Multi-Frequency GNSS for Polarimetric Measurements of Sea Surface Parameters

Brian Breitsch

...

2018 May 11

The Concept:

dielectric constant of sea water \(\varepsilon\)

dependent on frequency, temperature, and salinity

GPS satellite transmitting signals at three frequencies

(1.1-1.5 GHz)

High-gain dish antenna collects right-hand circular (RHC) and left-hand circular (LHC) polarized signals

want to try to measure these

Receiver measures received signal power at multiple frequencies and grazing angles

\theta
\theta

The Theory:

N_\text{air} \approx 1
\Re_V = {\varepsilon\sin\theta - \sqrt{\varepsilon - \cos^2\theta} \over \varepsilon\sin\theta + \sqrt{\varepsilon - \cos^2\theta} }
N_\text{water} = \sqrt{\varepsilon}

non-magnetic material

GPS satellite transmits RHP

\(R = \) RHC,  \(L =\) LHC,  \(V = \) vertical,  \(H = \) horizontal

\Re_H = {\sin\theta - \sqrt{\varepsilon - \cos^2\theta} \over \sin\theta + \sqrt{\varepsilon - \cos^2\theta} }
\Re_R = {1 \over 2} \left( \Re_V + \Re_H \right)
\Re_L = {1 \over 2} \left( \Re_V - \Re_H \right)

complex Fresnel relations

refractive indices

reflected power

R = |\Re|^2

FOR SPECULAR REFLECTION

\theta_g
\theta_e
\theta_g
R_E
h
R_{RT}
R_{ET}

More Theory:

L1

L2

L5

LHC

RHC

increasing temperature

increasing salinity

assume constant sea surface parameters, then fit curve to data

Cleaning the Data:

L1

L2

L5

different transmitted power

tropospheric scintillation irrelevant data

use this part

Results So Far...

LHC

RHC

Other Factors / Next Steps:

  • algorithm corrupted by other frequency-dependent trends in SI
    • local multipath
    • differing satellite antenna gain patterns
    • attempt to model and remove
  • current approach appears very noisy
    • what is the estimated uncertainty of the measurement?
    • what is the sensitivity?
  • is this technique worth the effort?

References

Text

Zavorotny, Valery U., and Alexander G. Voronovich. "Scattering of GPS signals from the ocean with wind remote sensing application." IEEE Transactions on Geoscience and Remote Sensing 38.2 (2000): 951-964.

Valencia, E., et al. "Improving the accuracy of sea surface salinity retrieval using GNSS‐R data to correct the sea state effect." Radio Science 46.6 (2011).

http://www.salinityremotesensing.ifremer.fr/sea-surface-salinity/salinity-distribution-at-the-ocean-surface