MOLECULAR NITROGEN FLUORESCENCE LIDAR FOR REMOTE-SENSING OF THE AURORAL IONOSPHERE

We describe two types of molecular nitrogen fluorescence lidars which can be used to determine excited or ionized nitrogen density in the io nosphere during moderate or strong aurora. The lidars excite nitrogen already excited or ionized through impact with high-energy auroral ele ctrons. Several different configurations are considered for both types of lidar. The first type of lidar is a conventional fluorescence lida r which operates in the first postive system (N-2(A(3) Sigma(u)(+))--> N-2(B-3 Pi(g))) or the first negative system (N-2(+)(X(2) Sigma(g)(+)) -->N-2(+)(B-2 Sigma(u)(+))). Several different lasers are considered. The choice of laser determines the bands for excitation and fluorescen ce. The second type of lidar first pumps excited N-2 to a higher energ y state and then-does conventional fluorescence lidar on that state. T his lidar utilizes two lasers. The first laser, the pump, operates in the first positive system. The second laser, the probe, operates in th e second positive system (N-2(B-3 Pi(g))-->N-2(C-3 Pi(u))). Both lidar s are described in detail and results of signal to noise calculations are performed using reasonable system parameters.