P-band is better for forest biomass estimation because it doesn't attenuate as rapidly with increasing biomass.  Also, because P-band does not decorrelate as rapidly, one can do multiple pass interferometry to estimate height and biomass and to help "beat down" the error from a single measurement.  Longer wave lengths than P-band would also be wonderful but they would suffer increasing background from the Earth's Faraday rotation.

please check the following link for your study

http://www.bioline.org.br/pdf?st15166

http://www.ipublishing.co.in/jggsvol1no12010/EIJGGS2038.pdf

http://www.nrsc.gov.in/sites/all/pdf/prrisat.pdf

http://www2.bren.ucsb.edu/~fd/Pubs/melack_et_al95.pdf

P-band, as planned for the BIOMASS mission by ESA, is penetrating into the forest and sensitive to major biomass constituents (but also sensitive to ground conditions, which can be compensated by tomography).

High frequency such as X-band has recently been shown to produce high biomass accuracy for boreal forests by means of TanDEM-X single pass interferometry combined with a DTM. Here the sensitivity is for forest height and vegetation density, vital for biomass estimation. C-band should have similar characteristics.

A combination of P and C or X-band may be quite useful in the future since the sensitivities are quite different.

Thank you very much all for your response and sorry for my delayed communication.

For example, in temperate and boreal forest the response of the radar (L and P-band) are much better in comparison with the tropical forest (their complex structure, heterogeneity and density have a big influence in these). But the behaviour of the coniferous forest can be similar to boreal forest for its structure (pines). The L-band from Alos Palsar (free data) for example, has good results estimating biomass (in coniferous forest better than broadleaf forest). Then, I have a doubt, when you explained to me about the P-band: The saturation level in coniferous forest can be lowest than broadleaf forest if I use P-band instead L-band?...Their structure can influence in the saturation level, or this saturation is more relative to the technical aspects like polarization or specific band. In this case if I use C or X-band (just the canopy surface and small branches are penetrated by these bands) maybe my saturation level would be more highest using this bands?

Thanks, regards!