Geoscience Reference
In-Depth Information
Table 3 Standard deviation and average difference of dynamic tie points
Surface type
19 GHz H (K)
19 GHz V (K)
37 GHz V (K)
T
B
;
diff
T
B
;
std
T
B
;
diff
T
B
;
std
T
B
;
diff
T
B
;
std
OW
0.53
2.47
1.60
1.30
1.23
1.12
−
MYI
2.56
4.65
−
2.50
3.71
−
0.36
5.60
FYI
2.11
2.62
0.86
2.80
0.74
3.53
−
−
T
B
;
fix
;
T
B
;
diff
¼
avg T
B
;
dyn
ð
5
Þ
where T
B
;
dyn
fixed tie point.
Table
3
lists the standard deviation and average difference of all the dynamic tie
points in winters from 1998 to 2007. It shows that the average difference T
B
;
diff
between the average dynamic tie point T
B
;
dyn
and the
is the dynamic tie point, T
B
;
fix
is the
fixed tie point T
B
;
fix
for open
water at 19 and 37 GHz V is larger than one standard deviation, which means tie
points for open water at the two channels are not well estimated. Among all the tie
points, those for multiyear ice are most unstable. For
first year ice and multiyear ice,
the average difference T
B
;
diff
is smaller than T
B
;
std
in all channels, which means tie
points for
first year ice and multiyear ice are estimated well.
In order to evaluate the sensitivity of ice concentrations to changes in the tie
points, we de
ne two parameters, the
first one is
avg
ð
C
MY
þ
C
MY
Þ
2
C
SEN1
¼
;
ð
6
Þ
this is half of the average change of ice concentration if two modi
ed sets of tie
points are used, where C
MY
þ
and C
MY
are the multiyear ice concentration retrieved
with the tie points increased and decreased by one standard deviation respectively.
For three used channels and three surface types, this results in nine sensitivity
parameters C
SEN1
given in Table
4
. There, in addition the sensitivity C
SEN2
is given,
C
SEN2
¼
C
SEN1
T
B
;
diff
=
T
B
;
std
;
ð
7
Þ
which describes the difference of multiyear ice concentration caused by the
difference of tie points.
Table 4 Sensitivity parameters of the dynamic tie points
Surface type
19 GHz H (%)
19 GHz V (%)
37 GHz V (%)
C
SEN1
C
SEN2
C
SEN1
C
SEN2
C
SEN1
C
SEN2
OW
0.027
0.006
0.26
0.32
0.07
0.08
−
MYI
0.26
0.14
2.46
1.66
1.48
0.10
−
−
FYI
0.39
−
0.31
−
6.32
1.94
2.94
0.61
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