This limit of detectability occurs where the VIL signal starts to increase with range around bin 250. The large increase in the signal around the range bin 500 was the result of radiation backscattered from a cirrus cloud. To remove the noise dominated points, the points where the raw signal was within the noise regime had to be determined. At far ranges, the raw backscattered signal becomes linear with range when the backscattered power is plotted on a natural log scale. This was a result of both the attenuation of the transmitted pulse in the atmosphere and the range squared decrease of the signal.
Shot noise occurs along with the raw signal.
If the shot noise was random, as expected, then the noise should occur as a Gaussian distribution about the raw data. This would not affect the slope of the VIL data with range in Figure 15 . This process was applied to each VIL raw profile where the VIL backscatter signal was sorted according to their magnitudes. The sorted values were approximated using a straight line median fit. The straight line median fit was first applied to the whole sorted profile.