KEMMERER ET AL.; ERTS-I MENHADEN EXPERIMENT 



the study area. A comprehensive description of 

 the area is given by Christmas (1973). 



The target fish species for the study was the 

 small (mean weight about 85 g), herringlike, 

 surface-schooHng Gulf menhaden (Brevoortia 

 patronus). These fish occur along the Gulf of 

 Mexico coast and are considered to be an estua- 

 rine-dependent species. They are used com- 

 mercially as a source of fish meal, oil, and con- 

 densed soluble proteins. In the Mississippi Sound, 

 menhaden are fished from about mid-April to 

 October by twin purse seine boats assisted by 

 spotter pilots flying light aircraft. The spotter 

 pilots direct the purse boats to the menhaden and 

 then through radios notify the boat captains when 

 to encircle a school with their purse seine. Once 

 a school is captured and concentrated in the net, 

 a larger mother or carrier vessel is brought along- 

 side and the fish are pumped into the hold of the 



ship. 



Menhaden are plankton feeders using a sieve- 

 like branchial apparatus to strain plants and 

 animals from the water (Reintjes, 1969). Their 

 characteristic schooling behavior, which seems 

 innate from late larval stage to old age, makes 

 them particularly available to commercial 

 fishing. School size varies from about 25 to in 

 excess of 2,000 m^ (surface area) and averages 

 about 125 m^. Although Gulf menhaden have been 

 the subject of many investigations (Christmas 

 and Gunter, 1960; Gunter and Christmas, 1960; 

 Reintjes, Christmas, and Collins, 1960; and 

 Rounsefell, 1954), little is known about their 

 distribution in relation to environmental para- 

 meters. 



DATA ACQUISITION 



Data acquisition events were divided into four 

 operations categories: main day, secondary day, 

 special purpose, and commercial fishing oper- 

 ations. Main day activities occurred at or near the 

 time of selected ERTS-1 overpasses (7 August, 

 25 August, and 28 September 1972) and included 

 an intensive sea-truth sampling effort-up to 

 144 stations were occupied. Only a few sea-truth 

 stations were occupied during secondary day 

 missions, which were conducted weekly, weather 

 permitting, to record temporal environmental and 

 fishery changes. Special purpose missions were 

 designed to satisfy limited objectives and as such 

 did not follow set schedules. Oceanographic and 

 fisheries data were obtained from one to three 



commercial fishing vessels, usually on three days 

 of each week, June through September 1972. 



ERTS-1 and Aircraft 

 Environmental Sensors 



A number of oceanographic parameter sensors 

 were used during the experiment from NP3A 

 (NASA) and D18 Beechcraft'' (NASA/ERL) air- 

 craft at altitudes ranging from 610 to 7,620 m. The 

 sensors included a RC 8 camera, RS-14 scanner, 

 PRT-5 radiation thermometer. KA 62 multiband 

 camera, Hasselblad EL-500 cameras, RS-18 

 thermal IR scanner, multifrequency microwave 

 radiometer, and an Exotech spectroradiometer. 

 The sensors were configured to measure sea- 

 surface temperature, water color as a function of 

 wavelength, surface current patterns, surface 

 salinity, and surface turbidity patterns. 



The ERTS-1 satellite, launched on 23 July 

 1972, operates in a circular sun-synchronous 

 near polar orbit at an altitude of 915 km. It circles 

 the earth every 103 min, completing 14 orbits per 

 day and providing repetitive coverage of specific 

 areas every 18 d. Two consecutive orbits, 24 h 

 apart, are required for complete coverage of the 

 study area. 



The only environmental sensor aboard the satel- 

 lite operating during the study was a multispec- 

 tral scanner (MSS) which provided images in four 

 discrete portions of the light spectrum (Freden, 

 1972): Band 4, 0.5-0.6 micron; Band 5, 0.6-0.7 

 micron; Band 6, 0.7-0.8 micron; and Band 7, 0.8- 

 1.1 microns. 



Sea-Truth Oceanographic Parameter 

 Measurements 



Sea-truth measurements during main day data 

 acquisition events were taken from 25 research 

 boats. Because two orbits 24 h apart of ERTS-1 

 were required for complete coverage of the study 

 area, only about half of these measurements coin- 

 cided with the passage of the satellite. On 7 and 

 25 August 1972, coincidental measurements oc- 

 curred for the western portion of the study area, 

 resulting in a 24-h difference for measurements 

 from the eastern portion. A main day occurred on 

 28 September 1972, which did not correspond to 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



377 



