The Canadian Operational Research Aerosol Lidar Network (CORALNet)

The Canadian Operational Research Aerosol Lidar Network (CORALNet) was established in 2008 to look at the degree of long-range transported aerosols.  Aerosols are tiny particles suspended in the air. Some occur naturally (biogenic), coming from volcanoes, dust storms, forest and grassland fires, living vegetation and sea spray while others result from human activities (anthropogenic), such as burning fossil fuels and altering natural surface cover.

Aerosols are important to understand for a number of reasons. They affect the earth's climate by interacting with the sun and earth's radiation and by modifying clouds. Aerosols also affect human health and decrease visibility, so it is important to understand the processes that influence aerosol concentrations in the atmosphere in order to protect our quality of life.

The establishment of CORALNet is increasingly important as scientists work to understand the roles of man-made, locally-produced air pollutants as well as those which move into the area via meteorological “highways” and their impacts on air quality.  The situation is further complicated by naturally-produced airborne particles like desert dust and forest fire plumes that can travel great distances around the globe and can occasionally have significant impacts on air quality. 

CORALNet is currently composed of five lidar systems (four are currently active) strategically located at sites across Canada. These sites were chosen to cover the entire country and to maximize the ability to monitor both long-range transport events as well as regional air quality issues.  The sites from west to east are University of British Columbia, Bratt’s Lake, Centre For Atmospheric Research Experiments(Egbert), University of Sherbrooke and Acadia University.  The first of the sites, CORALNet-UBC began collecting data on April 16th, 2008.

The technique used by CORALNet is known as Lidar (an acronym for LIght Detection and Ranging).  Similar to radar, Lidar uses light waves instead of radio waves to look at very small particles in the atmosphere (generally invisible to the naked eye).  A laser beam is directed into the sky and, using a telescope, some of the light that is scattered back from the tiny airborne particles is collected to show the degree of air pollution which is transported over long distances.

Every 10 seconds the system provides vertical aerosol profiles from near ground to 20 km into the sky. It operates 24 hours a day, seven days a week except during precipitation events and when aircraft fly over the site. The system is operated remotely and the data, which are updated every hour, are publicly available on this website.

Why Is CORALNet Important:

• Canadians value the quality of the air they breathe and are becoming increasingly aware of the effects that poor air quality can have on their health.
• The Government of Canada is committed to monitoring and communicating information about air quality to Canadians. The Government of Canada is taking concrete action to support clean air by establishing stringent emission standards and regulations.
• Air pollutants do not respect borders. Environment Canada scientists must look at how air pollutants travel to understand air quality.
• The information gleaned through CORALNet will provide decision-makers with solid scientific information on which to base policies to address air pollution and reduce its effects on human and environmental health. The research will contribute to improvements in air quality forecasting, as well as contribute to a better scientific understanding of the effects of climate change.

An Example of Long-Range Transport

Very few aerosol lidar measurements are acquired along the west coast of North America.  The UBC (University of British Columbia) CORALNet site will attempt to help partially fill this void and provide the much needed presence on this side of the Pacific Rim to monitor such events as Asian Dust, forest fire plumes and local air quality issues in the complex Lower Fraser Valley.  Measurements made from RASCAL (Rapid Acquisition SCanning Aerosol Lidar), Environment Canada’s mobile scanning lidar facility, performed some “proof-of’concept” measurements in 2005 and consequently captured the first documented case of long-range transport of Saharan dust over a pathway spanning Asia and the Pacific to Western North America.  The image below shows a 32 hour lidar snapshot of the event.  The area marked by “A” shows the Saharan dust layer subsided in a ridge along the west coast of Canada.  Although a weak event compared to the Asian Trans-Pacific dust events of 1998 and 2001, this novel case highlights the possibility that Saharan sources may contribute episodically to the aerosol burden in western North America.   Monitoring the frequency and magnitude of events such as this is one of the goals of CORALNet.

Technical Specifications

The lidar systems being deployed for CORALNet use identical transmitter and receiver assemblies and where necessary are housed in a modified cargo trailer.  The trailer modifications include a roof hatch assembly, basic meteorological tower, radar interlock system, climate control system and leveling stabilizers.  The unit can be operated via an internet link and requires an external power source.  A precipitation sensor is used to operate the roof hatch and three pan/tilt webcams capture sky conditions and monitor the lidar system’s health.  A remote control interface is used to control all vital components of the system, including the ability to provide hard resets of the laser electronics.

The laser is the new Continuum Inlite III (small footprint) laser operating at 1064/532nm with a pulse repetition rate of 10Hz.  The energy output is approximately 150mJ @ 532nm and 130mJ @ 1064nm.  The system emits two wavelengths and measures a return signal at three channels (1064nm, 532 both polarizations).