During the second field program of the Montreal Experiment on Regional Mixing and Ozone (MERMOZ-II), the Climate and Atmospheric Research Directorate (CARD) of AES deployed a 915 MHz wind profiling radar and a 1064 nm Nd:YAG lidar at a farm in St Polycarpe, PQ. Both instruments were used to monitor the daily evolution of the planetary boundary layer. One objective of the project was to compare the rather different ways of remotely sensing the convective boundary layer depth; the lidar measures constituents whereas the radar measures a combination of turbulence and gradients. Since the two instruments each produce many megabytes of data per day, automated extraction of the boundary layer depth has been undertaken.
The two week project provided a variety of boundary layer evolutions, varying from almost textbook days, to exceedingly complicated ones. Results show that the lidar and radar measurements of the boundary layer depth agree well when the term "boundary layer depth" has a clear meaning, especially during the morning evolution from the nocturnal boundary layer. Later in the day, when stronger convection sets in, the boundary layer depth, at least over a single point at a single time, is difficult to define. The lidar tends to do better in this situation, at least until clouds start to form.
In terms of automating the boundary layer depth estimation, techniques looking for maxima and maximum gradients were examined. As other investigators have seen both have advantages for the radar, but the critical factor is using temporal continuity to prevent the algorithms from following random short term features. Even with this there is some tendency for the lidar algorithm to pick up on residual layers if not given some guidance about where to look.