A certain circularly scanning radar with a fan beam has a rotation rate of 3 seconds per revolution. The azimuth beam width is \(3^{\circ}\), and the radar uses a PRI of 600 microseconds. The radar pulse width is \(2 \mu\) s and the radar searches a range window that extends from \(15 \mathrm{~km}\) to \(100 \mathrm{~km}\). It is desired that the false alarm rate not be higher than two false alarms per revolution. What is the required probability of false alarm? What is the minimum SNR so that the minimum probability of false alarm can be maintained?