Can Sea Clutter and Indoor Radio Propagation be Modeled as Strange Attractors?

Sea clutter is the backscattered returns from a patch of the sea surface illuminated by a radar pulse. The amplitude waveforms of sea clutter and indoor radio propagation are very complicated. Can the apparent randomness of these waveforms be attributed to be generated by low-dimensional chaos? Based on the assumption that a chaotic attractor is characterized by a noninteger fractal dimension and a positive Lyapunov exponent, Haykin et al (1992) concluded that sea clutter while Tannous et al (1991) concluded that indoor radio propagation data were chaotic. However, a numerically estimated non-integral fractal dimension and a positive Lyapunov exponent may not be sufficient indication of chaos. Other researchers have also indirectly questioned the chaoticness of the sea clutter. We employ a more stringent criterion for low-dimensional chaos developed by Gao and Zheng (Phys. Rev. E, 1994) to study a two minute duration sea clutter data provided by Haykin, and indoor radio propagation data measured at UCLA, and show that these data are not chaotic. We carry out a multifractal analysis and find that sea-clutter data can be modeled as multiplicative multifractals with a lognormal envelope distribution, while the radio propagation data can be modeled as a weak multifractal in the sense of structure function technique.