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1

Laboratory measurements of remote sensing reflectance of selected phytoplankton species from the Baltic Sea

Soja-Woźniak M., Darecki M., Wojtasiewicz B., Bradtke K.

Oceanologia

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2018

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No. 60 (1)

86--96

EN

Results of unique laboratory measurements of remote sensing reflectance (Rrs) of several phytoplankton species typically occurring in high abundances in the Baltic Sea waters are presented. Reflectance spectra for diatoms: Cyclotella meneghiniana and Skeletonema marinoi and Dolichospermum sp., Nodularia spumigena and sp. were analysed in terms of assessment of their characteristic features and the differences between them. These species contain similar pigments, which results in general similarities of reflectance spectra, i.e. decrease of reflectance magnitude in the blue and red spectrum regions. However, hyper-spectral resolution of optical measurements let us find differences between optical signatures of diatoms and cyanobacteria groups and between species belonging to one group as well. These differences are reflected in location of local maxima and minima in the reflectance spectrum and changes in relative height of characteristic peaks with changes of phytoplankton concentration. Wide ranges of phytoplankton concentrations were analysed in order to show the persistence of Rrs characteristic features. The picoplankton species, Synechococcus sp. show the most distinct optical signature, which let to distinguish separate cluster in hierarchical cluster analysis (HCA). The results can be used to calibrate input data into radiative transfer model, e.g. phase function or to validate modelled Rrs spectra.

2

Performance of operational satellite bio-optical algorithms in different water types in southeastern Arabian Sea

Minu P., Lotliker A. A., Shaju S. S., Ashraf P. M., Kumar T. S., Meenakumari B.

Oceanologia

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2016

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No. 58 (4)

317--326

EN

The in situ remote sensing reflectance (Rrs) and optically active substances (OAS) measured using hyperspectral radiometer, were used for optical classification of coastal waters in the southeastern Arabian Sea. The spectral Rrs showed three distinct water types, that were associated with the variability in OAS such as chlorophyll-a (chl-a), chromophoric dissolved organic matter (CDOM) and volume scattering function at 650 nm (β650). The water types were classified as Type-I, Type-II and Type-III respectively for the three Rrs spectra. The Type-I waters showed the peak Rrs in the blue band (470 nm), whereas in the case of Type-II and III waters the peak Rrs was at 560 and 570 nm respectively. The shifting of the peak Rrs at the longer wavelength was due to an increase in concentration of OAS. Further, we evaluated six bio-optical algorithms (OC3C, OC4O, OC4, OC4E, OC3M and OC4O2) used operationally to retrieve chl-a from Coastal Zone Colour Scanner (CZCS), Ocean Colour Temperature Scanner (OCTS), Sea-viewing Wide Field-of-view Sensor (SeaWiFS), MEdium Resolution Imaging Spectrometer (MERIS), Moderate Resolution Imaging Spectroradiometer (MODIS) and Ocean Colour Monitor (OCM2). For chl-a concentration greater than 1.0 mg m−3, algorithms based on the reference band ratios 488/510/520 nm to 547/550/555/560/565 nm have to be considered. The assessment of algorithms showed better performance of OC3M and OC4. All the algorithms exhibited better performance in Type-I waters. However, the performance was poor in Type-II and Type-III waters which could be attributed to the significant co-variance of chl-a with CDOM.

3

Revisiting the role of oceanic phase function in remote sensing reflectance

Freda W., Piskozub J.

Oceanologia

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2012

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No. 54 (1)

29-38

EN

The effect of angular structure differences between measured and best-fit analytical phase functions of the equivalent backscattering ratio on calculated reflectance values was studied and shown to be significant. We used a Monte Carlo radiative transfer code to check the effect of choosing different analytical (several Fournier-Forand (1994) and Henyey-Greenstein (1941)) phase functions with backscattering ratios identical to the "classical" average Petzold function. We show that the additional variability of the resulting water leaving radiance is about 7% (4% between the Fournier-Forand functions themselves) for most scenarios. We also show a previously unknown maximum of the discrepancy (up to 10%) for highly scattering waters. We discuss the importance of relative differences in phase function for different angular ranges to this maximum and to the behaviour of the discrepancy as a function of solar zenith angle.

4

Inherent optical properties and remote sensing reflectance of Pomeranian lakes (Poland)

Ficek D., Meler J., Zapadka T., Woźniak B., Dera J.

Oceanologia

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2012

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No. 54 (4)

611-630

EN

This paper describes the results of comprehensive empirical studies of the inherent optical properties (IOPs), the remote sensing reflectance Rrs(λ) and the contents of the principal optically active components (OAC) i.e. coloured dissolved organic matter (CDOM), suspended particulate matter (SPM) and chlorophyll a, in the waters of 15 lakes in Polish Pomerania in 2007-2010. It presents numerous spectra of the total absorption a(λ) and scattering b(λ = bp(λ) of light in the visible band (400-700 nm) for surface waters, and separately, spectra of absorption by CDOM aCDOM(λ) and spectra of the mass-specific coefficients of absorption ap*(SPM)(λ) and scattering bp*(SPM)(λ) by SPM. The properties of these lake waters are highly diverse, but all of them can be classified as Case 2 waters (according to the optical classification by Morel & Prieur 1977) and they all have a relatively high OAC content. The lakes were conventionally divided into three types: Type I lakes have the lowest OAC concentrations (chlorophyll concentration Ca = (8.76 š 7.4) mg m-3 and CDOM absorption coefficients aCDOM(440) = (0.57 š 0.22) m-1 (i.e. mean and standard deviation), and optical properties (including spectra of Rrs(?) resembling those of Baltic waters. Type II waters have exceptionally high contents of CDOM (aCDOM(440) = (15.37 š 1.54) m-1), and hence appear brown in daylight and have very low reflectances Rrs(?) (of the order of 0.001 sr-1). Type III waters are highly eutrophic and contain large amounts of suspended matter, including phytoplankton ((CSPM = (47.0 š 39.4) g m-3, Ca = (86.6 š 61.5) mg m-3; aCDOM(440) = (2.77 š 0.86) m-1). Hence the reflectances Rrs(?) of these type of waters are on average one order of magnitude higher than those of the other natural waters, reaching maximum values of 0.03 sr-1 in ? bands 560-580 nm and 690-720 nm (see Ficek et al. 2011). The article provides a number of empirical formulas approximating the relationships between the properties of these lake waters.

5

Model of seawater polluted by oil-in-water emulsion as a response to the increasing shipping activities

Rudź K.

Journal of Polish CIMAC

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2012

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Vol. 7, no 1

209-217

EN

Intensive shipping affects marine environment in an extent degree, increasing seawater pollution by hazardous substances, including fuel oil and crude oil. Bilge water from ship power plants usually contains a mixture of dispersed oils, which form spherical droplets of diameter ranging from 0.01 to 10..m. Present methods for detection of dispersed oil require taking a water sample or putting a measuring device into seawater, which allows only to gather point data from limited locations. In order to meet the demand of remote monitoring of endangered zones, a study of optical properties of oil-in-water emulsions was conducted. Presented model of seawater polluted by oil-in-water emulsion can potentially enable remote optical detection of oil-in-water emulsion in visible bands. It is based on the fact that oil droplets become additional absorbents and attenuators in water body. Optical analyses consist of calculations of spectral absorption and scattering coefficients and scattering phase functions for oil emulsions on the basis of Lorentz-Mie theory including measurements of refractive index and determination of oil droplets size distribution. The radiative transfer theory is applied to simulate the contribution of oil emulsion to the remote sensing reflectance. Presented system for radiative transfer simulation is based on Monte Carlo code and it involves optical tracing of virtual photons.

6

Modelling of seawater polluted by light and heavy crude oil droplets

Rudź K., Darecki M., Toczek H.

Journal of KONES

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2012

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Vol. 19, No. 2

473-480

EN

Significant amounts of crude oil transported from offshore fields to the refineries using tankers or pipelines, demand increased control of seawater pollution. Tanker accidents resulting in oil spills drive much attention, as they influence local marine life and coastal industry. However, the most significant annual amount of crude oil enters the sea in the form of oilin- water emulsion as a result of standard tanker operations, offshore oil extraction and daily work of refineries. Many branches of science are challenged to provide new methods for oil detection, less expensive, more sensitive and more accurate. Remote satellite or airborne detection of large oil spills is possible using joint techniques as microwave radars, ultraviolet laser fluorosensors and infrared radars. Some methods are capable to deal with oil streaks detection and estimation of oil thickness. Although there is currently, no method to detect small concentration of oil droplets dispersed in seawater. Oil droplets become additional absorbents and attenuators in water body. They significantly change seawater inherent optical properties, which imply the change of apparent optical properties, detectable using remote sensing techniques. To enable remote optical detection of oil-in-water emulsion, a study of optical properties of two types of crude oil was conducted. Radiative transfer theory was applied to quantify the contribution of oil emulsion to remote sensing reflectance (Rrs). Spectra of Rrs from in situ measurements in Baltic Sea were compared to Rrs spectra of seawater polluted by 1 ppm of crude oil emulsion, collected using radiative transfer simulation. The light crude oil caused a 9-10% increase of Rrs while the heavy one reduced Rrs up to 30% (model accuracy stayed within 5% for considered spectral range). Results are discussed concerning their application to shipboard and offshore oil content detection.

7

Emulsified fuels of machine origin in seawater - a contribute to remote detection

Rudz K.

Journal of KONES

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2011

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Vol. 18, No. 2

385-390

EN

Development of industry and trade in the last few decades caused a huge increase in the pollution of the world's oceans. Substantial contributors to marine pollution come with the rivers from land-based sources including the by-products of industry, run-off from agriculture activities such as biocides as well as effluents from urban areas. Moreover, a significant amount of marine pollution is caused by shipping and maritime activities. The operation of ship plants gives a real possibility for engine oils and fuels to reach the marine environment. Discharge waters contain a certain amount of petroleum derivatives in the form of dispersed droplets (oil-in-water emulsion). The presence of oil emulsion cause measurable changes in the optical properties of seawater. It is conceptually possible to detect these changes using a standard radiance or irradiance reflectance meter. Hence, a set of radiative transfer simulation has been carried out. This paper presents a computed photon trace simulation based on the Monte Carlo code, applied to the marine environment. The results are presented as reflectance spectra for the models of Baltic Sea and ocean water both pure and polluted by oil emulsion. It is shown that even small amounts of petroleum pollution rise the values of irradiance reflectance and cause a spectral shift by certain conditions. A possibility for remote evaluation of oil pollution is discussed as well as the perspective for improving the interpretation of shipboard and offshore light field analyses.

8

Emulsified fuels of machine origin in seawater - a contribute to remote detection

Rudz K.

Journal of KONES

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2011

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Vol. 18, No. 3

375-381

EN

Development of industry and trade in the last few decades caused a huge increase in the pollution of the world's oceans. Substantial contributors to marine pollution come with the rivers from land-based sources including the by products of industry, run-off from agriculture activities such as biocides as well as effluents from urban areas. Moreover, a significant amount of marine pollution is caused by shipping and maritime activities. The operation of ship plants gives a real possibility for engine oils and fuels to reach the marine environment. Discharge waters contain a certain amount of petroleum derivatives in the form of dispersed droplets (oil-in-water emulsion). The presence of oil emulsion cause measurable changes in the optical properties of seawater. It is conceptually possible to detect these changes using a standard radiance or irradiance reflectance meter. Hence, a set of radiative transfer simulation has been carried out. This paper presents a computed photon trace simulation based on the Monte Carlo code, applied to the marine environment. The results are presented as reflectance spectra for the models of Baltic Sea and ocean water both pure and polluted by oil emulsion. It is shown that even small amounts of petroleum pollution raise the values of irradiance reflectance and cause a spectral shift by certain conditions. A possibility for remote evaluation of oil pollution is discussed as well as the perspective for improving the interpretation of shipboard and offshore light field analyses.