Abstract
A new open--source software tool, called GLAM BioLith--RT (Glacier Lakes Assisted Melting Biological Lithological Radiative Transfer), has been developed for modeling of Radiative Transfer (RT) in water bodies containing suspended lithic particles , phytoplankton, dissolved salts, and colored dissolved organic matter. Although our objective is an application to glacial lakes of High Mountain Asia, the model has potential application for the study of seawater, organic-rich lakes, rivers, etc. The tool is built on a solid foundation of an existing published open-source code called WASI, which has been reviewed and augmented with new capabilities, notably the addition of a suspended lithic particle grain size parameterization. GLAM BioLith-RT operates in both a forward modeling and inverse modeling mode. The forward mode is specifically designed to compute the reflectance spectra of glacier lakes from inherent optical water properties. Conversely, in the inverse mode, measured spectral reflectance is employed with other inputs to derive best fitting water component properties (e.g., suspended particles concentration). The inverse modeling includes Bayesian Optimization of the output which is a significant advance over the existing software. We have tested the code for sensitivity to noise, and uncertainties in input parameters. The model succeeds in nearly reproducing the hyperspectral reflectance of some glacial lakes in Nepal as observed by the EO-1 Hyperion hyperspectral imager. The inverse modeling approach, when supported up by validated forward modeling, offers a means for remote sensing characterization of suspended sediment load in glacial lakes and rivers and hence, use of suspended sediment as a proxy for glacial activity; and many other potential applications in other thematic areas.
Highlights
Satellite multispectral imaging offers much-used capabilities for efficient mapping of lakes and rivers (Chikita et al, 1999; Wessels et al, 2002; Giardino et al, 2010; Watson et al, 2017)
We developed and tested, on synthetic and real data, a new open-source software tool named GLAM BioLith-Radiative Transfer (RT) that can be used for remote sensing reflectance simulation and water components concentration retrieval in surface water of a lake, river, or sea
The primary goal of this paper is to present GLAM BioLith-RT, a new open–source software tool for modeling RT in water bodies
Summary
Satellite multispectral imaging offers much-used capabilities for efficient mapping of lakes and rivers (Chikita et al, 1999; Wessels et al, 2002; Giardino et al, 2010; Watson et al, 2017). Relevant to the application motivating this work, we observe that glacial lakes have wide-ranging visible colors in the visible (Figure 1) and differing Near Infrared (VNIR) and Short-wave Infrared (SWIR) reflectances (Giardino et al, 2010). These “colors” are caused by suspended sediment. There is a physical link between the observed photon flux (radiance) and the optical properties of the components comprising the makeup of glacier lakes The latter can be accounted by adequately describing the absorption coefficient, backscattering coefficient, beam attenuation coefficient, and single backscattering albedo which are Inherent Optical Properties (IOP) of a water body. The physical link between water components concentrations, IOPs, incoming light geometric distribution, atmospheric conditions, and AOPs are usually described by the Radiative Transfer (RT) equation which accounts for the balance of photons (scattered, absorbed) to model and compute the spectral reflectance collected by the remote sensor [e.g., Bio-Lithological Optical/Radiative Transfer (RT) models (Giardino et al, 2012)]
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