Monitoring Lakes Surface Water Velocity with SAR: A Feasibility Study on Lake Garda, Italy

Abstract

The SAR Doppler frequencies are directly related to the motion of the scatterers in the illuminated area and have already been used in marine applications to monitor moving water surfaces. Here we investigate the possibility of retrieving surface water velocity from SAR Doppler analysis in medium-size lakes. ENVISAT images of the test site (Lake Garda) are processed and the Doppler Centroid Anomaly technique is adopted. The resulting surface velocity maps are compared with the outputs of a hydrodynamic model specifically validated for the case study. Thermal images from MODIS Terra are used in support of the modeling results. The surface velocity retrieved from SAR is found to overestimate the numerical results and the existence of a bias is investigated. In marine applications, such bias is traditionally removed through Geophysical Model Functions (GMFs) by ascribing it to a fully developed wind waves spectrum. We found that such an assumption is not supported in our case study, due to the small-scale variations of topography and wind. The role of wind intensity and duration on the results from SAR is evaluated, and the inclusion of lake bathymetry and the SAR backscatter gradient is recommended for the future development of GMFs suitable for lake environments.

A Satellite-Based Tool for Mapping Evaporation in Inland Water Bodies: Formulation, Application, and Operational Aspects

“…The two LSWT time series (Figure 5b) are strongly correlated (0.906) and show a high NSE (0.906), and the RMSE of 1.745 • C is relatively small compared to the range of LSWT (standard deviation of ±5.75 • C from CCI-Lakes database). The latter tends to be 0.5 • C warmer than the simulated water temperature, which is consistent with what was observed by the authors during the calibration and validation of the model against remotely sensed data from multiple sensors datasets (e.g., Landsat8, AVHRR, MODIS-Aqua, see [35], MODIS-Terra, see [57]).…”

“…In general, the different behavior of the two sub-basins results from the different ways they exchange heat through the water surface, which is a direct consequence of the different morphological characteristics as well as different atmospheric forcing. This also causes a typical surface temperature gradient, with the southern part of the lake being warmer than the northern part, which is visible from either in-situ data or remote sensing imagery [35,57,58].…”

Evaluation of Macrophyte Community Dynamics (2015–2020) in Southern Lake Garda (Italy) from Sentinel-2 Data

“…Wind and wave erosion were always also likely to influence this zone given its location at the south of the lake and the prevailing northerly winds, coupled with a potential fetch of 50 km. The wind event in May 2019 was estimated using ERA5 data as no in situ data was available but estimated wave heights of 0.4 m were close to previous estimates on typical high-wind-speed days of 0.5 m [88]. The wind event is likely to have played a role in the loss of dense macrophytes in 2019, and local newspapers recorded the storm as causing substantial crop damage and felling trees.…”

“…This indicated that the influence of exposure to waves was one of the principal drivers (favoring the damage, breakage, or uprooting of macrophytes) as shallower areas of 3 m or less are often exposed to wave action [15,16]. In addition, the area to the west, partially in the lee of the head of the peninsula, had more macrophytes and experienced less loss, and recent models have indicated that this area may be more protected given the direction of wind vectors [88].…”

Projected Water Levels and Identified Future Floods: A Comparative Analysis for Mahaweli River, Sri Lanka

“…Natural disasters often occur due to recent climate changes. Several studies have focused on climate change and its' effect detection where Remote sensing methods are highly used in these methodologies [71].…”