Table 1. Freeboard statistics of the study area for each year. 
  
  
  
  
  
  
  
Year Number of shots Mean (16) 
2003 7644 0.46 (+/- 0.37) 
2004 5036 0.47 (+/- 0.39) 
2005 5732 0.36 (H- 0.31) 
2006 5352 0.49 (+/- 0.43) 
2007 6104 0.54 (+/- 0.44) 
2008 1736 0.44 (+/- 0.41) 
2009 1608 0.50 (+/- 0.38) 
0.6 
e 
0.5 d MAE UE & 
& Ye ene oue m 2 
0.4 
® 
E 03 
0.2 
0.1 
0 
2003 2004 2005 2006 2007 2008 2009 
Year 
Figure 5. Mean freeboard (Fb) for the whole study area. 
14 — — M 
  
  
  
  
  
  
  
  
12 = 
9- # TR 
= ü Lg , 
: des set 
es 
= 0.8 
E 
2 
^ 0.6 8 MY 
B “FY 
0.4 des: ud 23 : # 
# Zz A 
0.2 
0 
2003 2004 2005 2006 2007 2008 2009 
Year 
Figure 6. Mean freeboard for multiyear (MY) and firstyear (FY) 
sea ice in McMurdo Sound. 
The methodology so far employed involves assessment of the 
elevation retrievals along track. When assessing smaller 
geographical regions the data scarcity becomes very apparent. 
Here, we filled in these gaps using a Natural Neighbour 
interpolation method to generate freeboard maps of the area. An 
example for 2003 is shown in Figure 7. The accurate 
representation of sea ice areas between  groundtrack 
measurements is a crucial step to developing spaceborne 
assessment of sea ice freeboard. 
588 
  
  
Figure 7. Natural neighbour interpolation of separated multiyear 
(MY) and firstyear (FY) sea ice in McMurdo Sound for 
Sept/Oct/Nov 2003 overlaid upon a mid October 2003 Envisat 
ASAR image. Mean freeboard of MY = 1.1 m, FY = 0.4 m. 
In addition to the freeboard assessment, the Envisat Advanced 
Synthetic Aperture Radar (ASAR) instrument was used to 
investigate changes in MY and FY sea ice extent. ASAR Wide 
Swath imagery from mid October of each year indicates that the 
MY sea ice extent experienced a very large increase in area 
from 2004 to 2005 (Figure 8). A large area of FY sea ice up the 
western coastline persisted through the 2004 melt season into 
2005 increasing the initial area of MY sea ice in 2003 by 254 
%. In the following years this MY sea ice area experienced a 
gradual decline. 
12000 
10000 
8000 
6000 
4000 
2000 
0 Et Mateo RARE DRE E ERR — 
2003 2005 2007 2009 
Year 
—FY 
Area(Km?) 
somme RAY 
  
Figure 8. Multiyear (MY) and firstyear (FY) sea ice extent for 
the mid October period in each year for McMurdo Sound. 
Extensive HL measurements were carried out in November 
2009. By means of differential GPS measurements to remove 
helicopter altitude variations and ground validated air to surface 
laser measurements freeboard was obtained. Two field sites 
from that campaign are within 2km and 100 m of two ICESat 
tracks 15 and 9, respectively. The field measurements are 
temporally separated from their respective ICESat tracks by 
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