Offshore Metallic Platforms Observation Using Dual-Polarimetric TS-X/TD-X Satellite Imagery: A Case Study in the Gulf of Mexico

Satellite-based synthetic aperture radar (SAR) has been proven to be an effective tool for ship monitoring. Offshore platforms monitoring is a key topic for both safety and security of the maritime domain. However, the scientific literature oriented to the observation of offshore platforms using SAR imagery is very limited. This study is mostly focused on the analysis and understanding of the multipolarization behavior of platforms’ backscattering using dual-polarization X-band SAR imagery. This study is motivated by the fact that under low incidence angle and moderate wind conditions, copolarized channels may fail in detecting offshore platforms even when fine-resolution imagery is considered. This behavior has been observed on both medium- and high-resolution TerraSAR-X/TanDEM-X SAR imagery, despite the fact that platforms consist of large metallic structures. Hence, a simple multipolarization model is proposed to analyze the platform backscattering. Model predictions are verified on TerraSAR-X/TanDEM-X SAR imagery, showing that for acquisitions under low incidence angle, the platforms result in a reduced copolarized backscattered intensity even when fine resolution imagery is considered. Finally, several solutions to tackle this issue are proposed with concluding remark that the performance of offshore observation

Oil spill and ship detection using high resolution polarimetric X-band SAR data

Among illegal human activities, marine pollution and target detection are the key concern of Maritime Security and Safety. This thesis deals with oil spill and ship detection using high resolution X-band polarimetric SAR (PolSAR). Polarimetry aims at analysing the polarization state of a wave field, in order to obtain physical information from the observed object. In this dissertation PolSAR techniques are suggested as improvement of the current State-of-the-Art of SAR marine pollution and target detection, by examining in depth Near Real Time suitability

Editorial for the Special Issue "Remote Sensing of Target Detection in Marine Environment"

First paragraph: Remote sensing is a powerful tool used to obtain an unprecedented amount of information about the ocean from a distance, usually from satellites or aircrafts. Measurements collected by active and passive remote sensing instruments can be used for both marine and maritime applications. They allow monitoring of vast areas of the Earth that are difficult to access and sample using traditional methods. Within this context, the observation of targets at sea, e.g.; man-made targets (ships or oil/gas rigs/platforms and wind turbines) and natural targets (icebergs, surfactants, etc.) is nowadays a very hot-topic in the field of global monitoring of environment and security

Sea Oil Seep Monitoring Using a Time Series of Co-Polarized Coherent SAR Measurements

In this study, coherent co-polarized synthetic aperture radar (SAR) information is exploited for sea oil seep monitoring purposes. A time series of 33 TerraSAR-X StripMap SAR data, collected over a well-known oil seep in Gulf of Mexico, is exploited to analyze the influence of incidence angle and wind conditions on the co-polarized phase difference (CPD). Furthermore, the benefits of using phase information for oil seep observation are assessed. Experimental results show that: i) incidence angle has a remarkable effect in broadening/shrinking the CPD statistical distribution and, ii) the CPD provides spatial information on the oil seep damping properties

Multi-polarization SAR ship detection: a fair comparison using the TanDEM-X pursuit monostatic mode

This study aims at contrasting full-polarimetric (FP) SAR with single-polarimetric (SP) SAR for ship detection purposes. In fact, although the importance of FP SAR observations is nowadays well established in many Earth Observation applications, including maritime surveillance, it is also well-known that the major drawbacks that limit the use of FP SAR in maritime applications (like oil and ship detection) are the reduced swath width and azimuth resolution. Within this context, several polarimetric ship detectors have been developed and all of them share the common result that FP data result in a remarkable increasing of observation performance (both in terms of detection and missed target rates). However, a fair inter-comparison between FP and SP detectors is still a challenge. In fact, the performances of PolSAR detectors can only be directly compared with the ones obtained using one of the channels, e.g. the HH channel in case of ship. This comparison strategy is quite fair and it is preferred over the repeat pass method as for satellite acquisitions the unavoidable time lag between data-takes introduce differences that are not easy to discard, e.g. different wind and sea state conditions. It is obvious that the “repeat pass” comparison strategy would be fairer if the two acquisitions were simultaneous (or close to be simultaneous) and made by two twin sensors. In this sense and for the purposes of this study, we have exploited the pursuit monostatic configuration of the TanDEM-X constellation jointly with the planned science phase acquisitions campaign to set up a scenario that consists of the satellite duo (TerraSAR-X and TanDEM-X) that was able to collect (almost simultaneously, i.e.; the twin satellites are flying in two orbits separated of circa 76km) pairs of independent X-band SAR measurements using the standard single receiving antenna mode (SRA) and the experimental dual receive antenna mode (DRA). The former allows collecting data in either SP or dual-polarization coherent mode; while the latter provides FP measurements. Under this configuration, two exceptional coordinated TerraSAR-X/TanDEM-X data-takes were collected in Gulf of Mexico where the scene, which includes both ships and oil rigs, was observed in a single-pol (HH) and FP configuration. Experiments undertaken on this data set clearly demonstrate that, although FB SAR observations are characterized by a coarser azimuth spatial resolution (doubled with respect to SP observations), FP detection performance is significantly better than SP one when FP information is properly exploited (i.e. both amplitudes and the inter-channel phases must be exploited)

On the backscattering of offshore platforms via single and dual-polarization TerraSAR-X data

The recent discovery of a significant number of oil and gas deposits in the seabed increased the amount of offshore installations [1]. Offshore platforms are potential environmental threats, with chronic oil and gas spillage but also at risk of accident when exposed to extreme weather conditions, e.g. hurricane, or machine failures. Moreover, with the advent of deep water drilling technology, their installation is not fixed to the seabed and their location is not limited to coastal water anymore. For these reasons they are obstacles for yachts, low flying airplanes and merchant ships making at risk the safety of maritime traffic. In conclusion, a system capable of mapping and monitor offshore platform independently of weather condition and wide coverage is needed. Due to their size and construction material, offshore platforms might be easily detected and mapped by using satellite Synthetic Aperture Radar (SAR) medium resolution imagery [2]. However, the measurements reported in our recent study [3] show that the information provided by backscattered intensity collected in single-polarization is not always sufficient to effectively observe offshore platforms. Exploiting a time series of dual-polarization TerraSAR-X data acquisitions over a cluster of offshore platform in the Gulf of Mexico, different factors affecting the backscattering, including polarization, resolution and incidence angle, are analysed. Finally in this paper we also address how incoherent and coherent polarimetric observables can be exploited to trigger the detection although the single polarimetric observation may fai

Backscattering analysis of metallic platforms in Gulf of Mexico via multi-polarization

The recent discovery of a significant number of oil and gas deposits in the seabed increased the amount of offshore installations. Offshore platforms are potential environmental threats, obstacles for yachts, low flying airplanes and merchant ships making at risk the safety of maritime traffic. In principle, any metallic target over the ocean surface is responsible for a lager backscattering compared to the one coming from the surrounding sea surface. For this reason, offshore platforms are expected to appear in SAR intensity images as spots brighter than the background sea. However, the measurements reported in this paper show that information provided by backscattered intensity collected in single-polarization is not always sufficient to effectively observe offshore platforms. Exploiting the multi-polarization capabilities of TerraSAR-X, different factors affecting the backscattering, and hence their detection, of offshore platforms is deeply analysed. In particular, under different viewing geometries, all dual-polarimetric modes are investigated

A Combination of Traditional and Polarimetric Features for Oil Spill Detection using TerraSAR-X

Synthetic aperture radar (SAR) images are operationally used for the detection of oil spills in the marine environment, as they are independent of sun light and weather-induced phenomena. Exploitation of radar polarimetric features for operational oil spill detection is relatively new and until recently those properties have not been extensively exploited. This paper describes the development of a oil spill detection processing chain using coherent dual-polarimetric (copolarized channels, i.e., HHVV) TerraSAR-X images. The proposed methodology focuses on offshore platform monitoring and introduces for the first time a combination of traditional and polarimetric features for objectbased oil spill detection and look-alike discrimination.Atotal number of 35 feature parameters were extracted from 225 oil spills and 26 look-alikes and divided into training and validation dataset. Mutual information content among extracted features have been assessed and feature parameters are ranked according to their ability to discriminate between oil spill and look-alike. Extracted features are used for training and validation of a support vector machine-based classifier. Performance estimation was carried out for the proposed methodology on a large dataset with overall classification accuracy of 90% oil spills and 80% for look-alikes. Polarimetric features such as geometric intensity, copolarization power ratio, span proved to be more discriminative than other polarimetric and traditional features

Meteo-Marine Parameters and Their Variability Observed by High Resolution Satellite Radar Images.

New radar satellites image the sea surface with resolutions as high as 1 m. A large spectrum of ocean processes can be estimated using such Earth observation data. These data have been applied to investigations of geophysical processes as well as to forecast model validations and near-real-time services. The numerous processes, parameters, and features observed in high-resolution synthetic aperture radar images include winds, waves (with wavelengths as small as 30 m), oil slicks, waterline changes, changes in seabed morphology in shallow waters, wakes and bow waves of ships, underwater topography, wave energy flux along wave tracks from deep water to the coast, and breaking waves. New algorithms have been developed that are capable of taking into account fine-scale effects in coastal areas