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Browsing by Author "Bayram, Haluk"

Now showing 1 - 4 of 4
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    Aerial Radio-based Telemetry for Tracking Wildlife
    (2017-04-10) Bayram, Haluk; Stefas, Nikolaos; Isler, Volkan
    This paper considers the problem of choosing measurement locations of an aerial robot in an online manner in order to localize an animal with a radio collar. The aerial robot has a commercial, low-cost antenna and USB receiver to capture the signal. It uses its own movement to obtain a bearing measurement. The uncer-tainty in these measurements is assumed to be bounded and represented as wedges. The measurements are then merged by intersecting the wedges. The localization un-certainty is quantified by the area of the resulting intersection. The goal is to reduce the localization uncertainty to a value below a given threshold in minimum time. We present an online strategy to choose measurement locations during execution based on previous readings and analyze its performance with competitive analysis. We also validate the strategy in simulations and in field experiments over a 5 hectare area using an autonomous aerial robot equipped with a directional antenna.
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    Gathering Bearing Data for Target Localization
    (2015-09-28) Bayram, Haluk; Vander Hook, Joshua; Isler, Volkan
    We consider the problem of gathering bearing data in order to localize targets. We start with a commonly used notion of uncertainty based on Geometric Dilution of Precision (GDOP) and study the following bi-criteria problem. Given a set of potential target locations and an uncertainty level U, compute an ordered set of measurement locations for a single robot which (i) minimizes the total cost given by the travel time plus the time spent in taking measurements, and (ii) ensures that the uncertainty in estimating the target’s location is at most U regardless of the targets’ locations. We present an approximation algorithm and prove that its cost is at most 28.9 times the optimal cost while guaranteeing that the uncertainty is at most 5.5U. In addition to theoretical analysis, we validate the results in simulation and experiments performed with a directional antenna used for tracking invasive fish.
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    Robotic Surveying of Apple Orchards
    (2015-06-18) Roy, Pravakar; Stefas, Nikolaos; Peng, Cheng; Bayram, Haluk; Tokekar, Pratap; Isler, Volkan
    We present a novel system for surveying apple orchards by counting apples and estimating apple diameters. Existing surveying systems resort to active sensors, or high-resolution close-up images under controlled lighting conditions. The main novelty of our system is the use of a traditional low resolution stereo-system mounted on a small aerial vehicle. Vision processing in this set up is challenging because apples occupy a small number of pixels and are often occluded by either leaves or other apples. After presenting the system setup and our view-planning methodology, we present a method to match and combine multiple views of each apple to circumvent these challenges and report results from field trials. We conclude the paper with an experimental analysis of the diameter estimation error.
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    UAV Landing at an Unknown Location Marked by a Radio Beacon
    (2019-07-29) Stefas, Nikolaos; Bayram, Haluk; Isler, Volkan
    We consider the problem of minimizing the time to approach and land near a target radio beacon at an unknown location with an Unmanned Aerial Vehicle (UAV). We show that a cone-like region exists above the target inside of which bearing measurements of a directional antenna lose directionality: signal recordings in all directions yield similar signal strength. We present a geometric model of this region based on antenna simulations and data collected with a real system. Our main contribution is a strategy that takes advantage of a UAV's ability to change altitude and exploits a special structure occurring when approaching the target beacon from above to reduce the flight time required to land near the beacon. We analyze the performance of our strategy and demonstrate through simulations that by exploiting this structure we can achieve shorter flight times than our previous work.