LiDAR - Light Detection And Ranging - is an instrument that uses electro magnetic pulses, typically in VIS spectral range, to detect and optically characterise atmospheric aerosols. The key quantities derived using this instrument are profiles of backscatter and extinction due to aerosol presence in the atmosphere from which one can derive the Aerosol Optical Depth (AOD) which is a unitless measure of aerosol load. An optical depth of less than 0.05 indicates a clear sky with relatively few aerosols and maximum visibility, whereas a value of 1 indicates hazy conditions. Optical depths above 2 or 3 represent very high concentrations of aerosols.

It is important to monitor and predict AOD due to their impacts on human health and climate, for example near-real-time AOD forecasts are used to provide situational awareness for civilian aviation, military operations, and air quality alerts.

Aerosol forecasts are produced using models which use satellite data to define the initial state.

Air quality models can predict up to a couple of days in advance, but it is hard to predict any further as the pollutants are short lived in the atmosphere. These models are important for air quality management as they are widely used to both identify source contributions to air quality problems and assist in the design of effective strategies to reduce harmful air pollutants, as well as for warning the public on epsiodes of bad air quality.

Featured Educator

• Dr Pepijn Veefkind, Senior Scientist, KNMI

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