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Abstracts of Presentations

 

Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 7, 2008

 

2008 REUs and RETs

 

Using COSMIC and GPS Observations to Study Geomagnetic Storms in the Ionosphere
Presentation (PDF)
Rebecca Cooper, Wittenberg University

 

This project focused primarily on analyzing space-based observations from the FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere & Climate) constellation of satellites. The goal was to study ionospheric storm-time dynamics by incorporating a new type of satellite data based on satellite to satellite radio occultation. FORMOSAT-3/COSMIC is a recently launched system of six satellites whose primary sensor is a GPS receiver. This radio occultation technique uses GPS data to enable measurements which contain information about vertical profiles of the ionospheric electron density. One advantage of using FORMOSAT-3/COSMIC is that it can observe over the oceans and undeveloped ground areas, where there are no ground based GPS receivers. We first retrieved COSMIC data from CDAAC (COSMIC Data Analysis and Archive Center) and then computed and verified its total electron content (TEC) measurements. Once COSMIC data was verified, it was incorporated into the ground based TEC maps. We then analyzed new TEC maps which combined both COSMIC and ground based GPS data to look for evidence of the effects of geomagnetic storms. We will describe these procedures and our results in this document.

 

Annual Variations of the Upper Atmosphere: IPY Observations
Presentation (PDF)
Trevor David, Vassar College

 

The International Polar Year (IPY) is a large-scale collaborative effort guided towards a wide variety of polar region research from March, 2007 through March, 2009. This project examines the output from atmospheric research facilities participating in the IPY. During the IPY the longest continual ionospheric monitoring campaign was carried out using incoherent scatter radars across the globe. Incoherent scatter radars (ISRs) are the most powerful ground-based instruments for observing the Earth's upper atmosphere, mv allowing for the study of a large number of physical parameters over a wide altitude range. This project analyzes data collected during the low solar activity and geomagnetically quiet period between March, 2007 and March, 2008 from four ISRs at both mid- and high-latitudes. These sites include the MIT Millstone Hill radar in Massachusetts, the Poker Flat radar in Alaska, the EISCAT radar in Svalbard, and the Sondrestrom radar in Greenland. Harmonic fitting of the data for both seasonal and local time variations was performed to generate empirical models for three basic ISR parameters: electron density, electron temperature, and ion temperature. Annual variations of ionospheric properties with local time and altitude were then investigated and compared for each site after solar and magnetic activity effects had been removed.

 

A Statistical Survey of Sub-Auroral Polarization Streams
Presentation (PDF)
Marc Miskin, Rensselaer Polytechnic Institute

 

We conducted a statistical analysis of ~1200 Millstone Hill incoherentscatter radar (ISR) measurements of the state of the ionospheric plasma in a region of fast flow known as the Sub-Auroral Polarization Stream (SAPS) [Foster and Burke, EOS Trans. AGU, 2002]. Specifically, SAPS channel midpoint plasma velocities, electron densities, and calculated ion fluxes were examined over a range of magnetic latitudes, KP indexes, and F10.7 indexes. A notable discovery is that SAPS channel flux remains constant at ~1014 electrons/(m2*s) within a solar local time window of 17 to 22 hours, with a slow decay in flux magnitude beyond this region. Further, this conclusion appears to be invariant to both geomagnetic activity and the passage of the daylight terminator through the studied local time window. Ultimately, this implies that the electric field within a SAPS channel self-regulates to preserve a continuous material flow even under conditions of abating conductivity. Such results have considerable implications for studies of magnetosphere/ionosphere coupling at mid-latitudes.

 

A Power Amplifier Design for 440MHz
Presentation (PDF)
Robert Moffatt, Massachusetts Institute of Technology

 

The goal of this project was to design and construct a 440MHz, solid-state, 1000W, 50dB amplifier which could be used in the Millstone Hill Incoherent Scatter Radar (ISR). The amplifier will replace a medium-power klystron amplifier which has been in use since the construction of the radar system. The project involved selection of suitable UHF MOSFET transistors, impedance matching based on the transistor models provided in the datasheets, and the design of several PCBs. In addition to the electrical design, a mechanical layout and test enclosure was designed for the purpose of both RF shielding and heat dissipation.

 

Studying the Mesosphere using a Low Cost Spectrometer
Presentation (PDF)
Carl Craig, Emory University

 

By using Direct TV dishes, Haystack Observatory has developed VSRTs. The Direct TV dishes are roughly 76 cm in diameter. The VSRT can be used to study data showing the conditions of the mesosphere using the spectral line of 11.072 GHz. The goal of the research project is to make a more efficient spectrometer by using the 11.072 GHz line with lower system noise temperature as well as to create a web-based interface to easily access the data. The beam of the spectrometer points south at an azimuth of 205° and intersects the mesosphere off the coast of Delaware. As a result of analyzing data that has accrued over the past several weeks, the improved spectrometer shows the ozone signal clearly throughout the night but very little during the day.

 

On Pivotal Studies of U,V Weighting Functions; New Methods for Precision Radio Imaging
Presentation (PDF)
Dillon Foight, Embry-Riddle Aeronautical University

 

Future radio telescope arrays, such as the Square Kilometer Array (SKA), will implement large numbers of small diameter dishes configured over large areas. This has the advantage of a naturally large field of view, due to the small diameter of the individual dishes, and increased sensitivity and dynamic range. However, a major problem for these large arrays is instrumental response to radio sources outside the desired field of view. These effects can cause disruption of the primary source of observation, and limit the effectiveness of current imaging processes. One approach to this problem is to utilize a weighting function in the (u,v) plane, which provides dynamic control over the field of view in the image plane. This has the effect of reducing the noise contributions from secondary sources, as well as offering considerable advantages over current methods which attempt to eliminate non-primary sources by averaging observations in both time and frequency. In this paper, the effectiveness of this method is tested on observational data from the MERLIN array by comparison to current methods. The method was also tested in its capacity to handle large blocks of corrupted or missing data. Both Jinc and Gaussian functions were tested as weighting functions. Compared to time and frequency averaging, both functions were superior in reducing the noise contributions from distant sources.

 

Analysis and Simulations of 6T MWA Solar Data
Presentation (PDF)
Pauli Kehayias, Tufts University

 

The first set of interferometric data for the Murchison Widefield Array (MWA) prototype was collected in April, 2008 using six of the 32 tiles currently installed. Two hours of solar observations at 85 MHz and 180 MHz were analyzed to search for solar activity and to evaluate the instrument's performance. Four of the twelve input signals (two inputs per tile) were determined to be bad. No solar events were found, though four types of strongly monochromatic short-lived transient events, believed to be radio frequency interference, were identified and characterized. The bandshape stability over time for several baselines was examined. Bandshapes were found to maintain their shapes but had time-varying amplitudes. Simulations were done to determine whether the background radio sky, the Sun, or the instrument are responsible for the bandshape variation. The background radio sky explanation is unlikely to be the primary cause, and changing baseline fringe spacings and array responses at different orientations are being investigated.

 

Searching for Transients with the MWA
Presentation (PDF)
Munier Salem, Cornell University

 

The Murchison Widefield Array (MWA)'s unprecedented field of view and sensitivity allow observations across an entire hemisphere of sky. The All Sky Monitor (ASM) software of the MWA will utilize this novel capability to provide real-time detection of low frequency radio transients. This summer the ASM code was improved in multiple areas. The beam formation code was optimized by expressing the beam as a product of two factors, thus dramatically decreasing the run time. The ASM's calculated array beam was made more accurate by including a dipole-response model and instrumental gains and phases ascertained from calibration. The ASM uses this beam to produce the theoretical response of the array, a so-called "dirty image" of the night sky, in the array's pointing direction. Differences between the snapshot dirty images and the theoretical images are then used to detect deviations from the static sky. A new binning algorithm that sums snapshot images facilitates integration of data over a variety of timescales and with staggered intervals; the ASM can now perform rudimentary statistical analyses of these integrations to detect radio transients. We will present preliminary results obtained by applying the ASM detection software to a six-tile dataset.

 

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