The performances of Electro-Optical (EO) systems such as visible or infrared cameras, lasers, operating within the
Marine Surface Boundary Layer (MSBL), i.e. at heights up to a few tens of meters above the sea surface, are disturbed
by various propagation mechanisms: molecular attenuation, aerosol extinction, refraction and turbulence. Refraction is
responsible for focusing and defocusing of rays, detection range limitations, mirage formation and angular deviation.
These refraction phenomena can be efficiently described using ray-tracing in conjunction with bulk estimations of the
refractivity profiles based on the Monin-Obukhov (MO) theory. For stable atmospheric conditions (i.e. air temperature
greater than sea temperature), the accuracy of the model predictions has been strongly discussed in the recent years. By
using measurements of apparent target elevations recorded during the VAMPIRA trial, this paper aims at clarifying this
discussion.
The performances of Electro-Optical (EO) systems such as visible or infrared cameras, lasers, operating within the Marine Surface Boundary Layer (MSBL), i.e. at heights up to a few tens of meters above the sea surface, are disturbed by various propagation mechanisms: molecular attenuation, aerosol extinction, refraction and turbulence. Refraction is responsible for focusing and defocusing of rays, detection range limitations, mirage formation and angular deviation. The refractive index depends on atmospheric pressure, air temperature and air humidity. Within the optical transmission bands, it also depends on the wavelength. In this paper, the results provided by two different formulations of the refractive index associated with the same ray tracing program are compared and discussed.
The performances of Electro-Optical (EO) systems such as visible or infrared cameras, lasers, operating within the Marine Surface Boundary Layer (MSBL), i.e. at heights up to a few tens of meters above the sea surface, are disturbed by various propagation mechanisms: molecular and aerosol extinctions, refraction and turbulence. By using meteorological measurements collected in various coastal areas (French Atlantic coast, Mediterranean Sea, North Sea), we present in this paper, a statistical study of the distributions of some of the relevant EO propagation parameters.
PIRAM is a french bulk model that computes, within the MSBL, vertical refractivity profiles and refractivity gradients calculated for each optical transmission window as well as for radar bands. PIRAM also computes the Cn2 vertical profiles. Under unstable situations, subrefraction occurs and reduces the optical horizon. Near the horizon an intervisibility zone may be observed: any source (target) located in this zone will be seen by an EO sensor under two distinct apparent elevation angles. We developed, a few years ago, a simple ray-tracing algorithm using PIRAM refractivity outputs, to compute optical horizons and intervisibility ranges for a given atmospheric situation. More recently, we have added new capabilities to our ray-tracing program; now, it also computes the refractance parameter and the optical path between a given optical source or target and the considered EO sensor. Atmospheric turbulence effects are quantified by several parameters such as the scintillation variance, the atmospheric coherence length or the standard deviation of the angular displacement. All these parameters are computed by taking into account the exact optical path and the complete Cn2 vertical profile. Our first comparisons with the values provided by the Canadian IRBLEM software lead to promising results.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.