RELATIONSHIPS BETWEEN REMOTELY SENSED FOREST STRUCTURE AND BIOMASS: FOURIER STRUCTURE FROM LiDAR AND InSAR AND PENETRATION AT MICROWAVE FREQUENCIES

Resumo

This paper proposes the correlation of biomass with Fourier transforms of LiDAR and InSAR vegetation density measurements at vertical and horizontal Fourier spatial frequencies, as a means to estimate biomass. It further suggests that each Fourier frequency of leaf area density could be modeled as a harmonic oscillator, in which leaf area itself provides a restoring force to constrain it to some nominal value. Preferred Fourier frequencies for tropical forest stands at La Selva Biological Station, Costa Rica, with vertical wavelengths of 12 to 18 m and 5-7m are shown from LIDAR as an update to previous work. These two wavelengths are close to the average height and crown depth of forest stands measured. As an example of different kinds of modeling, it is suggested that biomass be considered a complex quantity with amplitude representing the usual biomass, and the phase representing some undetermined characteristic of the forest. Finally, since structure-based biomass estimation will presumably improve with signal penetration, a diffraction calculation of penetration through holes at L- and C-band shows that the diffractive component of penetration from C-band is greater than or equal to that at L-band, countering to some extent the lower penetration at C-band due to the frequency dependence of water's extinction.