Exploring the Potential of TanDEM-X Data in Rice Monitoring

Abstract:

In this work, phenological parameters such as growth stage, calendar estimation, crop density and yield estimation for rice fields are estimated employing TanDEM-X data. Currently, crop monitoring is country-dependent. Most countries have databases based on cadastral information and annual farmer inputs. Inaccuracies are coming from wrong or missing farmer declarations and/or coarsely updated cadastral boundary definitions. This leads to inefficient regulation of the market, frauds as well as to ecological risks. An accurate crop calendar is also missing, since farmers provide estimations in advance and there is no efficient way to know the growth status over large plantations. SAR data is of particular interest for these purposes.

The proposed method includes two step approach including field detection and phenological state estimation. In the context of precise farming it is substantial to define field borders which are usually changing every cultivation period. Linking the SAR inherit properties to transplanting practice such as irrigation, the spatial database of rice-planted agricultural crops can be updated. Boundaries of agricultural fields will be defined in the database, and assignments of crops and sowing dates will be continuously updated by our monitoring system considering that sowing practice variously changes depending on the field owner decision. To define and segment rice crops, the system will make use of the fact that rice fields are characterized as flooded parcels separated by path networks composed by soil or rare grass. This natural segmentation is well detectable by inspecting low amplitude and coherence values of bistatic acquisitions.

Once the field borders are defined, the phenology estimation of crops monitored at any time is the key point of monitoring. In this aspect the wavelength and the polarization option of TanDEM-X are enough to characterize the small phenological changes. The combination of bistatic interferometry and Radiative Transfer Theory (RTT) with different polarization provides a realistic description of plants including their full morphology (stalks, tillers, leaves and panicles).