J. Kusmierczyk-Michulec

Sea‐spray aerosol particles generated in the surf zone

To assess the properties of aerosol particles generated over the surf zone, two experiments were held at the pier of Scripps Institution of Oceanography (SIO), La Jolla CA, and at the pier of the U.S. Army Corps of Engineers Field Research Facility (FRF) in Duck NC. On both sites concentrations of surf‐generated sea spray particles, wave parameters and meteorological conditions were measured. The surf‐aerosol concentrations in the diameter range 0.2–10 microns were obtained from the difference in aerosol size distributions measured upwind and downwind of the surf zone. It was found that the flux of surf‐generated particles at diameters at formation can be expressed in terms of wave energy dissipation, which itself is related to the properties of the incoming wavefield and the bathymetry of the beach. Although the flux can also be modeled in terms of wind speed, this relation is considered to be not universal and limited to low‐ to medium wind speeds. In Duck NC, two transport experiments were performed under offshore flow conditions. In this case, the surf‐aerosol concentrations were obtained from the differences in three aerosol size distributions, measured just before and just behind the surf zone and up to 16 km downwind (out to sea). No significant decrease in concentration was observed at the farthest range, which suggests that an appreciable amount of surf‐generated aerosols is advected over tens of kilometers.

Aerosol properties over the Indian Ocean Experiment (INDOEX) campaign area retrieved from ATSR-2

Aerosol retrieved algorithms for ATSR-2 have been applied over land and water using data from the Indian Ocean Experiment (INDOEX) Intensive Field Phase (IFP) in February and March 1999. The goal was the extension of the ATSR-2 algorithms, developed for application over the U.S. east coast and Europe, to other areas with different types of aerosols and to explore the feasibility of deriving spatial variations in the aerosol composition. The ATSR-2 algorithm was extended with absorbing aerosols, and AERONET data were used to test the retrieved spectral aerosol optical depth (AOD). The resulting maps of AOD at 0.659 μm, Angstrom coefficient and urban/industrial aerosol contribution to the AOD over the ocean are evaluated by comparison with in situ data. AOD over land is in the range 0.18-0.45 with values up to 0.7 when biomass burning aerosol is present and decreases gradually over water with increasing fetch to 0.15 near the Intertropical Convergence Zone (ITCZ). Angstrom coefficients over land are in the range 1.5-2.0. Over water these values gradually decrease to almost zero. Over land urban/industrial aerosol dominates, and, as expected, over water the anthropogenic influence gradually decreases with fetch and the relative contribution of marine aerosol increases. South of the ITCZ the anthropogenic effect is negligible. Copyright 2006 by the American Geophysical Union.

Aerosol optical thickness retrieval over land and water using Global Ozone Monitoring Experiment (GOME) data

An algorithm for the retrieval of the aerosol optical thickness over land and over water from Global Ozone Monitoring Experiment (GOME) data is presented. The cloud fraction in the GOME pixels is determined using the Fast Retrieval Scheme for Clouds From the Oxygen A Band (FRESCO) algorithm. Surface contributions to the top of atmosphere reflectance are determined from the GOME surface reflectance database. The aerosol retrieval algorithm uses lookup tables that were created using the radiative transfer model 6S. The algorithm allows retrieving the aerosol types characterized by Angstrom coefficients in the range from -0.1 to 2.8; i.e., the range of values observed by the AERONET ground-based measurements. Validation of the algorithm done using the AERONET Sun photometer data for 12 sites in Europe and Africa, for the year 1997, shows very good agreement. The correlation coefficient between the satellite retrieval and AERONET data for the wavelength of 440 nm is 97%, and for 670 nm it is 94%. Validation of the algorithm for the year 2000 was done for a few sites with similar results. The algorithm has been successfully tested over an island influenced by Saharan dust (i.e., Cape Verde, 16oN, 22oW and over a site located near the Saharan desert (i.e., Bondoukoui, 11oN, 3oW). For other sites located near the Saharan desert such as Bidi Bahn (14oN, 2oW) and Banizombou (13oN, 2oE), the agreement was very good at 440 nm. The algorithm has not been tested over other bright surfaces such as ice-covered regions. Examples of the spatial distribution of the aerosol optical thickness over Europe, north Africa, and the North Atlantic for the year 1997 and 2000 are presented.

Aerosol remote sensing over the ocean using MSG‐SEVIRI visible images

With its observational frequency of 15 minutes, the Meteosat Second Generation (MSG) geostationary satellite offers a great potential to monitor aerosol transport using Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) data. To explore this potential, an algorithm for the retrieval of aerosol optical properties has been developed for use over the ocean. It is a multispectral algorithm based on the single-view algorithm for the Along Track Scanning Radiometer (ATSR-2) (Veefkind and de Leeuw, 1998) which has been adapted to the corresponding channels of SEVIRI (635 nm, 810 nm and 1640 nm). The SEVIRI Aerosol Retrieval Algorithm (SARA) provides the Aerosol Optical Depth (AOD) for these channels. To illustrate its capabilities, the application of this algorithm to two cases is presented: (1) a forest-fire smoke plume advected from Spain and Portugal over the Atlantic Ocean in August 2006, and (2) an outbreak of Saharan dust over the Western Mediterranean Sea in February 2006. The results obtained are validated with AERONET ground-based measurements for two coastal stations, and compared with the retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites. The diurnal variations of the aerosol optical depth observed at the AERONET sites are well reproduced, and the spatial patterns retrieved using the SARA algorithm are in reasonable agreement with those observed by MODIS.

Ångström coefficient as a tracer of the continental aerosols

The variation of the extinction coefficient with wavelength can be presented as a power law function with a constant (related to the power factor) known as the Ångström coefficient. When the particle size distribution is dominated by small particles, usually associated with pollution, the Ångström coefficients are high; in clear conditions they are usually low. Long residence time of air masses over land and in particular the passage over large urban areas cause high concentrations of fine particles and thus high values of the Ångström coefficients. The opposite effect can be observed over water. The longer the time that the air masses spent over water the more evident is a change in the aerosol size distribution caused by the deposition of continental aerosols. As a result of this process the measured Ångström coefficient values become much smaller. Therefore this parameter is a good tracer for the concentration of aerosols originated over land. The relation between the Ångström coefficient and TOS (time over sea) is demonstrated on three data sets. The first data set includes measurements collected at the Irish Atlantic coast in 1994 and 1995, the second one, data collected within the Rough Evaporation Duct (RED) experiment that took place off Oahu, Hawaii in 2001. The third one represents data collected at the Baltic Sea during cruises in 1997and 1998.

The Advanced Navy Aerosol Model (ANAM): validation of small-particle modes

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.

Influence of aerosols on off-axis laser detection capabilities

The radiation coming from a laser which operates in the coastal zone can be detected not only when a detector is placed in front of the laser beam but also when it is located outside the main beam direction. The reason is that in a real detection scheme the power collected by a detector not only comes from direct radiation but also from other radiation sources, like port scattering, aerosol scattering and background radiation. Their relative contributions depend on many factors, i.e. laser features, collecting optics features, meteorological conditions, etc. An important contributor is aerosol scattering and its intensity depends on the aerosol composition and particle density. It was found that more humid conditions cause a decrease in the direct radiation and an increase in the diffuse component. This effect depends on the contribution of hygroscopic and non-hygroscopic aerosols. In the marine-continental atmosphere, represented by a mixture of sea-salts (SSA), anthropogenic salts (WS) and organic carbon (OC), a change in relative humidity from 80% to 95% can change the result for the predicted irradiance level on the sensor by more than a factor of three. Dust-like (DL) particles produce much stronger scatter irradiance than other aerosol types, independently of the off-axis distance.

Transmissometer versus sun photometer measurements of the aerosol optical properties

Atmospheric aerosol particles affect the Earths radiative balance both in the cloud-free and the cloudy atmosphere. The direct effect of aerosols is related with scattering and absorption of solar radiation, and as a consequence, reduction of the amount of radiation reaching the surface. The best parameter that quantifies this effect is the aerosol extinction, which can be derived from vertical, as well as, horizontal measurements. The purpose of this paper is to compare the aerosol optical properties registered by two types of instruments. The first is a standard 5-wavelength hand-held sun photometer yielding the vertical column extinction, the second a 7-wavelength transmissometer developed at TNO. This multi-band transmissometer provides horizontal, path-integrated transmission data at 7 wavelengths within the visible/infra red spectral range. The data used in the comparison were collected during an experiment near Scripps Pier in La Jolla near San Diego, in November 2006.

Novel Aerosol Retrieval Algorithms For SCIAMACHY For Application Over Water And Land

Two aerosol retrieval algorithms of the SCanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) are developed for application over water and over land. The one for application over water uses IR spectral channels taking advantage of the common assumption of a black surface to obtain information about optical properties of aerosols. Next, this information is combined with data in the visible channels to benefit from the fill spectral range offered by SCIAMACHY, The IR-derived aerosol properties are used as a fust guess for the retrieval in the visible range where the surface properties are accounted for on the basis of the measured surface reflectance spectra. In contrast, for the retrieval of aerosol properties over land the starting point is the UV spectral range where the surface is dark. Next, the UV-derived aerosol properties are used for the retrieval in the visible and IR channels. Look-up tables were prepared for the following aerosol types: sea-salt, dust-like particles, black and organic carbon and water+oluble particles, The aerosol mixtures were constructed in such a way that thd \alues of the resultant Ongstr*m coefficients cover the whole range of possible values as found e.g. in the AERONET databases [1].

A New Algorithm To Retrieve AOD With ATSR-2 Data

The single and dual view algorithms for the retrieval of aerosol optical depth (AOD) and Angstrom coefficients in cloud fi-ee areas over sea and land using data from the Along Track Scanning Radiometer 2 (ATSR-2) on board the European Remote Sensing satellite (ERS-2) has been applied over the east coast of the United States [1, and 2] and over Europe [3], In this contribution the generalisation of the algorithms for application over other areas is reported, A severe drawback during previous application to retrieve the AOD over Europe [3] was that over land there is no reliable cloud flag, Therefore a cloud-screening scheme developed by Koelemeijer and Stammes, [4] was applied. This semiautomatic algorithm requires manual interference which renders the application very time consuming. Therefore, the fust step to geheralise the ATSR-2 algorithms was the inclusion of an automated cloud detection scheme. The next step was the inclusion of other aerosol types than the continental and sea salt aerosols that are included in the original algorithms, Optical properties of soot (black carbon) and dust aerosols have been used to prepare look up tables (LUT ‘s) for implementation in the ATSR-2 algorithms, Due to the fact that the algorithms will be tested with data from the INDOEX experiments, the aerosol data obtained from this experiment were used as in~uts to determine the appropriate aerosol mixtures. Preliminary results from application of the algorithms to ATSR-2 data over the INDOEX area are shown. Comparison of the retrieved AOD with ground based sun photometer measurements from the AERONET data-base for the Male Island on 16* of February 1999 shows that the data agree within 0,05 at 0,659 ~m.