Zimmermann and Rooper: Comparison of echogram measurements for distinguishing seafloor substrates 
299 
F V Gladiator 2003 shallow 
to 
E c 
2 <D 
g> I 
LU 03 
Cl) 
E 
FV Gladiator 2003 deep 
0.090 
0.080 
0.070 
0.060 
0.050 
0.040 
0.030 
0,020 
0.010 
0.000 
100 120 
140 160 180 
200 
RV Resolution 2003 
RV Pallasi 2004 
RV Rangithi 1 999 
RV John P. Tully 2002 
0.180 
0.160 
0.140 
0.120 
0.100 
0 080 
0.060 
0.040 
0 020 
0.000 
60 80 100 120 140 
Figure 3 
Significant relationships between QTC (Quester Tangent Corporation, Sidney, British Columbia, 
Canada) IMPACT™ generated echogram measurements and depth for the shallow and deep FV 
Gladiator 2003 data sets, the RV Resolution 2003 cruise, the C.C.G.S. RV John P. Tully 2002 
cruise, the RV Pallasi 2004 cruise, and the RV Rangithi 1999 cruise. Note the different scales 
on the x axes. 
division by standard deviation; Manly, 1994; Legen- 
dre and Legendre, 1998) revealed that more PCs were 
required to explain the same total amount of variance 
as the QTC IMPACT PCA method (Fig. 5). Thus the 
lack of standardization within the QTC IMPACT PCA 
method can have a strong effect. For example, across 
all six data sets, some EMs such as EM 15 were always 
large (>0.938), some such as EM 166 were always small 
(<0.006), and some such as EMs 1 and 102 generally had 
larger ranges and were more variable. Within the first 
group of EMs (1-23), EM 1 was always < EM 2, EM 2 
was always < EM 3, etc., up to EM 16, which was always 
> EM 17, which was always > EM 18, etc., up to EM 23. 
Thus these variables have constricted ranges which can 
affect PCA. Additionally, the strong correlations between 
neighboring variables within the first. (EMs 1-23) and 
fifth (EMs 102-166) groups indicate that these EMs 
are either measuring nearly the same echo component, 
