Mission-Oriented Autonomy for Intelligent, Adaptive, and Multi-Agent Remote Sensing of Ice Sheets using Unmanned Aerial Systems

Throughout our history, humanity has been developing and progressing technology in order to help us better understand the world in which we live. As climate change becomes an increasingly urgent global crisis, scientists have been tasked with developing models for better understanding the complex dynamics involved, as well as to more accurately forecast the long term effects on our environment. With respect to sea level rise, both our knowledge of these dynamics and the accuracy of these models can be improved through the routine collection of crucial data concerning glacier ice thickness and bedrock topology. To accomplish this, innovative solutions are being developed by groups of inter-disciplinary research teams, combining fields such as earth-science, radar systems, data science, and aerospace engineering. Through this collaboration, we have the potential to leverage breakthroughs in unmanned systems technology and miniaturized, specialized sensors for comprehensive, precise, and routine data collection of key polar research objectives. As Unmanned Aerial Systems (UASs) have become more reliable research platforms in recent years, they now have the capability to perform these remote sensing operations at a reduced cost compared to manned operations, while also providing repeatable, precision tracking capabilities along flight lines, enabling the surveying of tightly-spaced grids, and removing human flight crews from hazardous polar environments. However, the payload, range, and wind constraints for these platforms severely restrict their operational sensing footprint. Additionally, UASs generally have a much smaller wingspan compared to manned aircraft typically used in Earth Science missions, which becomes a challenging factor for incorporating efficient directive antennas at the low operating frequencies required for glacial sounding. The aim of this work is to address these issues and to enhance mission efficiency and the overall quality of data collection for these operations through the implementation of onboard mission-oriented autonomy that includes cognitive decision-making for intelligent survey operations, adaptive functionalities, and a scalable, robust framework for multi-agent operations. As opposed to conventional methods for polar research operations which generally involve single-agent missions, using standard waypoint guidance and fixed-routes planned by human operators, the unique contributions of the developed mission-oriented autonomy in this work include: 1) Automated flight line generation for rapid and reliable mission planning of tightly-spaced flight lines required for cross-track synthetic aperture radar processes and surface clutter suppression, with required spacing based on the operating frequency of the onboard radar system. 2) Implementation of Dubins Path guidance methods into polar research operations for precision end-to-end survey of mission flight lines while taking into account the kinematic constraints of the fixed wing aircraft, as well as for efficiently traversing to and from a home loiter location during mission operations. 3) Cognitive, real-time optimal path planning through mission flight lines utilizing both deterministic and stochastic Traveling Salesman Problem heuristics. 4) Modifications to these Traveling Salesman Problem heuristics for ensuring safe, feasible, and reliable operations in real-time by taking into account aircraft range constraints. 5) Collaborative Multi-Agent survey operations utilizing space partitioning and Hungarian Assignment for distributed task allocation, as well as morphing potential fields for collision avoidance. 6) Modifications for Multi-Agent deployment scheduling to reduce inter-agent interference for sensitive radar systems to improve coherency of the collected data, and to rapidly and efficiently deploy agents into and out of survey areas. 7) Modifications for Heterogeneous flight operations for increasing operational capabilities through cross-platform collaboration. 8) Failsafe features to instill robustness in Multi-Agent operations with respect towards accommodating and adapting to single-agent system failures, by automatically re-planning collaborative survey operations. In this work, the motivation for the creation of this mission-oriented autonomy is discussed, along with the methodology of each of the autonomy features, and the framework for implementation onto UAS platforms. Case studies are conducted for past and future polar research deployments using unmanned systems to assess the potential improvements in operational capabilities and data collection for the developed autonomy compared to conventional methods. Finally, the developed autonomy is implemented onto an embedded system for preliminary flight testing and validation, as well as used for intelligent mission planning for a manned operation

Analysis of a Radar system for UAV Tracking using MATLAB

Volume 7 Issue 6 (June 201

Development and Improvement of Airborne Remote Sensing Radar Platforms

With the recent record ice melt in the Arctic as well as the dramatic changes occurring in the Antarctic, the need and urgency to characterize ice sheets in these regions has become a research thrust of both the NSF and NASA. Airborne remote sensing is the most effective way to collect the necessary data on a large scale with fine resolution. Current models for determining the relationship between the world's great ice sheets and global sea-level are limited by the availability of data on bed topography, glacier volume, internal layers, and basal conditions. This need could be satisfied by equipping long range aircraft with an appropriately sensitive suite of sensors. The goal of this work is to enable two new airborne radar installations for use in cryospheric surveying, and improve these systems as well as future systems by addressing aircraft integration effects on antenna-array performance. An aerodynamic fairing is developed to enable a NASA DC-8 to support a 5-element array for CReSIS's MCoRDS radar, and several structures are also developed to enable a NASA P-3 to support a 15-element MCoRDS array, as well as three other radar antenna-arrays used for cryospheric surveying. Together, these aircraft have flown almost 200 missions and collected 550 TB of unique science data. In addition, a compensation method is developed to improve beamforming and clutter suppression on wing-mounted arrays by mitigating phase center errors due to wing-flexure. This compensation method is applied to the MVDR beamforming algorithm to improve clutter suppression by using element displacement information to apply appropriate phase shifts. The compensation demonstrated an average SINR increase of 5-10 dB. The hardware contributions of this work have substantially contributed to the state-of-the-art for polar remotes sensing, as evidenced by new data sets made available to the science community and widespread use and citation of the data. The investigations of aircraft integration effects on antenna-arrays will improve future data sets by characterizing the performance degradation. The wing-flexure compensation will greatly improve beam formation and clutter suppression. Increased clutter suppression in airborne radars is crucial to improving next generation ice sheet models and sea-level rise predictions

Linearization using Digital Predistortion of a High-Speed, Pulsed, Radio Frequency Power Amplifier for VHF Radar Depth-Sounder Systems

Depth-sounding radar systems provide the scientific data that are useful in modeling polar ice sheets and predicting sea-level rise. These radars are typically deployed on crewed aircraft; however, crewed missions over polar regions are difficult and dangerous. Thus, CReSIS is developing uninhabited aerial vehicles (UAVs) from which fine-resolution measurements can be made over vast areas. These fine-resolution measurements require highly linear power amplifiers (PAs) to create low range side-lobe levels. However, highly linear PAs are typically less efficient and require large and bulky heat sinks for heat dissipation, which increases the payload weight and decreases flight time. Furthermore, the linear FM chirp signal used for these radar systems creates Fresnel ripples and side-lobes will be generated when there are deviations from the ideal rectangular spectrum amplitude even with efficient windowing techniques, such as a Tukey window. Therefore, a 100 W, high-speed, pulsed, VHF power amplifier was developed and linearized using memoryless digital predistortion (DP) to obtain high linearity and high efficiency. The DP linearization decreased near-range side-lobe levels 11 dB from -46 dBc to -57 dBc, with a maximum reduction in the far-range side-lobe levels of 17 dB over the Tukey (transmit) and Blackmann2 (receive) windowing alone. The high-speed switching circuit reduced current consumption to 117 mA (or 3.28 W at +28 V) for a 10-us pulse at 1-kHz PRF

UAVs for Science in Antarctica

Remote sensing is a very powerful tool that has been used to identify, map and monitor Antarctic features and processes for nearly one century. Satellite remote sensing plays the main role for about the last five decades, as it is the only way to provide multitemporal views at continental scale. But the emergence of small consumer-grade unoccupied aerial vehicles (UAVs) over the past two decades has paved the way for data in unprecedented detail. This has been also verified by an increasing noticeable interest in Antarctica by the incorporation of UAVs in the field activities in diversified research topics. This paper presents a comprehensive review about the use of UAVs in scientific activities in Antarctica. It is based on the analysis of 190 scientific publications published in peer-reviewed journals and proceedings of conferences which are organised into six main application topics: Terrestrial, Ice and Snow, Fauna, Technology, Atmosphere and Others. The analysis encompasses a detailed overview of the activities, identifying advantages and difficulties, also evaluating future possibilities and challenges for expanding the use of UAV in the field activities. The relevance of using UAVs to support numerous and diverse scientific activities in Antarctica becomes very clear after analysing this set of scientific publications, as it is revolutionising the remote acquisition of new data with much higher detail, from inaccessible or difficult to access regions, in faster and cheaper ways. Many of the advances can be seen in the terrestrial areas (detailed 3D mapping; vegetation mapping, discrimination and health assessment; periglacial forms characterisation), ice and snow (more detailed topography, depth and features of ice-sheets, glaciers and sea-ice), fauna (counting penguins, seals and flying birds and detailed morphometrics) and in atmosphere studies (more detailed meteorological measurements and air-surface couplings). This review has also shown that despite the low environmental impact of UAV-based surveys, the increasing number of applications and use, may lead to impacts in the most sensitive Antarctic ecosystems. Hence, we call for an internationally coordinated effort to for planning and sharing UAV data in Antarctica, which would reduce environmental impacts, while extending research outcomes.info:eu-repo/semantics/publishedVersio

Bed topography of Jakobshavn Isbrae, Greenland, and Byrd Glacier, Antarctica

This is the published version. Copyright 2015 International Glaciological SocietyThis paper presents the bed topography of Jakobshavn Isbrae, Greenland, and Byrd Glacier, Antarctica, derived from sounding these glaciers with high-sensitivity radars. To understand the processes causing the speed-up and retreat of outlet glaciers, and to enable the development of next-generation ice-sheet models, we need information on bed topography and basal conditions. To this end, we performed measurements with the progressively improved Multichannel Coherent Radar Depth Sounder/Imager (MCoRDS/I). We processed the data from each antenna-array element using synthetic aperture radar algorithms to improve radar sensitivity and reduce along-track surface clutter. We then applied array and image-processing algorithms to extract the weak bed echoes buried in off-vertical scatter (cross-track surface clutter). At Jakobshavn Isbrae, we observed 2.7 km thick ice ∼30 km upstream of the calving front and ∼850 m thick ice at the calving front. We also observed echoes from multiple interfaces near the bed. We applied the MUSIC algorithm to the data to derive the direction of arrival of the signals. This analysis revealed that clutter is dominated by the ice surface at Jakobshavn Isbrae. At Byrd Glacier, we found ∼3.62 km thick ice, as well as a subglacial trench ∼3.05 km below sea level. We used ice thickness information derived from radar data in conjunction with surface elevation data to generate bed maps for these two critical glaciers. The performance of current radars must be improved further by ∼15 dB to fully sound the deepest part of Byrd Glacier. Unmanned aerial systems equipped with radars that can be flown over lines spaced as close as 5 m apart in the cross-track direction to synthesize a two-dimensional aperture would be ideal for collecting fine-resolution data over glaciers like Jakobshavn near their grounding lines

UAVs for the Environmental Sciences

This book gives an overview of the usage of UAVs in environmental sciences covering technical basics, data acquisition with different sensors, data processing schemes and illustrating various examples of application

An Improved Gain Wing-Integrated Antenna Design for Meridian UAS and Sensor-Driven Wing Sizing Approach

Ice sheets in Antarctic and Arctic regions are undergoing rapid changes, causing a rise in sea level with direct impacts on society and the global system. Airborne remote sensing offers a robust way to study changes occurring in this region and the effects on climate. The Center for Remote Sensing of Ice Sheets (CReSIS) has flown many missions in polar regions to collect data on bed topography, basal conditions, and deep internal layers by using high-sensitivity radar and advanced processing algorithms. The goal of the current study is two-fold. First, a new wing-integrated antenna concept is developed for the Meridian, an Unmanned Aerial System (UAS) designed at the University of Kansas. Second, preliminary wing-sizing equations are derived from wing-integrated antenna performance analyses. The purpose of both studies is to improve both current and future UAS sensor-platforms used for remote sensing applications, such as those currently supported by CReSIS. An improved design of a wing-integrated airborne antenna array is presented by performing an antenna trade study for three low-profile antennas. This study seeks to improve not only the gain of the antenna system but the aircraft performance by developing a structurally-embedded design. Three candidate antenna designs are carried forward to the detailed design stage. These designs include a planar dipole embedded in the lower wing skin of the vehicle, a planar dipole offset a quarter-wavelength from the conductive lower wing-skin via a custom support structure, and a quarter-wave patch antenna integrated inside the wing. Considering the existing wing size limitations for antenna array integration into the Meridian wing, two different designs are recommended—the first design strictly optimizing antenna performance for the given wing size limitations and the second design improving both the electrical and vehicle performance over the original design. The planar dipole antenna offset from a ground plane offers the best results in terms of antenna performance within aircraft’s dimensional constraint. In the first design, when antenna performance is given priority, the final offset array design results in a gain improvement of about 6 dB over existing Vivaldi system. Since the ratio of received power to transmitted power is proportional to square of the gain (by Friis equation), for an antenna acting as a transmitter and receiver, the gain is actually doubled (i.e. about 12 dB improvement in gain) in decibel (dB) scale. However, this design significantly increased drag, which is expected to reduce the vehicle range by ~31% compared to the Vivaldi system. This design also adds a total additional weight of 84 lbs. due to the antenna supporting structure and modifications made to the existing Meridian wing. The second design, a dipole array embedded in the wing (bay) skin, offers advantages for both aircraft and sensor performance. The advantages, particularly from a sensor perspective, are relatively small. When compared to the existing Vivaldi system, the embedded antenna design results in ~6% increase in aircraft range, and about 2.5 dB (actually about 5 dB by Friis equation) increase in gain. This design adds an extra weight of 9.5 lbs. per wing due to composite material modifications. The results of these two systems illustrate the constant compromise that occurs between vehicle and sensor performance, and the difficulty to optimize both systems simultaneously. This study then extends toward a sensor-driven wing sizing study, in which sensor performance requirements are considered in the preliminary design process of wing sizing. The conclusions drawn based on this study are specifically applicable to dipole (half wavelength) antenna design. Considering the higher electrical performance offered by a ground plane, a single planar dipole antenna was simulated with a ground plane. The ground plane is assumed to be the lower skin of an aircraft. The ground plane length, width, and offset from the antenna were varied. For ground plane length sizing, the width and offset parameters are kept constant, while the ground plane extension outside of the antenna edge is varied. The ground plane width and offset sizing were performed in a similar manner by keeping all other variables constant. It is determined that ground plane length and width should be 50% of the wavelength extended outside the antenna edges and the ground plane-antenna offset should be kept at 15% of the wavelength for maximum dipole antenna performance. Relationships for wing ground plane span, wing chord, and thickness are derived from extensive parametric electromagnetic simulations that provide optimum antenna performance for generic planar dipole antenna. The relationships derived are for the ground plane (conductive) portion of the wing. These equations provide a useful tool that can inform the designer of expected sensor performance while determining the wing parameters