Cryospheric Sensing Using GNSS-R - GNSS Remote Sensing: Theory, Methods and Applications - page 248

Chapter 11
Cryospheric Sensing Using GNSS-R

11.1 Dry Snow Monitoring

When ice entirely retains sub-freezing temperatures and no melting occurs it is
called dry snow. Its density is very low, and L-band signals can penetrate a few
hundreds of meters of snow depth. Dry snow zones occur within the interior regions
of the Greenland and Antarctica ice sheets, where total ice depth can be of a few
kilometers. The deeper the layer of snow, the older its age. The snow layers, down
to where L-band signals can penetrate, correspond to the snow accumulated in the
last a few thousands of years (e.g. Spikes et al. 2004 ; Arthern et al. 2006 ; Fujita et al.
2011 ) (it depends on the actual time series of accumulation rates and snow vertical
profile of density). Understanding the climatology of these regions is important to
understand how these ice sheets might respond to climate change. In particular,
better maps of snow accumulation are needed to understand and predict ongoing
changes in the size of the Antarctic ice sheet (e.g. Wingham et al. 1998 ), important
in driving global sea level (e.g. Church et al. 2001 ). These regions would be densely
sampled by a potential future GNSS-R space-based mission in a polar orbit ( Fabra
2013 ).
A GNSS-R experiment was conducted at Dome Concordia, Antarctica, taking
data during 12 days in December 2009. Two GNSS antennas were deployed: a
zenith-looking Right-Hand Circular Polarized (RHCP) antenna for geodetic posi-
tioning, and a dual-polarized (RHCP + LHCP) horizon-looking antenna to collect
the signals reflected off the snow. The system was mounted on top of the 45 m
high American Tower, and connected to a dedicated GNSS-R receiver (GOLD-RTR
( Nogués-Correig et al. 2007 )), and pointing over a pristine snow area of flat and
smooth surface. Details of the set-up can be found in Cardellach et al. ( 2012 ) and
Fabra ( 2013 ).
The experimental work concluded that

￿ L-band GNSS signals penetrate into dry snow down to 200-300 m depth;

￿ The signals reflected off these smooth surfaces have long coherence times;