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New simple statistical formulas for estimating surface concentrations of suspended particulate matter (SPM) and particulate organic carbon (POC) from remote- sensing reflectance in the southern Baltic Sea

Woźniak S. B., Darecki M., Zabłocka M., Burska D., Dera J.

Oceanologia

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2016

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No. 58 (3)

161--175

EN

In a step taken towards improving the new system for the satellite monitoring of the Baltic Sea environment, officially started in Poland recently (SatBałtyk System, see http://www. satbaltyk.pl), a new set of simple statistical formulas was derived. These combine the empirically determined spectral values of remote-sensing reflectance Rrs(λ) with the mass concentrations of suspended particulate matter (SPM) and particulate organic carbon (POC) in southern Baltic surface waters. The new formulas are based on 73 empirical data sets gathered during 4 research cruises on board r/v Oceania during spring and late summer in the open waters of the southern Baltic and coastal regions of the Gulf of Gdańsk. Correlations of SPM and POC concentrations with reflectance or reflectance ratios in various spectral bands were tested. Several variants of candidate statistical relationships, which can be used later in the construction of simple local remote sensing algorithms for the waters in question, are introduced here. These relationships utilise either absolute values of Rrs at a selected waveband, mostly from the yellow, red or near infrared part of the light spectrum, or Rrs ratios for two different wavebands, mostly ratios of blue to yellow, blue to red and blue to infrared or green to yellow and green to red spectral band. From the numerous simple approximate relationships established, the following two, characterised by large correlation coefficients r2 and small standard error factors X, may serve as examples: SPM [g m-3] = 1480(Rrs(710))0.902 (with the factors r2 = 0.86; X = 1.26) (the unit of Rrs(λ) is [sr-1]) and POC [g m-3] = 0.814(Rrs(555)/Rrs(589))-4.42 (r2 = 0.75; X = 1.37). From the practical standpoint, taking into consideration light wavelengths that are close to or concurrent with the currently available spectral bands used in satellite observations of the Baltic Sea, another two formulas (using the same spectral ratio) are worth pointing out: SPM [g m-3] = 2.6(Rrs(490)/Rrs(625))-1.29 (r2 = 0.86; X = 1.25) and POC [g m-3] = 0.774(Rrs(490)/Rrs(625))-1.18 (r2 = 0.66; X = 1.44). The paper also presents a number of intermediate statistical relationships between SPM and POC concentrations, Rrs spectra and light backscattering coefficients in order to illustrate the simplified physical justification for some of the observed direct statistical relationships, presented as the main content of this work.

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Simple statistical formulas for estimating biogeochemical properties of suspended particulate matter in the southern Baltic Sea potentially useful for optical remote sensing applications

Woźniak S. B.

Oceanologia

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2014

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No. 56 (1)

7--39

EN

Simple statistical formulas for estimating various biogeochemical properties of suspended particulate matter in the southern Baltic Sea are presented in this paper. These include formulas for estimating mass concentrations of suspended particulate matter (SPM), particulate organic matter (POM), particulate organic carbon (POC) and total chlorophyll a (Chl a). Two different approaches have been adopted. The first approach was to use the available empirical material (the results of field measurements and laboratory analyses of discrete water samples) and find statistical formulas for estimating the biogeochemical properties of suspended particulate matter from those of inherent optical properties (IOPs), which are potentially retrievable from remote sensing measurements. The second approach was to find formulas that would enable biogeochemical properties of suspended particulate matter to be estimated directly from spectral values of the remote-sensing reflectance Rrs. The latter was based on statistical analyses of a synthetic data set of Rrs obtained from numerical simulations of radiative transfer for which the available empirical material on seawater IOPs and biogeochemistry served as input data. Among the empirical formulas based on seawater IOPs that could be used as a step in two-stage remote sensing algorithms (the other step is estimating certain IOPs from reflectance), the best error statistics are found for estimates of SPM and POM from the particulate backscattering coefficient bbp in the blue region of light wavelengths (443 nm), and for estimates of POC and Chl a from the coefficient of light absorption by the sum of all non-water (i.e. suspended and dissolved) constituents of seawater an, in the blue (443 nm) and green (555 nm) parts of the spectrum respectively. For the semi-empirical formulas under consideration, which could serve as starting points in the development of local one-stage (direct) remote sensing algorithms, the best error statistics are found when SPM, POM and POC are estimated from the same blue-to-red band reflectance ratio (Rrs (490)/ Rrs(645)) (with estimated SPM reaching a better precision than estimated POM and POC), and when Chl a is estimated from the green-to-red band ratio (Rrs(555)/Rrs(645)).

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Inherent optical properties of suspended particulate matter in the southern Baltic Sea

Woźniak S.B., Meler J., Lednicka B., Zdun A., Stoń-Egiert J.

Oceanologia

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2011

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No. 53 (3)

691-729

EN

The inherent optical properties (IOPs) of suspended particulate matter and their relations with the main biogeochemical characteristics of particles have been examined in the surface waters of the southern Baltic Sea. The empirical data were gathered at over 300 stations in open Baltic Sea waters as well as in the coastal waters of the Gulf of Gdańsk. The measurements included IOPs such as the absorption coefficient of particles, absorption coefficient of phytoplankton, scattering and backscattering coefficients of particles, as well as biogeochemical characteristics of suspended matter such as concentrations of suspended particulate matter (SPM), particulate organic matter (POM), particulate organic carbon (POC) and chlorophyll a (Chl a). Our data documented the very extensive variability in the study area of particle concentration measures and IOPs (up to two orders of magnitude). Although most of the particle populations encountered were composed primarily of organic matter (av. POM/SPM = ca 0.8), the different particle concentration ratios suggest that the particle composition varied significantly. The relations between the optical properties and biogeochemical parameters of suspended matter were examined. We found significant variability in the constituent-specific IOPs (coefficients of variation (CVs) of at least 30% to 40%, usually more than 50%). Simple best-fit relations between any given IOP versus any constituent concentration parameter also highlighted the significant statistical errors involved. As a result, we conclude that for southern Baltic samples an easy yet precise quantification of particle IOPs in terms of the concentration of only one of the following parameters - SPM, POM, POC or Chl a - is not achievable. Nevertheless, we present a set of best statistical formulas for a rough estimate of certain seawater constituent concentrations based on relatively easily measurable values of seawater IOPs. These equations can be implemented in practice, but their application will inevitably entail effective statistical errors of estimation of the order of 50% or more.

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Algorithms for the remote sensing of the Baltic ecosystem (DESAMBEM). Part 2: Empirical validation

Darecki M., Ficek D., Krężel A., Ostrowska M., Majchrowski R., Woźniak S.B., Bradtke K., Dera J., Woźniak B.

Oceanologia

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2008

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No. 50 (4)

509-538

EN

This paper is the second of two articles on the methodology of the remote sensing of the Baltic ecosystem. In Part 1 the authors presented the set of DESAMBEM algorithms for determining the major parameters of this ecosystem on the basis of satellite data (see Woźniak et al. 2008 - this issue). That article discussed in detail the mathematical apparatus of the algorithms. Part 2 presents the effects of the practical application of the algorithms and their validation, the latter based on satellite maps of selected Baltic ecosystem parameters: the distributions of the sea surface temperature (SST), the Photosynthetically Available Radiation (PAR) at the sea surface, the surface concentrations of chlorophyll a and the total primary production of organic matter. Particular emphasis was laid on analysing the precision of estimates of these and other parameters of the Baltic ecosystem, determined by remote sensing methods. The errors in these estimates turned out to be relatively small; hence, the set of DESAMBEM algorithms should in the future be utilised as the foundation for the effective satellite monitoring of the state and functioning of the Baltic ecosystem.

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Algorithm for the remote sensing of the Baltic ecosystem (DESAMBEM). Part 1: Mathematical apparatus

Woźniak B., Krężel A., Darecki M., Woźniak S.B., Majchrowski R., Ostrowska M., Kozłowski Ł., Ficek D., Olszewski J., Dera J.

Oceanologia

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2008

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No. 50 (4)

451-508

EN

This article is the first of two papers on the remote sensing methods of monitoring the Baltic ecosystem, developed by our team. Earlier, we had produced a series of detailed mathematical models and statistical regularities describing the transport of solar radiation in the atmosphere-sea system, the absorption of this radiation in the water and its utilisation in a variety of processes, most importantly in the photosynthesis occurring in phytoplankton cells, as a source of energy for the functioning of marine ecosystems. The comprehensive DESAMBEM algorithm, presented in this paper, is a synthesis of these models and regularities. This algorithm enables the abiotic properties of the environment as well as the state and the functioning of the Baltic ecosystem to be assessed on the basis of available satellite data. It can be used to determine a good number of these properties: the sea surface temperature, the natural irradiance of the sea surface, the spectral and spatial distributions of solar radiation energy in the water, the surface concentrations and vertical distributions of chlorophyll a and other phytoplankton pigments in this sea, the radiation energy absorbed by phytoplankton, the quantum efficiency of photosynthesis and the primary production of organic matter. On the basis of these directly determined properties, other characteristics of processes taking place in the Baltic ecosystem can be estimated indirectly. Part 1 of this series of articles deals with the detailed mathematical apparatus of the DESAMBEM algorithm. Part 2 will discuss its practical applicability in the satellite monitoring of the sea and will provide an assessment of the accuracy of such remote sensing methods in the monitoring of the Baltic ecosystem (see Darecki et al. 2008 - this issue).

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Modelling the light absorption properties of particulate matter forming organic particles suspended in sea water. Part 3. Practical applications

Woźniak B., Woźniak S.B., Tyszka K., Ostrowska M., Ficek D., Majchrowski R., Dera J.

Oceanologia

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2006

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No. 48 (4)

479-507

EN

This paper brings to a close our cycle of articles on modelling the light absorption properties of particulate organic matter (POM) in the sea. In the first two parts of this cycle (Woźniak et al. 2005a,b) we discussed these properties with reference to various model chemical classes and physical types of POM. We have put these results into practice in the present third part. As a result of the appropriate theoretical speculations, logically underpinned by empirical knowledge, we selected 25 morphological variants of marine organic detritus, to which we ascribed definite chemical compositions and physical types. On this basis and using known spectra of the mass-specific coefficients of light absorption by various naturally occurring organic substances (systematised in Parts 1 and 2), we determined the absorption properties of these 25 morphological groups of particles, that is, the spectra of the imaginary part of the refractive index n'p(?) (in the 200-700 nm range) of the particulate matter. They can be applied, with the aid of Mie's or some other similar theory, to calculate the bulk optical properties (absorbing and scattering) of such sets of particles in the sea.

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Modelling the light absorption properties of particulate matter forming organic particles suspended in seawater. Part 1. Model description, classification of organic particles, and example spectra of the light absorption coefficient and the imaginary par

Woźniak B., Woźniak S. B., Tyszka K., Dera J.

Oceanologia

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2005

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No. 47 (2)

129-164

EN

Data on organic substances in the sea are applied to distinguish hypothetical chemical classes and physical types of suspended particulate organic matter (POM) in seawater. Spectra of the light absorption coefficients of particulate matter apm(?) and the imaginary refractive index n'p(?), are assessed for some of these classes and types of POM in seawater, that is, for live phytoplankton cells and phytoplankton-like particles. The spectral characteristics of these coefficients are established and the probable ranges of variability of their absolute magnitudes defined on the basis of the mass-specific coefficients of light absorption by the various organic substances forming the particles. Also presented are mathematical relationships linking the coefficients apm(?) and n'p(?) for the various chemical classes of POM with their physical parameters, such as the relative contents of organic matter, water, air or some other gas. This article is part of a bio-optical study undertaken by the authors, the objective of which is to implement remote sensing techniques in the investigation of Baltic ecosystems (Woźniak et al. 2004).

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Modelling the light absorption properties of particulate matter forming organic particles suspended in seawater. Part 2. Modelling results

Woźniak B., Woźniak S. B., Tyszka K., Ostrowska M., Majchrowski R., Ficek D., Dera J.

Oceanologia

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2005

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No. 47 (4)

621-662

EN

Model spectra of mass-specific absorption coefficients a*OM(?) were established for 26 naturally occurring organic substances or their possible mixtures, capable of forming particulate organic matter (POM) in the sea. An algorithm was constructed, and the set of spectra of a*OM(?) was used to determine the spectra of the imaginary part of the complex refractive index n'p(?) characteristic of different physical types and chemical classes of POM commonly occurring in sea water. The variability in the spectra and absolute values of n'p for the various model classes and types of POM was shown to range over many orders of magnitude. This implies that modelling the optical properties of sea water requires a multi-component approach that takes account of the numerous living and non-living fractions of POM, each of which has a different value of n'p.

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Heat and salt fluxes in the West Spitsbergen Current area in summer

Piechura J., Osiński R., Petelski T., Woźniak S. B.

Oceanologia

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2002

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No. 44 (3)

307-321

EN

Fluxes of radiation, sensible and latent heat, and fluxes of heat and salt within the upper layer of the ocean were calculated on the basis of measurements carried out in the area of the Norwegian-Atlantic and West Spitsbergen Currents during summer 2000. The sea surface radiation balance was calculated from direct measurements of downward and upward short-wave (solar) radiation, the net radiation fluxes and sea surface temperature. The daily doses of radiation energy reaching and leaving the sea surface were also estimated. To calculate the vertical heat fluxes in the atmospheric boundary layer the bulk parameterisation method was used. In most cases, the calculated heat fluxes were rather low, the average sensible heat flux was c. 10 W m-2, and the latent heat flux about one order of magnitude higher; this is what could be expected in summer. Salt fluxes to the air in the process of aerosol production are very small and can be neglected. In summer the highest quantities of heat and salt are exchanged during mixing with surrounding waters. According to our measurements, Atlantic Water on its northward course from about 70oN to 79oN loses about 100 TW of heat and 900 × 103 kg of salt. We thought it could be interesting to find out what happens to them. Some preliminary results of our investigation are presented here.

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A simple formula for the net long-wave radiation flux in the southern Baltic Sea

Zapadka T., Woźniak S.B., Woźniak B.

Oceanologia

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2001

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No. 43 (3)

265-277

EN

This paper discusses problems of estimating the net long-wave radiation flux at the sea surface on the basis of easily measurable meteorological quantities (air and sea surface temperatures, near-surface water vapour pressure, cloudiness). Empirical data and existing formulae are compared. Additionally, an improved formula for the southern Baltic region is introduced, with a systematic error of less than 1 W -2 and a statistical error of less than 20 W -2.

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Preliminary comparison between various models of the long-wave radiation budget of the sea and experimental data from the Baltic Sea [commun.]

Zapadka T., Woźniak S.B.

Oceanologia

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2000

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No. 42 (3)

359-369

EN

This paper discusses existing models of long-wave radiation exchange between the sea surface and the atmosphere, and compares them with experimental data. The latter were based on empirical data collected in the southern Baltic during cruises of r/v `Oceania'. To a greater or lesser extent, all the models were encumbered with significant systematic and statistical errors. The probable reasons for these discrepancies are given.