Ku-Band Sea Surface Radar Backscatter at Low Incidence Angles under Extreme Wind Conditions

Li, Xiuzhong; Zhang, Biao; Mouche, Alexis; He, Yijun; Perrie, William

doi:10.3390/rs9050474

Cited by 16 publications

(10 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Here, the values a = −0.3958 and b = 8.7875 are obtained. Their magnitudes are both much smaller than the results given in [22] possibly due to the fact that the NRCS from PR and KuPR flagged as rain free is selected here whereas that is not the case As shown in Figure 12c, the NRCS is almost insensitive to wind speed and approximately depends linearly on the incidence angle at extremely high wind speeds larger than about 37 m/s. The NRCSs are averaged over the extreme wind speed range of 37-45 m/s at different incidence angles with the Satellite/H*Wind data and plotted versus the incidence angle in Figure 13.…”

Section: Further Analysis On the Imapct Of Wave Breakingmentioning

confidence: 65%

“…This can only be caused by the relatively smooth ocean surface resulting from wave breaking. It has been indicated in [22] that the wave breaking can reduce the drag coefficient and make the ocean surface at high winds relatively smooth. At nadir, the rougher the sea surface, the lower the NRCS, whereas near 18 • , the opposite is true.…”

Section: Further Analysis On the Imapct Of Wave Breakingmentioning

confidence: 99%

“…A few studies have been devoted to understanding the altimeter backscatter response to high wind speeds (e.g., [21]). Only Li et al [22] reported the NRCS at low incidence angles (0-18 • ) under extreme wind conditions and suggested that the standard quasi-specular scattering theory is not enough to explain the radar signatures at severe winds where the impact of wave breaking may become a significant contributor for the low-incidence NRCS. The way wave breaking works and the relative role of quasi-specular scattering and wave breaking effects at low incidence angles under weak to severe winds still remain to be further discussed.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Understanding Ku-Band Ocean Radar Backscatter at Low Incidence Angles under Weak to Severe Wind Conditions by Comparison of Measurements and Models

et al. 2020

View full text Add to dashboard Cite

The rain-free normalized radar cross-section (NRCS) measurements from the Ku-band precipitation radars (PRs) aboard the tropical rainfall measuring mission (TRMM) and the global precipitation measurement (GPM) mission, along with simultaneous sea surface wind truth from buoy observations, stepped-frequency microwave radiometer (SFMR) measurements, and H*Wind analyses, are used to investigate the abilities of the quasi-specular scattering models, i.e., the physical optics model (PO) and the classical and improved geometrical optics models (GO and GO4), to reproduce the Ku-band NRCS at low incidence angles of 0–18° over the wind speed range of 0–45 m/s. On this basis, the limitations of the quasi-specular scattering theory and the effects of wave breaking are discussed. The results show that the return caused by quasi-specular reflection is affected significantly by the presence of background swell waves at low winds. At moderate wind speeds of 5–15 m/s, the NRCS is still dominated by the quasi-specular reflection, and the wave breaking starts to work but its contribution is very small, thus, the models are found in excellent agreement with the measurements. With wind speed increasing, the impact of wave breaking increases, whereas the role of standard quasi-specular reflection decreases. The wave breaking impact on NRCS is first visible at incidence angles near 18° as wind speed exceeds about 20 m/s, then it becomes dominant when wind speed exceeds about 37 m/s where the NRCS is insensitive to wind speed and depends linearly on incidence angle, which cannot be explained by the standard quasi-specular scattering theory.

show abstract

Section: Further Analysis On the Imapct Of Wave Breakingmentioning

confidence: 65%

Section: Further Analysis On the Imapct Of Wave Breakingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Understanding Ku-Band Ocean Radar Backscatter at Low Incidence Angles under Weak to Severe Wind Conditions by Comparison of Measurements and Models

et al. 2020

View full text Add to dashboard Cite

show abstract

“…The research on the electromagnetic scattering model of the sea surface can not only help to estimate and optimize the target recognition algorithm, but also be used to supplement experimental data [2][3][4]. The high-resolution radar characteristics of the sea surface under high wind conditions at low grazing angles (LGA) have been a point of discussions and in-depth analysis in recent years [5][6][7][8]. Under high wind conditions, the wave energy increases due to sea-air interactions, and wave breaking occurs.…”

Section: Introductionmentioning

confidence: 99%

A Volume-Surface Composite Scattering Model for Nonlinear Ocean Surface With Breaking Waves and Foam Layers Under High Wind Conditions

Zhang¹,

Su²,

Wu³

2019

PIER B

View full text Add to dashboard Cite

Electromagnetic scattering from the sea surface is of great significance in ocean remote sensing especially under high wind conditions. A novel volume-surface composite scattering model of nonlinear rough sea surfaces with breaking waves and foam layers under high wind conditions is presented in this study. Based on the semi-deterministic facet scattering model (SDFSM), using a ray tracing method combined with impedance equivalent edge currents (RT-IEEC) and vector radiative transfer theory (VRT), the backscattering characteristics of the sea surface with breaking waves and foam layers are investigated. The crest-and static-foam coverage was introduced to determine the breaking point and foam coverage distribution. The dependence of the backscattering coefficient of the sea surface with and without breaking waves and foam layers on the incident angle, wind speed, and the polarization are discussed in detail. The results of numerical simulations are analyzed and compared with the measured data from the relevant references which verifies the validity of our volume-surface composite scattering model. The synthetic aperture radar (SAR) image simulations of the surface with and without the breaking waves and foam layers are compared, and the combined effects of the breaking waves and whitecaps are analyzed.

show abstract

“…Quantitative assessments of the radar backscatter for low incidence angles in Ku band have been presented also very recently [9], but their scope is generally limited to the estimation of radar cross-section. Thus, it is now well established that nadir RCS is not very sensitive to surface roughness in the low to moderate wind conditions, but phase and coherence have not been investigated yet.…”

Section: Theoretical Model Of Specular Returns From Inland Watersmentioning

confidence: 99%

Envisat RA-2 Individual Echoes: A Unique Dataset for a Better Understanding of Inland Water Altimetry Potentialities

Abileah¹,

Scozzari

Vignudelli

2017

Remote Sensing

View full text Add to dashboard Cite

Abstract:The exploitation of synthetic aperture properties in nadir-looking radars is opening new scenarios in the framework of satellite radar altimetry. Both recent and upcoming missions including Cryosat-2, Sentinel-3, Sentinel-6 and SWOT take benefit from the coherent processing of radar data, aimed at improving range measurements in particular contexts, such as ice, open ocean, coastal zone, and even inland waters. This work investigates the possibilities offered by current and future satellite radar altimetry missions for the study of inland water bodies, probing into the peculiarities of the expected radar returns and their potential usage. In this regard, signals collected by the RA-2 instrument (Radar Altimeter 2) onboard the Envisat mission offer an unprecedented possibility, even with a relatively low pulse repetition frequency, to analyze the peculiarities of actual signals for detecting and ranging small water surfaces. In particular, the RA-2 instrument offers a global archive of Individual Echoes (IEs), collected at the native sampling rate of 1795 Hz, in addition to the 18 Hz data obtained by incoherent averaging, which are typically delivered to the users as standard products. RA-2 shares with future radar platforms such as Sentinel-6 a continuous and interleaved working modality, as was recommended by the scientific community in designing next missions' requirements. This is a further reason to consider the usage of RA-2 IEs as particularly attractive. Whilst only available for a small percentage of the earth's surface, sufficient IE data exist to study the height retrieval capability of these echoes, in particular for what concerns small water bodies, where we show that enough coherence is exhibited for focusing relatively narrow surfaces and range them correctly. A peculiar aspect of this work lies in the assumption that most of the returned echoes (in RA-2 IEs) are specular. A theoretical framework is developed according to this assumption, which is validated by investigating real RA-2 data and observing their related specular features. In particular, we discuss how specular echoes are expected to be very common in inland altimetry, and are most often associated with small to medium size lakes and rivers. This paper illustrates the expected electromagnetic behavior of specular water targets by exploiting the classical radar cross-section (RCS) theory for specular surfaces. Results from the model are compared with real IE data in three selected case studies, regarding two rivers of variable width and one flood plain, in order to check different hydrological regimes. The model very closely matches the data in all cases, making the results of this validation activity very promising. In particular, we demonstrate the feasibility of using satellite radar altimetry in rivers much smaller than what was considered possible until now.

show abstract

Ku-Band Sea Surface Radar Backscatter at Low Incidence Angles under Extreme Wind Conditions

Cited by 16 publications

References 40 publications

Understanding Ku-Band Ocean Radar Backscatter at Low Incidence Angles under Weak to Severe Wind Conditions by Comparison of Measurements and Models

Understanding Ku-Band Ocean Radar Backscatter at Low Incidence Angles under Weak to Severe Wind Conditions by Comparison of Measurements and Models

A Volume-Surface Composite Scattering Model for Nonlinear Ocean Surface With Breaking Waves and Foam Layers Under High Wind Conditions

Envisat RA-2 Individual Echoes: A Unique Dataset for a Better Understanding of Inland Water Altimetry Potentialities

Contact Info

Product

Resources

About