3.5 Volume Scattering

Volume scattering is defined as the scattering occurring in a medium when electro-magnetic radiation transmits from one medium to another medium. Figure 3.5.1 shows the schematic model of volume scattering for two examples; (a)scattering by widely distributed particles such as rain drops and (b)scattering in uneven media with different permittivities. Scattering by trees or branches, subsurface or soil layers, snow layers etc. are examples of volume scattering.

Volume scattering can be observed if microwave radiation penetrates into a medium. The penetration depth is defined as the distance when the incident power attenuates to 1/e (exponential coefficient).

The intensity of volume scattering is proportional to the discontinuous inductivity in a medium and the density of the heterogeneous medium. The scattering angle depends on surface roughness, average relative permittivity and wavelength.

The receiving intensity is proportional to multiplication of the intensity and the volume involved in the region of range gate and beam width as shown in the example in Figure 3.5.3. Volume scattering in the case of rainfall, shown in Figure 3.5.2, is represented as a function of wavelength and Z factor as follows.

where : wavelength
D : diameter of rain drop
k : constant (k = (-1) / (+2))
Z : Z factor (Z= Di)

In the case of soil and snow, volume scattering occurs together with surface scattering, although the surface scattering is small as shown in Figure 3.5.3. There will exist an error for the measurement of surface scattering coefficient because of the effect of volume scattering.

In the case of forest as shown in Figure 3.5.4, it is necessary to introduce a model of the volume scattering by leaves and branches as well as surface scattering by the crown of trees, and corner reflection effects due to the soil and vertical tree trunks.

Copyright © 1996 Japan Association of Remote Sensing All rights reserved