Coordinate Registration of OTHR-SW Remotely-Sensed Data by Sea-Land

Transitions Identification

Università di Firenze Dipartimento di Elettronica

e Telecomunicazioni

F. Sermi, F. Cuccoli, L. Facheris, D. Giuli

IEEE Gold 201029, 30 April 2010 – Naval Academy,

Livorno, Italy

Consorzio Nazionale Interuniversitarioper le Telecomunicazioni (centro

RaSS)

OTHR-SWMain feature:• Huge Surveillance Area (comparable in surface with that of satellite constellations or airborne radar networks).Main Problem:• Eterogeneous & Unstable nature of the Ionosphere introduces uncertainty in the evaluation of the actual signal path.

The coordinate registration (CR) procedure allows to associate digital data to coordinates that determine univocally its position on the Earth

surface.Without a correct CR procedure OTHR-SW data are useless.

The radar echo needs to be geo-referenciate!

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Remote sensing with HF radars

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The huge surveillance area of OTHR-SW systems and the interaction between EM waves in the HF band and sea swells can be employed to gather environmental data

on a very large scale.Since the ‘70s several methods have been proposed to extract sea-state

information from the OTHR-SW echo.

2L

2gLv

2vf

Like other measurements, environmental data are useless without an appropriate CR.

Typical CR Method

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• the updating time is generally longer than the coherence time of the Ionosphere, hence the ionospheric model is generally approximated.

Remarks:

• a dense network of ionosondes (displaced within the surveillance area) is needed to account for the ionospheric heterogeneity;

Proposed CR Method 1/2

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• the CR process basically consists in a cross-correlation (hence low computational cost) and can be applied for every echo involving at lest a sea/land transition.

Remarks:• there is no need for data from sources external to the system;

Proposed CR Method 2/2

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• Besides the coastline profiles, other geo-morphological features of the surveillance area could be employed as reference by this method.

In other terms…

• The proposed CR method employs the a priori knowledge of the coastline profiles within the surveillance area in order to geo-referenciate the OTHR-SW received echo;• The CR process basically consists in the cross-correlation between the received echo and the clutter profile of the surveillance area for the selected azimuthal direction;• The method can be applied to every echo relative to a radar footprint characterized by at least one sea/land transition;

• Its relatively low computational cost allows the CR process to be directly introduced in the OTHR-SW system radar routine;

• The process could allow to gather real time information about the Ionosphere in order to continuously update an opportunely parametrized ionospheric model.

OTHR-SW Scenario & Parameters

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HF signals and the Ionosphere

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• The interaction between HF signals and the Ionosphere depends on the couple [,f], (namely incidence angle and frequency).

• In the simulated scenario we supposed to operate with constant frequency and we hypothesized negligible the differences of within the same 3dB radar beam.• Nevertheless this effect needs to be taken into account in a real scenario …

Radar Footprint Reconstruction

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Reconstructed radar footprints:A: the Ionosphere is modeled as a perfect reflecting mirror at a given height;B: a locally-homogeneous electron density profile is associated to the Ionosphere.Simulated echoes:The black curve is associated to A, while the red one is associated to B.

Results and ConclusionsA simplified OTHR scenario confirms that the sea/land transitions can be profitably used for the real time CR of the OTHR-SW signals.

The method is jet to be tested in a scenario that accounts for the dependence of the ionospheric reflection height from the incidence angle of the ray.

The developed method is optimal for the application in a complex coastline profiles scenario.

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After the analisys of the surveillance area by the OTHR-SW system, other geomorphological features (beside the coastal profiles) could be employed in the CR method.

Coordinate Registration of OTHR-SW Remotely-Sensed Data by Sea-Land

Transitions Identification

Università di Firenze Dipartimento di Elettronica

e Telecomunicazioni

F. Sermi, F. Cuccoli, L. Facheris, D. Giuli

IEEE Gold 201029, 30 April 2010 – Naval Academy,

Livorno, Italy

Consorzio Nazionale Interuniversitarioper le Telecomunicazioni (centro

RaSS)