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. 2023 Jul 6;23(13):6185.
doi: 10.3390/s23136185.

Ocean-Surface Wave Measurements Using Scintillation Theories on Seaborne Software-Defined GPS and SBAS Reflectometry Observations

Lung-Chih Tsai  1   2 , Hwa Chien  1   3 , Shin-Yi Su  1 , Chao-Han Liu  4 , Harald Schuh  5   6 , Mohamad Mahdi Alizadeh  5   6   7 , Jens Wickert  5   6
Affiliations

Ocean-Surface Wave Measurements Using Scintillation Theories on Seaborne Software-Defined GPS and SBAS Reflectometry Observations

Lung-Chih Tsai et al. Sensors (Basel). .

Abstract

In this study, a low-cost, software-defined Global Positioning System (GPS) and Satellite-Based Augmentation System (SBAS) Reflectometry (GPS&SBAS-R) system has been built and proposed to measure ocean-surface wave parameters on board the research vessel New Ocean Researcher 1 (R/V NOR-1) of Taiwan. A power-law, ocean-wave spectrum model has been used and applied with the Small Perturbation Method approach to solve the electromagnetic wave scattering problem from rough ocean surface, and compared with experimental seaborne GPS&SBAS-R observations. Meanwhile, the intensity scintillations of high-sampling GPS&SBAS-R signal acquisition data are thought to be caused by the moving of rough surfaces of the targeted ocean. We found that each derived scintillation power spectrum is a Fresnel-filtering result on ocean-surface elevation fluctuations and depends on the First Fresnel Zone (FFZ) distance and the ocean-surface wave velocity. The determined ocean-surface wave speeds have been compared and validated against nearby buoy measurements.

Keywords: GPS/GNSS reflectometry; ocean-surface wave measurement; radio scintillation; software-defined GPS receiver.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Geometry of a GPS&SBAS-R observation on rough ocean surface. The dash green ellipse represents the corresponding FFZ area on the x-y plane, and the origin is located at the SPP, i.e., the center of FFZ. The GPS&SBAS-R receiver is located at an elevation height of h and a horizontal distance of d from the SPP; therefore, the total distance D is equal to sqrt(d2 + h2).
Figure 2
Figure 2
Theoretical power spectrum of GPS/GNSS-R scattered field (shown as the blue line) as a function of normalized spatial frequency κ/κF in log scale. A Fresnel-filter function is also shown as the red line.
Figure 3
Figure 3
The (left panel) shows a picture of the R/V NOR1, where the red circle indicates the positions of two GPS&SBAS receiving antennas. The (right panel) shows the two GPS&SBAS-R receiving antenna installations by dotted red rectangles.
Figure 4
Figure 4
Views to the surrounding oceans of the GPS&SBAS-R observations from the R/V NOR1.
Figure 5
Figure 5
The shipping route of the R/V NOR1 during the GPS&SBAS-R experiment dated from DOYs 349 to 357, 2021, and colored in hours since the start. The red squares represent the validation locations of five CWB buoys from No. 1 to 5, and the digital terrain map of Taiwan is also shown.
Figure 6
Figure 6
An example log–log plot on the relative Fourier power spectra with respect to four time series of GPS&SBAS-R signal acquisition data recorded by the NOR1-L system on DOY 356, 2021. The derived break frequencies and spectral indexes of the signal spectrum analyses of reflectometry observations on different GPS and SBAS satellites are also shown.
Figure 7
Figure 7
The (left panel) shows the azimuth-distance tracks of GPS&SBAS-R SPPs obtained from both the NOR1-L and NOR1-R system observations during 15 ± 0.5 UT on DOY 351, 2021. The (right panel) shows a scatterplot of the corresponding effective breaking frequencies versus the FFZ distances of all GPS&SBAS-R observations, and it also shows two rectangular hyperbola curves corresponding to a least-squares, fitting surface-wave speed and the validation surface-wave speed measured by the buoy at Xiao Liuqiu Station (XLS). The coded colors represent the different GPS&SBAS-R observations from GNSS satellite numbers, where No. 1 to 32 represent GPS satellites, and 33 to 50 represent SBAS satellites.
Figure 8
Figure 8
As in the (right panel) of Figure 7 but the results of respective GPS&SBAS-R observations nearby Fugui Cape Station (in the upper-left panel), Chenggong Station (in the upper-right panel), Hualien Station (in the lower-left panel), and Guishan Island Station (in the lower-right panel).
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References

    1. Martín-Neira M. A Passive Reflectometry and Interferometry System (PARIS): Application to ocean altimetry. ESA J. 1993;17:331–355.
    1. Lin B., Katzberg S.J., Garrison J.L., Wielicki B.A. Relationship between GPS signals reflected from sea surfaces and surface winds: Modeling results and comparisons with aircraft measurements. J. Geophys. Res. 1999;104:20713–20727. doi: 10.1029/1999JC900176. - DOI
    1. Zavorotny V.U., Voronovich A.G. Scattering of GPS signals from the ocean with wind remote sensing application. IEEE Trans. Geosci. Remote Sens. 2000;35:951–964. doi: 10.1109/36.841977. - DOI
    1. Rius A., Aparicio J.M., Cardellach E., Martín-Neira M., Chapron B. Sea surface state measured using GPS reflected signals. Geophys. Res. Lett. 2002;29:2122. doi: 10.1029/2002GL015524. - DOI
    1. Clarizia P.C., Ruf C.S., Jales P., Gommenginger C. Spaceborne GNSS-R minimum variance wind speed estimator. IEEE Trans Geosci. Remote Sens. 2014;52:6829–6843. doi: 10.1109/TGRS.2014.2303831. - DOI

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