The effect of artificial rain on wave spectra and multi-polarisation X band radar backscatter

Braun, Nicole; Gade, Martin; Lange, Philipp

doi:10.1080/01431160110106032

Cited by 30 publications

(29 citation statements)

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“…d) Bragg waves of unequal amplitude moderately advected by larger-scale motions, as for wind-generated waves looking nearly along the wind direction. (Braun et al, 2002;Contreras et al, 2004). These are symmetric so that no azimuthal intensity variation is present in short waves produced by rainfall.…”

Section: Principles Of Surface Current Measurement Using Coherent Micmentioning

confidence: 99%

Measurement of river surface currents with coherent microwave systems

Plant

Keller

Hayes

2005

IEEE Trans. Geosci. Remote Sensing

108

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River surface currents have been measured using coherent microwave systems from a bridge, a cableway, several riverbanks, a helicopter, and an airplane. In most cases, the microwave measurements have been compared with conventional measurements of near-surface currents and found to be accurate to within about 10 cm/s. In all cases, the basis for the microwave measurement of surface current is the Doppler shift induced in the signal backscattered from the rough water surface. In this paper, we outline the principles of the measurements and the various implementations that have been used to make microwave measurements of surface currents. CW microwave systems have been used from a bridge to make long-term measurements of surface currents; these are compared with current-meter measurements and with time series of stage. A compact CW system has been developed and used on a cableway to measure surface currents at various distances across a river; these measurements have been compared with acoustic ones. Pulsed Doppler radars have been used to measure river surface currents from a riverbank, a helicopter, and an airplane. In the first two cases comparisons with both current-meter and acoustic measurements have been made. We suggest that the CW system would be preferable to the pulsed Doppler radar to make such measurements from helicopters in the future. Finally, we consider the implications of our experiments for the measurement of surface currents from aircraft or satellites using interferometric synthetic aperture radars (INSARs). We find that a combination along-track, crosstrack INSAR is necessary but that significant limitations are inherent in the technique.

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Section: Principles Of Surface Current Measurement Using Coherent Micmentioning

confidence: 99%

Measurement of river surface currents with coherent microwave systems

Plant

Keller

Hayes

2005

IEEE Trans. Geosci. Remote Sensing

108

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“…In both types of experiments, gravity waves with frequencies less than 5 Hz were damped by the rain and the damping rate was found to be independent of the rain rate. Wave amplification has also been observed for higher wave frequencies (Poon et al 1992;Yang et al 1997;Braun et al 2002;Harrison 2012) but only in the presence of wind. Tsimplis & Thorpe (1989) proposed that the observed rain-induced wave damping results from the rain-generated turbulence where a near-surface high eddy viscosity layer viscously damps the surface waves.…”

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confidence: 88%

“…Veron and L. Mieussens an effect that has been used to locate patches of rainfall in the open ocean (Bliven et al 1993;Atlas 1994;Chen et al 1998;Braun, Gade & Lange 2002;Contreras et al 2003;Weissman et al 2012), reduced surface roughness, or wave damping, has the opposite effect and instead enhances the radar backscatter signal (Guymer, Quartly & Srokosz 1995;Quartly, Guymer & Srokosz 1996). Thus, in order to improve the satellite measurements in rainy conditions, a physical understanding of the rain-induced wave damping mechanism is necessary if adequate parameterizations are to be developed.…”

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confidence: 97%

“…The available experimental data are, for the most part, focused on quantifying the rain-induced wave damping in a laboratory environment, where waves are shorter than approximately 0.5 m in wavelength (Manton 1973;Tsimplis & Thorpe 1989;Poon, Tang & Wu 1992;Tsimplis 1992;Yang, Tang & Wu 1997;Braun et al 2002;Harrison 2012;Peirson et al 2013). Some of these experiments were performed using mechanically generated, monochromatic waves (Tsimplis & Thorpe 1989), while others used wind-generated wave fields (Poon et al 1992).…”

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confidence: 99%

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A kinetic model for particle–surface interaction applied to rain falling on water waves

Véron

Mieussens

2016

J. Fluid Mech.

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We present a model for estimating the momentum flux from water drops falling onto a moving free surface. The theory is based on a kinetic approach whereby individual drops are modelled as point particles with mass and velocity, and are described collectively by a distribution function f (t, x, v, r). We show that the resulting momentum flux can be readily incorporated into free-surface Navier-Stokes and Euler models. As an illustration of this approach we examine the interaction between rainfall and linear deep-water surface waves. This particular application is not fundamentally different from the study of Le Méhauté & Khangaonkar (J. our methodology is more general and is novel in its use of a kinetic approach with an all-purpose drop distribution function. The applicability of the model to linear surface waves is found to be valid for surface-wave wavelengths ranging from approximately 3 to 250 m. We further show that rainfall modifies the usual wave dispersion relationship and induces wave amplification, or damping, depending on the rain rate, the rain impact angle and the wavelength of the surface wave. We solve for the amplification and damping rates analytically and show, among other results, that rain falling vertically will always damp the surface waves.

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“…E-mail: pkbhaskaran@naval.iitkgp.ernet.in Article 1992). Based on wind-wave tank experiments, Braun et al (2002) have shown that modification of sea-surface roughness by striking raindrops depends strongly on corresponding wavelength of the surface waves. Precipitation is usually associated with strong downdraft which on reaching seasurface spreads radially outwards as a strong local surface wind thereby causing an increase in sea-surface roughness.…”

Section: Introductionmentioning

confidence: 99%

Parameterization of rain induced surface roughness and its validation study using a third generation wave model

Kumar

Subrahamanyam

2009

Ocean Sci. J.

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The effect of raindrops striking water surface and their role in modifying the prevailing sea-surface roughness is investigated. The work presents a new theoretical formulation developed to study rain-induced stress on sea-surface based on dimensional analysis. Rain parameters include drop size, rain intensity and rain duration. The influences of these rain parameters on young and mature waves were studied separately under varying wind speeds, rain intensity and rain duration. Contrary to popular belief that rain only attenuates surface waves, this study also points out rain duration under certain condition can contribute to wave growth at high wind speeds. Strong winds in conjunction with high rain intensity enhance the horizontal stress component on the sea-surface, leading to wave growth. Previous studies based on laboratory experiments and dimensional analysis do not account for rain duration when attempting to parameterize sea-surface roughness. This study signifies the importance of rain duration as an important parameter modifying sea-surface roughness. Qualitative as well quantitative support for the developed formulation is established through critical validation with reports of several researchers and satellite measurements for an extreme cyclonic event in the Indian Ocean. Based on skill assessment, it is suggested that the present formulation is superior to prior studies. Numerical experiments and validation performed by incorporating in state-of-art WAM wave model show the importance of treating rain-induced surface roughness as an essential pre-requisite for ocean wave modeling studies.

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The effect of artificial rain on wave spectra and multi-polarisation X band radar backscatter

Cited by 30 publications

References 0 publications

Measurement of river surface currents with coherent microwave systems

Measurement of river surface currents with coherent microwave systems

A kinetic model for particle–surface interaction applied to rain falling on water waves

Parameterization of rain induced surface roughness and its validation study using a third generation wave model

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