The PRT-5 was piloted by the author in a NMFS twin- 
engine aircraft over the survey flight track (Fig. 1) at ele- 
vations between 152 and 304 m (500 and 1,000 ft). Low 
stratus bases at 243 and 304 m (800 to 1,000 ft) common 
to the coastal areas were encountered on most flights 
during the 3-yr period. On numerous occasions, flights 
were rescheduled due to very low stratus or fog condi- 
tions. Only on rare occasions was there an absence of 
haze or low stratus, middle and high clouds, the type of 
conditions that would allow direct comparison of satellite 
data with the low altitude temperature surveys. 
Calibration measurements, or “ground truth,” were 
obtained from surface sources for each flight either from 
observations taken at the end of the Scripps Institution 
of Oceanography pier, La Jolla, Calif., or from the U.S. 
Naval Undersea Center’s (NUC) oceanographic tower 
located approximately 2.8 km (1% n.mi.) off Mission 
Beach, San Diego, Calif. Most comparative obser- 
vations were taken over the oceanographic tower as it is 
located offshore, and the temperature of surrounding sur- 
face waters are relatively stable when compared with 
those near the outer surf zone at Scripps pier. Simul- 
taneous sea surface temperature observations were made 
with either a surface bucket thermometer off Scripps 
pier, or a surface thermistor temperature reading from 
the NUC oceanographic tower. To obtain a comparative 
reading, the aircraft was flown over the pier or tower at 
an elevation of about 45.7 m (150 ft). At the moment the 
aircraft passed over the pier or tower, the radiative sur- 
face of the structures, being much warmer than the sea 
surface, would produce a response from the infrared 
detector to make a synchronous mark on the tempera- 
ture analog recorder chart. The analog recorder chart was 
driven at a speed of 2.54 cm (1 in) per minute. 
The temperature analog chart was keyed to the 
“ground truth’? temperature measurement, and the 
chart was read to determine a 1-min average tempera- 
ture, with a slide rule averaging readout device 
developed by the author (Squire 1971). The 1-min tem- 
perature averages were plotted on the flight track, and 
1°F (0.56°C) isotherms were contoured from the data. 
The weekly isotherm charts were given limited distribu- 
tion to a list of interested fishing and scientific organiza- 
tions and their personnel. 
Isotherm charts are shown in the Appendix for all sur- 
veys in 1972, 1973, and 1974 (1972, Figs. 1-28; 1973, Figs. 
29-61; 1974, Figs. 62-90). For conversion of °F to °C see 
comparative temperature data on each figure. 
RESULTS 
Isotherm charts were developed for each of the 90 
survey flights. Distribution of survey flight effort by 
month for the 3-yr period is as follows: 
Month Flights 
April 12 
May 13 
June 10 
July lO 
August 14 
September 12 
October 14 
June has the least number (10) of flights during the 
survey period, reflecting the problems of conducting 
aerial surveys during a period when persistent low stratus 
is most present over the coastal waters off San Diego. 
The general trend of sea surface temperature during 
the 3-yr period showed that 1973 was cooler than 1972, 
which was an “E] Nifio” year with above-normal warm- 
ing along the west coast of North and South America 
(Miller and Laurs 1975). Temperatures in 1974 were 
warmer than those observed in 1973, but not as warm as 
those experienced in 1972. However, in 1974, an 
anomalous warming period occurred in early July off 
southern California, and the highest temperatures were 
recorded at that time. Examples of isotherm patterns ob- 
served during surveys having the lowest average tem- 
perature (2 April 1973) and the highest average tem- 
perature (19 July 1974) are shown in the Appendix, 
Figures 31 and 76. 
Semimonthly isotherm charts of the northeastern 
Pacific, developed from ship data, are issued by the 
NMFS Southwest Fisheries Center. To develop data for 
comparative purposes, weekly temperatures were then 
averaged by semimonthly periods for each month, 1 
through 15 days and 16 through 30/31 days, for the 3 yr of 
data from temperatures observed at locations along the 
survey flight track, as shown in Figure 1. Isotherm charts 
in 1°F with °C equivalents drawn to these semimonthly 
data are presented in Figures 2 to 15. 
The only time series of infrared sea surface tempera- 
ture data available for comparison with the 1972 to 1974 
data off San Diego is the 1963-68 data resulting from the 
cooperative program with the U.S. Coast Guard. During 
these surveys, ground truth calibration checks were also 
made over the NUC oceanographic tower. Comparing 
1963-68 monthly average temperatures (to the nearest 
whole °F) for the area off Mission Beach (NUC tower 
area) with those observed in the same location during the 
1972-74 surveys, we note an average difference of less 
than 1°F (0.56°C). The average temperature for 1963-68 
was 63.4°F (17.4°C) and for 1972-74 was 64.1°F (17.8°C). 
Average monthly temperatures rounded to the nearest °F 
for the 3-yr period were observed (Table 1) to be the same 
for April, warmer 2°F (1.12°C) for May, 3°F (1.68°C) for 
June, 1°F (0.56°C) for July, the same for August, 1°F 
(0.56°C) less for September, and 2°F (1.12°C) less for 
October. 
A general description of sea surface temperature pat- 
terns that would be typical of those usually observed off 
San Diego during the weekly surveys is as follows: Tem- 
peratures that are greater than any other locations in the 
survey area are usually found north offshore and to the 
northwest of La Jolla. From off La Jolla Point to Pacific 
Beach and continuing southwest and offshore to the 
southwest is an area of upwelling with generally lower 
temperatures than those to the north. Evidences of this 
