嗜桖仦媄囡out) (103)
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LIST OF TABLES
5.1Topcon Legacy-E and PDL Data Link speci?cations (39)
5.2Sick LMS221speci?cations (41)
5.3BEI MotionPak II speci?cations (43)
5.4PNI TCM2-50speci?cations (45)
5.5Rainwise WS-2000speci?cations (47)
5.6Pelco Esprit speci?cations (49)
5.7CruzPro TL30speci?cations (50)
9.1Topcon GPS:known UTM position(in meters) (88)
9.2Topcon GPS:measured UTM position(in meters) (88)
9.3Topcon GPS:relative positioning error(in meters) (89)
9.4Topcon GPS:average satellite visibility at NGRIP (91)
9.5TCM:stability and response to vibration (100)
9.6MotionPak II:stability and response to vibration (100)
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1.INTRODUCTION
With the possible melting of the polar ice caps and the gradual rise in sea level, the polar regions of the Arctic and Antarctica have become key targets for earth science researchers.The potential impacts from these ecological changes are still not well understood.By monitoring changes to the ice sheets,researchers may be able to develop and improve theories regarding the long-term impacts and how the ice sheets play a role globally.Due to the adverse conditions of polar environments,?eld research and the collection of data can be quite di?cult.Mobile robots provide useful means for automating the collection of research data in the?eld by reducing the risks due to human involvement and improving accuracy.
At the University of Kansas,the Polar Radar for Ice Sheet Measurement (PRISM)project[61]focuses on the task of developing a radar system capable of measuring the thickness and other characteristics of the polar ice sheets.To accomplish this goal,we are developing an autonomous mobile robot.It is our goal to utilize the PRISM rover to operate in both Greenland and Antarctica with limited supervision(refueling and remote monitoring).
In the past,robotics research has been focused on developing robust sensor suites and algorithms in order to provide reliable,robust,precise,and safe autonomy.However,less research has been conducted regarding sensing and navigation for robotic vehicles on an ice sheet.Sensor modalities must be fully tested and evaluated for operations on the ice sheets to ensure that the robot will have the same functionality,reliability,and precision that is expected in other types of environments.
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1.1Motivation
Extensive research exists in the area of mobile robotics and sensors.This research addresses a speci?c application area that presents unique challenges.When designing a mobile robot for working in polar environments,special care must be taken with the selection of sensors with a focus on both survivability and reliability.
In this section,the challenges of operating in polar environments is discussed. We then provide a brief overview of the PRISM mobile robot that has been designed developed to address these challenges.An overview of the approach to address these issues is also presented.
1.1.1Polar Traversal
Polar research often relies on data collection and traversal of the ice sheets of Greenland and Antarctica.In June of2001,a workshop analyzed the feasibility and resourcefulness of using mobile robots similar to planetary rovers for collection of scienti?c data on the ice sheets[13].This group de?ned several tasks with which an autonomous rover could aide,including:traverses with detailed and tedious paths,extremely remote and/or inhospitable environments,data collection parallel to a manned traversal,and data collection at slow speeds.In2002, researchers at NASA’s Jet Propulsion Laboratory proposed additional research that proposed that utilizing mobile robotics for polar exploration can provide future bene?ts toward planetary exploration[7].
Both groups discussed the numerous challenges that exist with polar traversals.These challenges include deep and blowing snow,crevasse detection and avoidance,sastrugi detection and avoidance,and limited supervision.Several of these challenges directly relate to the sensing capabilities of an autonomous rover,which will be addressed in this thesis,along with a number of additional challenges.
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Sensing in the polar regions can be more challenging than in more hospitable environments including sub-zero temperatures and high wind speeds.Equipment may be damaged as a result of such temperatures and wind speeds.
Vision can be limited due to the lack of contrast on the icy surface.With this lack of depth perception,natural obstacles are often overlooked.For instance, sastrugies,snow drifts that form as a result of wind erosion,have heights of up to one meter.In addition,crevasses in the ice sheet are encountered that remain invisible because they are covered in snow.
Sensors for positioning and localization also experience di?culties in the polar 7d21773343323968011c92dfpasses are less e?ective due to their close proximity to the magnetic poles.GPS satellite coverage near the polar regions is reduced because the satellite network focuses primarily on more populated or strategic areas. If there are not enough visible satellites,GPS position accuracy is reduced,or position information becomes unavailable.
Despite these limitations,research in polar environments has proven invalu-able.For the PRISM project,the radar images that are taken of the ice are used to support glaciologists and geophysicists who address research areas such as global warming.Atmospheric researchers can utilize data collected from ice cores and other measurements to uncover the history of the planet’s climate and its geological history over thousands of years.By developing a robust mobile robot for polar environments,we can uncover details that will support future research in polar environments.
1.1.2Polar Radar for Ice Sheet Measurement(PRISM)
Project
The Polar Radar for Ice Sheet Measurement project is currently underway at The University of Kansas[61].The project’s goal is to develop radar systems to measure polar ice sheet properties in order to accurately determine their
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mass balance and other features.Such data will help researchers determine the contributions of polar ice sheet melting to global climate change and rising sea levels.
Two radar systems have been developed for this task[23].A monos-tatic/bistatic synthetic aperture radar(SAR)has been developed to generate a two-dimensional view of basal conditions of the Polar Ice Sheet.A wide-band, dual mode radar will also be utilized to determine aspects of ice sheet depth and accumulation[23].
In order accommodate these two radar systems,two vehicles have been employed.The?rst is a manned tracked vehicle that will tow an antenna array for the bistatic/monostatic SAR and also carry an on-board dual-mode radar.A second uninhabited rover will be utilized to carry a second SAR.When operating in bistatic mode,the rover will operate as a receiver.The two vehicles will move along side one another in a coordinated pattern.The autonomous rover will traverse a wide area along side the tracked vehicle collecting data to build the radar image.
Intelligent on-board systems are responsible for coordinating the two vehicles.Based on data received from the radars and the current state of the autonomous rover,this system will indicate areas of interest and assign autonomously waypoints for coordinated navigation.
In addition,the PRISM project has an extensive educational outreach program directed at both K-12students and the general public.The outreach opportunities also include collaboration with Haskell Indian Nations University in Lawrence,Kansas[25].Outreach activities include maintaining a website with polar news and live updates from PRISM team members from the?eld[11,61].
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1.1.3The PRISM Mobile Robot
The research presented in this thesis directly facilitates the goal of PRISM to develop a semi-autonomous mobile robot[1,24,56].This robot is responsible for the transportation of the radar system and the computing equipment across polar ice sheets.It will primarily operate autonomously with the ability for a user to override the control system and operate it remotely.In the past,this robot has been also refereed to by the acronym“Mobile Antarctic Robotic Vehicle with Intelligent Navigation,”or MARVIN.For this thesis,it shall be referred to as either the PRISM mobile robot or the PRISM rover.
Figure1.1:PRISM mobile robot.
The PRISM rover,as shown in Figure1.1,is the result of our e?ort[1,24,56].
A signi?cantly modi?ed version of a six-wheeled Bu?alo All Terrain Vehicle(ATV)
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[27]was used as the mobile base.Actuators were utilized for controlling the throttle and steering.An enclosure was constructed on top of the base platform to provide a protected environment suitable for computing equipment.To facilitate intelligent and reliable mobility,a suite of sensors were integrated to provide the vehicle with perception capabilities.These sensors will be discussed in more detail throughout this thesis.
1.2Approach
The approach used to address the challenges related to the sensor suite for the PRISM mobile robot was performed in a number of steps.The?rst step involved an extensive literature search.By reviewing existing literature regarding sensors, a list of potential sensors was compiled.In addition,a literature search was performed to study existing research projects that utilize mobile robots for polar or planetary applications.By learning from the work of past researchers,some sensor modalities can be eliminated based on previously known weaknesses encountered in these environments.
The next main task was to de?ne the criteria for the sensors that were to be selected for the PRISM rover.Project related criteria were de?ned such as the needs of other researchers and their equipment.In addition,the educational outreach requirements were de?ned.Since the vehicle will be operating in a hostile environment,environmental requirements such as operating temperature range and ruggedness were also de?ned.Based on the requirements de?ned,a suite of sensors were selected.
