Now showing items 21-29 of 29

    • Spectral estimation of signal and noise power in rayleigh lidar measurements of the middle atmosphere

      Wang, Weiyuan (2003-08)
      A Rayleigh lidar has been operated at Chatanika, Alaska (65°N, 147°W) since November 1997. The lidar observations yield temperature and density measurements in the stratosphere and mesosphere (40-80 km). This thesis presents a systematic engineering analysis of the retrieval methods used to determine both the temperature and density profiles as well as the density perturbations. Statistical and spectral analysis techniques are used to determine the total power in the density perturbations and estimate the power component due to geophysical variability and the power component due to instrumental noise. The power in the density perturbations is used to characterize the gravity-wave activity at this high-latitude site. Seventy-four nights of observation yielded 60 observation periods of data of sufficient quality to estimate the rms amplitude of the relative density perturbation in the 40-50 km altitude region at 30 min resolution. For these observations the average rms amplitude has a value of 0.43%. Preliminary investigation of campaign measurements in the spring of 2003 indicates that higher values of rms wave amplitude are associated with the presence of mesospheric inversion layers.
    • Mapping and predicting the ionospheric effects to communication systems in northern aurora areas using the global positioning system

      Wang, Lingyun (2002-08)
      This thesis focuses on mapping and predicting ionospheric effects to communication systems in northern high latitude areas using GPS (Global Positioning System). The monitoring of ionospheric scintillation and TEC (Total Electron Content) over Fairbanks, Alaska has been achieved by using the GSV4004 GPS Ionospheric Scintillation and TEC Monitor (GISTM), which has been installed on the roof of Duckering Building at UAF since September 2001. The algorithm of acquiring equivalent vertical TEC above Fairbanks from various satellite measurements is given in detail. Both an empirical ionosphere model, IRI, and a physics-based ionosphere model, PIM, are used to verify the TEC real field measurement. Another signal estimation method, BP neural network, is used to forecast the TEC short-term variation, which can give better performance than the other two. The relationships among TEC, amplitude scintillation and phase scintillation are analyzed. Multipath effects and the impact to GPS performance from ionospheric scintillation are discussed. Lastly the TEC and scintillation index mapping around Fairbanks is presented.
    • Numerical modelling of electromagnetic wave propagation in a hallway

      Venkatasubramanian, Arun (2003-08)
      This research involves the numerical modelling of electromagnetic wave propagation, (1) to calculate the electric and magnetic fields at any point in a hallway for a known transmitter and receiver antenna pattern and orientation and (2) to determine the wave normal direction of the electromagnetic wave using the electric fields calculated in (1). The results of the numerical simulation are compared with measurements for two hallways. Both the transmitter and receiver employ vertically oriented /4 dipoles operating at 2.4 GHz. Our work has led to the following new results: (1) The calculated signal power varies as 1/r² whereas the measured data varies as 1/r¹·⁴, where r is the transmitter receiver separation distance, (2) The temporal clustering of calculated multipath arrival times qualitatively agrees with the Saleh-Valenzuela model [1987], (3) For an SNR of 0 dB, the standard deviation of the error in the DOA estimate for the direct path signal is 2̃° and 4̃ ̊for the azimuth and elevation angles respectively. (4) In the presence of multi path, the DOA estimate shows an error of 50 ̊in the elevation and 125 ̊in the azimuth.
    • Development of high spectral resolution iron Boltzmann lidar

      Hou, Tao (2002-12)
      An initial iron (Fe) Boltzmann lidar was developed in winter 2000-2001 at Poker Flat Research Range (PFRR). This resonance lidar system supported Fe concentration measurements. An initial Fe Boltzmann temperature measurement was made in December 2000. This initial system was fundamentally limited by the 1 pm tuning resolution of the laser. During the winter of 2001-2002, a control system was developed to increase the resolution of the laser tuning to 0.09 pm. Fe cooncentration and Fe Boltzmann temperature measurements were made and an experimental analysis of the measurements was developed. This thesis presents lidar observations of the mesospheric Fe layer over these two winters, the principle of Boltzmann Fe lidar, the design and validation of the new laser tuning capability and the new temperature measurements. A complete error analysis is also presented. This full engineering analysis demonstrates that the tuning control system yields significant improvements in both the Fe concentration and temperature measurements.
    • Design and implementation of a microcontroller-based closed-loop tuning-controller for a tunable dye laser

      Peshave, Manasi (2004-05)
      This thesis presents the design, implementation and testing of a microcontroller-based closed-loop tuning-controller (CLTC) for a tunable dye laser. The specific goal is to precisely control and maintain the tuning of a tunable dye laser. This laser is used as a transmitter in a resonance lidar system that operates at 589nm and measures the mesospheric sodium layer. During operation, the operating frequency (or tuning) of the laser drifts due to environmental changes and the resonance signal (and measurement quality) is reduced. The controller uses the current signal from a sodium Hollow Cathode Lamp (HCL) to sense changes in the laser tuning. The CL TC incorporates both analog and digital circuitry. The amplifiers in the analog circuit have both sufficient slew rate (>5 V/us) and gain-bandwidth product (45x10⁶ Hz) to accurately capture the HCL signal. A high pass filter in the analog circuit removes the floating bias of the HCL and provides a stable signal to the digital circuit. The digital circuit is based on a Motorola 68HC12 microcontroller. The microcontroller monitors the signal from the HCL as it scans the laser wavelength and tunes the laser to the wavelength that maximizes the amplitude of the HCL signal. The CL TC can scan the laser at the resolution determined by the mechanical hardware of the laser system (0.14 pm), which is a factor of six times greater than resolution provided by the manufacturer software (1 pm). Our tests show that the CL TC can both tune the laser to and maintain the laser at the resonance frequency. The microprocessor software can be readily changed to accommodate changes in the optical sensor and the scanning methodology.
    • Performance analysis for remote power systems in rural Alaska

      Chubb, Tyler (2004-12)
      Due to the logistical difficulties involved in maintaining a rural Alaskan power generation facility, it is extremely important that the system function as efficiently as possible. Presently, many rural generation systems are not equipped with automated monitoring that enables knowledgeable personnel to view the performance of the system from a distant location. Consequently, system deficiencies resulting in increased fuel consumption and operating expense often go unnoticed as do potential system improvements. This thesis describes the design and implementation of a sophisticated monitoring system that consists of measurement sensors connected to an internet enabled data recorder. The monitoring system was used to continuously record the various forms of energy entering and leaving a diesel generator operating on the UAF campus. While in operation, the monitoring system was instrumental in identifying several measures that could be taken to improve the operating efficiency of the generator and also provided sufficient means to examine the economic feasibility of their implementation. The measures that were examined included heat recovery, conditioning of output power, and improvement of operating techniques.
    • Wireless communication protocol architectures for nanosensor networks

      Zhang, Zhongping (2004-05)
      Recent developments in micro fabrication and nanotechnology will enable the inexpensive manufacturing of massive numbers of tiny computing elements with sensors. New programming paradigms are required to obtain organized and coherent behavior from the cooperation of large numbers of sensor nodes. The individual nodes are identical, randomly placed and unreliable. They communicate with a small local neighborhood via wireless broadcast. In such environments, where individual nodes have limited resources, aggregating the node into groups is useful for specialization, increased robustness, and efficient resource allocation. In this paper, an application-specific self-organization protocol stack is developed. The clustering process is divided into phases. The first phase is to know the neighbor nodes. The second phase is to set up the cluster and routing. A 'find maximum clique algorithm' is used to set up clusters. A back off method is used to set up the hop field and routing. Group leaders set up a TDMA schedule for steady state operation. This schedule ensures that there is no conflict among in the same cluster and between clusters. Direct-sequence spread spectrum (DS-SS) is used to avoid inter-group conflict. The limited power resource is a challenge in nanosensor networks. This paper uses two different ways to analyze energy consumed in nanosensor networks, energy cost field and bit flow method. Sensor node deployment, cluster size, and propagation condition effect are discussed in this paper by those two methods respectively.
    • Design of microcontroller based generic radar controller

      Kolatkar, Aditi (2004-05)
      Increasingly radar stations contain multiple radar systems, each individually controlled. Non-standard control requires that a user of multiple systems learn each system separately. Additionally, multiple radar controllers make coordination of multiple systems difficult. The goal of this thesis is to design a generic radar controller that can be used to operate any pulsed radar system or multiple radar systems simultaneously. The Generic Radar Controller attempts to meet and improve upon the specifications of a previous radar controller and collapse its rack-mounted system into a single PC card. The University of Alaska Generic Radar Controller (UAF-GRC) is a microcontroller based PC card with a minimum of 16 control channels. Each channel can be individually programmed to provide pulses of 400 ns duration up to several milliseconds and variable pulse repetition intervals with a timing resolution of 10 ns. The hardware and software issues that appeared during the design phase are discussed in the thesis. The thesis concludes with improvements of UAF-GRC over the previous radar controller.
    • Comparison and verification of the performance of a Stateflow model on a C166 microcontroller board

      Grandham, Jyothsna (2005-05)
      The IMPROVE data library is a collection of continuous and intermittent physiological observations of 59 patients in the Intensive Care Unit (ICU), recorded for one complete day at the Kuopio University Hospital. These data consisted of patient data stored as annotation and record files. The IMPROVE data library also provided the information regarding four disorders (Hypovolaemia, Cardiac Failure, Hypervolaemia and Oxygen-Content related problems) in terms of the patient data. An available model designed in Stateflow generated the risk levels for the patients. The goal of this thesis is to analyze the risk levels generated from the simulation and compare them with the physician's diagnosis. The main objective of this work is to evaluate the performance of the Stateflow model that interprets the risk level of the four disorders, for a particular patient at any instant of time and later implement it on an Infineon C 166 microcontroller board. The various limitations encountered during the implementation on the microcontroller board are discussed in the thesis. To demonstrate the rapid prototyping capabilities of using the microcontroller board a speed-comparison analysis of implementing the Stateflow model on various computers was performed.