Impact of the spatial resolution of satellite remote sensing sensors in the quantification of total suspended sediment concentration: A case study in turbid waters of Northern Western Australia

The impact of anthropogenic activities on coastal waters is a cause of concern because such activities add to the total suspended sediment (TSS) budget of the coastal waters, which have negative impacts on the coastal ecosystem. Satellite remote sensing provides a powerful tool in monitoring TSS concentration at high spatiotemporal resolution, but coastal managers should be mindful that the satellite-derived TSS concentrations are dependent on the satellite sensor’s radiometric properties, atmospheric correction approaches, the spatial resolution and the limitations of specific TSS algorithms. In this study, we investigated the impact of different spatial resolutions of satellite sensor on the quantification of TSS concentration in coastal waters of northern Western Australia. We quantified the TSS product derived from MODerate resolution Imaging Spectroradiometer (MODIS)-Aqua, Landsat-8 Operational Land Image (OLI), and WorldView-2 (WV2) at native spatial resolutions of 250 m, 30 m and 2 m respectively and coarser spatial resolution (resampled up to 5 km) to quantify the impact of spatial resolution on the derived TSS product in different turbidity conditions. The results from the study show that in the waters of high turbidity and high spatial variability, the high spatial resolution WV2 sensor reported TSS concentration as high as 160 mg L-1 while the low spatial resolution MODIS-Aqua reported a maximum TSS concentration of 23.6 mg L-1. Degrading the spatial resolution of each satellite sensor for highly spatially variable turbid waters led to variability in the TSS concentrations of 114.46%, 304.68% and 38.2% for WV2, Landsat-8 OLI and MODIS-Aqua respectively. The implications of this work are particularly relevant in the situation of compliance monitoring where operations may be required to restrict TSS concentrations to a pre-defined limit.

人类活动对近岸海域的影响已引发广泛关注，因为此类活动会增加近岸海域的总悬浮泥沙（Total Suspended Sediment, TSS）总量，进而对近岸生态系统造成负面影响。卫星遥感为高时空分辨率下的总悬浮泥沙浓度监测提供了强有力的技术手段，但近岸海域管理者需注意：卫星反演得到的总悬浮泥沙浓度会受到卫星传感器辐射特性、大气校正方法、空间分辨率以及特定总悬浮泥沙反演算法局限性的影响。本研究针对西澳大利亚州北部近岸海域，探讨了卫星传感器不同空间分辨率对总悬浮泥沙浓度定量反演的影响。研究分别对中分辨率成像光谱仪（MODerate resolution Imaging Spectroradiometer, MODIS）-Aqua、陆地卫星8号陆地成像仪（Operational Land Imager, OLI）以及WorldView-2（WV2）所反演的总悬浮泥沙产品进行了定量分析：上述传感器的原始空间分辨率分别为250米、30米与2米，本研究同时将其数据重采样至5千米的较低空间分辨率，以此量化不同浊度条件下空间分辨率对总悬浮泥沙反演产品的影响。研究结果表明：在高浊度且空间变异性强的海域，高空间分辨率的WV2传感器反演得到的总悬浮泥沙浓度最高可达160 mg·L⁻¹，而低空间分辨率的MODIS-Aqua反演得到的总悬浮泥沙浓度最大值仅为23.6 mg·L⁻¹。针对空间变异性强的浊水环境，降低各卫星传感器的空间分辨率后，WV2、陆地卫星8号OLI以及MODIS-Aqua的总悬浮泥沙浓度反演值的变异性分别达114.46%、304.68%与38.2%。本研究的结论在合规监测场景中尤为重要，此类场景往往要求将总悬浮泥沙浓度控制在预设限值以内。