Sea Surface Temperature Distributions Obtained 
Off San Diego, California, Using an Airborne 
Infrared Radiometer 
JAMES L. SQUIRE, JR.’ 
ABSTRACT 
Sea surface temperature surveys were conducted weekly off San Diego, Calif., using an airborne 
infrared radiometer during the months of April through October 1972-74. A total of 90 surveys were 
made over the 320-mile flight track. The analog chart record of temperature was keyed to a ‘‘ground 
truth’? temperature measurement and read to determine 1 min average temperatures which were 
plotted on the flight track and 1°F (0.56°C) isotherms were contoured from the data. The trend of sea 
surface temperatures during the 3-yr period showed warmer temperatures in 1972, which was an ‘‘El 
Nino”’ year, cooler in 1973, warmer than 1973 in 1974, but not as warm as 1972. In early July 1974, an 
anomalous warming period occurred and highest average temperatures of 73°F (22.7°C) were record- 
ed in 19 July 1974. Lowest average temperature of 54°F (12.2°C) was recorded on 2 April 1973. 
The 1972-74 survey temperatures taken over the ‘‘ground truth”’ calibration site were compared 
with a time series of temperature observations taken during the same months from 1963 to 1968. The 
average temperature during 1963-68 was 63.4°F (17.4°C) and for 1972-74, 64.1°F (17.8°C), a difference 
of less than 1°F (0.56°C). Average monthly temperature differences, 1963-68 compared with 1972-74, 
shows April the same, warmer 2°F (1.12°C) for May, 3°F (1.68°C) for June, 1°F (0.56°C) for July, same 
for August, 1°F (0.56°C) less for September, and 2°F (1.12°C) less for October. 
INTRODUCTION 
Synoptic sea surface temperature surveys with an air- 
borne infrared radiometer were first conducted off the 
Pacific coast in August 1963 over the coastal waters of 
Washington, Oregon, and California by the National 
Marine Fisheries Service’s (NMFS) Tiburon Fisheries 
Laboratory at Tiburon, Calif. Surveys over three areas 
were conducted in cooperation with the U.S. Coast 
Guard, and these surveys are being continued as part of 
the U.S. Coast Guard oceanographic program. The first 5 
yr of surveys (1963-68) were reviewed by the author 
(Squire 1971). The objective of the coastal program was 
to increase the general knowledge about the nearshore 
temperature structure, to define areas of nearshore up- 
welling, and to develop temperature data that may be 
useful in relating the distribution and relative abun- 
dance of major coastal species of fishes to sea surface 
temperature and its changes. 
The initial surveys, conducted monthly, were broad in 
geographical scope and in time. The data have been use- 
ful in computing average catch temperatures for salmon 
off central California, and for a number of pelagic species 
common to southern California waters (Squire unpubl. 
manuscr.). However, this broad-based survey did not 
cover some of the more important coastal fishing areas in 
Southwest Fisheries Center La Jolla Laboratory, National Marine 
Fisheries Service, NOAA, La Jolla, CA 92038. 
sufficient detail and at short enough time intervals to 
permit the determination of the relation of changes in 
catch composition and catch rates to short-term tem- 
perature fluctuations. 
To determine short-term temperature effects, an area 
having a heavy amount of fishing effort and catch was 
selected for detailed study. This area covered the 
southern California coastal waters from near Del Mar, 
Calif., to south of the United States-Mexico border, and 
to about 22.3 km (12 n.mi.) offshore. The area, known by 
the project name of ‘“‘San Diego Test Area’ encompasses 
the major sportfishing grounds off La Jolla, Point Loma, 
and about the Coronado Islands off Mexico. 
The airborne temperature surveys used a “‘ladder- 
type” search pattern, modified to accommodate navi- 
gational aids. These surveys were flown once each week, 
1 April through 31 October during 1972 to 1974. A total of 
90 surveys was made, each requiring about 2 h to com- 
plete. 
OPERATIONAL PROCEDURES 
The airborne sea surface temperature sensing unit 
used in the study was a Barnes research radiometer 
(PRT-5) modified with a special lens filter system to 
restrict the viewing range in the infrared spectrum to 
10.5 to 12.5 nm. This spectral range approximates the 
infrared range that is used in the ITOS (NOAA, National 
Environmental Satellite Service) series weather satellite. 
