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The results of applying the empirical orthogonal functions (EOF) method to decomposition and approximation of aerosol size distributions are presented. A comparison was made for two aerosol data sets, representing coastal and oceanic environments. The first data set includes measurements collected at the Irish Atlantic coast in 1994 and 1995, the second one data collected during the Rough Evaporation Duct (RED) experiment that took place off Oahu, Hawaii in 2001. The main finding is that aerosol size distributions can be represented by a superposition of the mean size distribution and the first eigenvector multiplied by an amplitude function. For the two aerosol data sets the mean size distribution is very similar in the range of small particles sizes (radius 1μm). It is also reflected by the spectral shape of the eigenvector. The differences can be related to the type of aerosols present at both locations, and the amplitude function can be associated to meteorological conditions. The amplitude function also indicates the episodes with the maximum/minimum continental influence. The results of this analysis will be used in upgrades of the ANAM model.

The presence of atmospheric aerosols along the line of sight of infrared and electro-optical sensors greatly determines the range performance of these devices. On the one hand the aerosol particles scatter background (including sun) radiance into the field of view of the sensor, on the other hand they contribute to the atmospheric contrast reduction of the target. Proper knowledge of aerosol characteristics such as composition, concentration and size distribution is of vital importance for the prediction of their scattering and extinction characteristics. It is however found to be very difficult to collect accurate information on the particle size distribution (PSD) of aerosols. One of the reasons is the variation of the PSD along the path, which is likely to occur in a coastal area such as the San Diego Bay. One way to overcome these problems is the use of a multi-band transmissometer, as was done in previous measurement campaigns in the Baltic Sea [1] and in the Persian Gulf area [2]. The TNO seven-band optical/IR transmissometer system, providing path averaged transmission data for the intervening atmosphere, is operating at wavelengths between 0.4 and 14 μm,. In this spectral band, scattering in light hazy conditions is dominated by particles with a diameter of less than 4 μm. In order to simulate the transmission losses by scattering in various spectral bands a special calculation tool has been developed. This tool, described in this paper, allows detailed investigation of the possibilities of the retrieval of the PSD from multi-band transmission data. The slope in the plots of the transmission versus wavelength is directly related to the slope of the (lognormal) PSD plots (known as Junge exponent). The average transmission in a selected number of spectral bands is directly correlated to the average particle concentration (known as Junge coefficient). The principle of the methodology is illustrated with data collected during a measurement campaign, carried out over the San Diego Bay in August 2005. In this campaign we used six of the seven spectral bands, providing data over a 7.2 km over water path. It is shown that the retrieval method is very successful and the data correspond well with those, simultaneously collected with in-situ Particle Measurement Systems (PMS), located on both sides of the path. In addition to the path averaging, another advantage of the transmissometer PSD's, is the accuracy, being an order of magnitude higher than that of the PMS probes due to the fact that the measurement volume is more than a million times larger. A detailed analysis is given of the transmission data, showing peculiar effects were in the 2.3 urn band around 19.00 UTC during most of the days. These effects are especially well illustrated in plots where the transmission in one spectral band is plotted against the transmission in another band for various times of the day.

The Navy Aerosol Model (NAM, available in MODTRAN) is widely used as a tool to assess the aerosol extinction in the marine atmospheric surface layer. NAM was built as a regression model in the 1980s to represent the aerosol extinction at deck height as a function of the meteorological conditions. The recently developed Advanced Navy Aerosol Model (ANAM) utilizes additional experimental evidence to supersede NAM by correcting the underestimation of the concentration of aerosols larger than a few microns. More importantly, ANAM provides the aerosol extinction as a function of height between the surface and several tens of meters. Present-day naval surveillance and threat scenarios require detection of targets at the horizon, such as sea-skimming missiles, or small targets such as rubber boats. In either case, the propagation path from sensor to target is likely to come very close to the wave surface and in order to estimate detection ranges, an assessment of the transmission losses along the path is necessary. To answer the question posed in the title, we assess the two models using two meteorological data sets (784 cases) representative of diverse maritime conditions in regions of interest around the world.

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.

The application of long-range infrared observation systems is challenging, especially with the currently available high spatial resolution infrared camera systems with resolutions comparable with their visual counterparts. As a result of these developments, the obtained infrared images are no longer limited by the quality of system but by atmospheric effects instead. For instance, atmospheric transmission losses and path radiance reduce the contrast of objects in the background and optical turbulence limits the spatial resolution in the images. Furthermore, severe image distortion can occur due to atmospheric refraction, which limits the detection and identification of objects at larger range. EOSTAR is a computer program under development to estimate these atmospheric effects using standard meteorological parameters and the properties of the sensor. Tools are provided to design targets and to calculate their infrared signature as a function of range, aspect angle, and weather condition. Possible applications of EOSTAR include mission planning, sensor evaluation and selection, and education. The user interface of EOSTAR is fully mouse-controlled, and the code runs on a standard Windows-based PC. Many features of EOSTAR execute almost instantaneous, which results in a user friendly code. Its modular setup allows its configuration to specific user needs and provides a flexible output structure.

An infrared signal or a laser beam propagating along a horizontal near-surface path will encounter substantial perturbations. The fluxes of momentum and heat near the surface are relatively large, and these in turn cause large changes in the propagated intensity, direction, and coherence. It is important to be able to accurately model the separate effects that generate changes in a propagated beam, and it is also important to combine the different factors accurately. We will present some evidence from field experiments to demonstrate how refractivity changes on a ten-minute scale are manifested in a recorded infrared transmission signal. The EOSTAR (Electro-Optical Signal Transmission and Ranging) model is used to provide performance predictions for the experimental work. The EOSTAR model is built upon a geometrical optics approach to infrared propagation: a ray is traced through the propagation environment, and path-dependent perturbations to the signal can be determined. The primary computational tool for analysis of refractive effects in the EOSTAR model is a geometrical optics module that produces a ray-trace calculation for a given refractive environment. Based on the vertical profiles of temperature, humidity, refractive index structure parameter, and the calculated ray trajectories, EOSTAR calculates the path-integrated and spectrally-resolved transmission, background-radiation and path-radiation, as well as the scintillation and blur for a point source at any range and height position.

A first version of the integrated model EOSTAR (Electro-Optical Signal Transmission and Ranging) to predict the performance of electro-optical (EO) sensor systems in the marine atmospheric surface layer has been developed. The model allows the user to define camera systems, atmospheric conditions and target characteristics, and it uses standard (shipboard) meteorological data to calculate atmospheric effects such as refraction, turbulence, spectrally resolved transmission, path- and background radiation. Alternatively, the user may specify vertical profiles of meteorological parameters and/or profiles of atmospheric refraction, either interactively or in data files with a flexible format. Atmospheric effects can be presented both numerically and graphically as distorted images of synthetically generated targets with spatially distributed emission properties. EOSTAR is a completely mouse-driven PC Windows program with a user-friendly interface and extended help files. Most calculations are performed in real-time, although spectral transmission and background radiation calculations take up to a few seconds for each new meteorological condition. The program can be used in a wide range of applications, e.g., for operational planning and instruction.

An extensive data set of aerosol vertical concentration profiles (height range 0.5-15 meters, diameter range 10-75 micron), acquired with the Rotorod3 device at various geographical locations has been statistically analyzed. The analysis supplied a parameterization for the 4th (large particle) lognormal mode in the Advanced Navy Aerosol Model (ANAM). The analysis revealed a positive correlation between concentration and wind speed, and a negative correlation between concentration and height. No clear dependence of radius and width on meteorological parameters has been found. Numerical simulations with the Dutch-French SeaCluse model supported the results of the statistical analysis. The present version of ANAM predicts the experimental aerosol concentration to within a factor of 3. This result was confirmed using an independent data set. Initial extinction calculations with the ANAM indicate that the addition of the 4th mode changes aerosol extinction values by about 20% as compared to NAM calculations. Closer to the surface, this number is even higher due to the height dependence of the 4th mode.

The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. The model that is most frequently used for the prediction of aerosols and their effect on extinction in the marine atmosphere is the US Navy Aerosol Model (NAM). However, NAM can be significantly less reliable in coastal areas than on the open ocean. Based on an extensive series of measurements conducted on the island of Inisheer (Irish West Coast), an empirical aerosol model for the coastal zone formulated as an extension of NAM, in which coastal effects are modeled as a function of fetch, has been developed. This work is extended to the Mediterranean using an aerosol dataset recorded on the island of Porquerolles in the Bay of Toulon (France) and has been coupled with the Mie theory to give a code for the extinction, the code MEDiterranean EXtinction (MEDEX).

The Advanced Ray Tracing with Earth Atmospheric Models (ARTEAM) aims at a description of the electro-optical propagation environment in the marine atmospheric surface layer. For given meteorological conditions, the model evaluates height- and range-resolved transmission losses, refraction and turbulence effects. These results are subsequently applied to an electro-optical sensor with given specifications to evaluate the effective range and performance of the sensor under the prevailing meteorological conditions. Finally, for specified sensor-target geometry, the model calculates characteristic parameters for geometrical and spectral intensity, scintillation, blur and image distortion. ARTEAM is developed with an extensive Graphical User Interface (GUI) for Windows environments.

Contains fulltext : 56698.pdf (Publisher’s version ) (Closed access) We assessed the role of the human mirror neuron system (MNS) in complementary actions using functional magnetic resonance imaging while participants prepared to execute imitative or complementary actions. The BOLD signal in the right inferior frontal gyrus and bilateral inferior parietal lobes was greater during preparation of complementary than during imitative actions, suggesting that the MNS may be essential in dynamically coupling action observation to action execution. 2 p.

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

This paper discusses techniques to describe the aerosol and the electro optical properties of the marine atmosphere from 15 meters down to the tops of the highest wave. Emphasis is placed on the experimental Rotorod technique to measure the concentrations of giant sea salt droplets. Data from these devices are parameterized using a lognormal function that is in turn related statistically to parameters such as wind speed, atmospheric stability and height above the surface. The new lognormal function is combined with the Navy Aerosol Model (NAM) to develop a first version of the Advanced Navy Aerosol Model (ANAM). Thus, ANAM allows the construction of an aerosol size distribution at any level from the wave tops to 15 meters an the assessment of electro optical parameters from this distribution using Mie theory. The first results of the ANAM model are compared to experimental data.

Aerosol concentrations over the surf were measured during the EOPACE (Electro-Optical Propagation Assessment in Coastal Environment) Surf-i experiment in La Jolla, California. Particle size distributions were measured on the beach (at three levels) and across the surf (one level). Concentrations of droplets smaller than i im in diameter are little affected by the surf, while those with diameters in the 1-10 im range increase by up to two orders of magnitude. Clear vertical gradients were observed, which vary with particle size. No relation could be established between the surf production and wind speed or wave properties. Extinction coefficients at visible and infrared wavelengths calculated from the particle size distributions show that these are enhanced by a factor of 30 to 100, depending on the wavelength. Using the measured concentrations as boundary condition, calculations with a simple dispersion model show the gradual decrease in the concentration with fetch in off-shore winds. In on-shore winds the surf-enhanced aerosol concentration is effective over only a short range, but nevertheless significant transmission losses may occur. Obviously, these conclusions apply only to the surf encountered during this specific experiment. The effects of the surf in other areas and other ambient conditions will be assessed from the analysis of data collected at a different location and in different conditions.

Various atmospheric propagation effects are limiting the long range performance of electro-optical imaging systems. These effects include absorption and scattering by molecules and aerosols, refraction due to vertical temperature gradients and scintillation and blurring due to turbulence. In maritime and coastal areas, ranges up to 25 km are relevant for detection and classification tasks on small targets (missiles, pirates). From November 2009 to October 2010 a measurement campaign was set-up over a range of more than 15 km in the False Bay in South Africa, where all of the propagation effects could be investigated quantitatively. The results have been used to provide statistical information on basic parameters as visibility, air-sea temperature difference, absolute humidity and wind speed. In addition various propagation models on aerosol particle size distribution, temperature profile, blur and scintillation under strong turbulence conditions could be validated. Examples of collected data and associated results are presented in this paper.©2013 Society of Photo-Optical Instrumentation Engineers (SPIE)