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Abstracts of Presentations


Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 8, 2013



Designing, Simulating, and Testing the Power Subsystem for RAPID
Presentation (PDF)

Poornima Aggarwal, Cooper Union

This project is driven by the necessity to create a self-containing, reliable power subsystem for each unit in the RAPID array. RAPID seeks to create a transportable, reconfigurable, and flexible antenna array for collecting radio interferometric data from observations around the globe. The power subsystem has three main components, a photovoltaic panel to generate power, a battery to store the power, and a charge controller to regulate how the power generated is distributed between the battery and load. Many factors must be taken into consideration during the design process such as cost, efficiency and mobility of the hardware. A Python simulation program is presented to predict how the hardware will operate under different load scenarios and geographic conditions; as well as a test bed implementing the components and allowing for real time voltage, current, and solar radiation measurements to be taken. After determining which hardware would be best suited for RAPID, this project aims to develop a method for predicting the feasibility of running different experiments given the amount of solar radiation at the desired location and time of year by combining data from both the simulation and the test bed.


Volcanic Effects in the Upper Atmosphere
Presentation (PDF)

Anirudh Chiti, Cornell University

Large volcanic eruptions have a well observed impact on the lower atmosphere and climate. In the past forty years, two eruptions, El Chichon in 1982 and Pinatubo in 1991, released significant amounts of aerosols. The effects of these two volcanos have been studied in the stratosphere (10km - 50km), but not in the upper atmosphere. This project attempted to find traces of the two eruptions at altitudes of 250km to 500km through temperature trend studies. An ion temperature trend model was refined and then used to subtract solar, geomagnetic, annual, semi-annual, and correlated effects from Millstone Hill Incoherent Scatter Radar (ISR) data. After subtraction, the ion temperature residuals were studied around the years 1982 and 1991 for anomalous dips. Additionally, the model's validity was checked by a separate model that used altitude spline fitting as opposed to median binning. The spline fitting model gave finer altitude resolution and qualitatively agreed with our model, thus showing consistency of observed trends and residual effects. The original modeling technique was then applied to the Sondrestrom and St. Santin ISR sites to validate temperature trends and volcanic effects at different locations. Then, global satellite drag measurements of electron density were analyzed for traces of volcanic activity with an updated model. Effects of the 1982 El Chichon eruption appeared to exist in all sets with relevant data (Millstone Hill, St. Santin, and satellite drag measurements), but the 1991 Pinatubo eruption was not as consistently present. Further study is needed to understand the theoretical effects of volcanic activity at those altitudes and gauge the significance of the observed temperature residuals.


Development of a Low Cost Spectrometer for the Small Radio Telescope (SRT), Very Small Radio Telescope (VSRT), and Ozone Spectrometer
Presentation (PDF)

Marc Higginson-Rollins, University of Kentucky

Several instruments used for education, outreach and scientific investigations could benefit from a low cost spectrometer. These include the Small Radio Telescope known as the "SRT", a very small radio telescope known as the "VSRT", and an 11 GHz Ozone spectrometer. The SRT is used to observe the Sun and the 21-cm hydrogen line. The SRTs, which until recently were available commercially, are still in operation at many universities and are used for student projects including measuring the Galactic rotation curve of our Galaxy. These instruments, which were initially primarily used to help teach students how to analyze scientific data, are now used for scientific investigations that have resulted in publications in science journals. Recently a low cost USB "dongle" for digital TV has become available. It has been adapted for use as a software defined radio by amateur radio groups. Linux-based software was developed to adapt the device to form a low cost digital spectrometer for the SRT by integrating open source code into the existing C code written for the SRT. Some challenges faced when trying to integrate the USB TV dongle into the SRT system and software will be discussed. To test the effectiveness of the USB TV Dongle based SRT several astronomical observations were made and compared to the older SRT system. These observations show promise for the device replacing older SRT systems at a fraction of the cost and effort and as a possible replacement for the VSRT and Ozone spectrometer.


The Instrumental Effects on VLBI Polarization in Event Horizon Telescope
Presentation (PDF)

Michael Kosowsky, Brandeis University

We analyzed March 2013 230 GHz polarimetry data from Event Horizon Telescope observations in order to figure out the necessary calibration needed to account for instrumental polarization.  We used a Markov Chain Monte Carlo fitting algorithm to find the instrumental D-terms and the antenna gains with very low reduced chi-squared. Consequently, we have found very likely results for the gains of the SMT, the phased CARMA array, and a single comparison CARMA antenna. The MCMC code is able to be expanded to include other EHT stations as well.


Study of Ionosphere Total Electron Content for the Broadband Geodetic VLBI Fringe Model
Presentation (PDF)

Carlos Mulero-Hernandez, University of Puerto Rico, Mayaguez

The radio telescopes used for Geodetic Very Long Baseline Interferometry (VLBI) receive signals from distant astronomical objects to provide a measure of the Earth’s shape and variable rotation. However, the propagation of these signals through the Earth's ionosphere and any other plasma between the radio source and the telescope introduces a systematic error in the geodetic observable. This dispersive delay has become more critical in light of the accuracy goals set forth in the VLBI2010 specifications for the VLBI Geodetic Observing System (VGOS)  which are 1mm for position and 0.1 mm/yr for stability. In order to achieve such geodetic accuracy, this error must be accurately removed. In this work we present an investigation of the accuracy of the dispersive component of delay as determined by the broadband geodetic VLBI technique.  We will describe the features and implementation of a frequency-dependent forward model of this dispersive delay for VLBI.  The application of this model yields an estimate of the combined ionospheric and extraterrestrial total electron content (TEC) using a nonlinear parametric search. We assess the quality of this VLBI-based TEC estimate by comparing it with TEC values obtained using nearby GPS systems.


Passive Radar Imaging of Meteor Trails
Presentation (PDF)

Shayan Sohbatzadeh, University of Florida

I will discuss the development of single site passive radar interferometry and its application to the detection of meteor trails. Near earth space contains small pieces of matter known as meteoroids, some of which intersect the earth’s orbit and are then called meteors. The larger meteoroids produce a visible emission, a meteor. Meteors also have a plasma trail that can be detected by radar. Concepts explored in the project include passive radar, adaptive filtering, radar interferometry, and correlation. The software implemented to support the needed mathematical analysis techniques will be described. An overview of the experimental system, data collection, and the results of the radar analysis will be presented.


Daily Variations of Lower Thermospheric Tides at Middle Latitude and Their Association with Sudden Stratospheric Warming Events
Presentation (PDF)

Rebecca Steeves, North Carolina State University

Sudden Stratospheric Warming (SSW) events have been shown by both observations and model results to couple the polar stratosphere to the low latitude ionosphere. Studies have suggested that a partial driver of the connection is the amplification of tides due to the SSW that reaches maximum at mid-latitudes. This study aims to increase the understanding of the coupling processes at mid-latitudes to establish possible SSW effects on dominant tidal structures. We utilize lower thermospheric (100-130 km) data collected from the Millstone Hill Incoherent Scatter Radar (ISR) (42.6N, 288.5E) during the Northern Hemispheric winter experimental campaigns classified as either SSW events or non-SSW events. The campaign set is comprised of two SSW events, one minor and one major, along with three non-SSW events. We also examine environmental characteristics such as temperature, zonal wind, and planetary wave activity (zonal wave numbers 1 and 2) from National Center for Environmental Prediction (NCEP) data for each campaign to distinguish any noteworthy characteristics. Comparison of the campaigns concentrates on the amplitudes and phases in the zonal and meridional winds. The altitudes of analysis lie in the range between 100 km and 124 km where the dominant tides were extracted at 3 km increments. Dominant tidal structures are the 12-hour tide and 6-hour tide, indicated by the Lomb-Scargle spectral analysis. The study focuses on these tides to show differences between campaigns and daily variations. A common trend found among the campaigns, both SSW and non-SSW events, is large day-to-day variability and evidence of oscillations with periods on the order of 2-4 days. Differences in phases show the most distinction between campaign subsets, especially in the meridional component.




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