Linking vegetation spectral reflectance with ecosystem carbon phenology in a temperate salt marsh
Linking vegetation spectral reflectance with ecosystem carbon phenology in a temperate salt marsh
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DOI：
10.1016/j.agrformet.2021.108481
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发表时间：
2021-09
影响因子：
6.2
通讯作者：
A. Hill;A. Vázquez‐Lule;Rodrigo Vargas
中科院分区：
文献类型：
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作者：
A. Hill;A. Vázquez‐Lule;Rodrigo Vargas
盐沼是一个重要的陆地-水生界面，由于生物物理控制和空间有限的土地覆盖，在地球系统模型中仍然代表性不足。一个有前途的方法，以提高代表性的近端遥感产生物候信息的应用，但我们缺乏详细的知识，近端传感器和指数在这些生态系统内的表现。我们使用涡度协方差（EC）测量的净生态系统生产力（NEP），并推导出生态相关的物候参数（即，phenoperiods）用作碳物候学基准。这些基准与植被指数和来自星载的光谱波段（即，MODIS）或普通的近端传感器（即，Phenocam和光谱反射传感器; SRS）。Phenocam衍生指数，其排除红外波长（即，植被对比指数; VCI和绿度色度坐标; GCC），与NEP基准密切一致，并提供了碳汇季节长度的最佳预测（基准的1-6天内）。虽然从植被中分离红外线（NIRv）提供了改进，但利用红外波段的其他指数（即，归一化差异植被指数（NDVI）和增强型植被指数（EVI）主要低估了季节开始日期（基准前5-30天），而高估了季节结束日期（基准后7-47天）。这些差异是最大的指数来自MODIS和SRS传感器，具有较窄的全宽半高光谱带宽和尖锐的方向角。phenocam（VCI和GCC）提供了最准确的物候参数，同时提供近红外（NIR）响应，可以生成有关冠层结构和功能季节变化的额外信息。盐沼环境和植被特性（包括立枯生物量）的独特特征可以为常用的植被指数（NDVI，EVI）带来解释挑战。仅利用可见光波长（VCI，GCC）或隔离植被的近红外反射率（NIRv）从近端传感器中提取信息，为研究盐沼中的碳物候提供了改进。
Salt marshes constitute an important terrestrial-aquatic interface that remains underrepresented in Earth System Models due to constraining biophysical controls and spatially limited land cover. One promising approach to improve representativeness is the application of proximal remote sensing to generate phenological information, yet we lack detailed knowledge on how proximal sensors and indices perform within these ecosystems. We use measurements of net ecosystem productivity (NEP) from eddy covariance (EC) and derive ecologically-relevant phenology parameters (i.e., phenoperiods) to use as carbon phenology benchmarks. These benchmarks are compared against vegetation indices and spectral bands derived from spaceborne (i.e., MODIS) or common proximal sensors (i.e., phenocam and spectral reflectance sensors; SRS).Phenocam derived indices, which exclude infrared wavelengths (i.e., vegetation contrast index; VCI and greenness chromatic coordinate; GCC), aligned closely with NEP benchmarks and provided best predictions of carbon sink season length (within 1–6 days of benchmark). Although isolating infrared from vegetation (NIRv) offered improvements, other indices utilizing infrared bands (i.e., normalized difference vegetation index; NDVI and enhanced vegetation index; EVI) primarily underestimated season start dates (5–30 days prior to benchmark) while overestimating season end dates (7–47 days after benchmark). These discrepancies are greatest for indices derived from MODIS and SRS sensors, which have narrower full width half maximum spectral bandwidths and sharper orientation angles. The phenocam (VCI and GCC) provides the most accurate phenology parameters while offering near-infrared (NIR) response which can generate additional information on seasonal changes in canopy structure and function.The distinctive characteristics of the salt marsh environment and vegetation properties including standing dead biomass can introduce interpretation challenges for commonly used vegetation indices (NDVI, EVI). Incorporating information from proximal sensors utilizing only visible wavelengths (VCI, GCC) or isolating the near-infrared reflectance of vegetation (NIRv) offers improvements for studying carbon phenology within salt marshes.