Numerical Modeling of the Propagation Environment in the Atmospheric Boundary Layer over the Persian Gulf

Abstract

Strong vertical gradients at the top of the atmospheric boundary layer affect the propagation of electromagnetic waves and can produce radar ducts. A three-dimensional, time-dependent, nonhydrostatic numerical model was used to simulate the propagation environment in the atmosphere over the Persian Gulf when aircraft observations of ducting had been made. A division of the observations into high-and low-wind cases was used as a framework for the simulations. Three sets of simulations were conducted with initial conditions of varying degrees of idealization and were compared with the observations taken in the Ship Antisubmarine Warfare Readiness/ Effectiveness Measuring (SHAREM-115) program. The best results occurred with the initialization based on a sounding taken over the coast modified by the inclusion of data on low-level atmospheric conditions over the Gulf waters. The development of moist, cool, stable marine internal boundary layers (MIBL) in air flowing from land over the waters of the Gulf was simulated. The MIBLs were capped by temperature inversions and associated lapses of humidity and refractivity. The low-wind MIBL was shallower and the gradients at its top were sharper than in the high-wind case, in agreement with the observations. Because it is also forced by land-sea contrasts, a sea-breeze circulation frequently occurs in association with the MIBL. The size, location, and internal structure of the sea-breeze circulation were realistically simulated. The gradients of temperature and humidity that bound the MIBL cause perturbations in the refractivity distribution that, in turn, lead to trapping layers and ducts. The existence, location, and surface character of the ducts were well captured. Horizontal variations in duct characteristics due to the sea-breeze circulation were also evident. The simulations successfully distinguished between high-and low-wind occasions, a notable feature of the SHAREM-115 observations. The modeled magnitudes of duct depth and strength, although leaving scope for improvement, were most encouraging.

Estimation of Surface Duct Using Ground-Based GPS Phase Delay and Propagation Loss

“…Assuming that the atmosphere is a spherically symmetric and layered refractive medium, the GPS signal path is approximated as a function of r only. The phase path is determined according (6) where the angle  is the spherical angle between 1 r and 2 r . Hence, the excess phase path is defined as: Assuming that the atmosphere is a spherically symmetric and layered refractive medium, the GPS signal path is approximated as a function of r only.…”

“…These characteristics have significant impacts on radar target detection and target tracking because failure to consider a ducting environment may yield false radar returns. Therefore, the study of atmospheric ducts can not only improve the performance of radar or communications systems but can also contribute to research into the atmospheric boundary layer [6][7][8][9].…”

Brief review on PE method application to propagation channel modeling in sea environment

“…The propagation conditions in coastal and maritime regions are often complicated by the high variability of the meteorological parameters and sea surface state [1][2][3], which makes the preliminary assessment of microwave propagation in those regions difficult and sub- The evaporation duct is practically always present over the ocean at lower latitudes, its thickness increases ing the summer months and during the daytime [8,22]. On a worldwide basis surface-based ducts are known to ear about 14 % of the time, in certain regions -up to 50 % of the time [22,23].…”

“…Section 2.2 provides more details on the most widely used numerical hnique, the split-step Fourier-transform (SSF) method, to solve the PE, discussing also the boundary condition at tween the top of the region of negative gradient (the trapping layer) and either the level at which M exceeds the value at the top of the trapping layer (in this case elevated duct is formed) or the Earth's surface (surface-based duct). A special case is the evaporation duct (surface duct) for which the negative gradient of M is due to evaporation from large bodies of water [7][8][9][10] and thus it is typical for coastal and maritime regions (the different physical mechanisms of ducts formation are not addressed in this paper, for them the reader is referred to Reddy and Reddy [3], Babin et al [7], and Mesnard and Sauvageot [10]). The duct types are schematically presented on Fig.…”

Coastal effects on radar propagation in atmospheric ducting conditions

“…If sufficient bending towards the ground occurs, the ray may become trapped in a duct. Detailed studies of the nature and distribution of ducts using, among other tools, special aircraft observations and numerical models, have been made off the Californian coast (Burk & Thompson 1997;Haack & Burk 2001), in the Baltic Sea (Anderson et al 1997) and the Persian Gulf (Atkinson et al 2001;Plant & Atkinson 2002;Zhu & Atkinson 2004. Observations at Barcelona, later supported by output from a numerical model, outlined seasonal variation of duct occurrence over one point on the coast of north east Spain (Bech et al 2000(Bech et al , 2002a(Bech et al , 2002b(Bech et al , 2004.…”