Achille Ciappa

Oil spill hazard assessment using a reverse trajectory method for the Egadi marine protected area (Central Mediterranean Sea)

The Egadi Marine Protected Area (MPA) on the western side of the Sicily Channel (Central Mediterranean) is exposed to a high risk of oil pollution from the tanker routes connecting the eastern and western basins of the Mediterranean Sea. Areas where an oil spill would do most damage, and thus where surveillance should be concentrated, are identified in this study by Lagrangian tracers tracked backwards in time from points along the MPA perimeter using data spanning six years from 2006 to 2011. Results indicate that the areas where oil surveillance would be most beneficial are segments of the tanker routes south of Sicily (highly frequented) and north of Sicily (scarcely frequented), both extending about 150 miles from November to March and 100 miles in the other months. The third route, close to the Tunisian shore, is the most frequented by oil tankers but the threat period is limited to November and December.

A new perspective on oil slick detection from space by NOAA satellites

In this paper an extension of the Split Window Technique algorithm, to account for small surface emissivity variations, is presented. This algorithm has been used, along with an adaptive filtering pattern recognition approach, in order to detect oil spills on the sea surface under the assumptions of thermal equilibrium between the oil polluted areas and the surrounding water, of weak horizontal sea surface temperature gradients (i.e., <1°C) in the area of interest and of a horizontal uniform atmospheric water vapour distribution over the discharged area. AVHRR/2 data acquired both on the Gulf of Genoa in April 1991 during an oil pollution episode following the wreck of the Haven tanker and on the Persian Gulf during war operations in January-February 1991 were considered. Comparing satellite retrieved polluted areas with in situ observations available in literature and high spatial resolution satellite observations (Landsat and SPOT), the algorithm has proved to supply satisfactory results in detecting oil contaminated areas.

Sea surface transport derived by frequent revisit time series of COSMO SkyMed SAR data

The surface transport of ‘SAR detectable’ features on sea is accurately estimated by couples of overlapping COSMO SkyMed ScanSAR images acquired with a very short time lag (below the hour). Tests performed with the two satellites constellation during 2008 (4 operative by 2010) provided pairs of overlapping images with a time shift of 48 minutes and with a repeat time from 12 to 24h. The short time lag acquisition has two advantages: the first is that the pair of overlapping images is a sort of time derivative from which an accurate estimate of the surface transport can be extracted, the second is that the deformation of the ‘tracked features’ in the short time interval is minimal and a large number of objects can be tracked, even with the only automated processing. The sea surface transport is a crucial data in case of marine emergencies and the accurate estimate greatly improves the surveillance and the forecasting capability. Overlapping and short time lagged SAR imagery provide surface transport data of detectable objects with all-weather conditions.

The Terra Nova Bay (Antarctica) polynya observed by MODIS ice surface temperature imagery from May to June 2009

We have examined the development of the Terra Nova Bay polynya (TNBP) using a two-month sequence of Moderate Resolution Imaging Spectroradiometer (MODIS) ice surface temperature (IST) images, complemented by a set of synthetic aperture radar (SAR) images. Results of a comparison between the clear-sky ISTs and the contemporaneous SAR images revealed that the polynya is characterized in the ISTs by a warm core and in the SARs by a bright backscattering area, due to the presence of seawater and grease ice. The activity of the polynya during the period was highly dynamic, with opening and closing phases that had similar temporal length scales, sometimes of less than 24 h. The recent activity of the polynya is evidenced in the SARs by alternate bright and dark backscatter bands formed during openings and calm periods and transported offshore by the ice drift. The thermal fronts that separate the warm core of the polynya from the surrounding ice sheet appeared sharp during the opening phase and smooth during the closing phase. The spatial resolution of 1 km of MODIS ISTs, compared with space-borne passive microwave systems with maximum resolution of approximately 10 km, provides a smaller area for the TNBP than do passive microwave data. The polynya area was detectable up to 80% of time with a revisit time of a few hours, giving an average area of ∼1300 km2 and peaks up to 3000 km2. The polynya is forced by katabatic winds that have a warm signature, which is also visible in the IST sequence. Katabatic airflows descending from the Reeves Glacier valley contribute to the opening of the polynya in the central part of the bay, while airflows descending from the surrounding glacier valleys contribute to the opening in the north and south of the bay.

COSMO-SkyMed mission: risk management applications over China, Myanmar and Haiti conducted during 2008

Between 2007 and 2008, Agenzia Spaziale Italiana (ASI) and Ministero della Difesa (Italian Ministry of Defence) launched three out of the four X-band SAR (synthetic aperture radar) satellites of the Constellation of Small Satellites for Mediterranean Basin Observation (COSMO-SkyMed) dual-use (civilian and defence) mission, dedicated to Earth observation. The results received from the utilization of the two operative satellites of the constellation reveal the significant achievement of the X-band SAR sensor and the importance of a fast response time in risk management applications. This article presents the qualitative analyses and results related to a set of risk management applications of the year 2008 by ASI and e-GEOS pertaining to China, Myanmar and Haiti.

Circulation and Lagrangian Dispersal in the Gulf of Vlora (Albania)

Abstract Hydrodynamic and pollutant transport models are useful tools for evaluating remediation options for polluted water bodies. In this work, a Lagrangian-partide approach is used to simulate the three-dimensional pollutants transport in the Gulf of Vlora (Albania) coming from the fresh water outflow from the Vjosa River located in the northern sector of the gulf. Results indicate that the sedimentation processes are strongly dependent on the local meteorology, which is able to modify considerably the circulation of the gulf. Numerical simulations were used to estimate the water circulation and the fate of pollutants in different meteo-oceanographic scenarios identified by the analysis of the oceanographic data collected during two oceanographic cruises carried on during the Centro Internazionale di Scienze del Mare (CISM) project. Suspended sediments are simulated by a large number of Lagrangian elements, the trajectories of which are drawn on the basis of the sea current, settling velocity, and dispersion phenomena. The model was calibrated on the basis of biogeochemical experimental data consisting of concentrations of metals measured in water and in bottom samples, collected during the CISM project performed in the framework of the Interreg III Italia-Albania program. Results of the simulations show that the pollutants coming from the river tend to spread rapidly and undergo rapid dilution for southern and eastern wind regimes. Under northern and western winds a variable percentage of the fine-grained part of sediments discharged by the river penetrates and settles inside the gulf, in accordance with the experimental data.

Technical Note: On masking land pixels in empirical orthogonal function analysis of sequences of sea surface images

Implications of masking land pixels in series of images of the sea surface are investigated. The study is carried out by means of analytical and numerical arguments. An algorithm that performs empirical orthogonal function (EOF) analysis by selecting from original images only the subset of unmasked pixels, has been set up and used on an exemplar dataset constituted by 206 images of the sea level anomaly (SLA) provided by the Topex/Poseidon mission over the Mediterranean Sea. It is shown that, as far as singular value decomposition (SVD) and spatial EOF analyses are involved, different masking values of land pixels modify the relative importance of empirical functions (EOFs) and the corresponding temporal coefficient, while results obtained with temporal EOF analysis remain unchanged.

Use of COSMO-SkyMed data for innovative and operational applications

Since the launch of the first COSMO-SkyMed satellite back in 2007, e-GEOS has always been in first line in the analysis of VHR SAR data and development of new applications. In this paper we will present some of the latest activities in the Earth Observation domain, with special focus on the use of COSMO-SkyMed data for real operational services, for interferometric-based services and for some innovative applications in new fields.

Variability of the East Greenland Current in Fram Strait From Subdaily COSMO-SkyMed X-SAR Imagery

Sea ice speed vectors were extracted from COSMO-SkyMed X-band SAR images acquired twice per day from March 2013 to December 2014 over the East Greenland current (EGC) in western Fram Strait. Only winter periods (October-May) were investigated. Maximum ice speed of 81.7 cm/s to SW was detected at 80°N 0°W between November22 and 23, 2013. At 79°N between 7° and 5°W, sea ice speed vectors were mostly directed to S-SW but reversed to the north for short periods. Using ERA-Interim atmospheric data, the southward component of the ice speed (max. +71.7, min. -30.9 cm/s) was correlated (R = 0.93) to the cross-strait sea level pressure gradient. Ice speeds due to the EGC were obtained by subtracting the wind-induced ice speed component estimated by linear regression. Results for winter 2013-2014 show that the mean southward component of the EGC (9.4 cm/s, σ = 3.0) accounted more than half of the mean sea ice speed (17.7 cm/s, σ = 7.2). The EGC oscillated between 5 and 15 cm/s and sustained the southward ice export during short periods when the wind reversed to north. Satellite-based measurements of the surface EGC are the complement to hydrographic measurements in Fram Strait, but further investigation is required to understand how the apparent variability of the current is influenced by the thickness of the ice transiting in the strait or by wind induced north-to-south oscillations of the sea surface in the strait.

Utilisation of the COSMO-SkyMed Constellation for coherent and incoherent monitoring

SAR systems are recently used to generate robust and projectable information about maritime traffic, ice extent and geohazards. By utilising multiple SAR satellites dynamic information can be derived at variable temporal scales. Therefore acquisition systems and processing techniques become a key issue which is requested to work in a robust and efficient way. This paper will present generalized concepts for a monitoring approach that address unmatched or interferometric acquisitions. Its goal is to show the potential of increasing the acquisition rate but also to illustrate limitations resulting from the specific monitoring schemes and their combination. The paper will visualise practical examples derived from realized studies and projects. Finally we can conclude that an agile multi satellite and multi-mode SAR system, such as COSMO-SkyMed, is well suited to monitor to dynamic phenomena on the earth’s surface. The practicability needs to be discussed in detail case by case related to the real world requirements.