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GNSS Reflectometry for Sea Ice Detection
- GNSS-R for sea ice detection
[1]
- © Y. Zhu (GFZ)
Yongchao Zhu (Successful
finalization December 2018)
Faculty VI - Planning
Building Environment, Technical University Berlin
School of
Geodesy and Geomatics, Wuhan University
GFZ Potsdam
Global Navigation Satellite System (GNSS) has been widely used
to provide positioning, navigation and timing services in civil and
military domains since it became fully operational in 1993. In
addition to these fundamental services and applications, GNSS could be
also used for remote sensing of atmospheric parameters; for instance,
by launching LEO satellites and observing refraction signals from GNSS
satellites with negative elevation angles. This GNSS-based remote
sensing technique termed GNSS radio occultation (GNSS-RO) could be
used to estimate the tropospheric water vapor, temperature, pressure,
and ionospheric total electron content (TEC) with a high resolution.
Meanwhile, GNSS signal reflection over a specific surface, a source of
positioning error, which cannot be easily neutralized, could be used
to retrieve the surface geophysical parameters. This remote sensing
technique is termed GNSS Reflectometry (GNSS-R). The ocean’s surface
characteristics (ie. ocean surface height, roughness, wind speed and
wind direction) could be estimated by GNSS-R. It could be also applied
for land applications such as the retrieval of ground vegetation
condition and soil moisture. This study focuses on sea ice detection
using GNSS-R. GNSS-R can be used to retrieve main parameters of sea
ice (i.e. thickness, concentration, surface roughness and ice
permittivity). These parameters can be combined to help characterize
different ice types including new ice, young ice, thin first-year ice,
first-year ice, and multiyear ice. Sea ice thickness is a key
parameter for classification and characterization of sea ice masses,
which influence the temperature and circulation pattern of both the
ocean and atmosphere and thus can be used for analyses of the
Earth’s climate. In the first stage, GNSS-R is used for sea ice
coverage detection using UK TechDemoSat-1 data (available online:
www.merrbys.co.uk [2]). A new differential Delay-Doppler Map (DDM) is
proposed and the ice coverage detection result is validated against
data from National Snow & Ice Center, USA (http://nsidc.org [3]).
Then, the study presents a potential sea ice concentration detection
method based on GNSS reflection amplitudes considering sea ice
permittivity and roughness, which are important parameters for sea ice
classification and characterization. The reflection power of cross-
and co-polar signals shall be predicted. For this purpose, the Fresnel
reflection coefficients for representative examples of sea ice, sea
water and snow with circular polarizations at L-band are presented
firstly. The simulated polarimetric ratio for satellites observed at
low elevation angle (10°-30°) is then calculated considering sea ice
permittivity and roughness. The potential use of reflected GNSS
signals for sea ice detection is evaluated through ice concentration
measurements. The results show that reflection power loss increases
with the increase of sea ice concentration. In addition, the elevation
angle has little effect on power gain for low elevation angle 10° -
30°
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hesis-Yongchao_Zhu.pdf