## 4 Results and Discussion
### Regional-Scale Mapping and Monitoring of Rice Areas in Asia: A Way Forward  
We have demonstrated that rice area can be accurately classified with X-band HH polarization SAR images across multiple environments and management conditions. We have also demonstrated that a large number of scenes covering a large geographic extent can be quickly analyzed using automated processing combined with rule-based parameters that can be derived by the operator based on information gathered from field observations. SAR-based rice mapping is not new, but the opportunity to develop operational rice monitoring services based on SAR data is new, and there is a great deal of interest and activity in the region. In addition to national-level projects, several consortia are demonstrating the value of rice crop monitoring with SAR across Asia and elsewhere. The Swiss Agency for Development and the Cooperation-funded RIICE project [30] are exploring both public and private sector applications in food security and crop insurance with the aim to build capacity in-country to sustain such services. The Asia-RiCE [31] component of the GEO Global Agricultural Monitoring (GEOGLAM) initiative aims to ensure that rice crop monitoring issues are given suitable priority and attention within the scope of the full GEOGLAM initiative [32], including the development of the observation requirements. Another project conducted by the Asian Development Bank and supported by the Japan Fund for Poverty Reduction aims to improve the quality and timeliness of rice crop area and production estimates and forecasts through SAR data [33]. In Europe, the ERMES (An Earth Observation Model-based Rice Information Service) project aims to develop a prototype of downstream service dedicated to the rice sector based on assimilation of EO and _in situ_ data within crop yield modeling [34]. In short, there is a clear demand and increasing capacity for using SAR data to monitor rice crops on a large scale. Current and forthcoming SAR systems, such as CSK, TSX, RADARSAT-2, RISAT-1, Sentinel-1 and ALOS-2, offer an unparalleled opportunity to deliver regular and systematic acquisitions of the rice crop in Asia. This could provide information on seasonal rice area, planting dates, crop growth parameters, harvest dates and the impact of flood, drought and wind on the crop. This can be realizedonly if acquisition plans are aligned to the rice crop extent and rice crop calendar across Asia and if acquisitions are frequent enough. Unfortunately, so far, a key challenge is that countrywide systematic acquisitions are still non-existent. In the past three decades, attempts to obtain application-oriented SAR data archives have been carried out by ESA (ERS-Tandem), NASA/JPL (Shuttle Radar Topographic Mission), JAXA (ALOS PALSAR-1) and DLR/EADS Astrium (TanDEM-X) for topographic and forest applications. We hope that space agencies will follow this model for a wider spectrum of land applications and that, in the medium term, common strategies will be pursued. Field data collection for validation and calibration of remotely sensed data is the most challenging technical aspect of large-scale rice crop monitoring. The development of protocols for rapid and low-cost field assessments is essential if such monitoring systems are to become operational. These protocols could be based on existing field and farmer surveys that are carried out under current reporting by ministries of agriculture or statistics. Furthermore, the use of smart phones or tablet devices to collect field data (such as photos, GPS coordinates, field observations and farmer surveys) and transmit the data via the mobile network or Wi-Fi network to a central database should be explored. From our experience in this study across six countries and 13 sites, we recommend the following:  
1.