P £A r AX d an 

 Pr = ^— ^ 1 (6) 



H-n AX f (Yjj, + Yf)m 2 R 2 



where the approximations for Yg, and Yf are Yj, * &l + bj,/6 and 

 Yf a af + bf/1.5. With laser excitation wavelength in the range 

 400 nm ^ Xg, i 650 nm and with X f = 685 nm, the value of Yf is more than 

 2 times the value of Yg, determined from the data taken from Vineyard Sound 

 (ref. 22) and Chesapeake Bay (ref. 23)- The equations given in references 8 

 to 14 for the power received by a laser fluorosensor system range from a factor 

 of 2irm 2 larger to a factor of Yg, less than equation (6). Equation (6) 

 is felt to be the correct representation of the power received, and the concen- 

 tration of chlorophyll a in vivo can be obtained by solving for n in equa- 

 tion (6). Thus, 



n = 



? r ki\ AX f (Y2, + Yf)m 2 R 2 



I (7) 



This is the basic relationship used with all single- and multiple-wavelength 

 laser fluorosensor systems for determination of chlorophyll a in vivo 

 concentrations. 



SINGLE-WAVELENGTH LASER FLUOROSENSOR SYSTEMS 



The first laboratory tests involving laser-induced fluorescence of algae 

 were conducted by Hickman and Moore (ref. 9) in 1970 using a nitrogen laser 

 operating at 337 nm and two algal species, Anacystis nidulans (a blue-green 

 algae) and Chlorella pyrenoidosa (a green algae). The fluorescence of chloro- 

 phyll a contained in the algae was detected at 680 nm. Laboratory experiments 

 revealed that laser-induced fluorescence from a chlorophyll a concentration of 

 6 ug/liter which was contained in Anacystis nidulans was remotely detectable 

 from less than 1 m. Projections of these measurements suggested that an air- 

 borne laser/receiver system could detect these same concentrations of chloro- 

 phyll a in vivo from a distance of 100 m. Friedman and Hickman (ref. 10) were 

 the first to state that various algal species could be identified by detection 

 of their fluorescence signatures using a tunable laser as the excitation 

 source. They concluded that if only chlorophyll a in vivo is of interest, the 

 optimum excitation wavelength is 600 ±50 nm and the optimum detection wave- 

 length is 685 nm. Measurement of concentrations as low as 1 ug/ liter for 

 chlorophyll a in vivo from a distance of 500 m using a 100-kW peak power laser 

 was calculated to be feasible. 



The first field test of a single-wavelength laser system for the detection 

 of chlorophyll a contained in algae was conducted in December of 1971 by Mumola 

 and Kim (ref. 11) from a fixed platform on the Thimble Shoals Channel Pier of 

 the Chesapeake Bay Bridge Tunnel. A coaxial, flash-lamp-pumped, rhodamine 6G 

 dye laser was used as the excitation source, and a 15-cm-diameter telescope, 



11 



