Measured spectrum and polarization of wideband radar signal from forest stand

We report on an experiment regarding the spectra of super-wide band radar (SWBR) backscatter amplitude generated by forest canopy. The larch forest stand of 100 × 100 m², used as an object of study, was located 50 km to the north from the city of Krasnoyarsk, Russia, with the average tree height, diameter, and density of trees being of 14.2 m, 0.116 m, and 0.38 trees/m². All data were recorded in August 2003. The SWBR, radiating pulses with duration of 1.5 ns and 0.15 ns, was mounted on the tower at the height of 21.5 m, the range and viewing angle being of from 3 to 100 m and from 50° to 75°, respectively. The backscatter was recorded as a function of distance. Noticeable correlation was found between the positions of peaks of the backscatter signal and those of single trees. This suggests similarity in spatial structure of the radar signal and inhomogenieties inside the forest canopy. Subsequently the record of backscatter was turned into the analytical signal. Finally, the module of analytical signal was processed to evaluate its spatial spectrum. Thus attained spectra were shown to follow a combination of the power laws, with two exponents being distinguished at the low and high frequencies. This type of spectra remained for vertical, horizontal, and cross polarizations. The discovered features of the backscatter spectra were proposed to be applied for the classification of forests, using SWBR technique.