HR: 1330h
AN: SH42C-0552    [PDF]
TI: A new Design for a Very low Frequency Satellite Based Radio Interferometer
AU: * Oberoi, D
EM: doberoi@haystack.mit.edu
AF: MIT Haystack Observatory, Off Route 40, Westford, MA 01886 United States
AU: Pin\c{c}on, J
EM: jlpincon@cnrs-orleans.fr
AF: LPCE-CNRS, 3A, Av. de la Recherche Scientifique, Orleans, 45071 France
AB: The non-transparency and severe propagation effects of the Earth's ionosphere do not allow electromagnetic waves lower than a few tens of MHz to be studied from the ground. To study the universe in this last, yet unexplored, part of the spectrum with the sensitivity and the resolution demanded by the scientific objectives, a dedicated space borne radio interferometer working at these frequencies is needed. Designs for space based Very Low Frequency (VLF, $<$ 30 MHz) interferometers have been discussed in literature for the past many years. All the proposed designs are based on transmitting the Nyquist sampled time series from each of the receptors of the interferometer to the Earth and doing offline correlations, as in VLBI. The inherently large data rates and the comparatively narrow telemetry bandwidth to the Earth limit these designs to providing narrow radio frequency (RF) bandwidths of observation and few bits per sample (125 kHz at 1 bit/sample, Jones et al. 2000, Geophys. Mono. Series, 119, 339-349). This adversely impacts the scientific capabilities of the mission. In principle, this hurdle can be overcome by reducing the volume of data to be transmitted to the Earth by doing appropriate real time data analysis on board. The phenomenal increase in the capabilities of space qualified hardware in the recent past now have brought close to meeting the requirements of a practical implementation of this concept. We present a new design for a space based VLF interferometer based on this approach, which can provide $\sim$2 orders of magnitude larger RF bandwidth coverage. In addition to on-board data processing, this design incorporates several other new features as well. We propose to use three dipole elements per satellite rather than two, to capture all the independent information impinging on the satellite. The design will implement a Radio Frequency Interference (RFI) mitigation scheme designed to identify and discard the parts of the band with strong RFI in real time. We strongly recommend an overlap in frequency range with upcoming ground based low frequency instruments like the Low Frequency Array (LOFAR) to benefit from the detailed information about the sky made available by them and to have a better handle on calibration. The hardware needed to implement this design is expected to become available in very near future, making this the design of choice for a VLF space interferometer.
DE: 6924 Interferometry
DE: 6954 Radio astronomy
DE: 6969 Remote sensing
DE: 6982 Tomography and imaging
DE: 6994 Instruments and techniques
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting