An optical wireless location (OWL) system is introduced for indoor positioning. The OWL system makes use of a mobile photoreceiver that facilitates triangulation by measuring angle-of-arrival (AOA) bearings from LEDs in an optical beacon grid. The photoreceiver has three photodiodes (PDs), arranged in a corner-cube, to facilitate differential photocurrent sensing of the incident light AOA, by way of azimuthal ϕ and polar θ angles. The AOA error for indoor positioning is characterized empirically. Optical AOA positioning is shown to have a fundamental advantage over known optical received signal strength (RSS) positioning, as AOA estimation is insensitive to power and alignment imbalances of the optical beacon grid. The OWL system is built, and a performance comparison is carried out between optical AOA and RSS positioning. It is shown that optical AOA positioning can achieve a mean 3-D positioning error of only 5 cm. Experimental design and future prospects of optical AOA positioning are discussed.
The area1 extent of prairie dog towns in Wind Cave National Park (WCNP) has increased at an alarming rate in the past 20 years. An inventory method was needed to replace the time and labor intensive ground survey method, i.e. rod and transit. Color infrared (CIR) aerial photography (1,370 m above ground) provided a useful product for rapidly and accurately delineating prairie dog towns. Extent was determined by measurements on the CIR film to be 608 ha or 5.3% of the total WCNP area. Ground measurements, taken near the time of the aircraft overflight, included general vegetation description of each prairie dog town and a vegetation sampling from 0.25 m* plot on a stratified, random basis. The ground data helped explain and identify the variations recorded on the CIR film. Soil and topographic information were used with the CIR film to determine likely expansion potential and probable direction of growth of the 11 major prairie dog towns in WCNP. The prairie dog town inventory and expansion potential of each town has probable usefulness in the development of management plans.
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