Dynamic Averaging Method to Detect Sea Surface Current From Radar Images

2017 ◽  
Author(s):  
Andreas P. Wijaya
Keyword(s):  
Dispersion Relation ◽  
Current Velocity ◽  
Synthetic Data ◽  
Additional Term ◽  
Surface Current ◽  
Peak Frequency ◽  
Sea Surface ◽  
Radar Images ◽  
Linear Waves ◽  
The Difference

One important parameter in reconstructing and predicting the sea surface elevation from radar images is the surface current. The common method to derive the current is based on 3DFFT with which the (absolute) frequency is derived from a series of images and is fitted to the encounter dispersion relation that consist of the intrinsic exact dispersion relation for linear waves with an additional term that contains the current velocity to be found. The derived dispersion relation will be inaccurate because the images contain many inaccuracies from noise, shadowing, and other radar effects. This paper proposes an alternative method to determine the surface current. Following the method of the Dynamic Averaging and Evolution Scenario (DAES) as presented in [1], the idea is to choose the current velocity that minimizes the difference between an image at a previous time that has been evolved to the time of another image. In order to reduce inaccuracies, an averaging procedure over various images is applied. The method is tested on synthetic data to quantify the accuracy of the results. The robustness of the method will be investigated for several cases of different current parameters (speed and direction) for ensembles of seas with different peak frequency of characteristic sea states.

Phase Resolved Wave Prediction From Synthetic Radar Images

2014 ◽  
Author(s):  
P. Naaijen ◽  
A. P. Wijaya
Keyword(s):  
Wave Field ◽  
Significant Wave Height ◽  
Sea Surface ◽  
Radar Images ◽  
Wave Prediction ◽  
Wave Elevation ◽  
Linear Waves ◽  
Directional Wave ◽  
2D Fft ◽  
Linear Propagation

A method is presented for the inversion of images of the sea surface taken by nautical radar into wave elevation that is specifically suitable for the prediction of the wave elevation outside the observation domain covered by the radar. By means of a beam-wise analysis of the image obtained by a scanning radar, the image information is translated into wave elevation. Subsequently a 2D FFT is applied in order to obtain the directional wave components required for a linear propagation of the wave field. Assuming knowledge of the significant wave height, a method to obtain the correct scaling of the wave prediction is proposed. The proposed method is verified using synthetic radar images which are modelled by applying shadowing and tilt effect to synthesised short crested linear waves.

Sea-State Monitoring Via X-Band Marine Radar Images Sequences: A New Approach for an Accurate Surface Currents Estimation

2009 ◽  
Author(s):  
Francesco Serafino ◽  
Claudio Lugni ◽  
Francesco Soldovieri
Keyword(s):  
Synthetic Data ◽  
Surface Current ◽  
Key Factors ◽  
State Monitoring ◽  
Sea State ◽  
Reconstruction Procedure ◽  
Factors Affecting ◽  
Radar Images ◽  
X Band ◽  
Marine Radar

This work deals with the sea state monitoring starting from marine radar images collected on a moving ship. For such a topic, one of the key factors affecting the reliability of the reconstruction procedure is the determination of the equivalent surface current that also accounts for the speed of the moving ship. Here, we propose a method able to evaluate also high values of the sea surface current. The reliability of the proposed procedure is shown by a numerical analysis with synthetic data. Finally, we present some preliminary results with measurements collected on a moving ship.

scholarly journals Estimation of Sea Surface Current from X-Band Marine Radar Images by Cross-Spectrum Analysis

2019 ◽  
Vol 11 (9) ◽  
pp. 1031 ◽  
Author(s):  
Zhongbiao Chen ◽  
Biao Zhang ◽  
Vladimir Kudryavtsev ◽  
Yijun He ◽  
Xiaoqing Chu
Keyword(s):  
Current Velocity ◽  
Wave Spectrum ◽  
Surface Current ◽  
Least Square ◽  
Spectral Approach ◽  
Spectral Correlation ◽  
Radar Images ◽  
X Band ◽  
Marine Radar ◽  
The Cross

The cross-spectral correlation approach has been used to estimate the wave spectrum from optical and radar images. This work aims to improve the cross-spectral approach to derive current velocity from the X-band marine radar image sequence, and evaluate the application conditions of the method. To reduce the dependency of gray levels on range and azimuth, radar images are preprocessed by the contrast-limited adaptive histogram equalization. Two-dimensional cross-spectral coherence and phase are derived from neighboring X-band marine radar images, and the phases with large coherences are used to estimate the phase velocity and angular frequency of waves, which are first fitted with the theoretical dispersion relation by different least square models, and then the current velocity can be determined. Compared with the current velocities measured by a current meter, the root-mean-square error, correlation coefficient, bias, and relative error are 0.15 m/s. 0.88, –0.05 m/s, and 7.79% for the north-south velocity, and 0.14 m/s, 0.86, 0.06 m/s, and 10.75% for the east-west velocity in the experimental area, respectively. The preprocessing, critical coherence, and the number of images for applying the cross-spectral approach, are discussed.

scholarly journals Measuring ocean total surface current velocity with the KuROS and KaRADOC airborne near-nadir Doppler radars: a multi-scale analysis in preparation for the SKIM mission

Ocean Science ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1399-1429
Author(s):  
Louis Marié ◽  
Fabrice Collard ◽  
Frédéric Nouguier ◽  
Lucia Pineau-Guillou ◽  
Danièle Hauser ◽  
...  
Keyword(s):  
Surface Wave ◽  
Wind Speed ◽  
Current Velocity ◽  
Surface Current ◽  
Sea Surface ◽  
Line Of Sight ◽  
Velocity Signal ◽  
Ka Band ◽  
Ku Band

Abstract. Surface currents are poorly known over most of the world's oceans. Satellite-borne Doppler wave and current scatterometers (DWaCSs) are among the proposed techniques to fill this observation gap. The Sea surface KInematics Multiscale (SKIM) proposal is the first satellite concept built on a DWaCS design at near-nadir angles and was demonstrated to be technically feasible as part of the European Space Agency Earth Explorer program. This article describes preliminary results from a field experiment performed in November 2018 off the French Atlantic coast, with sea states representative of the open ocean and a well-known tide-dominated current regime, as part of the detailed design and feasibility studies for SKIM. This experiment comprised airborne measurements performed using Ku-band and Ka-band Doppler radars looking at the sea surface at near-nadir incidence in a real-aperture mode, i.e., in a geometry and mode similar to that of SKIM, as well as an extensive set of in situ instruments. The Ku-band Radar for Observation of Surfaces (KuROS) airborne radar provided simultaneous measurements of the radar backscatter and Doppler velocity in a side-looking configuration, with a horizontal resolution of about 5 to 10 m along the line of sight and integrated in the perpendicular direction over the real-aperture 3 dB footprint diameter (about 580 m). The Ka-band RADar for Ocean Current (KaRADOC) system, also operating in the side-looking configuration, had a much narrower beam, with a circular footprint only 45 m in diameter. Results are reported for two days with contrasting conditions, a strong breeze on 22 November 2018 (wind speed 11.5 m s−1, Hs 2.6 m) and gentle breeze on 24 November 2018 (wind speed 5.5 m s−1, Hs 1.7 m). The measured line-of-sight velocity signal is analyzed to separate a non-geophysical contribution linked to the aircraft velocity, a geophysical contribution due to the intrinsic motion of surface waves and the desired surface current contribution. The surface wave contribution is found to be well predicted by Kirchhoff scattering theory using as input parameters in situ measurements of the directional spectrum of long waves, complemented by the short wave spectrum of Elfouhaily et al. (1997). It is found to be closely aligned with the wind direction, with small corrections due to the presence of swell. Its norm is found to be weakly variable with wind speed and sea state, quite stable and close to C0=2.0ms-1 at the Ka band, and more variable and close to C0=2.4ms-1 at the Ku band. These values are 10 %–20 % smaller than previous theoretical estimates. The directional spread of the short gravity waves is found to have a marked influence on this surface wave contribution. Overall, the results of this study support the feasibility of near-nadir radar Doppler remote sensing of the ocean total surface current velocity (TSCV).

scholarly journals Influence of Sea Surface Current on Wave Height Inversion in Shadow Statistical Method

Information ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 303
Author(s):  
Yanbo Wei ◽  
Yike Liu ◽  
Zhizhong Lu ◽  
Yuying Zhang
Keyword(s):  
Dispersion Relation ◽  
Statistical Method ◽  
Wave Height ◽  
Significant Wave Height ◽  
Surface Current ◽  
Sea Surface ◽  
Significant Wave ◽  
First Order ◽  
Order Dispersion ◽  
The Ideal

Currently, the research on the inversion of wave height by using the shadow statistical method attracts more attention, due to the benefit of without external calibration equipment. Under the assumption of the sea wave satisfying the ideal first-order dispersion relation, the wave period is used to describe the relationship between wave slope and significant wave height. However, the influence of the sea surface current is ignored during the process of extracting the wave height, since the ideal first-order dispersion relation is adopted. By deeply investigating the theoretical derivation process, the retrieving accuracy of wave height is deteriorated when the surface current exists. To solve this problem of the shadow statistical method, the influence of the surface current on the wave height inversion is investigated and is considered in the first-order dispersion relation for retrieving significant wave height in this paper. The synthetic and the collected X-band marine radar images are utilized to certify the influence of sea surface current on the inversion of the significant wave height. The experimental results demonstrate that the inversion accuracy of the significant wave height can be improved when the influence of the surface current is taken into account.

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