Faculty of Science and Technology

Effects of the Ionosphere on Space Based Radars

Prof. Paul S. Cannon

Chief Scientist

Communications Division

Centre for Propagation and Atmospheric Research

QinetiQ

The presentation will start by introducing the principles of space based synthetic aperture radars together with a summary of the effects that the ionosphere can have on satellite to ground transmissions. The presentation will then go on to describe some measurements which have been made of channel impulse response of the ionosphere near 150 and 400 MHz.

This is first determination of ionospheric distortion, comprising the simultaneous characterization of both multipath and Doppler, on wideband, transionospheric VHF and UHF signals. The measurements took place as part of the test phase of the United Kingdom-United States Wideband Ionospheric Distortion Experiment during the evening (1000 UT) of 18 January 2005. This characterization has been achieved using the ALTAIR radar at the Ronald Reagan Ballistic Missile Defense Test Site on Kwajalein Atoll (9.395 N, 167.469 E (12.87 N, 237.16 E corrected geomagnetic)) in the Pacific, in conjunction with a low Earth orbiting, constant radar cross-section, passive satellite (calibration sphere). During the period when the two-way S4 index was above 0.8 on both channels, the median coherency times were 43 and 96 ms at VHF and UHF, respectively (at 1.5s). The corresponding median coherency bandwidths were 0.8 and 2.1 MHz.

These measurements will be compared with theoretical calculations.