Rice Monitoring in Spain by means of Time Series of TerraSAR-X Dual-pol Images
Juan M Lopez-Sanchez(1), J David Ballester-Berman(1) and Irena Hajnsek(2)
(1) University of Alicante, P.O. Box 99, 03080 Alicante, Spain
(2) German Aerospace Center (DLR), P.O. Box 1116, 82234 Wessling, Germany
The potential of X-band dual-pol SAR images for the monitorization of rice fields and its application for helping farming practices has been assessed in the framework of the project LAN0021 of the pre-launch AO of TerraSAR-X.
The test site consists of an area of 20 km x 30 km in the SW of Spain, where rice is cultivated annually from May-June to September-October. During the 2008 campaign, the local association of rice farmers is collecting several ground truth parameters on a weekly basis. For this research project, important cultivation conditions, as well as the phenological stage and vegetation height, have been acquired in more detail over 8 parcels.
Three different time series of dual-pol TerraSAR-X images have been ordered simultaneously to the cultivation period: VH/VV with incidence angles of 22 and 40 degrees, and HH/VV with 30 degrees.
All the available images have been employed for analyzing the sensitivity of the following observables to the growth of the plants:
- Backscattering coefficients at different polarizations.
- Ratios of backscattering coefficients at different polarizations.
- Phase differences between different polarization channels.
- Cross-correlations between polarimetric channels.
- Polarimetric observables provided by target decomposition: entropy, alpha, etc.
This study is also intended to review the main conclusions of previous works in this area, mostly carried out at other bands (C-band) or with airborne sensors.
Results provided by this study in its present form have already confirmed a clear correlation between the HH/VV power ratio and the early growth stages, as well as the excellent performance of this ratio for discriminating rice fields from other crop types, as a consequence of the important double-bounce interaction between the stems and the flooded ground, which is specific of this crop type.
In addition, the phase difference between the copolar channels, which can be measured thanks to the coherent acquisition mode of this sensor, also has demonstrated to be sensitive to the vegetation growth.