Inland waters are the crucial water resources to support drinking, industrial and agricultural usages worldwide. Secchi disk depth (SD) is usually adopted as a reliable proxy for water quality and trophic state evaluation. However, traditional measuring approaches are less suitable for monitoring large water bodies or a large number of lakes in extensive areas because of the dynamic nature and patchy distribution of SD, particularly for lakes in remote areas. Remote sensing could be an effective tool for monitoring SD of inland waters through monitoring the water leaving radiance.

Remote sensing derived water clarity has been reported in many countries with specific models established for different satellite overpasses concurrent with in situ measured SD, but national water clarity remained unknown in China.

A study led by Prof. SONG Kaishan from the Northeast Institute of Geography and Agroecology of the Chinese Academy of Sciences quantified the water clarity for lakes >8 ha in China using Landsat OLI imagery data for the first time. The study was published online in Remote Sensing of Environment.

Based on field measurements of SD value and Landsat imagery data, the researchers confirmed a combination of the Red/Blue band ratio and rhos atmospheric correction derived from remote sensing reflectance was the most effective approach for estimating SD at national scale. The researchers eventually used the approach to map SD at a national scale with OLI images mainly acquired in 2016. The national water clarity was averaged to 176 cm in 2016 with large spatial variability due to the marked variation between turbid waters in the east plain area and clean water across the Tibet Plateau.

Water clarity may provide useful information to evaluate the impacts of climate change and anthropogenic activities on lakes at national, continental and even global scales. “This method has the potential to retrieve SD with archived Landsat imagery to determine the temporal variation of SD at national or continental scale which can be used to support inland water management and decision-maker for improving water quality” said Prof. SONG Kaishan.

The study entitled “Quantification of lake clarity in China using Landsat OLI imagery data” has been published online in Remote Sensing of Environment.

Contact:

Prof. SONG Kaishan, Ph. D

Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China

Tel: 86-431-85542364

E-mail: songks@iga.ac.cn