Water Optical Property of High-Altitude Lakes in the Tibetan Plateau

Abstract

Measurements from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) from 2012 to 2019 are used to derive the normalized water-leaving radiance spectra nLw(λ ) in high-altitude lakes over the Tibetan Plateau (TP) (elevation of ~4 km). nLw(λ ) spectra in various lakes in the TP show a significant water optical property diversity in terms of nLw(λ ) spectral shapes, their magnitudes, and their spatial and temporal variations. In the TP major lakes, nLw(λ ) spectra in Lake Namtso and Siling Lake show enhancements at the blue wavelengths of 410 and 443 nm [nLw(410) and nLw(443)], and peak at the wavelength of 486 nm [nLw(486)]. In Lake Ngangze, the nLw(λ ) spectrum shows the optical feature of typical eutrophic waters. Its nLw(λ ) peaks at the green wavelength of 551 nm [nLw(551)] with its value ~2.5 mW cm⁻² μ m⁻¹ sr⁻¹. In Dogai Coring Lake, the typical nLw(λ ) spectrum is similar to those of many smaller and medium size lakes in the TP, and nLw(λ ) spectra are featured with the peak at the green band nLw(551) with another notable red band nLw(671) over ~1.0 mW cm⁻² μ m⁻¹ sr⁻¹, as well as a nonnegligible contribution at the near-infrared (NIR) band nLw(745). This implies that the suspended particle matter (SPM) in the lake plays a significant role in water nLw(λ ) spectra in Dogai Coring Lake and other similar lakes in the TP. The diversity of water optical property in the TP lakes reflects the fact of the regional diversification of processes in various TP lakes and poses potential challenges to the development of remote sensing algorithms for water biological and biogeochemical products in the TP lakes.