M.I.T. HAYSTACK OBSERVATORY
Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 16, 2001
GPS Stabilized Frequency Sources for Passive Radar
A. Cristina Fernandes
Wichita State University (KS)
Radio astronomy and radar are two areas where precise timing and synchronization are required. For this synchronization to be possible a highly stable oscillator is needed to provide an accurate time and frequency reference. It is not always practical to have atomic clocks in radio receivers, especially when numerous locations must be synchronized over a wide geographic region. One alternative to the need for atomic clocks is to take advantage of signals from the Global Positioning System (GPS). These signals contain precision timing information, which can be used to stabilize and synchronize a low cost oscillator using an appropriate phase locked loop circuit. The goal of this project is to build an oscillator that is phase synchronized to a GPS receiver's one pulse per second reference signal using a digital phase locked loop combined with a direct digital synthesis chip (DDS). This design has been realized using off the shelf components and a custom printed circuit board. The circuit is a prototype whose design will be integrated into coherent digital radio receivers for applications such as Passive Radar, which require precise synchronization over distances of several hundred kilometers.
Tests of a Digital Receiver for the Small Radio Telescope
Yale University (CT)
As an educational tool, the Small Radio Telescope (SRT) is continuously being modified and improved in both software and hardware. Its original analog receiver allowed users to observe only 1420 MHz hydrogen emission and strong continuum sources like the sun; this limitation prompted development of a digital version to expand the telescope's capabilities. The digital receiver, which has replaced the analog on our telescope, has an increased stability and sensitivity which greatly extends the scope of research possible with the SRT. This flexibility necessitated a search for appropriate radio sources, eventually concentrated on OH masers. Calibration and equipment tests, as well as software updates, are ongoing as the refinement of the receiver continues. This talk will describe the research and testing process for the digital receiver and outline some of the projects now available to the SRT.
VLBI Polarimetry Study of J1058+0133
University of California, Berkeley
Recent studies suggest that BL Lacertae objects differ from quasars in their magnetic field orientation throughout the VLBI jet. Generally, BL Lacs are known to exhibit B-fields oriented perpendicular to the jet axis, while quasars exhibit B-fields parallel to the jet. However, this relatively simple classification system is somewhat arbitrary, and it is complicated by Faraday rotation and depolarization. The blazar J1058+0133 is the first VLBI source observed to have both parallel and perpendicular magnetic fields simultaneously. It thus provides us with a unique opportunity to study shocked-jet models and the true relationship between magnetic field orientation and optical designations of blazars. Preliminary results of multi-frequency, multi-epoch VLBA data on this source will be presented, along with prospects for follow-up research.
Acoustic Monitoring and Signal Identification for Steerable Radar Antennas
University of North Texas
The Millstone Hill Steerable Antenna has been used to take ionospheric measurements for 23 years. The 46 meter antenna is fully steerable in both azimuth and elevation, enabling data to be taken from the entire sky. The antenna sits on four wheels atop a circular track.Two of these wheels have motors that drive the antenna in azimuth. Elevation movement is produced by two motors in a screw drive configuration balanced by counterweights. Regular maintenance is necessary to keep the antenna in good condition. However, many problems with the antenna are not detected until they require immediate repairs. With the use of an acoustic monitoring system, it may be possible to detect mechanical problems early on when they can be addressed by preventative maintenance at a lower cost in time and money. Detecting differences in mechanical structure will also help to present catastrophic failures.
The feasibility of an acoustic monitoring system for use with the Millstone Steerable Antenna (MISA) has been investigated using accelerometers, tilt sensors, acoustic microphones, and ultrasonic sensors. A signal conditioning circuit was constructed for the use with these sensors and a computer based data acquisition platform. An experimental plan was created to evaluate sensor performance with the MISA antenna at rest and in motion. An initial data set characterizing the sensor performance has been collected and analyzed.
Tracking CMEs with LOFAR
Interplanetary Scintillation Studies with a Large, Multi-beaming, Interferometric Phased Array
Interplanetary scintillation (IPS), a technique for measuring the diffraction of celestial radio source emissions through transient disturbances, has been used to detect and characterize solar wind and coronal mass ejections (CMEs) since the 1950s. High resolution mapping of plasma structures to the sun's surface and throughout the interplanetary medium requires near-simultaneous monitoring of multiple scintillating sources. Velocity measurements require highly accurate correlations over multiple baselines separated by distances appropriate to the characteristic size and evolution rate of the diffraction pattern. The Low Frequency Array (LOFAR), a new receiver array being developed by ASTRON, the Naval Research Laboratories, and the MIT Haystack Observatory, will feature the capability to form multiple highly sensitive, high-resolution beams simultaneously, and the 100 planned interferometric stations will span baselines of up to 400 km. In this talk, the potential of LOFAR for in-depth interplanetary and solar weather studies through IPS will be discussed and compared to the performance of peer IPS instruments.
Simultaneous 3mm and 7mm Observations of SiO Masers around R Cassiopeiae using VLBI
University of Arkansas
The observing technique of Very Long Baseline Interferometry (VLBI) gives a means by which to probe extended stellar atmospheres through study of their surrounding masers. On April 27, 2001, simultaneous 3mm and 7mm observations were made of SiO masers surrounding the long-period variable red giant R Cassiopeiae; this was the first attempt at observing these two frequencies simultaneously around an evolved star. Though the star was reaching a minimum, partial rings were detected in both the v=1, J2-1 and J1-0 and v=2, J1-0 transitions. Spatial registration of these maser transitions provide a test for model predictions, and certain ratios measured for the 7mm/3mm v=1 masers may prove to be a powerful constraint on the physical state and degree of mixing in the masing gas.
Modeling the Effects of Atmospheric Delay on VLBI and GPS
Very Long Baseline Interferometry (VLBI) and Global Positioning System (GPS) techniques have both become instrumental to fields such as geodesy and meteorology and to practical applications like airplane safety control. The radio signals, however, experience excess delay due to the presence of water vapor in the troposphere, the lower part of the atmosphere, and to the added effects of a hydrostatic component. My summer project has been to model these two layers and their gradients using a new and more accurate technique. The long-term goal is to be able to use these data to create a new mapping function of the asymmetric component of the wet atmosphere. A general explanation of the theory will be given, as well as a summary of my summer accomplishments.
MadrigaLite: Bringing the Madrigal Database to Your Desktop
University of New Hampshire
The Madrigal database is a large, live archive of information and scientific data collected from various instruments, output from theoretical models and analysis. However, there are times when the scope and complexity of the full Madrigal database is not needed, or desirable, or when accessing the internet is not convenient. MadrigaLite brings the Madrigal Database to your desktop, providing a simple, intuitive way to access and add datafiles to a Madrigal Compliant database, and access the datafiles associated with a given experiment. The technologies behind MadrigaLite, Java and XML are used with the intent of making MadrigaLite as platform independent as possible. In addition, MadrigaLite comes with conversion features built in, to allow experiments made in MadrigaLite to be added to the Madrigal or CEDAR databases, and likewise to view downloaded data from either one of these two sites.