Abstract
Abstract. Dust orientation has been an ongoing investigation in recent years. Its potential proof will be a paradigm shift for dust remote sensing, invalidating the currently used simplifications of randomly oriented particles. Vertically resolved measurements of dust orientation can be acquired with a polarization lidar designed to target the off-diagonal elements of the backscatter matrix which are nonzero only when the particles are oriented. Building on previous studies, we constructed a lidar system emitting linearly and elliptically polarized light at 1064 nm and detecting the linear and circular polarization of the backscattered light. Its measurements provide direct flags of dust orientation, as well as more detailed information of the particle microphysics. The system also has the capability to acquire measurements at varying viewing angles. Moreover, in order to achieve good signal-to-noise ratio in short measurement times, the system is equipped with two laser sources emitting in an interleaved fashion and two telescopes for detecting the backscattered light from both lasers. Herein we provide a description of the optical and mechanical parts of this new lidar system, the scientific and technical objectives of its design, and the calibration methodologies tailored for the measurements of oriented dust particles. We also provide the first, preliminary measurements of the system during a dust-free day. The work presented does not include the detection of oriented dust (or other oriented particles), and therefore the instrument has not been tested fully in this objective.
Highlights
Mineral dust is one of the most important aerosol types in terms of mass and optical depth (e.g., Tegen et al, 1997) and significantly impacts radiation (e.g., Li et al, 2004), while it interacts with liquid or ice clouds, modifying their optical properties and lifetimes (e.g., DeMott et al, 2003) and affecting in addition precipitation processes (e.g., Creamean et al, 2013)
Observations show that the coarse mode of dust (Weinzierl et al, 2017; Ryder et al, 2018), or even of giant dust particles, can be sustained during long-range transport
Geier and Arienti (2014) demonstrated that the linearly polarized measurements provided by most of the lidar systems are sufficient for discerning ice crystal orientation, this is not the case for smaller particles such as dust, for which we expect much lower differences than the order(s) of magnitude reported for oriented particles in clouds
Summary
Mineral dust is one of the most important aerosol types in terms of mass and optical depth (e.g., Tegen et al, 1997) and significantly impacts radiation (e.g., Li et al, 2004), while it interacts with liquid or ice clouds, modifying their optical properties and lifetimes (e.g., DeMott et al, 2003) and affecting in addition precipitation processes (e.g., Creamean et al, 2013). Geier and Arienti (2014) demonstrated that the linearly polarized measurements provided by most of the lidar systems are sufficient for discerning ice crystal orientation, this is not the case for smaller particles such as dust, for which we expect much lower differences than the order(s) of magnitude reported for oriented particles in clouds. What they suggested is to use light that is linearly polarized along a plane at an angle = 0, or circularly polarized light, and detect the backscattered light at different polarization planes. A table containing all acronyms and symbols is provided in the Supplement
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