Network technology aids in operating the LIDAR

The Davis LIDAR has been collecting new data on the upper atmosphere since February 2001 (Australian Antarctic Magazine #1, p 29). Operation of this complex instrument has been aided by novel applications of computer technology developed by the ASP and Science Technical Support groups.

Consideration of issues related to laser safety and weather necessitate that the LIDAR is not a fully autonomous system. However, a large amount of the control of the instrument is automatic, and the capability exists to operate and modify the observing program from any remote site with access to the Internet.

The LIDAR has three levels of instrument control. The bottom level is provided by dedicated microcontrollers. Each of these ‘modules’ performs a specific hardware task, such as firing the laser, moving a filter into the optical path, or running high speed rotating shutters. The most complex of the modules controls and monitors the operation of a Fabry-Perot spectrometer, which forms the heart of the detector system.

At the middle level of the control system are four networked PCs. The PCs do specific jobs; one is the main controller and communicates with the majority of the modules, a second controls the temperature inside the spectrometer, a third collects general monitoring data such as temperatures and voltages from around the system, and a fourth logs data from the spectrometer.

At the top level is a computer workstation that schedules the operation of the whole system through ‘jobs', passing commands to the PCs via the network. The workstation collates the data files produced, and does some real-time analysis for the operator to view. The data are then transmitted to Kingston for detailed analysis.

The majority of the electronic systems have been developed in-house using a design philosophy developed by Peter Yates and David Rasch. David and Lloyd Symons have developed the majority of the control software in PIC micro code and LabVIEW, while David Watts, Damian Murphy and Andrew Klekociuk have developed the analysis and job control system in IDL (Interactive Data Language).

The flexibility of the system means that the observing program can be rapidly altered when phenomena of specific interest are detected. An example of this ability involved detection of tenuous clouds in the stratosphere during July 2001 by Malcolm Lambert, the LIDAR physicist at Davis. These so-called Polar Stratospheric Clouds form at high latitudes in winter typically between altitudes of 15km and 25km. The clouds occur in regions where the temperature is below about −80°C, and are formed from crystals of sulphuric acid, nitric acid and water ice. The surfaces of the cloud particles provide a catalyst for the destruction of ozone, and so the observation of the clouds is of specific interest in understanding the nature of the Antarctic and Arctic ‘ozone holes'.

When the clouds were first detected above Davis, the LIDAR observing program was altered from Kingston to undertake high vertical resolution measurements. With 18 metre resolution, these are amongst the most detailed Antarctic observations that have been made using LIDAR, and show complex structure that is indicative of the passage of small temperature perturbations associated with propagating atmospheric waves. The clouds themselves were subvisual due to the lack of direct solar illumination in the polar mid-winter night and would have gone completely unnoticed if not for the LIDAR observations.

Further observing programs related to the clouds are planned with the aim of coordinating with other Antarctic ground-based and satellite measurements.

Andrew Klekociuk
Atmospheric and Space Physics Program,
Australian Antarctic Division

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