Cryospheric Sensing Using GNSS-R - GNSS Remote Sensing: Theory, Methods and Applications - page 256

11.3 Sounding the Sea Ice Conditions

Due to complex and varying conditions of sea ice, e.g. an inaccessible environment
and persistent cloud covering, it is very difficult to monitor sea ice conditions
with conventional instruments. Thus, measuring sea ice conditions mainly relies
on satellite radar techniques. However, no single sensor is capable of providing
the essential range of observations ( Livingstone et al. 1987 ; Rubashkin et al.
2000 ). For example, Synthetic-aperture radar (SAR) images have sufficient spatial
resolution to resolve detailed ice features, but repeat times of existing satellites are
relatively long when compared to the change rate of open water fraction in the
ice pack, although this aspect may be improved with more satellites in the future.
Furthermore, SAR data carry a substantial penalty in cost for image acquisition and
processing. In addition, space-borne passive microwave sensors may provide more
frequent coverage at several wavelengths, but they have substantially lower spatial
resolution. While optical and thermal sensors provide a middle ground in resolution
and temporal sampling between SAR and passive microwave satellites, they are
limited by cloud cover and visibility conditions.
The GPS reflectometry can measure the sea ice conditions as a new technique.
Komjathy et al. ( 2000 ) analyzed the aircraft experiment of GPS reflections from
Arctic sea ice and over the ice pack near Barrow, Alaska, USA. Correlations from
comparisons between RADARSAT backscatter and GPS forward scattered data
indicate that the GPS reflected signals could provide useful information on sea ice
conditions. The reflected signal shape was quite consistent for the moderate altitudes
of the airborne GPS receiver and the peak power changed significantly along the
flight track. This behavior of the reflected signal showed clearly the sensitivity to
ice condition, indicating that the GPS reflected signals can be used to determine the
ice features. In addition, as the effective dielectric constant of ice depends on various
factors, such as the ice composition, density, age, origin, salinity, temperature, mor-
phology ( Shohr 1998 ), the internal ice states can be determined with the reflection
coefficient over a frozen sea surface by the effective dielectric constant of ice and the
dielectric constant of the underlying water under some conditions ( Melling 1998 ).
In the future, GPS reflected signals might provide more detailed information and
internal states of sea ice, including the floe ridges, frost flowers, broken ice, and
fine-scale roughness at the snow-ice interface. Therefore, the reflected GPS signals
have a high potential and applications in sensing and investigating the sea ice state,
particularly for inaccessible and atrocious sea ice cover.

References

Arthern RJ, Winebrenner DP, Vaughan DG (2006) Antarctic snow accumulation mapped
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doi:10.1029/2004JD005667
Cardellach E, Fabra F, Rius A, Pettinato S, D' Addio S (2012) Characterization of dry-
snow sub-structure using GNSS reflected signals. Remote Sens Environ 124:122-134.

doi:10.1016/j.rse.2012.05.012