Problem
1. A focal plane array has 1024 x 1024 pixels with a pitch of 4.3 microns. Design a system that can identify a person and a tank 5 km. The system should also be able to detect a tank at 15 km. To identify a person or tank it take 7 line pairs. Assume that the person is 2 m tall by 1.5 m wide and the tank body is 4m long and 2 meters tall and the main gun projects an additional 2 meters past the body and has a width of 0.5m. To identify the tank, you need to see what kind of barrel is on the tank.
2. You are now asked to design a range finder that can determine the range to the target. Assume that the tank's total hemispherical reflectivity is 20% and the person's total hemispherical reflectivity is 4%. The largest the output beam can be exiting the final aperture of the coaxial transmitter/receiver is 300 mm. The source you are told to use is a 3 W (M2 = 1.5) Nd:Yag laser. (Is this laser powerful enough?) The best transmission you can have through an optic is 98 %. The min detectivity of your detector is 20 pW over the .049 mm2 area of the InGaAs detector. The detector saturates at 60 pW over the same area. (Assume that the inputted wavefront of the Gaussian propagating laser beam is a plane wave. (This puts requirements on the f# of the final lens in the receiver) Assume that the transmission of the air to and from the stationary target is 93%. Sketch the system labeling all the components of the range finder.
Is the beam diverging or collimated leaving the exit aperture of the system? What is the efficiency of your transmitter? (You may assume that the laser is polarized in the transmitting path.)
What is the transmission of the receiver path? Why can't the receiver efficiency be greater than 50% on the receiver path?