Abstract
In this study we evaluate the capabilities of three satellite sensors for assessing water composition and bottom depth in Lake Garda, Italy. A consistent physics-based processing chain was applied to Moderate Resolution Imaging Spectroradiometer (MODIS), Landsat-8 Operational Land Imager (OLI) and RapidEye. Images gathered on 10 June 2014 were corrected for the atmospheric effects with the 6SV code. The computed remote sensing reflectance (Rrs) from MODIS and OLI were converted into water quality parameters by adopting a spectral inversion procedure based on a bio-optical model calibrated with optical properties of the lake. The same spectral inversion procedure was applied to RapidEye and to OLI data to map bottom depth. In situ measurements of Rrs and of concentrations of water quality parameters collected in five locations were used to evaluate the models. The bottom depth maps from OLI and RapidEye showed similar gradients up to 7 m (r = 0.72). The results indicate that: (1) the spatial and radiometric resolutions of OLI enabled mapping water constituents and bottom properties; (2) MODIS was appropriate for assessing water quality in the pelagic areas at a coarser spatial resolution; and (3) RapidEye had the capability to retrieve bottom depth at high spatial resolution. Future work should evaluate the performance of the three sensors in different bio-optical conditions.
Highlights
Since the 1980s, satellite remote sensing represents an opportunity for synoptic and multi-temporal viewing of water quality of lakes [1,2,3]
The retrieval of water components and bottom properties was achieved with physics-based models, which basically enable the correction of atmospheric effects, the conversion of the water reflectance first into inherent optical properties (IOPs) and into concentrations of water components such as chl-a, suspended particulate matter (SPM) and coloured dissolved organic matter (CDOM)
A physics-based approach which allows the concentration of water constituents and bottom depth from satellite images to be retrieved has been applied in southern Lake Garda
Summary
Since the 1980s, satellite remote sensing represents an opportunity for synoptic and multi-temporal viewing of water quality of lakes [1,2,3]. Garda mostly used MERIS and Landsat TM imagery to assess water composition in the lake [23,38,39,40], while airborne imaging spectrometry was used to assess bottom depth and benthic cover [41,42,43]. In all those studies, the retrieval of water components and bottom properties was achieved with physics-based models, which basically enable the correction of atmospheric effects, the conversion of the water reflectance first into inherent optical properties (IOPs) and into concentrations of water components such as chl-a, SPM and coloured dissolved organic matter (CDOM). The models results were evaluated with in situ data collected during the satellite overpasses
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