RFI Mitigation in Radio Astronomy
Project overview:
A very small fraction of the radio spectrum below 30 GHz is allocated for radio astronomy research, but cosmic radiation is present at all frequencies. We are developing techniques for making astronomical observations at frequencies occupied by active users of the radio spectrum. Our recent efforts have concentrated on 1200-1350 MHz band into which the 1420.4 MHz spectral line of neutral hydrogen from distant galaxies is Doppler shifted. This frequency range is mainly occupied by aircraft traffic control radar.
Alok Singhal, Dr. Fisher and Dr. Hogg (NRAO) are investigating the influence of detailed galaxy dynamics on the absolute magnitude - HI line width relation that is extensively used to derive distances to galaxies and, hence, the distribution of galaxies in the universe. The physical connection between and galaxy's brightness and its rotational speed is not well understood, so the strong correlation between its absolute magnitude and its HI line width is remarkable and largely empirical. Alok is looking for clues in the data base of galaxy observations that may shed some light on the dynamics that produce this relationship.
Alok Singhal and Dr. Fisher have been analyzing data samples of
signals
from radars in Virginia and Puerto Rico, which are seen by the
Green Bank, WV and Arecibo, PR radio telescopes. We have shown
that very strong radar signals can be removed from the radio
astronomy data (see here),and
we are planning to extend this technique to integration times of
an hour or more. A byproduct of these data is a map of the high
terrain near the radio observatories
Jit Sarkar, an
undergraduate engineering student, is working on a senior thesis
to develop a hardware device for generating blanking signals that
are synchronous with the radar pulses received by the GBT
Qing Zhang, a graduate student in the Engineering and Computer
Science Dept., and her advisers, Dr. Yibin Zheng and Dr. Steven
Wilson, are collaborating with Drs. Fisher and Bradley on the
development of signal
processing algorithms for minimizing the data loss in radar pulse
excision from radio astronomy data. Her techniques involve the
use of digital filters matched to the radar signal, threshold
detection, and automatic deletion of individual samples from
the data before the Fourier transform process to generate the
power spectrum.
Drs. Fisher and Bradley have a collaborative program of RFI
mitigation research with
Engineering an Computer Science faculty and students of Brigham
Young University. This research is concentrating on coherent
signal cancellation techniques as applied to GBT and
VLA observations. This
collaboration presents opportunities to UVa astronomy graduate
students for the application of RFI mitigation to scientific
projects which may be difficult or impossible without them.
For additional Information please e-mail Rick Fisher:
rfisher@nrao.edu.
