A simple model of light transmission through the atmosphere over the Baltic Sea utilising satellite data (original) (raw)
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A simple model of light transmission through the atmosphere over the Baltic Sea utilising
2008
A simple spectral model of solar energy input to the sea surface was extended to incorporate space-borne data. The extension involved finding a method of determining aerosol optical thickness (on the basis of AVHRR data) and the influence of cloudiness (on the basis of METEOSAT data) on the solar energy flux. The algorithm for satellite data assimilation involves the analysis of satellite images from the point of view of cloud identification and their classification with respect to light transmission. Solar energy input values measured at the Earth’s surface by traditional methods were used to calibrate and validate the model. Preliminary evaluation of the results indicates a substantial improvement in the accuracy of * The work is a part of a project supported by the Polish State Committee for Scientific Research (now the Ministry of Science and Higher Education) – grant No. PBZ–KBN 056/P04/2001. The complete text of the paper is available at http://www.iopan.gda.pl/oceanologia/ 12...
OCEANOLOGIA
The results of two methods used to estimate the aerosol optical thickness over the Baltic Sea are compared. The standard method is based on measurements of the direct component of the downward irradiance at the sea surface in 8 spectral bands (412, 443, 490, 510, 555, 670, 765, 865 nm -the same as SeaWiFS). In the pyranometric method, Baltic aerosols are assumed to be a mixture of model aerosol types with strictly defined optical properties, i.e. maritime, continental and stratospheric types. Their proportion in the Baltic aerosol is found from broadband spectral downward irradiance measurements (V IS, IR) using the radiative transfer model. Simultaneous measurements of the spectral downward irradiance and its direct component on cloudless days in the southern Baltic were used in the comparison. The pyranometric method of estimating the aerosol optical thickness proved to be a satisfactory tool. Depending on the wavelength, the statistical errors in it are not in excess of ± 0.06 to ± 0.08.
Seasonal variability in the optical properties of Baltic aeros
Oceanologia, 2011
A five-year dataset of spectral aerosol optical thickness was used to analyse the seasonal variability of aerosol optical properties (the aerosol optical thickness (AOT) at wavelength λ = 500 nm, AOT(500) and theÅngström exponent for the 440-870 nm spectral range, α(440, 870)) over the Baltic Sea and dependence of these optical properties on meteorological factors (wind direction, wind speed and relative humidity). The data from the Gotland station of the global radiometric network AERONET (Aerosol Robotic Network, http://aeronet.gsfc.nasa.gov) were taken to be representative of the Baltic Sea conditions. Meteorological observations from Fårosund were also analysed. Analysis of the data from 1999 to 2003 revealed a strong seasonal cycle in AOT(500) and α(440, 870). Two maxima of monthly mean values of AOT(500) over the Baltic were observed. In April, an increase in the monthly mean aerosol optical thickness over Gotland most probably resulted from agricultural waste straw
Journal of Geophysical Research, 1999
Measurements of atmospheric extinction at sea-viewing wide-field-of-view sensor wavelengths were carried out during the Lagrangian Experiment on the Baltic Sea within the Baltic Sea System Study project, July 2-15. 1997. The empirical orthogonal functions method was applied to the aerosol optical lhickness spectra. allowing three air mass types, containing different aerosol types, to be distinguished: continental, continental-maritime, and maritime, corresponding to different residence times of air masses over the Baltic Sea. The amplitude of the aerosol optical thickness, describing the temporal variabili .ty, was found to be strongly affected by the atmospheric stability. The contribution of the aerosol radiance to the atmospheric radiance depends directly on the aerosol type. the wavelength/•, and the solar zenith angle 0•. The most significant contribution of more than 30% was detected for the continental and continental-maritime aerosol .types, for 0s = 30 ø, and at ,• = 865 nm.
Acta Geophysica, 2014
In this paper we describe the results of a research campaign dedicated to the studies of aerosol optical properties in different regions of both the open Baltic Sea and its coastal areas. During the campaign we carried out simultaneous measurements of aerosol optical depth at 4 stations with the use of the hand-held Microtops II sun photometers. The studies were complemented with aerosol data provided by the MODIS. In order to obtain the full picture of aerosol situation over the study area, we added to our analyses the air mass back-trajectories at various altitudes as well as wind fields. Such complex information facilitated proper conclusions regarding aerosol optical depth and Ångström exponent for the four locations and discussion of the changes of aerosol properties with distance and with changes of meteorological factors. We also show that the Microtops II sun photometers are reliable instruments for field campaigns. They are easy to operate and provide good quality results.
Inherent Optical Properties of the Baltic Sea in Comparison to Other Seas and Oceans
Remote Sensing
In order to retrieve geophysical satellite products in coastal waters with high coloured dissolved organic matter (CDOM), models and processors require parameterization with regional specific inherent optical properties (sIOPs). The sIOPs of the Baltic Sea were evaluated and compared to a global NOMAD/COLORS Reference Data Set (RDS), covering a wide range of optical provinces. Ternary plots of relative absorption at 442 nm showed CDOM dominance over phytoplankton and non-algal particle absorption (NAP). At 670 nm, the distribution of Baltic measurements was not different from case 1 waters and the retrieval of Chl a was shown to be improved by red-ratio algorithms. For correct retrieval of CDOM from Medium Resolution Imaging Spectrometer (MERIS) data, a different CDOM slope over the Baltic region is required. The CDOM absorption slope, S CDOM , was significantly higher in the northwestern Baltic Sea: 0.018 (±0.002) compared to 0.016 (±0.005) for the RDS. Chl a-specific absorption and a d [SPM] *(442) and its spectral slope did not differ significantly. The comparison to the MERIS Reference Model Document (RMD) showed that the S NAP slope was generally much higher (0.011 ± 0.003) than in the RMD (0.0072 ± 0.00108), and that the SPM scattering slope was also higher (0.547 ± 0.188) vs. 0.4. The SPM-specific scattering was much higher (1.016 ± 0.326 m 2 g −1) vs. 0.578 m 2 g −1 in RMD. SPM retrieval could be improved by applying the local specific scattering. A novel method was implemented to derive the phase function (PF) from AC9 and VSF-3 data. b was calculated fitting a Fournier-Forand PF to the normalized VSF data. b was similar to Petzold, but the PF differed in the backwards direction. Some of the sIOPs showed a bimodal distribution, indicating different water types-e.g., coastal vs. open sea. This seems to be partially caused by the distribution of inorganic particles that fall out relatively close to the coast. In order to improve remote sensing retrieval from Baltic Sea data, one should apply different parameterization to these distinct water types, i.e., inner coastal waters that are more influenced by scattering of inorganic particles vs. open sea waters that are optically dominated by CDOM absorption.
Optical properties of north-eastern Baltic Sea in spring and summer 2007
2008
Underwater irradiation profiles in the north-eastern Baltic Sea near the Estonian northern and north-western coast, near Helsinki, and in the central part of Gulf of Finland were measured in spring and summer 2007. The vertical profiles of downwelling and scalar irradiance in the PAR region were measured in situ using a frame completed with two planar and a spherical PAR sensor. The measuring system allows the calculation of the mean attenuation coefficients of a water column of scalar irradiance (Ko). Optical density of the sea water was varying from 0.13 m -1 (Tallinn-Helsinki line, May) up to 0.85 m -1 (Tallinn-Helsinki line, April). The concentrations of optically active substances were highly variable; the chlorophyll a concentration varied from 0.7-21.4 mg m -3 , the suspended particulate matter concentration from 1-7 mg l -1 and the concentration of dissolved organic matter from 2.1-5.8 mg l -1 . The water transparency was much better in May compared to April 2007. Also, it is seen, that excepting the stations immediately near the port and ship line, the Gulf of Finland was quite clear, especially in May. Correlations between the water depth and optical density were calculated for the shallows near Hiiumaa. Water quality based on measurements conducted in summer 2007 at North-Western Estonian coastal waters indicates that the water quality was on average satisfactory; associating values for diffuse attenuation coefficient was 0.5 m -1 , Secchi depth 3.7 m and chlorophyll a concentration 8 mg m -3 .
Atmospheric Chemistry and Physics, 2017
Retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satellite, 12 years (2003-2014) of aerosol and cloud properties were used to statistically quantify aerosol-cloud interaction (ACI) over the Baltic Sea region, including the relatively clean Fennoscandia and the more polluted central-eastern Europe. These areas allowed us to study the effects of different aerosol types and concentrations on macro-and microphysical properties of clouds: cloud effective radius (CER), cloud fraction (CF), cloud optical thickness (COT), cloud liquid water path (LWP) and cloud-top height (CTH). Aerosol properties used are aerosol optical depth (AOD), Ångström exponent (AE) and aerosol index (AI). The study was limited to low-level water clouds in the summer. The vertical distributions of the relationships between cloud properties and aerosols show an effect of aerosols on low-level water clouds. CF, COT, LWP and CTH tend to increase with aerosol loading, indicating changes in the cloud structure, while the effective radius of cloud droplets decreases. The ACI is larger at relatively low cloud-top levels, between 900 and 700 hPa. Most of the studied cloud variables were unaffected by the lower-tropospheric stability (LTS), except for the cloud fraction. The spatial distribution of aerosol and cloud parameters and ACI, here defined as the change in CER as a function of aerosol concentration for a fixed LWP, shows positive and statistically significant ACI over the Baltic Sea and Fennoscandia, with the former having the largest values. Small negative ACI values are observed in central-eastern Europe, suggesting that large aerosol concentrations saturate the ACI.