DOPPLER SPECTRUM STATISTICS OBTAINED FROM 3 DIFFERENT-FREQUENCY RADARAURORAL EXPERIMENTS

Three coherent radar systems, Halley (PACE), SABRE and COSCAT are empl oyed to investigate the properties of auroral plasma irregularities, E ach radar is sensitive to a different irregularity wavelength. Halley typically observes, irregularities of 10.7 m wavelength, SABRE observe s I m wavelength and COSCAT 16 cm wavelength. A comparison is made bet ween the irregularity characteristics at the different wavelengths. In order to account far the variations between the different data sets i t is important to consider each radar's observing geometry in addition to the differences in irregularity wavelength. A special investigatio n is conducted on the width of the backscatter spectrum, a measure of the coherence of the backscattered signal. The variation of the freque ncy spectral width with irregularity wave number is found to follow a k(1) dependence, Relationships between the width and irregularity phas e speed and the width and backscatter power are identified. Type-I coh erent scatter, typical of the Wick and COSCAT observations, exhibit mi nima in spectral width at phase speeds of the order of the ion-acousti c speed and the mean scattered power decreases as the spectral width i ncreases. In contrast, type-II spectra as observed by the Halley radar have minimum widths at phase speeds near 0 m s(-1) and there is an in crease in power as the width increases.