Laura Candela

A Prototype System for Flood Monitoring Based on Flood Forecast Combined With COSMO-SkyMed and Sentinel-1 Data

The use of synthetic aperture radar (SAR) data is presently well established in operational services for flood management. However, some events might be missed because of the limited area that can be observed through a SAR image and the need of programming SAR acquisitions in advance. To tackle these problems, it is possible to setup a system that is able to trigger the SAR acquisitions based on flood forecasts and to take advantage of the various satellite SAR sensors that are presently operating. On behalf of the Italian Civil Protection Department (DPC), a prototype of this kind of system has been setup and preliminary tested, using COSMO-SkyMed (CSK) and Sentinel-1 (S-1) data, to monitor the Po River (Northern Italy) flood occurred in November 2014. This paper presents the prototype system and describes in detail the near real-time flood mapping algorithm implemented in the system. The algorithm was previously developed to classify CSK images, and is modified here in order to be applied to S-1 data too. The major outcomes of the monitoring of the Po River flood are also analyzed in this paper, highlighting the importance of the in advance programming of the radar acquisitions. Results demonstrate the reliability of the flood predictions provided by the model and the accuracy of the flood mapping algorithm. It is also shown that, when CSK and S-1 data are simultaneously acquired, their joint use allows for an interpretation of some ambiguous radar signatures in agricultural areas.

The OPERA project: EO-based flood risk management in Italy

This paper illustrates some applications of COSMO-SkyMed (CSK) observations for rapid mapping of flooded areas and damages in small to medium size catchments. The results presented here have been obtained within the framework of the project “OPERA — Civil protection from floods” funded by the Italian Space Agency and run by a team of scientific research centres and private companies. The project aims to the systematic evaluation of the added value of the use of Earth Observation techniques into operational flood prediction chains. Due to the specific geomorphology of Italy, the focus is mainly on flash floods on small sized river catchments. Monitoring and modelling processes at proper space-time scales in this environment raise several issues to be solved, compared to applications in larger river basins. Here we address some related to the suitable use of CSK imagery.

Detection of floods and heavy rain using Cosmo-SkyMed data: The event in Northwestern Italy of November 2011

In this work, an automatic method to distinguish, in X-band SAR images such as those supplied by Cosmo-SkyMed, water surfaces (either flooded, or permanent water bodies) from artifacts due to heavy precipitation, is designed to improve flood detection accuracy. The method, mainly based on the fuzzy logic, consists of two main steps, i.e., the detection of low backscatter areas and the classification of each dark object present in the considered SAR image. The algorithm uses ancillary data, such as a local incidence angle map and a Land Cover map. Through the fuzzy logic, it integrates different rules for the detection of low backscatter areas (based on the standard deviation of the backscattering coefficient and on a well-established radar backscattering model), as well as different rules for the classification of the low backscatter (dark) areas (i.e., to distinguish water surfaces from artifacts) based on their geometrical and shape features and on both land cover and local incidence angle.

Flood mapping by SAR: Possible approaches to mitigate errors due to ambiguous radar signatures

The latest generation of synthetic aperture radar (SAR) systems allows providing emergency managers with near real time flood maps characterized by a very high spatial resolution. Near real time flood detection algorithms generally search for regions of low backscatter, thus assuming that floodwater appears dark in a SAR image. It is well known that this assumption is not always valid. For instance, in urban areas, the double bounce backscattering involving ground and vertical walls produce high radar return that can be further increased by the presence of the highly reflective floodwater. In addition, even mapping bare or scarcely vegetated inundated terrains, or crops totally submerged by water can turn out to be a difficult task. In fact, in the presence of significant wind that roughens the water surface, floodwater can appear bright in SAR images. This paper proposes possible strategies to cope with flood mapping using SAR data in urban areas and in the presence of significant wind. In particular, the use of the interferometric coherence for floodwater detection in urban areas and the use of an electromagnetic model able to simulate the radar return from shallow water as function of the wind field are proposed.

The PRISMA mission

PRISMA (PRecursore IperSpettrale della Missione Applicativa) is an innovative Italian Earth Observation mission using a Hyperspectral/Panchromatic instrument based on a pushbroom scanning technique. The PRISMA mission development is completely funded by ASI (Italian Space Agency) and includes the system development program and the related applications and research activities. The system program is in the development phase (ECSS standard C/D phase) in the framework of a contract signed between ASI and an Italian Industries Consortium, including also the system on orbit commissioning. The launch is planned for the beginning of 2018. Thanks to the Low Earth, Sun Synchronous orbit placement, PRISMA will acquire up to 200.000 km2 of daily Panchromatic/hyperspectral images within an Area of interest bounded by 180°W÷180°E - 70°S÷70°N, supporting many earth observation applications with relevant data. The Italian Science Community has been involved both in supporting the system development program, mainly for Calibration and Validation activities and algorithm developments, and in promoting research and applications based on Panchromatic/Hyperspectral remote sensed data.

One-day interferometry results with the COSMO-SkyMed constellation

COSMO-SkyMed is a Dual-Use (Civilian and Defence) End-to-End Earth Observation System aimed at establishing a global service supplying provision of data, products and services relevant to a wide range of applications, such as Risk Management, Scientific and Commercial Applications and Defence Applications. The system consists of a constellation of four LEO mid-sized satellites, each equipped with a multi-mode high-resolution SAR operating at X-band. Three out of four COSMO-SkyMed satellites have been successfully launched, while the remaining satellite will be deployed within 2010. The first two satellites have been launched in 2007 while COSMO-SkyMed-3 has been launched on October 25th 2008. Since its launch COSMO-SkyMed-3 has been put in an orbital position at 67,5° from COSMO-SkyMed-2, in the so-called “one-day interferometry configuration”. Since then COSMO-SkyMed-2 and COSMO-SkyMed-3 are providing a interferometric pairs for a wide range of applications.

Processing algorithms for COSMO-SkyMed SAR sensor

The COSMO-SkyMed (Constellation of Small satellites for the Mediterranean basin Observation) constellation is a project of the Italian Space Agency (ASI) tailored for risk management, coastal zone monitoring and sea pollution in a dual use approach (military and civil applications). The COSMO-SkyMed payload is constituted of a fixed antenna with electronic scanning capabilities in both the azimuth and the elevation planes. It has been designed to implement three different operation modes in order to acquire the images at the required resolution: Spotlight mode, Stripmap mode and ScanSAR mode. This paper describes the algorithms implemented to focus images acquired in the above three different modes together with the first results obtained using simulated and real data. Telespazio, in cooperation with Consorzio Innova and Digimat, is the prime-contractor of the COSMO-SkyMed CREDO project, in which is foreseen the development of a SAR ground processing chain.

Satellite soil moisture assimilation: Preliminary assessment of the sentinel 1 potentialities

First results of the assimilation of high-resolution Sentinel-1A based soil moisture products in a distributed, physically based, hydrological model are presented. A comprehensive evaluation of the assimilations impact on discharge predictions is provided. Results are further compared to those obtained when assimilating the lower-resolution ASCAT-based soil moisture product. The exercise was carried out within the MIDA project framework (funded by the Italian Space Agency) aiming at producing root zone soil moisture maps useful for flood risk management applications. The experimental site is the Orba River Catchment (Italy). The period of investigation is October 2014-February 2015. Using a relatively simple data assimilation technique (Nudging) the results of our case study show that overall the assimilation of currently available Sentinel-1 data only marginally improves discharge simulations. However, the impact becomes more significant when specifically considering predictions of high flow. Further improvements are expected when both Sentinel-1A and B data will be available.

SAR images co-registration parallel implementation

Image co-registration is basilar for interferometry SAR remote sensing applications. This paper describes a parallel implementation based on the Farm skeleton using the MPI library for the co-registration module of SAR Toolbox software.

Using COSMO-SkyMed data for flood mapping: Some case-studies

The COSMO-SkyMed mission is expected to give a fundamental contribution for flood mapping, because of the high revisit time and throughput achieved by the four satellites that form the constellation. To study the potentiality of COSMO-SkyMed radar data for this purpose, two inundation events are analyzed in this paper, namely the flood occurred in Myanmar in May 2008 and the event that took place in the city of Alessandria (Italy) in April 2009. For the first event, two radar images were considered, one temporally close to the peak of the event, and the other one acquired one week later. As for the Alessandria flood, a time series of images was available, so that an attempt to monitor the temporal evolution of the inundation was accomplished.