Inversion of inherent optical properties in optically complex waters using sentinel-3A/OLCI images: A case study using China's three largest freshwater lakes

Abstract

Inherent optical properties (IOPs) play an important role in underwater light field, and are difficult to estimate accurately using satellite data in optically complex waters. To study water quality in appropriate temporal and spatial scales, it is necessary to develop methods to obtain IOPs form space-based observation with quantified uncertainties. Field-measured IOP data (N = 405) were collected from 17 surveys between 2011 and 2017 in the three major largest freshwater lakes of China (Lake Chaohu, Lake Taihu, and Lake Hongze) in the lower reaches of the Yangtze River and Huai River (LYHR). Here we provide a case-study on how to use in-situ observation of IOPs to devise an improved algorithm for retrieval of IOPs. We then apply this algorithm to observation with Sentinel-3A OLCI (Ocean and Land Colour Instrument, corrected with our improved AC scheme), and use in-situ data to show that the algorithm performs better than the standard OLCI IOP product. We use the satellite derived products to study the spatial and seasonal distributions of IOPs and concentrations of optically active constituents in these three lakes, including chlorophyll-a (Chla) and suspended particulate matter (SPM), using all cloud-free OLCI images (115 scenes) over the lakes in the LYHR basin in 2017. Our study provides a strategy for using local and remote observations to obtain important water quality parameters necessary to manage resources such as reservoirs, lakes and coastal waters. water bodies that exhibit large variations in properties (Li et al., 2013). Several solution methods of SAAs have been developed to derive the

Retrieval of Secchi Disk Depth in Turbid Lakes from GOCI Based on a New Semi-Analytical Algorithm

“…where g0 =0.084 and g1 = 0.17 in Z SDZ algorithm, which were suggested for high scattering waters by [15].…”

“…According to field measured speed data that we collected, low wind speeds are dominant in Lake Hongze and Lake Taihu, and r aw = 0.022 was applied in this study. However, the variation of r aw would result in a high variation of mean coefficient variance value (CV = 50%) of Rrs at the spectral range of 400 to 800 nm [15], which definitely has a negative impact on the performance of Z SD models. Moreover, although a reliable method was used to reduce sun glint and ensure the accurate measurement of reflectance, it is still possible for glint to remain.…”

“…By this method, the inherent optical properties (IOPs) were first estimated while using the quasi-analytical algorithm (QAA), and then positing the reference wavelength at 550 or 670 nm further derived the Z SD . However, several obvious limitations of the original QAA become evident for applications in inland turbid waters [6,[13][14][15][16]. Firstly, the estimation method of the total absorption coefficient at the reference wavelength (550 or 670 nm) does not work in inland turbid waters with lower absorption, but high scattering coefficients; secondly, the original coefficients of the IOPs were calibrated while using the data from marine and coastal waters and inland waters.…”

Retrieval of Suspended Particulate Matter in Inland Waters with Widely Differing Optical Properties Using a Semi-Analytical Scheme

“…The QAA derives a and b b from R rs , which is referred to as Part I [54]. The second part of the QAA, which determines specific coefficients of each optically active component, was not assessed in this paper.…”

Effect of Satellite Temporal Resolution on Long-Term Suspended Particulate Matter in Inland Lakes

“…These lakes are subtropical shallow lakes with an average water depth range from 1.1 to 8.4 m, a Chla range from 0.55-240 µg/L (Mean ± STD. : 50.72 ± 49.94 µg/L), a SPM range from 1.39-170.42 mg/L (34.96 ± 55.99 mg/L), and absorption coefficient of CDOM at 443 nm ranges from 0.89-5.04 m −1 (0.89 ± 0.69 m −1 ) [22]. These lakes include those lakes linked to the rivers, eutrophic lakes, and turbid lakes.…”