Aerosols in the atmosphere scatter and absorb radiation, which reduces the transmission of electro-optical radiation through the atmosphere and impacts on the radiative balance of the planet. To accurately predict the performance of electro-optical systems for naval applications, fine-scale modeling of the atmospheric dynamics of aerosols in the coastal zone is crucial. To this end, the MIO laboratory has coupled the numerical meteorological model MESO-NH in its LES version to the particle extinction model MEDEX (Mediterranean Extinction Model MEDEX, Piazzola et al., 2003). The numerical aerosol concentrations in the Mediterranean coastal zone were compared to experimental data acquired in May 2008 on board a research vessel and on the island of Porquerolles. This provided insight in our capability to model the fine-scale spatiotemporal variation of aerosol and visibility for a coastal area of complex geography.
A comparison of aerosol data acquired at five different sites around the globe is presented. All data has been acquired with the same instrumentation and representative size distributions for marine air masses at 10 m/s wind speed have been selected for comparison. Differences in the concentrations of larger and smaller aerosols at the various sites are explained in terms of fetch, trade winds, shielding, pollution, seawater temperature and phytoplankton bloom. The differences in size distribution induce significant differences in the extinction coefficients from the VIS to the LWIR at the various sites. Consequently, the transmission over a specific range also varies significantly. This suggests that a detailed analysis of the conditions at each site is necessary in order to understand the exact aerosol behavior and to correctly predict electro-optical propagation effects due to aerosols.
The image quality of electro-optical sensors in the (lower-altitude marine) atmosphere is limited by aerosols, which
cause contrast reduction due to transmission losses and impact on the thermal signature of objects by scattering solar
radiation. The Advanced Navy Aerosol Model (ANAM) aims at providing a quantitative estimate of the aerosol effects
on the basis of standard meteorological parameters such as wind speed and relative humidity. For application in coastal
regions, the ANAM includes non-marine aerosols that are governed by an ill-defined tuning parameter: the air mass
parameter (AMP). The present paper proposes a new parameterization for assessing the effect of these non-marine
particles on the propagation. The new parameterization utilizes the Ångström coefficient, which can be experimentally
obtained with a sun photometer, and introduces new types of aerosols in ANAM. The new parameterization was tested
against experimental validation data acquired at Porquerolles Island at the French Riviera. The limited test data
suggested that the new parameterization is only partially efficient in capturing the aerosol signature of the coastal
environment. Nevertheless, the new Ångström coefficient algorithm avoids using the ill-defined AMP, and may thus be
useful to the ANAM community.
The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. While molecular extinction can be calculated using propagation codes such as MODTRAN (Berk et al., 1989), the influence of aerosols is much less easy to account for. However, concentrations and optical properties of aerosol particles in the atmosphere are quite variable both in time and space. Very few relevant models for the aerosol size distributions have been published during the last decades. One of the most used is the Navy aerosol model (NAM, Gathman, 1983), which is currently being upgraded to the advanced Navy aerosol model (ANAM, van Eijk and Merritt, 2006). NAM and ANAM are dedicated to open ocean, while coastal areas induce specific processes (Piazzola et al., 2000, and Bendersky et al., 2004). To include coastal effects for the prediction of aerosol concentrations and their effects on the extinction, Piazzola et al. (2003) proposed the aerosol extinction code MEDEX. We deal with the extension of the predictions of MEDEX on a regional scale. To achieve it, MEDEX is forced by the regional mesoscale meteorological model RAMS (Cotton et al., 2003) to account for the fine details of the coastal orography. Simulations are then compared to aerosol size distributions recorded in the Mediterranean. The results show a nonhomogeneous spatial coverage of the aerosol concentrations over the northern Mediterranean. In addition, we show the least performance of the coupling for unsteady conditions of the wave field.
Results from a quantitative model for the prediction of the sea-salt mass flux produced in the surf zone
are presented in this paper. The model relates the surf zone sea salt mass flux to the amount of wave
energy dissipated in the surf zone. In order to apply this aerosol emission model, a wave numerical
model is required to obtain estimates for the total wave energy dissipated in the surf zone, as well as for
the width of the surf zone. In the present work, we show using different wave models that the aerosol
emission model is not sensitive to the details of the formulation of the wave model, provided a clear
definition for the width of surf zone is adopted and the calibration of the numerical models is properly
done.
The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. The performance assessment of EO systems by propagation prediction codes then requires accurate aerosol models. However, concentrations and optical properties of aerosol particles in the atmosphere are very variable both in time and space. In particular, coastal areas induce specific physical processes. To include coastal effects in the model for the prediction of aerosol concentrations, Piazzola et al.1 proposed an extension of the Navy Aerosol Model (NAM2) to coastal areas. This work has been coupled with Mie theory to develop the aerosol extinction code MEDEX,3 which is based on an extensive series of measurements in the Mediterranean.
The present paper deals with the extension of the predictions of MEDEX to a regional scale. To achieve it, MEDEX has been coupled with a regional meso-scale meteorological model (RAMS). This allows taking into account the details of the orography of the coast and a better modelling of the unsteadiness for both meteorological and oceanic conditions. The results show the feasibility of extending the predictions of MEDEX to any coastal site.
The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. A few years ago, an empirical model was developed describing the aerosol size distributions in the Mediterranean coastal atmosphere near Toulon (France). This model has been coupled with Mie theory to yield the code MEDEX (MEDiterranean EXtinction) for the aerosol extinction. This contribution deals with the evaluation of MEDEX for aerosol data recorded near the Black Sea coast. For this site, MEDEX correctly predicts the aerosol extinction as function of wavelength, albeit with minor discrepancies below one micron. These differences are attributed to the uncertainty in predicting the concentrations of submicron particles. The comparison shows that MEDEX may be more generally applicable than to the Toulon area.
On the basis of a comprehensive series of measurements on the Irish Atlantic coast, an extension of the Navy Aerosol Model (NAM) for the coastal zone is proposed. As in NAM, the dependence of the aerosol concentration on meteorological parameters is parameterized using empirical coefficients. The effect of continental aerosols present in the coastal zone is modeled as a function of fetch. A reasonable agreement is found between the model and the aerosol size distributions as measured on the island Inisheer.
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.