The amount of radar backscatter received from a forest canopy depends upon the system frequency,
polarisation and incidence angle, as well as canopy parameters such as structure and
moisture. L-band signal penetrates deeper into the canopy than shorter wavelengths (e.g. Xand
C- band) and interacts with the larger canopy components (e.g. large branches, trunkground
interactions) rather than leaves or twigs. Fig 9 displays a comparison of HH and HV γ°
backscatter values for forest training samples at Longford and Sligo. The HH backscatter was
higher compared to the HV backscatter for both counties, with both the HH and HV backscatter
being higher in Sligo than Longford. The diversity in backscatter responses may be attributed
to the scattering processes associated with different forest conditions. Generally, dense
mature canopies will result in an increase in HV and HH backscatter. Forest canopies usually
depolarise the radar signal, resulting in a strong HV signal. However, strong HV backscatter
(and increased depolarisation) may also be caused by forest detritus left after a disturbance
event [40]. Such surface conditions would also lead to a strong HH signal, due to increased surface
roughness and additional corner reflectors.