IR propagation through the marine boundary layer: comparison of model and experimental data

Abstract

The propagation of IR radiation through the marine boundary layer is very much dependent on vertical temperature gradients. Due to the Air-Sea Temperature Difference (ASTD) the distance to the visible horizon for an imaging system can be shorter (ASTD < 0) or larger (ASTD > 0) than the distance to the geometric horizon. To analyse these phenomena FGAN-FOM took measurements in the mid and long wave IR. Location of the experiment was the Baltic Sea. A ship, equipped with IR point sources, was tracked while it was sailing in and out up to, and beyond, the horizon. Weather conditions during the measurement period showed interesting variations in ASTD and atmospheric turbulence (see paper 4884-11). Especially strong sub-refractive effects have been observed with ASTDs up to -5.0 °C. This paper deals with the analysis of the detection range of point targets under different meteorological conditions. Experimental results are compared with the propagation model IRBLEM (IR Boundary Layer Effects Model) which was developed by DRDC-RDDC -Valcartier, Canada.

Millimeterwave propagation within boundary layers over sea comparison of modelling and experimental data

“…If a single sensor approach is envisaged, millimeterwave radar should be taken into account. Bad weather performance is appreciably better than at IR frequencies [5] and detection is possible for ranges up to and over the horizon in the majority of environmental conditions in the Atlantic and Mediterranean and specifically in the Baltic Sea. Using high power output stages, ranges are not less than at classical frequencies, but problems due to multipath fadings are of minor importance.…”

“…They are discussed in detail in a separate paper [5]. While during the time period of measurements at the Baltic Sea under winter conditions mm-wave propagation was always sufficient to track the reference target up to or over the horizon, this is can not be generalized for all environmental conditions.…”

Influence of heterogeneous refractivity on optical wave propagation in coastal environments

“…Of course in many locations, such as remote marine regions, even sparse profile datasets may not be available. In such situations, it is common to employ the Monin-Obukhov similarity theory (Monin and Obukhov 1954) to estimate the vertical profile of refractivity (MO approach) based on a single near-surface measurement, e.g., an ocean buoy (Dion et al 2001;Doss-Hammel et al 2002;Stein et al 2003;Kunz et al 2004;Dion et al 2005). Neither the HH approach nor the MO approach considers heterogeneous refractivity induced by the mesoscale atmospheric structures.…”

Simulating an extreme over-the-horizon optical propagation event over Lake Michigan using a coupled mesoscale modeling and ray tracing framework

“…Under similar data-sparse situations, the atmospheric optics community commonly invokes the assumption of horizontal homogeneity. [8][9][10][11][12] The shortcomings of such an unphysical assumption were clearly illustrated by van Eijk and Kunz. 13 In this study, we make use of satellite-based data in tandem with in-situ measurements to avoid the assumption of homogeneity.…”

“…8,9 Positive (negative) values of ASTD are associated with super-refractive (subrefractive) conditions. Unfortunately, due to the low density of meteorological stations on Lake Michigan and along its shorelines, an accurate estimation of the ASTD values is not feasible for the propagation path between Grand Haven and Milwaukee.…”