Radar Imaging Mechanism of the Seabed: Results of the C-STAR Experiment in 1996 with Special Emphasis on the Relaxation Rate of Short Waves due to Current Variations

Hennings, Ingo; Lurin, Blandine; Didden, Norbert

doi:10.1175/1520-0485(2001)031<1807:rimots>2.0.co;2

Cited by 14 publications

(12 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[34] Calculated from DL, m r was exactly the relaxation rate of short waves due to current variations. With a value of 0.055 s −1 (18 s for the corresponding relaxation time) and a wind speed of 5.0 m s −1 , m r did not differ much from that measured in the North Sea [Hennings et al, 2001]. This value could be applied in the Sun glitter imaging model in order to interpret the intensity modulation.…”

Section: Discussionmentioning

confidence: 79%

“…Stronger currents occurred around the crests (Figures 8b and 9b) owing to the shallower water depths above the crests of sand waves, while lower magni-tudes were observed in the troughs. The parallel components U k showed only very slight variation while flowing through the sand waves (Figures 8d and 9d), and were not as obvious as those measured in the North Sea [Hennings et al, 2001], and nor were the variations in current direction (Figures 8c and 9c). In contrast, the perpendicular components U ?…”

Section: Currentmentioning

confidence: 79%

“…The method developed in this study provided an approach for future investigations, which might also be suitable for determining the relaxation rate for radars of other frequency bands. Compared with the approach used by Hennings et al [2001], the method developed in this study was more flexible, because it was not so sensitive to the experimental data.…”

Section: Discussionmentioning

confidence: 99%

“…The photograph was taken during Run 11 while the vessel was heading southward in the same direction as the tidal current and crossing a sand wave crest, and it simulated the imaging result from an optical sensor very well. Similar photographs were also taken over sand waves in the North Sea [Hennings et al, 2001]. The location of each separation of high and low roughened zones was determined by using video together with the DGPS.…”

Section: Advection Lengthmentioning

confidence: 99%

See 3 more Smart Citations

Sun glitter imaging of submarine sand waves on the Taiwan Banks: Determination of the relaxation rate of short waves

Shao¹,

Li²,

Li³

2011

J. Geophys. Res.

View full text Add to dashboard Cite

[1] Above sand waves on the seafloor, surface short waves, which are responsible for the radiance distribution in remote sensing imagery, are modulated gradually by the submarine topography. The relaxation rate m r characterizes the rate at which the short waves reach their saturation range after being disturbed. It is a key parameter in the weak hydrodynamic interaction theory and is also a most important parameter in the imaging mechanism used for mapping submarine bottom topography. In this study, a robust expression containing intensity and phase (advection effect) modulations of the perturbed action spectrum of short waves was deduced, by using the first-order weak hydrodynamic interaction theory. On the basis of the phase modulation, a method was developed to determine the relaxation rate in the Sun glitter imaging mechanism. The relaxation rates were estimated using in situ data measured on a cruise over the sand waves of the Taiwan Banks, a sea area between the East China Sea and the South China Sea, on 28-29 August 2006. Results showed that, under a wind speed of 5.0 m s −1 , the relaxation rate of short waves was about 0.055 s −1 in response to current variations and about 0.025 s −1 equivalently in response to sea bottom topographic variations. The former value could be applied to interpret the amplitude of submarine topography by using satellite imagery, while the latter one (equivalent relaxation rate m′ r ) could help to more accurately calibrate the spatial position of the retrieved sea bottom topography.

show abstract

Section: Discussionmentioning

confidence: 79%

Section: Currentmentioning

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Section: Advection Lengthmentioning

confidence: 99%

See 2 more Smart Citations

Sun glitter imaging of submarine sand waves on the Taiwan Banks: Determination of the relaxation rate of short waves

Shao¹,

Li²,

Li³

2011

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…Radar imaging experiments of strain rate generated effects from bottom topography or internal waves have mainly used satellite imagery, and, or, high grazing angles, for example Hennings et al (2001). Burdyugov et al (1987) and Kudryavtsev and Malinovskiy (1988) reported measurements of strain rate induced effects measured with low grazing angle radar.…”

mentioning

confidence: 99%

Low grazing angle radar imaging experiments over the South Falls sandbank

Lamont-Smith

Jackson

Shepherd³

et al. 2005

International Journal of Remote Sensing

View full text Add to dashboard Cite

A number of X-band radar data collection exercises have been conducted in the area of the South Falls sandbank, which were supported by two deployments with a research vessel that directly measured the tidal flow and water depth. Results from a total of 12 low grazing angle airborne radar data collections are presented. Nine sorties were flown with the Enhanced Surveillance Radar, using a synthetic aperture radar (SAR) mode. The other three aircraft sorties were flown using a real aperture scanning radar mode. For the scanning radar experiment, data were collected from around the sandbank on three successive days with grazing angles of 0.5u-4u. The wind speed remained relatively constant at 7-9 m s 21 during this experiment. The radar cross-section modulation was found to have a linear relationship with the estimated surface strain rate, and the constant of proportionality was found to be 500 s when the radar was pointing downwind or crosswind, and around 200 s when looking upwind. For the SAR mode data collection, a similar look-direction dependence was observed as the scanning mode data, and a strong wind speed dependence on the visibility of the sandbank was also seen. At 6u grazing angle and a peak strain rate of 5610 24 s 21 , the strength of the radar contrast decreased by approximately 1.7 dB for unit increase in the wind speed, and the radar contrast vanished for wind speeds much beyond 10 m s 21 .

show abstract

Analysis of current–topography interaction in remote sensing imaging procedures for shallow water topography

et al. 2017

View full text Add to dashboard Cite

Radar Imaging Mechanism of the Seabed: Results of the C-STAR Experiment in 1996 with Special Emphasis on the Relaxation Rate of Short Waves due to Current Variations

Cited by 14 publications

References 28 publications

Sun glitter imaging of submarine sand waves on the Taiwan Banks: Determination of the relaxation rate of short waves

Sun glitter imaging of submarine sand waves on the Taiwan Banks: Determination of the relaxation rate of short waves

Low grazing angle radar imaging experiments over the South Falls sandbank

Analysis of current–topography interaction in remote sensing imaging procedures for shallow water topography

Contact Info

Product

Resources

About