MICROWAVE SCATTERING PROFILES OF A RICE SAMPLE BY MEANS OF POLARIZATION COHERENCE TOMOGRAPHY Maria-Jose Sanjuan, Juan M. Lopez-Sanchez, J. David Ballester-Berman Signals, Systems and Telecommunication (SST) Group DFISTS, University of Alacant, P.O. Box 99, E-03080 Alacant/Alicante, Spain Phone / Fax: +34965909597 / 9750, E-mail: [email protected], [email protected], davidb@d¿sts.ua.es 1. INTRODUCTION A new 3D imaging technique, called Polarization Coherence Tomography (PCT), has been recently formulated and demonstrated in two scenarios: a Scots Pine forested area at L-band, and with wide-band indoor data of a maize sample [1, 2]. This method makes use of PolInSAR observables (complex interferometric coherences at different polarizations) in order to reconstruct the vertical pro¿le of microwave scattering of vegetation. This task is carried out by expanding the coherences by means of Legendre polynomials, and taking as inputs of the procedure the volume height and the ground topography. Single-baseline and dual-baseline cases have been illustrated in the literature. The applications of this algorithm are manifold. In the ¿eld of biophysical parameter retrieval of agriculture, this approach offers an important potential to recover information about the scattering processes that take place inside the volume, specially concerning the assumptions adopted for describing the scattering mechanisms along the vertical structure. Hence, this new technique could be also used for interpreting and validating the results and observations derived from existing retrieval approaches. 2. METHODOLOGY AND RESULTS In this paper we have applied the PCT technique to wide-band fully polarimetric data acquired from a rice sample in laboratory conditions. The scattering pro¿les provided by the PCT at different frequencies and polarizations have been related to the inversion results previously obtained in [3, 4]. We have applied the PCT technique to rice samples in order to obtain a more complete characterization of these plants. The short height of this kind of crop entails a limitation on the sensor con¿guration which has to do with the requirements of vertical wavenumber. This is related to the frequency band and the available baseline for ensuring enough sensitivity to the reduced volume thickness. As a matter of fact, only higher frequency bands, i.e. C- and X-bands, are suitable for radar remote sensing of rice. Besides, double-bounce mechanisms are expected to dominate the response because of the Àooded condition of soil, and the reconstruction of the scattering pro¿le should con¿rm this statement. Also, the capability of the PCT method to provide enough resolution for such a short crop is evaluated. The coherence tomography results have been also used to determine the relative contribution of different ground scattering components as a function of frequency. Speci¿cally, for modelling purposes it is desirable to con¿rm the observation conditions for which the double-bounce mechanism dominates the ground response and when a combined effect of ground returns, i.e. direct and double-bounce, must be assumed. In addition, a deep analysis of the resulting vertical pro¿les helps to explain some important mismatches between the theoretical coherences predicted by the oriented volume over ground (OVoG) model and the experimental ones. Inversion methods reported in previous works yielded underestimated values of effective height which may be related to the expected higher extinction for the HV channel than for the HH one. This fact disagrees with the distribution of experimental coherences, This work has been supported by the Spanish Ministry of Education and Science (MEC) and EU FEDER under Projects TEC2005-06863-C02-02 and HA2007-0075. where the lowest extinction corresponds to the crosspolar channel. Actually, the coherence tomography technique illustrates the position of the scattering centers at each polarization channel, and it also demonstrates that the propagation extinction inside the volume should be modelled in a more rigorous way than just with a constant value (i.e. as an exponential function). 3. REFERENCES [1] S. R. Cloude, “Polarization Coherence Tomography,” Radio Science, Vol. 41, April 2006. [2] S. R. Cloude, “Dual Baseline Coherence Tomography,” IEEE Geosci. Remote Sensing Letters, Vol. 4, No. 1, pp. 127–131, Jan. 2007. [3] J. D. Ballester-Berman, J. M. Lopez-Sanchez, J. Fortuny-Guasch, “Retrieval of biophysical parameters of agricultural crops using polarimetric SAR interferometry,” IEEE Trans. Geosci. Remote Sensing, Vol. 43, No. 4, pp. 683-694, April 2005. [4] J. M. Lopez-Sanchez, J. D. Ballester, Y. Marquez, “Model Limitations and Parameter-Estimation Methods for Agricultural Applications of Polarimetric SAR Interferometry,” IEEE Trans. Geosci. Remote Sensing, Vol. 45, No. 11, pp. 3481-3493, Nov. 2007.