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Assessment of methods for mangrove cover mapping on shrimp farms using high spatial resolution remote sensing

Münch, Finn Benjamin (2023) Assessment of methods for mangrove cover mapping on shrimp farms using high spatial resolution remote sensing.

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Abstract:Mangroves are tropical and subtropical coastal wetlands that provide valuable ecosystem services. Although mangroves have important environmental functions like climate regulation and water purification, they decline mainly due to anthropogenic influence. This development can be observed particularly well in the Mekong Delta in Vietnam, where the decline of the mangrove area is mainly triggered by the land use change from mangrove to shrimp farms. Addressing deforestation as well as the demand for more sustainable shrimp production, hybrid systems, called mixed mangrove-shrimp farms, aim to conserve 60% of mangrove cover and cultivate ecological shrimp in low-intensity aquacultures. Observation and mapping of mangrove ecosystems are necessary to provide evidence-based information for preserving and managing this natural resource. Satellite remote sensing offers more transparent and efficient mangrove monitoring than the currently applied laborious field surveys. Data on the present land cover in the study area was collected during a sampling campaign in March 2023. This study compared an object-based and a pixel-based approach to classify high-resolution imagery to assess mangroves on shrimp farms. A SPOT-7 image was classified using a Random Forest machine learning algorithm in eCognition to investigate the mangrove classification accuracy on mixed mangrove-shrimp farms in a Vietnamese protection and production forest. The resulting mangrove maps achieved an overall accuracy of 96% with a spatial resolution of 1.5 m. The McNemar test indicated that there is no statistically significant difference between the classification accuracy of the object-based and pixel-based approach. The discrepancy between the farmer’s perspective and the classification-based shrimp farm mangrove ratios suggested ground-based estimates to be challenging. Resulting from the spatial analysis, a higher mangrove ratio was revealed in the protection forest compared to the production forest. This indicates more successful mangrove conservation or reforestation on the shrimp farms in the protection forest zone, which correlates with the funding for mangrove sapling replantation in the respective forest zone. However, the continued replantation of Rhyzophora is likely to maintain the dominance of monocultures that may benefit timber production but do not preserve or reintroduce biodiverse mangrove ecosystems and their valuable services. Consequently, the application of a hybrid mangrove observation approach that uses satellite and UAV remote sensing data is proposed for the assessment of mangrove ratios on shrimp farms in the study area.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:38 earth sciences, 43 environmental science
Programme:Geoinformation Science and Earth Observation MSc (75014)
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