Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm23a0465s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SM23A-0465
Physics
2409 Current Systems (2708), 2471 Plasma Waves And Instabilities, 2487 Wave Propagation (6934), 2772 Plasma Waves And Instabilities
Scientific paper
RPI is a multi-mode instrument using three orthogonal thin-wire antennas - two long (nominal length of 500-m tip-to-tip) dipoles in the spin plane (X and Y antenna) and one short (nominal length of 20-m tip-to-tip) dipole along the spin axis (Z antenna). The X antenna is used for transmission and all three antennas are used for reception to measure three components of electric field. Unfortunately, on October 3, 2000, one of the X-axis monopoles was partially severed, apparently by a micrometeorite, reducing the dipole length to 340 m. On September 18, 2001 an unknown section of the Y antenna was lost. Therefore, it is difficult to estimate three components of wave electric field. Measurement of three components of electric field is important to determine wave normal directions of the received echoes and to estimate the radiated and received powers. We have used known source locations, relations for polarization and refractive index as a function of wave normal direction, and antenna orientations in order to interpret the amplitudes of electric field components as measured by three antennas. The RPI transmission frequency ranges from 3 kHz to 3 MHz, which allows multiple modes of propagation including whistler, Z, and free space modes. We analyzed two kinds of signals: 1) whistler mode waves from the ground transmitter observed at the IMAGE satellite, 2) discrete Z mode echoes propagating within the Z mode cavities. In both cases the wave normal direction is presumed to be known - vertical in the case of ground transmitter signal and parallel to the geomagnetic field in the case of discrete Z mode echoes. Ground transmitter signals in the frequency range 10-30 kHz are commonly observed when IMAGE is in the northern hemisphere. In one case, observed on October 2, 2002, NAA signal at 24 kHz was observed on three antennas. Voltages induced across X and Y antenna terminals were consistently ˜30-40 dB higher than those measured across the Z antenna. These observations can be explained by taking into account the differences in the three antenna lengths, their orientation, and the vertical wave normal direction. Discrete Z mode echoes result from reflections at the Z mode lower cutoff frequency (fz) when waves propagate in both upward and downward directions from the satellite. The expected polarization for these echoes based on parallel propagation is circular. The measured polarization showed significant deviations from circular polarization. We show that multipath propagation in Z mode cavities can explain these deviations from circular polarization. A further evidence of multipath propagation is provided by multiple time delays at each frequency for the discrete Z mode traces.
Benson Robert
Carpenter Donald L.
Li Jiying
Proddaturi R.
Reinisch Bodo
No associations
LandOfFree
Interpretation of Vector Electric Field Measurements by RPI Using Three Dipole Antennas on IMAGE does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Interpretation of Vector Electric Field Measurements by RPI Using Three Dipole Antennas on IMAGE, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Interpretation of Vector Electric Field Measurements by RPI Using Three Dipole Antennas on IMAGE will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1466008