Physics – Optics
Scientific paper
Nov 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004spie.5572..355r&link_type=abstract
Optics in Atmospheric Propagation and Adaptive Systems VII. Edited by Gonglewski, John D.; Stein, Karin. Proceedings of the SP
Physics
Optics
Scientific paper
Small-scale inhomogeneities of the atmospheric temperature field are caused by air turbulence and result in refractive index fluctuations, which in turn influence the propagation of optical beams. Understanding small density fluctuations in the atmosphere is important for the free-space laser communication and for high-resolution imaging through the atmosphere. The ultra-fast aircraft resistance thermometer constructed in the Institute of Geophysics, Warsaw University, measures the temperature of cloudless air and of warm clouds with 10 kHz sampling frequency. During a flight at the speed of 100 m/s, at low altitudes up to 2 km, this corresponds to the spatial resolution of the order of one centimeter. This resolution is sufficient for studying small density fluctuations in the atmospheric boundary layer. A streamlined shield protects the sensing wire of the thermometer from cloud droplets and other small particles suspended in the air but introduce aerodynamic disturbances in the form of vortices. The thermometer records the resulting fluctuations of temperature as noise. The shield sucks air and water collected on its surface through the suction slits. This suction also suppresses the disturbances. In this paper we analyze how the temperature measurements are influenced by: (i) turbulence generated behind the shield placed in front of the sensing wire; (ii) suction of air through the shield slits; (iii) cloud droplets of various space distributions, masses and velocities. We have carried out the 2D numerical simulations of the time-dependent, incompressible, viscous flow (the Navier-Stokes equation) around the shield placed in a uniform stream. We solved the particle path equations for an ensamble of droplets in the Stokes approximation. All the simulations are oriented toward optimization of the shield shape in order to (i) reduce noise in measurements at low and high altitudes and (ii) protect the sensing wire against ice crystals in flights at high altitudes.
Bajer Konrad
Haman Krzysztof E.
Rosa Bogdan J.
Szoplik Tomasz
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