Raman Lidar for Boundary-layer temperature profiling

The atmospheric boundary layer (ABL) is the layer of air which is directly affected by the Earth's surface and generally is between 100 metres to 3 kilometres high. It is therefore very important to understand how it develops as it will contain and chemically process all pollutants emitted in to it. Certain processes are known to occur whereby air masses can be lifted above the ABL and transported to remote locations. Here they can be mixed back in to the ABL and affect the pollutant concentration a long way downstream (in some cases several hundred miles). One type of ABL is known as the nocturnal boundary layer (NBL) which as its name suggests takes place during the night. In the NBL, temperature profiles are important as they determine the stability. It is this stability that affects the way the NBL develops which could include fog formation, mixing in of previously polluted air. The research suggested in this proposal will help understand the processes involved in the formation of these events which may ultimately lead to more accurate weather or pollution forecasts. To observe these temperature profiles it is possible to use weather balloons, but to routinely observe the temperature of the boundary layer this would be prohibitively expensive. A different technology can therefore be used to measure the temperature of the atmosphere with a high enough time resolution to observe mixing processes. This remote sensing technique is known as LIDAR (LIght Detection And Ranging) and it can be used to remotely measure properties of the atmosphere by probing it with light. Lidar can be used to measure trace gases like ozone, sulphur-dioxide and water vapour as well as physical properties of the atmosphere like wind, humidity and temperature. A lidar system is therefore proposed that will be able to measure the evolution of boundary layer temperature profiles during the development of the nocturnal boundary layer. The project will involve testing the technology to measure temperature profiles using a pre-existing lidar system which will be modified. This will result in the design of a compact and low power consumption lidar that can be used in field experiments to measure the NBL. The lidar system will use a new diode pumped solid state laser which will ultimately allow a higher time resolution of temperature profiles compared to traditional power hungry pulsed laser.