Sebastien Angelliaume

The new ONERA multispectral airborne SAR system in 2009

This paper provides an overview of the new airborne SAR system developed by the French Aerospace Lab ONERA over the last three years. This system, called SETHI, was developed according to the standard FAR25 applied to civil application. The main improvement compared to the previous ONERA airborne radar system RAMSES is that the antennas are located in two pods compatible with small aircrafts like the Falcon 20. This pod-based configuration allows the easy integration of any kind of payloads under the single certification of the pods by authorities.

Analysis of X-Band SAR Sea-Clutter Distributions at Different Grazing Angles

Modeling sea clutter is a difficult problem due to the interaction of the sea surface characteristics (wind speed and wind direction), the geometry of acquisition (grazing angle and azimuth angle), and radar parameters (frequency, polarization, and resolution). In synthetic aperture radar (SAR) imagery, the effect of coherent averaging and motion from the sea will also influence the statistics. An accurate description of the sea surface amplitude probability density function is important for robust target detection. The goal of this paper is to identify a common distribution which matches two different airborne SAR X-band data sets obtained from different locales and at different grazing angles. The first data set was collected by the French Aerospace Laboratory (ONERA) SETHI radar off the coast of France, at low grazing angles (3° and 10°). The second is the Ingara medium grazing angle (15°-45°) sea clutter data set collected by the Defence Science and Technology Organisation off the coast of Australia. In this paper, a number of recently developed distributions are considered, including the K+Rayleigh and Pareto+noise, both of which account for thermal noise. To measure the effectiveness of the model fit, the Bhattacharyya distance and the threshold error are computed with particular attention given to the tail region, where the threshold is determined in a detection scenario.

The ONERA Compact Ka-SAR

A concept of low-size and low-weight imaging Ka-Band radar is presented in this paper. This radar is embedded into an under-wing pod. This radar particularities are a low-size, a low-weight and a low-cost basis, making this radar suitable for future integration on board small vehicles, such as UAV. The radar definition and specifications will be detailed, together with the results obtained from in flight campaigns executed on 2006 and 2007. This SAR radar has been developed and built to fly on board an UAV-like vehicle. Indeed, this radar is designed and used by ONERA as a UAV radar test bench. Different upgrades are under study, such as a squint-angle acquisition mode or an increase of the polarimetry capacities. In addition, a complementary X band sensor is also manufactured. Current airplane used for testing applications is a STEMME S10-VT motorglider as the geometry of this airplane may be representative of a MALE UAV: wingspan is 23m large and weigh is about 900 kilograms.

Hyperspectral and Radar Airborne Imagery over Controlled Release of Oil at Sea

Remote sensing techniques are commonly used by Oil and Gas companies to monitor hydrocarbon on the ocean surface. The interest lies not only in exploration but also in the monitoring of the maritime environment. Occurrence of natural seeps on the sea surface is a key indicator of the presence of mature source rock in the subsurface. These natural seeps, as well as the oil slicks, are commonly detected using radar sensors but the addition of optical imagery can deliver extra information such as thickness and composition of the detected oil, which is critical for both exploration purposes and efficient cleanup operations. Today, state-of-the-art approaches combine multiple data collected by optical and radar sensors embedded on-board different airborne and spaceborne platforms, to ensure wide spatial coverage and high frequency revisit time. Multi-wavelength imaging system may create a breakthrough in remote sensing applications, but it requires adapted processing techniques that need to be developed. To explore performances offered by multi-wavelength radar and optical sensors for oil slick monitoring, remote sensing data have been collected by SETHI (Système Expérimental de Télédection Hyperfréquence Imageur), the airborne system developed by ONERA (the French Aerospace Lab), during an oil spill cleanup exercise carried out in 2015 in the North Sea, Europe. The uniqueness of this dataset lies in its high spatial resolution, low noise level and quasi-simultaneous acquisitions of different part of the EM spectrum. Specific processing techniques have been developed to extract meaningful information associated with oil-covered sea surface. Analysis of this unique and rich dataset demonstrates that remote sensing imagery, collected in both optical and microwave domains, allows estimating slick surface properties such as the age of the emulsion released at sea, the spatial abundance of oil and the relative concentration of hydrocarbons remaining on the sea surface.

The GO-SSA Extended model for all-incidence sea clutter modeling

The GO-SSA-Extended model is an extension of the physical GO-SSA model with augmented range of validity. It is obtained through the addition of extra empirical terms. This improved model can predict the backscatter reflectivity from the sea surface for the full range of grazing and azimuthal angles. This model compares favorably with Xband experimental measurements (VV and HH polarization) acquired by the ONERA and DSTO.

Compact PolInSAR for vegetation characterisation

In this paper, we analyse the potential associated with a compact polarimetry (CP) P band spaceborne SAR system. Indeed, this architecture allows polarimetric acquisition without the usual reduction in swath. The CP data is shown to be almost equivalent to the full polarimetric data over extended targets, and the PolInSAR analysis can be performed without a significant loss of performance.

Multifrequency Radar Imagery and Characterization of Hazardous and Noxious Substances at Sea

Maritime pollution by chemical products occurs at much lower frequency than spills of oil, however the consequences of a chemical spill can be more wide-reaching than those of oil. While detection and characterization of hydrocarbons have been the subject of numerous studies, detection of other chemical products at sea using remote sensing has been little studied and is still an open subject of research. To address this knowledge gap, an experiment was conducted in May 2015 over the Mediterranean Sea during which controlled releases of hazardous and noxious substances were imaged by an airborne SAR sensor at X- and L-band simultaneously. In this paper we discuss the experimental procedure and report the main results from the airborne radar imaging campaign.

Statistical analysis of low grazing angle high resolution X-band SAR sea clutter

This paper investigates the statistical analysis of two low grazing angle (3° and 10°) synthetic aperture radar datasets collected by ONERAs SETHI X-band radar off the coast of France. The focus of the work is to find the most suitable probability density function which matches the data. Particular attention is paid to the tail region, where the threshold is determined in a detection scenario. To measure the effectiveness of each model fit, the Bhattacharyya metric has been extended to measure the goodness of fit in this region.

The New ONERA Multispectral Airborne SAR System

This paper provides an overview of the new airborne SAR system developed by the French Aerospace Lab ONERA over the last two years. This system, called SETHI, was developed according to the standard FAR25 applied to civil application. The main improvement compared to the previous ONERA airborne radar system RAMSES is that the antennas are located in two pods compatible with small aircrafts like the Falcon 20. This pod-based configuration allows the easy integration of any kind of payloads under the single certification of the pods by authorities. In the first section a quick introduction presents the aircraft configuration (cabin and pods) with an overview of SETHI development. The second section describes the SETHI concept with the installation on board the Falcon 20 cabin, the hardware development to control and command all ONERA racks, the pods with their control and command systems. The last section illustrates the validation campaign which took place in September 2007 at Ni circmes Garons Airport in France.

Investigation of Azimuthal Variations From X-Band Medium-Grazing-Angle Sea Clutter

The Ingara X-band fully polarimetric medium-grazing-angle sea-clutter data set was collected in the Australian maritime environment over an angular range of 360° in azimuth and from 15° to 45° in grazing. This paper reports further analysis of this data set, focusing on understanding the azimuth variation to enable improved simulation accuracy and extraction of relevant geophysical parameters. This includes some original properties of the co- and cross-polarized normalized radar cross section as a function of the scattering geometry and sea surface parameters. We also assess the performances and limitations of recent sea surface scattering models in the light of this rich data set.