24 
TECHNICAL SURVEY 
100 
80 
Gi 
iGO 
iS 
E 
x= 
oO 
w 40 
= 1900 1715 
20 MARCH 1945 2 MARCH 1945 
: ee 
WATER SURFACE WATER SURFACE 
O L_ 0 = e 
340 350 360 370 380 390 400 340 350 360 370 380 390 
Ficure 11. M curves over the ocean at Antigua, British West Indies. 
much as 20 units or even more. 
The curves of Figure 6 were taken at Taboga 
Island, some 15 miles south of Balboa, at the eastern 
entrance to the Panama Canal. They show various 
familiar types of duets; two of the curves represent 
transitional cases where the M curve is steeper than 
standard but does not bend backward. 
Figure 7 illustrates the typical elevated duct found 
in the San Diego region. Both below and above the 
inversion region the M curve is standard. The various 
curves shown were measured at several distances on 
a flight from San Diego outward. 
Figure 8 is a set of M curves that were measured 
on the east coast of New Zealand, at a point some 
100 miles south of Cook Strait.??* These curves 
provide good examples of the type of M curves that 
consist of several very nearly linear sections. 
Figure 9 shows two soundings from the tropical 
Western Pacific. The curve at the left was taken at 
Biak Island, New Guinea, and is remarkable for the 
presence of two ducts, a ground-yased and an 
elevated one, The curve at the right was taken 
at Saipan. : 
Figure 10, taken near New Guinea, shows in more 
detail the structure of the low maritime duct which 
in this case is only about 30 ft high.? This type of 
duct has been studied carefully in the transmission 
experiments at Antigua in the West Indies which 
are reported in Chapter 4. Two typical soundings 
taken near Antigua are reproduced in Figure 11.1% 
