An Aerial Study of Hawaiian Wave Patterns 
K. O Emery 1 
Most of us who have had some experience at 
sea on small power or sailing boats have noted 
that the sea surface is crossed by usually more 
than a single train or set of waves. Each train 
can be identified by its direction, period, and 
height. Sometimes one train is so dominant that 
others may not be noticed. The Marshall Is- 
landers of the nineteenth century and earlier, 
past masters in the art of handling small boats, 
used wave trains as a navigational aid with their 
famous stick charts. The dominant train of 
waves, produced by the trade winds, was desig- 
nated by long parallel sticks tied to a rigid 
frame. Trains of smaller waves, some produced 
by bending around islands, were shown by small 
sticks attached at angles to the long ones. A brief 
review of these maps and of pertinent literature 
was given by Emery, Tracey, and Ladd ( 1954: 5). 
A better platform than a boat for mapping 
waves is an airplane because of its wider field 
of view and greater speed. The greater speed 
permits observations to be made at many points 
in an area during a period short enough to re- 
duce the effect of changes in winds. The first 
such wave maps made by aerial observation were 
for the sea off southern California in 1957-58 
(Emery, 1958). Each of four surveys at 3-month 
intervals exhibited three or four trains of waves, 
greatly complicating the identification of waves 
refracted or reflected by the island or mainland 
shores. In order to simplify the analysis it is 
necessary to study an area having only a single 
wave train. The Hawaiian Islands were thought 
to constitute such an area because they lie 
within the belt of trade winds, especially during 
summer. An opportunity for study there was 
provided by the convening of the Tenth Pacific 
Science Congress at Honolulu during the latter 
half of August, 1961. 
1 University of Southern California, Los Angeles 7, 
California. Now: Woods Hole Oceanographic Insti- 
tution, Woods Hole, Mass. 
Manuscript received January 10, 1962. 
Through the interest of the Office of Naval 
Research, flight facilities were made available by 
Fleet Air Wing Two, Naval Air Station, Barbers 
Point, Oahu. The aircraft was a Neptune (P2V), 
having a bombardier station with excellent visi- 
bility. Acting as recorders and photographers 
during one flight were Charles G. Johnson (U.S. 
Geological Survey) and Charles Roberts (U.S. 
Weather Bureau); and during the other flight 
Robert S. Dietz (U.S. Navy Electronics Labora- 
tory) and Joe S. Creager (University of Wash- 
ington). Appreciation is also due Doak C Cox 
(University of Hawaii) and Saul Price (U.S. 
Weather Bureau, Honolulu) for their critical 
reading of the manuscript. 
METHODS 
Flights were made on 31 August (1000-1700, 
local time) and 1 September (0800-1430). They 
covered a total distance of 4200 km at an alti- 
tude of 500 m. A total of 375 observation points 
were occupied at 2 -min intervals. Positions of 
the aircraft were based upon fixes at 10-20~min 
intervals using loran, radar, and visual methods. 
Observation was purely visual, although some 
photographs were taken for illustrative purposes. 
A specially devised peloras was held with the 
aircrafts true compass heading set on the disk 
in a fore-and-aft direction. Moveable arms piv- 
oted at the center of the disk were set parallel 
to the crests of separate wave trains, requiring 
constant visual checking and readjustment. At 
2 -min intervals the recorder noted the azimuth 
indicated by each arm. Comparison of results 
obtained at different headings of the aircraft 
indicate that the azimuths are correct within 
10°. Estimation of the azimuth of the crests of 
each wave train usually required viewing in a 
particular direction because the waves were most 
dearly seen when viewed away from the sun at 
a horizontal angle of about 45° to the wave 
crests and at a downward angle of 15 to 45°. 
Sometimes about 10 sec of viewing was required 
255 
