32a are caused by an opaque target referring to fig1 a as missile 10 approaches target 28 windown 26 will contact target 28 when this initial contact occurs radiation will be reflected from target 28 down field of view 22 to receiver 14 and signal 30a will increase above the threshold level as target 28 enters deeper into window 26 the amount of reflected radiation picked up by detector 14 will increase with signal 30 coinciding with this increase as window 26 passes through target 28 the amount of reflected radiation picked up by receiver 14 is greatly reduced until the detected radiation is minimal corresponding to this event signal 30a also declines until it is below threshold when window 26 passes completely through target 28 and no reflected radiation is picked up by receiver 14 window 24 will contact target 28 a signal 32a identical to signal 30a now occurs increasing as target 28 enters further into window 24 and decreasing as window 24 passes through target 28 until signal 32a also drops below threshold level this is the signature for an opaque target with signal 30a dropping below threshold level before signal 32a increases above threshold level in fig3 signal 30b and 32b are caused by an aerosol referring to fig1 b as missile 10 approaches the aerosol window 26 contacts the leading edge 34 of the aerosol and reflected radiation 18 begins to be received by receiver 14 causing 30b to increase above threshold.