Submitted as: model evaluation paper 26 May 2021

Submitted as: model evaluation paper | 26 May 2021

Review status: this preprint is currently under review for the journal GMD.

Turbidity maximum zone index: A novel model for remote extraction of turbidity maximum zone in different estuaries

Chongyang Wang1,, Li Wang1,, Danni Wang2, Dan Li1,3, Chenghu Zhou1,3,4, Hao Jiang1,3, Qiong Zheng1, Shuisen Chen1, Yangxiaoyue Liu1,3, Ji Yang1,3, Xia Zhou1, and Yong Li1,3 Chongyang Wang et al.
  • 1Guangdong Open Laboratory of Geospatial Information Technology and Application, Key Lab of Guangdong for Utilization of Remote Sensing and Geographical Information System, Guangdong Engineering Technology Center for Remote Sensing Big Data Application, Guangzhou Institute of Geography, Guangdong Academy of Sciences, Guangzhou 510070, China
  • 2Department of Resources and the Urban Planning, Xin Hua College of Sun Yat-Sen University, Guangzhou 510520, China
  • 3Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
  • 4State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
  • These authors contributed equally to this work.

Abstract. Recognizing and extracting estuarine turbidity maximum zone (TMZ) efficiently is important for kinds of terrestrial hydrological process. Although many relevant studies of TMZ have been carried out around the world, the method of extracting and criteria of describing TMZ vary greatly from different regions and different times. In order to improve the applicability of the fixed threshold in previous studies and develop a novel model extracting TMZ accurately in multi estuaries and different seasons by remote sensing imagery, this study estimated the total suspended solids (TSS) concentrations and chlorophyll a (Chla) concentrations in Pearl River Estuary (PRE), Hanjiang River Estuary (HRE) and Moyangjiang River Estuary (MRE) of Guangdong province, China. The spatial distribution characteristics of both TSS concentrations and Chla concentrations were analyzed subsequently. It was found that there was an almost opposite relationship between TSS concentration and Chla concentration in the three estuaries, especially in PRE. The regions of high (low) TSS concentrations are exactly corresponding to the relative low (high) Chla concentrations. Based on the special feature, an index named turbidity maximum zone index (TMZI), defining as the ratio of the difference and sum of logarithmic transformation of TSS concentrations and Chla concentrations, was firstly proposed. By calculating the values of TMZI in PRE on 20 November 2004 (low-flow season), it was found that the criterion (TMZI > 0.2) could be used to distinguish TMZs of PRE effectively. Compared with the true (false) color imagery and the rudimentary visual interpretation results, the TMZs extraction results by TMZI were mostly consistent with the actual distribution. Moreover, the same criterion was further applied in PRE on 18 October 2015. The high accuracy and good consistency across seasons were also found. The west shoal of PRE was the main distribution areas of TMZs. In addition, the good performance in extracting TMZs by this newly proposed index were also found in different estuaries and different times (HRE, 13 August 2008, high-flow season; MRE, on 6 December 2013, low-flow season). Compared to the previous fixed threshold (TSS or turbidity) methods, extracting TMZ by TMZI has a higher accuracy and better applicability. Evidently, this unified TMZI is a potentially optimized method to monitor and extract TMZs of other estuaries in the world by different satellite remote sensing imageries, which can be used to improve the understanding of the spatial and temporal variation of TMZs and estuarial processes on regional and global scales, and the management and sustainable development of regional society and nature environment.

Chongyang Wang et al.

Status: open (until 21 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2020-378', Anonymous Referee #1, 12 Jun 2021 reply

Chongyang Wang et al.

Chongyang Wang et al.


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Short summary
Turbidity maximum zone (TMZ) is a special phenomenon in estuary throughout the world. However, the method and criteria of extracting TMZ vary greatly. This study proposed an new index-turbidity maximum zone index based on the corresponding relationship of TSS concentration and Chla concentration, which could extract TMZs in different estuaries and seasons better.