Microwave Techniques for Measuring Directional Wave Spectra

Jackson, F. C.; Lyzenga, David R.

doi:10.1007/978-94-009-0627-3_5

Cited by 13 publications

(6 citation statements)

References 46 publications

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“…The final exponential term is the desired interferometric phase. When evaluated at , the phase of this term is given by (8).…”

Section: Appendix Squinted Ati-sar Response With Attitude/velocity Ermentioning

confidence: 99%

“…The phase at is (8) from which one estimates radial velocity in the direction of the squinted beam. In the case of a horizontal platform velocity and a horizontal baseline, (8) reduces to the expected result (9) where is the interferometric delay 2 . To estimate , one divides the measured phase by , where is obtained from an independent estimate of the platform velocity, .…”

Section: Dbi Point Source Responsementioning

confidence: 99%

“…Given a surface displacement spectrum , the coherence time can be estimated from the radial component of the RMS orbital velocity (see, e.g., [8]) (2) where incidence angle; wave propagation angle relative to look direction; spatial resolution; ocean wave radian frequency. Fig.…”

Section: A Ocean Surface Coherence Propertiesmentioning

confidence: 99%

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Dual-beam interferometry for ocean surface current vector mapping

Frasier

Camps

2001

IEEE Trans. Geosci. Remote Sensing

148

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Abstract-The recent use of along-track interferometry (ATI) in synthetic aperture radar (SAR) has shown promise for synoptic measurement of ocean surface currents. ATI-SARs have been used to estimate wave fields, currents, and current features. This paper describes and analyzes a dual-beam along-track interferometer to provide spatially resolved vector surface velocity estimates with a single pass of an aircraft. The design employs a pair of interferometer beams, one squinted forward and one squinted aft. Each interferometric phase is sensitive to the component of surface Doppler velocity in the direction of the beam. Therefore, a proper combination of these measurements provides a vector surface velocity estimate in one pass of the aircraft. We find that precise measurements dictate widely spaced beams and that the spatial resolution for the squinted SAR is essentially identical to the sidelooking case. Practical instrument design issues are discussed, and an airborne system currently in development is described. Through computer simulation, we observe the azimuthal displacement of interferometric phases by moving surfaces identical to those of conventional SAR and find that such displacement can bias the estimated surface velocity.

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“…The final exponential term is the desired interferometric phase. When evaluated at , the phase of this term is given by (8).…”

Section: Appendix Squinted Ati-sar Response With Attitude/velocity Ermentioning

confidence: 99%

Section: Dbi Point Source Responsementioning

confidence: 99%

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Dual-beam interferometry for ocean surface current vector mapping

Frasier

Camps

2001

IEEE Trans. Geosci. Remote Sensing

148

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“…where λ is the radar wavelength. The RMS radial velocity σ sea v r , according to [27,28], is evaluated as follows:…”

Section: Derivation Of Thementioning

confidence: 99%

Improved Analytical Formula for the SAR Doppler Centroid Estimation Standard Deviation for a Dynamic Sea Surface

Qiao

Лиу

2023

Remote Sensing

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The existing formulas for the synthetic aperture radar (SAR) Doppler centroid estimation standard deviation (STD) suffer from various limitations, especially for a dynamic sea surface. In this study, we derive an improved version of these formulas through three steps. First, by considering the ocean wavenumber spectrum information, a new strategy for determining the number of independent samples of the sea wave velocity field is adopted in the new formula. This is contrary to the method used in the existing formulas, where the number of SAR geometric resolution cells is taken as the number of samples assuming that adjacent SAR resolution cells are statistically uncorrelated. Second, the pulse repetition frequency and Doppler bandwidth are decoupled in the new formula, unlike in the existing formulas where they are unchangeably related to each other. Third, the effects of thermal noise and Doppler aliasing are jointly quantified in a mathematically exact manner instead of being treated separately, as in the existing formulas. Comprehensive SAR raw data simulations for the ocean surface show that the new formula has a better performance in predicting the Doppler centroid estimation STD than the existing formulas.

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“…Sensor-related parameters influencing the backscattering over the sea are geometric and radiometric resolution, surface roughness, polarization, incidence angle and frequency ( [28][29][30][31][32][33]). Generally, a calm water surface will scatter away the electromagnetic radiation (surface scattering) and it will appear relatively dark.…”

Section: Introductionmentioning

confidence: 99%

The InflateSAR Campaign: Evaluating SAR Identification Capabilities of Distressed Refugee Boats

et al. 2020

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Most of the recent research in the field of marine target detection has been concentrating on ships with large metallic parts. The focus of this work is on much more challenging targets represented by small rubber inflatables. They are of importance, since in recent years they have largely been used by migrants to cross the Mediterranean Sea between Libya and Europe. The motivation of this research is to mitigate the ongoing humanitarian crisis at Europe’s southern borders. These boats, packed with up to 200 people, are in no way suitable to cross the Mediterranean Sea or any other big water body and are in distress from the moment of departure. The establishment of a satellite-based surveillance infrastructure could considerably support search and rescue missions in the Mediterranean Sea, reduce the number of such boats being missed and mitigate the ongoing death in the open ocean. In this work we describe and analyze data from the InflateSAR acquisition campaign, wherein we gathered multiple-platform SAR imagery of an original refugee inflatable. The test site for this campaign is a lake which provides background clutter that is more predictable. The analysis considered a sum of experiments, enabling investigations of a broad range of scene settings, such as the vessel’s orientation, superstructures and speed. We assess their impact on the detectability of the chosen target under different sensor parameters, such as polarimetry, resolution and incidence angle. Results show that TerraSAR-X Spotlight and Stripmap modes offer good capabilities to potentially detect those types of boats in distress. Low incidence angles and cross-polarization decrease the chance of a successful identification, whereas a fully occupied inflatable, orthogonally oriented to the line of sight, seems to be better visible than an empty one. The polarimetric analyses prove the vessel’s different polarimetric behavior in comparison with the water surface, especially when it comes to entropy. The analysis considered state-of-the-art methodologies with single polarization and dual polarization channels. Finally, different metrics are used to discuss whether and to which extent the results are applicable to other open ocean datasets. This paper does not introduce any vessel detection or classification algorithm from SAR images. Rather, its results aim at paving the way to the design and the development of a specially tailored detection algorithm for small rubber inflatables.

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Microwave Techniques for Measuring Directional Wave Spectra

Cited by 13 publications

References 46 publications

Dual-beam interferometry for ocean surface current vector mapping

Dual-beam interferometry for ocean surface current vector mapping

Improved Analytical Formula for the SAR Doppler Centroid Estimation Standard Deviation for a Dynamic Sea Surface

The InflateSAR Campaign: Evaluating SAR Identification Capabilities of Distressed Refugee Boats

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