Abstract Reliable information on salt marsh extent and condition is crucial to promote effective management strategies towards their maintenance and recovery. Most of previous studies on salt marsh extent assessment used Landsat-derived Normalized Difference Vegetation Index (NDVI), being limited the current knowledge about the performance of other Vegetation Indices (VI). Based on Landsat imagery this study proposes a new methodology to map salt marsh extent in estuarine systems by combining Normalized Difference Water Index (NDWI) and VI, exploring their performance when using different VI. Moreover, it aims to assess the extent and condition changes between 1984 and 2018 in two salt marshes (Pancas and Corroios) located within Tagus Estuary. The VI best-performing salt marsh extent was determined and the methodology applied to assess salt marsh extent changes. Condition change was investigated by statistically analyzing spatially averaged VI over salt marsh extent change regions. Results demonstrated that NDWI and VI combined can be used to efficiently map the marsh extent and NDVI was the VI with the best performance. Corroios revealed mostly stable without noticeable changes in its extent and condition. Oppositely, Pancas registered a continuous seaward progression at a mean rate of 3 ha/year since 1984, while restricted upper regions dieback after 2004–2005, likely due to high soil salinity conditions. In general, NDVI performs better salt marsh extent, but others VI corrected to minimize soil effects perform better when tidal flats are entirely, or almost entirely, exposed, opening perspectives to the development of new methods combining the use of different VI to optimize salt marsh extent detection.

中文翻译：

---

评估 35 年 Landsat 影像的盐沼范围和条件变化：塔霍河口案例研究

摘要 关于盐沼范围和状况的可靠信息对于促进有效管理策略以维护和恢复盐沼至关重要。以前关于盐沼范围评估的大多数研究都使用了 Landsat 衍生的归一化差异植被指数 (NDVI)，限制了目前对其他植被指数 (VI) 性能的了解。本研究基于 Landsat 影像，提出了一种新方法，通过结合归一化差值水指数 (NDWI) 和 VI 来绘制河口系统中盐沼范围的地图，探索它们在使用不同 VI 时的性能。此外，它还旨在评估 1984 年至 2018 年间位于塔霍河口的两个盐沼（Pancas 和 Corroios）的范围和条件变化。确定了 VI 表现最佳的盐沼范围，并应用了评估盐沼范围变化的方法。通过对盐沼范围变化区域的空间平均 VI 进行统计分析来研究条件变化。结果表明，NDWI 和 VI 相结合可以有效地绘制沼泽范围，NDVI 是性能最好的 VI。Corroios 显示大部分稳定，其范围和状况没有明显变化。相反，自 1984 年以来，Pancas 以平均 3 公顷/年的速度连续向海推进，而在 2004-2005 年之后受限制的上部区域枯萎，可能是由于土壤盐分高。一般来说，NDVI 在盐沼范围内表现更好，但当潮滩完全或几乎完全暴露时，其他 VI 修正以最大限度地减少土壤影响，表现更好，