effect of both N and L on the navigation accuracy will be reported. While defining an optimal shape for the NAV-Landmarks is out of the scope of this paper, prescriptions about the beacons geometry will be provided. In particular, in this work the objects will be represented as high-visibility cubes. This shape satisfies, albeit in a non-optimal way, most of the design goals

Performance analysis of millimeter wave FMCW InSAR for UAS indoor operations

This paper discusses the performance of a novel millimeter wave radar sensor for UAS autonomous indoor operations. A sensor based on the interferometric Synthetic Aperture Radar (SAR) principle should be able to satisfy the stringent requirements set by indoor operations in terms of high-resolution three-dimensional mapping and autonomous navigation. A solution based on a Frequency Modulated Continuous Wave (FMCW) technology is proposed. The outlined nominal configuration serves as a basis to analyze the performance of the sensor in possible operational scenarios by means of a software simulator. Four different focusing algorithms are implemented and tested and capabilities of the novel sensor are finally discussed, demonstrating that high-resolution, high-quality observation of an assigned control volume can be achieved

FREQUENCY MODULATED CONTINUOUS WAVE SYNTHETIC APERTURE RADAR FOCUSING TECHNIQUES: A REVIEW IN THE FRAMEWORK OF INDOOR AUTONOMOUS OPERATIONS BY SMALL UNMANNED AERIAL SYSTEMS

This paper provides a review of FMCW SAR focusing techniques, in both time and frequency domains. Major advantages and disadvantages of each algorithms are highlighted with reference to indoor autonomous operations by small UAS. Simple example of operational scenarios are analyzed in order to give a practical comparison between each method

Compact millimeter wave FMCW InSAR for UAS indoor navigation

This paper presents a novel millimeter wave radar sensor for UAS applications, in particular autonomous navigation in indoor GPS-denied environment. The sensor is aimed at both navigation with obstacle detection and highresolution 3D mapping with moving target detection. Poor visibility due to dust, fog, smoke or flames often causes failure of state-of-the-art sensors for UAS, which are very sensitive to environmental conditions. On the contrary, a sensor based on the Interferometric Synthetic Aperture Radar (InSAR) principle has been identified as potential candidate to satisfy stringent requirements set by indoor autonomous operations. Main features of the architectural solution based on frequency-modulated continuous wave (FMCW) scheme and millimeter-wave technology are discussed. New procedures for system design are outlined and a set of nominal values for the system are provided. Finally, a software simulator, developed in order both to demonstrate that high-resolution, high-quality observation of an assigned control volume can be achieved and to assess mapping capabilities, is presented

Investigation on radar-based applications for mini-UAS and MAVs

This paper investigates the capability of a miniaturized radar sensor developed for mini Unmanned Aerial Systems (UAS) and Micro Aerial Vehicles (MAVs) to provide the flying platform with radar-based navigation and sense-and-avoid (SAA) functions. A radar sensor based on Frequency Modulated Continuous Wave (FMCW) technology developed by IMST GmbH is therefore exploited both for tracking, SAA, and Synthetic Aperture Radar (SAR) oriented acquisitions. Main challenges related with data interpretation are analyzed and the results suggest that valuable data for each envisaged application can be obtained

Indoor Operations by FMCW Millimeter Wave SAR Onboard Small UAS: A Simulation Approach

A dedicated system simulator is presented in this paper for indoor operations onboard small Unmanned Aerial Systems (UAS) by a novel millimeter wave radar sensor. The sensor relies on the principle of Synthetic Aperture Radar (SAR) applied to a Frequency Modulated Continuous Wave (FMCW) radar system. Input to the simulator are both design parameters for Synthetic Aperture Radar (SAR), which should be able to cope with the stringent requirements set by indoor operations, and information about platform navigation and observed scene. The scene generation task is described in detail. This is based on models for point target response on either a completely absorbing background or fluctuating background and ray tracing (RT) techniques. Results obtained from scene processing are finally discussed, giving further insights on expected results from high-resolution observation of an assigned control volume by this novel SAR sensor

MULTI-PURPOSES RADAR FOR REMOTE SENSING AND NAVIGATION BY MINI AND MICRO UNMANNED AERIAL VEHICLES

This paper investigates the capability of a miniaturized radar sensor developed for Micro Aerial Vehicles (MAVs) to cope with complex mission scenarios that involve integrating and satisfying either Synthetic Aperture Radar (SAR) or Interferometric SAR and navigation and Sense-and-Avoid (SAA) requirements. A radar sensor based on Frequency Modulated Continuous Wave (FMCW) technology developed by IMST GmbH is exploited both for SAR and SAA acquisitions. The set of tests helps with understanding main issues and problems related with integration of different requirements and demonstrate that valuable data for each envisaged application can be saved with a single acquisition, thus paving the road for further and more detailed investigations

Preliminary Study of a Millimeter Wave FMCW InSAR for UAS Indoor Navigation

Small autonomous unmanned aerial systems (UAS) could be used for indoor inspection in emergency missions, such as damage assessment or the search for survivors in dangerous environments, e.g., power plants, underground railways, mines and industrial warehouses. Two basic functions are required to carry out these tasks, that is autonomous GPS-denied navigation with obstacle detection and high-resolution 3Dmapping with moving target detection. State-of-the-art sensors for UAS are very sensitive to environmental conditions and often fail in the case of poor visibility caused by dust, fog, smoke, flames or other factors that are met as nominal mission scenarios when operating indoors. This paper is a preliminary study concerning an innovative radar sensor based on the interferometric Synthetic Aperture Radar (SAR) principle, which has the potential to satisfy stringent requirements set by indoor autonomous operation. An architectural solution based on a frequency-modulated continuous wave (FMCW) scheme is proposed after a detailed analysis of existing compact and lightweight SAR. A preliminary system design is obtained, and the main imaging peculiarities of the novel sensor are discussed, demonstrating that high-resolution, high-quality observation of an assigned control volume can be achieve

Experimental Analysis of Radar Odometry by Commercial Ultralight Radar Sensor for Miniaturized UAS

Autonomous navigation of miniaturized Unmanned Aircraft Systems (UAS) in complex environments, when Global Positioning System is unreliable or not available, is still an open issue. This paper contributes to that topic exploring the use of radar-only odometry by existing commercial ultralight radars. The focus is set on an end-to-end Multiple-Target Tracking strategy compliant with desired sensor and platform, which exploits both range and bearing measurements provided by the radar. A two-dimensional odometry approach is then implemented. Main results show real-time capabilities and standard deviation of errors in Forward and Cross-range directions smaller than 1.50 m and 3.00 m, respectively. Field test data are also used to discuss the potential of this technique, challenging issues, and future improvement