University of Twente Student Theses


Observing Waterlogging and its impact on Agriculture in Hungary using Radar and Optical Images

Mahmud, Ashfak (2022) Observing Waterlogging and its impact on Agriculture in Hungary using Radar and Optical Images.

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Abstract:The study aims to detect waterlogging dynamics in agricultural fields and quantify its effect on crop development at different growth stages using synthetic-aperture radar (SAR) and optical satellite images. Firstly, waterlogging dynamics (occurrence, extent, and timing) have been detected from Sentinel-1 (S1) and PlanetScope (PS) images. Hereafter, temporal profiles from Sentinel-1(S1) and Sentinel-2 (S2) have been used to understand the development of the crop in different growth stages. Finally, the impact of waterlogging has been quantified by comparing crop development in non-waterlogged (NWL) and waterlogged (WL) locations in different growth stages by the synergistic use of radar (S1) and optical (S2) images. A threshold value of Normalized Difference Water Index (NDWI) ≥ -0.27 on PS images was applied, and a threshold value of σ_VV^0 ≤ -16 dB on S1 images was employed to separate the waterlogged areas. Temporal profiles of σ_VH^0, σ_VV^0, cross-ratio (CR), and radar vegetation index (RVI) from S1 and Normalized Difference Vegetation Index (NDVI) from S2 have been generated for the season 2021 to observe crop development. Time series analysis from sample sites at the intra-field level has been done to see how the crop development is reflected in NWL and WL crops. Finally, patterns of NDVI deviation in NWL and WL locations are mapped at the intra-field level in different growth stages. Results show that PS detected 3.95% (7.17 〖km〗^2), where S1 spotted 3.76 % (6.83 〖km〗^2) of the area as waterlogging. CR and RVI from S1 and NDVI from S2 perform as a similar indicators of crop development monitoring. However, S2-derived NDVI shows an early increase and decrease than CR and RVI from S1 in the initial and senescence stages as NDVI is sensitive to chlorophyll, whereas CR and RVI are sensitive to biomass and vegetation water content (VWC). The highest NDVI differences (up to 0.4) between NWL and WL crops are noticed during the flowering and fruit development stage (May to mid-June). Due to less biomass being developed in the WL crop during leaf development and stem elongation stage in April, CR shows slightly lower values (2-3 dB) in WL locations. Similar to NDVI, the highest difference in CR and RVI between WL and NWL locations is found during May, when winter wheat shows maximum growth. A delay in crop growth in the WL location is also noticeable during crop development. The highest discrepancies between NWL and WL locations are found from January to March by combining S2-derived NDVI, and S1-derived scaled CR due to the sensitivity difference of NDVI and CR to waterlogging. From the leaf development and stem elongation to flowering and fruit development stages, the ratio of CR and NDVI responded similarly to crop growth in both waterlogging states. However, some inconsistencies are found during senescence due to the difference in the rate of biomass and chlorophyll loss in NWL and WL crops. The spatial patterns of NDVI deviation show that high and very high deviations coincide with the WL locations, especially when waterlogging has a longer duration, and the deviation is the highest during the flowering and fruit development stage. The study reveals that the synergy capabilities of optical and radar images are the potential for detecting waterlogging dynamics as well as assessing the difference in crop development between WL and NWL crops.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:38 earth sciences, 43 environmental science, 48 agricultural science
Programme:Geoinformation Science and Earth Observation MSc (75014)
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