Lo et al : Modeling performance of an airborne lidar survey system for anchovy 



277 



depth and the logarithmic laser energy for 

 both open ocean and coastal waters was 

 obtained (Fig. 8). Calculations of SNR^^ 

 were made at two laser power levels, and 

 logarithmic dependence was used to gen- 

 erate the curves. 



We calculated the maximum penetra- 

 tion depth for the NOAA lidar with a 

 power of 67 mJ and scaled that depth 

 with laser power (Churnside and Hunter, 

 1996; Table 3). For this calculation, we 

 assumed the presence of 10-cm anchovy 

 with a packing density of 0.5/m'^( Table 3). 

 Night flights at 100 m altitude were also 

 assumed. Two water types were used, one 

 typical of open ocean water (Jerlov type 

 IB) and one more typical of coastal water 

 (Jerlov type III) (Jerlov, 1968). 



The NOAA lidar presently in use is 

 capable of operating from a single-engine 

 plane; it weighs about 100 kg, requires less 

 than 1 kW of power, and the cost of its com- 

 ponents is about $50K. The penetration 

 depth for this system under these some- 

 what optimum conditions is estimated to 

 be about 45 m at 67 mJ (Fig. 8). Some cost 

 can be saved by using a lower-power laser 

 and smaller telescope, but not a gi-eat deal. 

 A savings of only about $10Kis likely even if one uses 

 an equivalent energy of 1 mJ. This amount of energy 

 still provides close to 32 m of depth penetration for 

 the conditions assumed in our study. 



On the other end, one can obtain approximately 

 57 m of penetration by using a system with an equiv- 

 alent pulse energy of 100 J (Fig. 8), but such a sys- 

 tem would be a very large and expensive to set up 



and operate. Part of the equivalent energy could be 

 obtained by using a larger telescope at a power only 

 a little over an order of magnitude of that currently 

 used — one that would emit a laser energy of lOJ. This 

 type of laser would require a custom design, with 

 a cost that we estimated to be in the order of one 

 million dollars. In addition, it would require about 

 100 kW of power, which cannot be supplied by a small, 



