## 4 Conclusions  
An EO dataset of SAR and optical images covering a time period of around 30 years was acquired from Vietnam's Mekong Delta region, to study the long term changes in land use, with a special emphasis on rice, other cultivated areas and aquaculture. Land-use maps were produced using automatic classification techniques and the resulting land-use maps were validated using the reference data collected in a field survey campaign. In classifications an overall accuracy of 77%-88% was achieved. Using the comprehensive EO data set in this study, it can be concluded that wide-area and up-to-date information on land-use and its changes can be obtained, which cannot be obtained by other means such as field surveys. We also observed that, together with the field validation data, the few interviews of local farmers provided a valuable contribution to analyzing the reliability and the accuracy of the land-use classification data. Therefore, additional _in-situ_ inquiries are worth considering in studies, where archived data from the past EO experiments is needed for analyzing the present situation or to complement a time series. The results presented here were limited by the amount of EO data available in the satellite image archives. Even though we carefully collected all available EO data acquired during the last 30 years, there were some caps in the areal extent, and this concerns mainly the optical EO data due to the cloudiness in the Mekong Delta region. Since the radar wavelengths penetrate clouds, SAR data is preferred. In order to carry out land-use change mapping, it is vital that SAR EO data is collected systematically throughout the year from the target area. However, it should be noted that image acquisition dates should always be carefully planned in order to interpret, e.g., multi-year rice crops. The spatial resolution of the results presented here are limited to the resolution of the satellite data available, some 150 m in Envisat ASAR. The modern high resolution SAR satellites, such as TerraSAR-X, COSMO-SkyMed, Radarsat-2, would give more detailed results on land use. However, the amount of data needed also increases due to the smaller image coverage, which also limits the total area under investigation. Therefore, the wide-swath mode of the SAR is expected to play an important role in wide-area land-use mapping. In the future, from the rice mapping point of view, the use of Sentinel-1 satellites of the European Space Agency appears to be a very promising approach, because they could allow continuous wide-area monitoring of areas such as the Mekong Delta region with a good temporal coverage. Up-to-date land-use maps from Vietnam are constantly needed to detect long-term trends in land-use and to be used as an aid in decision making when policies concerning farming actions are planned. This information can be produced from SAR satellite data, with the help of optical EO data. This study was done in cooperation with [PERSON] from the United Nations International Fund for Agriculture and [PERSON] from the European Space Agency. The authors would like to thank the organizers of the field survey and the local authorities taking part in the survey. In addition, authors would like to thank the anonymous reviewers for their valuable comments. The study was funded by the ESA through the project \"Earth Observation Information Services for United Nation International Fund for Agricultural Development, Annex E: Crop Type Monitoring in Vietnam\". The manuscript writing was partly funded by the Academy of Finland project: \"Mobile hyperspectral laser remote sensing\". The ENVISAT imagery was provided by ESA within the framework of Category-1 project 14134 \"Crop type monitoring in Vietnam\". The Landsat data were acquired from the data archives of the U.S. Geological Survey. The SPOT data were distributed by the Astrium Services/Spot Image S.A., France. [PERSON] wrote the majority of the paper. [PERSON] and [PERSON] designed the methodology used in the study.