Acoustic sensors are being employed on airborne platforms, such as Persistent Threat Detection System (PTDS) and
Persistent Ground Surveillance System (PGSS), for source localization. Under certain atmospheric conditions, airborne
sensors offer a distinct advantage over ground sensors. Among other factors, the performance of airborne sensors is
affected by refraction of sound signals due to vertical gradients in temperature and wind velocity. A comprehensive
experiment in source localization with an aerostat-mounted acoustic system was conducted in summer of 2010 at Yuma
Proving Ground (YPG). Acoustic sources on the ground consisted of one-pound TNT denotations and small arms
firings. The height of the aerostat was approximately 1 km above the ground. In this paper, horizontal, azimuthal, and
elevation errors in source localization and their statistics are studied in detail. Initially, straight-line propagation is
assumed; then refraction corrections are introduced to improve source localization and decrease the errors. The
corrections are based on a recently developed theory [Ostashev, et. al, JASA 2008] which accounts for sound refraction
due to vertical profiles of temperature and wind velocity. During the 2010 YPG field test, the vertical profiles were
measured only up to a height of approximately 100 m. Therefore, the European Center for Medium-range Weather
Forecasts (ECMWF) is used to generate the profiles for July of 2010.
Acoustic sensors are being employed on airborne platforms, such as Persistent Threat Detection System (PTDS)
and Persistent Ground Surveillance System (PGSS), for source localization. Under certain atmospheric conditions,
airborne sensors oer a distinct advantage over ground sensors. The performance of both ground and
airborne sensors is aected by environmental factors, such as atmospheric turbulence and wind and temperature
proles. For airborne sensors, the eects of refraction must be accounted for in order to determine the
source coordinates. Such a method for ground-to-air applications has been developed and is further rened here.
Ideally, knowledge of the exact atmospheric proles will allow for the most accurate mitigation of refractive
eects. However, acoustic sensors deployed in theater are rarely supported by atmospheric sensing systems that
retrieve real-time temperature and wind elds. Atmospheric conditions evolve through seasons, time of day,
and are strongly location dependent. Therefore, the development of an atmospheric proles database based on
a long time series climatological assessment will provide knowledge for use in physics-based bearing estimation
algorithms, where otherwise no correction would have been performed. Long term atmospheric data sets from
weather modeling systems are used for a climatological assessment of the refraction corrections and localization
errors over selected sites.
Electro-optical sensors are affected by the atmospheric turbulence, as quantified by the refractive index structure
parameter. The present study introduces a method to predict the meteorological-scale variations of this quantity near the
surface. The predictions are evaluated against long-term scintillometry measurements. The essential aspects of the
meteorological variability of the optical turbulence rate are captured. The method is illustrated to provide a global and
predictive assessment of the optical turbulence rate. It can also be used to analyze the corresponding climatological
distributions. Existing relationships can further be incorporated to form predictions of the mean optical sensing
performance.
The performance of an optical sensor may be affected by small-scale fluctuations of the atmosphere, quantified through the refractive index structure parameter Cn2. The values of Cn2 along the optical path are modulated by large eddy fluctuations of the atmospheric fields. The resulting variations in the optical propagation have been scarcely documented due to the difficulty in measuring them. In this study, we use a micro-meteorological model to diagnose Cn2 in 3D+time in the case of a convective boundary layer. The regions of high Cn2 match with the convective plumes that drive the boundary layer dynamics. The variability of Cn2 is larger in the bulk boundary layer, where the mean Cn2 is low; it decreases in the surface layer and in the inversion, where the mean Cn2 is large. The impact of this distribution on horizontal optical propagation is analyzed, based on well-known analytical solutions of wave propagation through turbulence. Despite the optical path averaging, a large variability remains for the wave coherence length and the scintillation rate. Implications in terms of optical applications are given. In conclusion, the challenges in extending our modelling approach to present-day weather prediction are discussed.
Conference Committee Involvement (7)
Optics in Atmospheric Propagation and Adaptive Systems
13 September 2017 | Warsaw, Poland
Optics in Atmospheric Propagation and Adaptive Systems
28 September 2016 | Edinburgh, United Kingdom
Optics in Atmospheric Propagation and Adaptive Systems
22 September 2015 | Toulouse, France
Optics in Atmospheric Propagation and Adaptive Systems
22 September 2014 | Amsterdam, Netherlands
Optics in Atmospheric Propagation and Adaptive Systems XVI
23 September 2013 | Dresden, Germany
Optics in Atmospheric Propagation and Adaptive Systems
25 September 2012 | Edinburgh, United Kingdom
Optics in Atmospheric Propagation and Adaptive Systems
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