Effects of spectral variability due to sediment and bottom characteristics on remote sensing for suspended sediment in shallow rivers

Siyoon Kwon; Hyoseob Noh; Il Won Seo; Yong Sung Park

doi:10.1016/j.scitotenv.2023.163125

Effects of spectral variability due to sediment and bottom characteristics on remote sensing for suspended sediment in shallow rivers

Sci Total Environ. 2023 Jun 20:878:163125. doi: 10.1016/j.scitotenv.2023.163125. Epub 2023 Mar 28.

Authors

Siyoon Kwon¹, Hyoseob Noh², Il Won Seo³, Yong Sung Park²

Affiliations

¹ Institute of Construction and Environmental Engineering (ICEE), Department of Civil and Environmental Engineering, Seoul National University, Seoul, South Korea.
² Department of Civil and Environmental Engineering, Seoul National University, Seoul 08826, Republic of Korea.
³ Institute of Construction and Environmental Engineering (ICEE), Department of Civil and Environmental Engineering, Seoul National University, Seoul, South Korea. Electronic address: seoilwon@snu.ac.kr.

PMID: 36990231
DOI: 10.1016/j.scitotenv.2023.163125

Abstract

Advances in remote sensing techniques for water environments have led to acquisition of abundant data on suspended sediment concentration (SSC). However, confounding factors, such as particle sizes, mineral properties, and bottom materials, have not been fully studied, despite their substantial interference with the detection of intrinsic signals of suspended sediments. Therefore, we investigated the spectral variability arising from the sediment and bottom using laboratory and field-scale experiments. In the laboratory experiment, we focused on measuring spectral characteristics of suspended sediment according to particle size and sediment type. The laboratory experiment was conducted under conditions of completely mixed sediment and non-bottom reflectance using a specially designed rotating horizontal cylinder. To investigate the effects of different channel bottoms under sediment-laden flow conditions, we performed sediment tracer tests in field-scale channels comprising sand and vegetated bottoms. Based on experimental datasets, we performed spectral analysis and multiple endmember spectral mixture analysis (MESMA) to quantify the effect of spectral variability of sediment and bottom on the relationship between hyperspectral data and SSC. The results showed that optimal spectral bands were precisely estimated under non-bottom reflectance conditions, and the effective wavelengths depended on the sediment type. The fine sediments had a higher backscattering intensity compared to the coarse sediments, and the reflectance difference according to the particle size difference increased as the SSC increased. However, in the field-scale experiment, the bottom reflectance substantially decreased the R2 in the relationship between the hyperspectral data and SSC. Nevertheless, MESMA can quantify the contribution of suspended sediment and bottom signals as fractional images. Moreover, the suspended sediment fraction had a clear exponential relationship with SSC in all cases. We conclude that MESMA-driven sediment fractions could be an important alternative for estimating SSC in shallow rivers, as it quantifies the contributions of each factor and then minimizes the bottom effect.

Keywords: Hyperspectral image; Intrinsic spectral signal; Multiple endmember spectral mixture analysis (MESMA); Optimal band ratio analysis (OBRA); Spectral variability; Suspended sediment.