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
GNSS Polarimetry of Sea Surface Reflections
By Brian Breitsch
GNSS Polarimetry of Sea Surface Reflections
Discussion on the sensitivity of multi-frequency GPS signals in measuring change in sea surface dielectric constant due to temperature and salinity parameters.
