River Flow Monitoring through MODIS and OLCI Multispectral Sensors: Comparison and Integration

Abstract:

In the context of RIDESAT - RIver flow monitoring and Discharge Estimation by integrating multiple SATellite data project, an ESA-funded Permanent Open Call project, a new methodology was proposed for estimating river discharge through the combination of satellite radar altimeter and multispectral sensors.

The methodology developed in the project included two phases. First, the single-instrument products (altimeter and multispectral sensors) are independently processed to generate a dataset of proxies of hydraulic variables strongly linked with river discharge (e.g. water level, flow velocity). Successively, these proxies are implemented into a physical formulation for the final estimation of the river discharge.

Here, we show the results derived by the first step related to the multispectral analyses. Images from OLCI Sentinel-3 and MODIS onboard Terra and Aqua are collected for the Po River reach from Piacenza to Pontelagoscuro stations, including a total of five ground stations, where cross-section, water level and river discharge were available for the period of analysis. The ratio between the reflectances of a dry and wet areas is exploited to monitor the river flow. In particular, each single sensor is separately analyzed to extract the time series of the reflectance ratio. Through a sensitivity analysis, the reflectance ratios are compared with the hydraulic features (river discharge, water level, surface width, flow velocity and flow area) to identify the potential of multispectral sensors for flow monitoring.

A further analysis behind the project is represented by the combination of all the four multispectral sensors with the purpose to obtain a dense time series. Indeed, the multi-mission approach provides significant advantages over single sensors contributing to improve the quality of the final products also in terms of temporal coverage. Moreover, due to the sensitivity of these sensors to the clouds, the use of multi-mission satellite with non-simultaneous passages enables to increase the chances to monitor the river.