A new Doppler lidar system has been developed to meet the requirements of unattended and autonomous operation. The University of Salford specification required a Doppler lidar system capable of providing high temporal (0.1 – 1.0 second) and spatial resolution (length scales of order 30 m) measurements of the wind velocity and backscatter within the atmospheric boundary layer. The system was required to be portable and rugged and capable of being used for field work and long term measurements. Eye safety and a minimum range of approximately 50m were required in order to facilitate measurements in complex urban environments.

The Salford Autonomous Lidar System (SALiS), operating at a wavelength of 1.5 microns, employs novel optical technology and the design approach has led to a new type of eye-safe Doppler lidar (class 1 or 1M) providing a high level of performance and exhibiting exceptional stability. The system has a modular design arranged in three separate units; the optical base unit, the weather-proof antenna and the signal processing and data acquisition unit. The base unit has approximate dimensions 56 cm x 54 cm x 18 cm and contains the optical source, interferometer, receiver and electronics. The weather-proof antenna is attached to the base unit via an umbilical. The antenna can be deployed permanently outside whilst the base unit and data acquisition system are housed within a laboratory environment. The signal processing has been developed with a view to providing a high level of flexibility with respect to the data acquisition parameters. Users are able to set parameters such as the length of the range gate, maximum range and number of pulses accumulated for each measurement and the spectral resolution. Some lidar system parameters are listed below. The lidar system also has the capability to perform diagnostic tests in order to monitor and log the status of the system.

Operating wavelength: 1.5 microns

Range gate length: User selectable typically 30 m

Minimum range: 30 m

Maximum range: 7 km

Temporal resolution: User selectable: typically 0.1 – 30 s

To fully test the Doppler lidar system and evaluate the system's performance and autonomous measurement capabilities the system will be involved in the international mesoscale meteorology research project – The Helsinki Testbed. The testbed is a collaboration between the Finnish Meteorological Institute (FMI) and the Vaisala meteorological measurements company together with other public, private and academic partners. The testbed will provide the opportunity for measuring, studying and predicting atmospheric processes and applications and seeks to enable and promote testing of new measurement systems. The testbed is located in and around Helsinki, Finland and is operational between January 2005 and September 2007. As well as long term measurements several intensive measurement campaigns will take place. Instrumentation sited at various locations in and around Helsinki includes nearly 300 surface weather stations, 5 optical backscatter profilers, 6 FMI ceilometers, 4 C-band Doppler radars, 1 dual polarization Doppler radar, 4 radiosonde sounding stations, 1 UHF wind profiler and a RASS.

The Salford University autonomous lidar system will participate in the Helsinki testbed research project during the August 2006 intensive observation period. The theme of this intensive measurement campaign is convection. The lidar system will be situated at Malmi airport which is sited approximately 10 km from the centre of Helsinki and 6 km from the sea. Other instruments sited at Malmi airport include the UHF profiler, RASS and a ceilometer. The testbed provides the ideal opportunity to evaluate the new autonomous lidar system enabling comparisons to be made between the lidar and other remote sensing and in situ instrumentation.

The presentation will provide an overview of the Salford University autonomous Doppler lidar system along with an evaluation of its performance during the Helsinki International Testbed project. Future research projects involving the lidar system will be discussed.