3. A downward-pointing very-near infrared laser is fired from a satellite and the beam comes
into contact with a horizontally uniform cloud. On entering the cloud, the radiance of the
beam is $L_0$. Inside the cloud, the beam is attenuated by scattering and absorption such that 10
m into the cloud, the radiance of the beam is 50% of $L_0$. If the cloud is 30 m thick, what is
the radiance of the beam when it emerges from the bottom of the cloud? Justify any
assumptions you make.
[20 marks]