Development of a Miniature Lidar Instrument for Plume Detection

Accurate knowledge of the vertical location of clouds and aerosols has critical implications for air quality, hazard avoidance, and decision making for operations involving national security. Aerosols impact air quality and can act as tracers of events (e.g., fires or potential terrorist event), providing key information on sources and transport (i.e., down-wind impact) of potentially harmful air masses. Knowing the height of aerosols and vertical structure of aerosol plumes is essential for predicting aerosol dispersion, transport, and visibility. Clouds obscure targets and can interfere with passive sensor measurements. Accurate vertical registration of clouds is a major limitation of passive sensors that has been shown to adversely impact passive microwave sounder retrievals if not properly estimated.

Passive optical and passive microwave sensors cannot provide height information accurately enough (10’s m) to provide reliable aerosol and cloud detection, and distinguishing multiple layers within an atmospheric column is challenging and often impossible for passive sensors. Laser remote sensing, or lidar, is a proven method for obtaining highly accurate height registration and can distinguish cloud phase as well as differentiating clouds from aerosols. Aerosols are rather easy to detect using lidar, and lidar is well suited to detecting background aerosols, aerosol plumes, plume boundaries, and internal structure of aerosol layers. A polarization-sensitive backscatter lidar coupled with multi-spectral and multi-angle polarimetry can provide additional information on aerosol type, optical depth, and particle microphysics that are relevant to air quality.

There is a need to develop inexpensive lidar profiling capability that can be readily deployed on unmanned aerial systems (UASs). The miniature lidar does not need to provide the fidelity of measurement capable from larger high-altitude or spaceborne lidars – simple layer detection with accuracy of 10’s m is all that is needed. Coincident multi-band measurements provided by a polarimeter are highly complementary to lidar measurements, enabling retrievals of aerosol plume heights and properties that augment the narrow lidar footprint (~1 m) with wider swath data (>>10 m). Coupled with an inexpensive polarized camera (i.e., polarimeter), three-dimensional monitoring of aerosol plume properties is enhanced by adding viewing swath, critical for decision aids related to hazard events, human health, transportation, and defense.

We are currently developing a small, coupled lidar-polarimeter system suitable for use on drones that can provide real-time determination of the vertical and horizontal location of clouds, aerosol plumes, and planetary boundary layer (PBL) height, along with a coarse determination of aerosol type. Advanced machine learning algorithms will be used to generate on-board data products that can be transmitted to a ground station to inform real-time decision making. We will provide an overview of the rationale and utility for such a sensor and highlight the present sensor design and expected performance.