Proceedings with Extended Abstracts (single PDF file) - Radio ...

.ON-LINE ADAPTIVE DC-GROUND-CLUTTER REMOVALJürgen RöttgerMax-Planck-Institut, 37191 Katlenburg-Lindau, Germany1. SummaryMST radar observations are frequently affected by partially strong clutter echoes from mountainsand other fixed targets. The same holds for and incoherent scatter (IS) radar observations of theD-region. At the EISCAT Svalbard Radar (an incoherent scatter radar for studies of the polar capupper atmosphere and ionosphere) for instance, the ground clutter even extends out to 100 km.This clutter is usually minimized by antenna optimization by means of suppressing horizontalside-lobes. Sato et al. (this issue, 2003) presented a new method suppressing sidelobes digitally.If there is a still remaining DC component, this can be removed by either interpolating the zerofrequencycomponent (not too elegant method, though) in the Doppler spectrum or by the socalledDC subtraction. The former method eliminates a significant part of the signal or may evenfail, when the atmospheric echo has a very narrow Doppler spectrum, comparable to the clutterspectrum. The latter method is usually done off-line on the raw data.Here the design proposal of a simple digital hardware filter is presented, which allows on-lineadaptive narrow-band-pass filtering (notching) for all individual range gates. It can be easilyimplemented into all MST radar systems and, due to its recursive and adaptive design, removesonly a very negligible part of the atmospheric signal. Standard post-detection DC-removalmethods are not required after this real-time on-line filtering.2. The problem and solutionGround clutter is not an unusual phenomenon in many radar applications and there exist severalmethods to eliminate the destructive effect on atmospheric and ionospheric observations. We willnot discuss here the methods used in meteorological radar or MST radar applications, since theseare described in the standard literature. These methods apply also for pulse coding, such ascomplentary codes.The EISCAT radar systems need different applications, when complex auto-covariance functionsare calculated before the ground clutter component is removed. This procedure was successfullyused and is described by Röttger (1992) in EISCAT UHF radar observations of the troposphere.For ionospheric observations again another method has to be applied. This holds in particularwhen phase coding is used and the phase coding sequence changes from pulse to pulse, as it is thecase in alternating codes. However, also effects on simple power profile and long pulse modulationsare obvious. We present here a method, which will allow to reduce the ground clutter bysome orders of magnitude. It will be described here for the most complicated application ofalternating codes in the incoherent scatter application, but the principle is also applicable forother kind of coded and single pulse modulations of IS and MST radars.377