Crop type mapping provides essential information to control and make decisions related to agricultural practices and their regulations. To map crop types accurately, it is important to capture their phenological stages and fine spatial details, especially in a temporally and spatially heterogeneous landscape. The data availability of new generation multispectral sensors of Landsat-8 (L8) and Sentinel-2 (S2) satellites offers unprecedented options for such applications. Given this, our study aims to display how the synergistic use of these optical sensors can efficiently support crop type mapping research while integrating an object-based image analysis (OBIA). Through the applied methods, we used the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM) and the flexible spatiotemporal data-fusion model (FSDAF) to blend L8 and S2 data and obtain reliable normalized difference vegetation index (NDVI) datasets with fine spatial and temporal resolution. Then the crop phenological information was extracted using a Savitzky–Golay filter and fused NDVI time series. Finally, a model combining phenological metrics and fused reconstructed NDVI as classification features was developed using a random forest (RF) classifier/OBIA approach. The results show that the FSDAF method creates more accurate fused NDVI and keeps more spatial details than ESTARFM. The FSDAF model was then used to create fused, high-resolution time-series products that were able to extract crop phenology in single-crop fields while providing a very detailed pattern relative to that from individual sensor time-series data. Moreover, combined L8 and S2 data by FSDAF produced highly significant overall classification accuracies (90.03% for pixel-based RF to 93.12% OBIA RF), outperforming individual sensor use (82.57% for L8-only; 88.45% for S2-only). Our proposed workflow highlights the advantage of spatiotemporal fusing and OBIA environment in spatiotemporally heterogeneous areas and fragmented landscapes, which represents a promising step toward generating fast, accurate, and ready-to-use agricultural data products.
Managers and policy makers demand information on agriculture dynamics and distribution for the establishment of plans and strategies. For this purpose, the use of remote sensing data constitute an essential key to follow-up the agricultural systems dynamics. The aim of this study is to define a method based on fitted Normalized Difference Vegetation Index (NDVI) time series extracted from Moderate Resolution Imaging Spectroradiometer (MODIS), trend analysis tests and machine learning approaches for assessing and monitoring farming systems in a semi-arid region of Morocco. NDVI time series were smoothed using TIMESAT software for the period between 2000 and 2018. Then, three trend analysis tests were conducted which are: monotonic trend (Mann-Kendall), Man-Kendall significance and median trend (Theil-Sen). In addition, Random Forest (RF) classification methods were performed to classify the main agricultural cover type over the study area for the 2017/2018 cropping season. The results demonstrated the ability of fitted NDVI data and RF classification to identify the main agricultural systems, which are: 1) irrigated annual crop, 2) irrigated perennial crop, 3) rainfed areas and 4) fallow. Analysis of trend patterns based on fitted NDVI values shows high variability over the farming systems. Irrigated annual and perennial crops present high improvement of biomass activity with a small inter-variability with significant trend. For the Rainfed area and fallow, these classes show a non-significant trend with low degradation of productivity. In addition, these results can constitute a relevant means of control and spatio-temporal monitoring of farming systems. Overall, the results are relevant for managers and policy makers to develop procedures and actions in order to prevent environmental and agricultural events resulted from the spatio-temporal changes in farming systems.
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