Specific Attenuation Coefficient Research Articles

骨等価溶液を用いた骨SPECT評価用ボディファントムの開発

We developed a custom-designed phantom for bone single photon emission computed tomography (SPECT)-specific radioactivity distribution and linear attenuation coefficient. The aim of this study was to evaluate the accuracy of the phantom. The lumbar phantom consisted of the trunk of a body phantom (background) containing a cylinder (vertebral body), a sphere (tumor), and a T-shaped container (processus). The vertebral body, tumor, and processus phantoms contained a K(2)HPO(4) solution of bone equivalent density and 50, 300 and 50 kBq/mL of (99m)Tc, respectively. The body phantom contained 8 kBq/mL of (99m)Tc solution. SPECT images were acquired using low-energy high-resolution collimation, a 128 × 128 matrix and 120 projections over 360° with a dwell time of 15 sec/view × 4 times. Thereafter, CT images were acquired at 130 kV and 70 ref mAs using adaptive dose modulation. The SPECT data were reconstructed with ordered subset expectation maximization with three-dimensional, scatter, and CT-based attenuation correction. Count ratio, linear attenuation coefficient (LAC), and full-width at half-maximum (FWHM) were measured. Count ratios between the background, the vertebral body, and the tumor in SPECT images were 463.8: 2888.0: 15150.3 (1: 6.23: 32.7). The LAC of the background and vertebral body in the CT-derived attenuation map were 0.155 cm⁻¹ and 0.284 cm⁻¹, respectively, and the FWHM measured from the processus was 15.27 mm. The precise counts and LAC indicated that the phantom was accurate and could serve as a tool for evaluating acquisition, reconstruction parameters, and quantitation in bone SPECT images.

Evaluation of a New Polarimetric Algorithm for Rain-Path Attenuation Correction of X-Band Radar Observations Against Disdrometer

A new algorithm called self-consistent with optimal parameterization (SCOP) for attenuation correction of radar reflectivities at low elevation angles is developed and evaluated. The SCOP algorithm, which uses optimal parameterization and best-fitted functions of specific attenuation coefficients and backscattering differential phase shift, is applied to X-band dual-polarization radar data and evaluated on the basis of radar observables calculated from disdrometer data at a distance of 35 km from the radar. The performance of the SCOP algorithm is compared with other algorithms [reflectivity-differential phase shift (ZPHI) and full self-consistent (FSC)] presented in the literature. Overall, the new algorithm performs similarly to ZPHI for the attenuation correction of horizontal-polarization reflectivity, whereas the FSC algorithm exhibits significant underestimation. The ZPHI algorithm tends to overestimate small rain-path attenuation values. All algorithms exhibit significant underestimation at high differential rain-path attenuation values, probably due to the presence of hail along the path of the radar beam during the examined cases. The new SCOP algorithm has the potential to retrieve profiles of horizontal and differential reflectivities with better accuracy than the other algorithms due to the low error of the parameterization functions used in it. Typical radar calibration biases and measurement noise are sufficient requirements to ensure low errors of the proposed algorithm. A real-time method to calibrate the differential reflectivity without additional measurements is also described.

A numeric evaluation of attenuation from ambient noise correlation functions

The ambient noise correlation function (NCF) calculated between seismic stations contains, under appropriate conditions, accurate travel time information. However, NCF amplitudes are highly debated due to noise source intensity and distribution, seismic intrinsic attenuation, scattering, and elastic path effects such as focusing and defocusing. We prove with various numerical simulations that the NCFs calculated for a uniformly dispersive medium using the coherency method preserve accurate geometrical spreading and attenuation decay. We show that for a wide range of noise source distributions, the coherency of the noise correlation functions matches a Bessel function decaying exponentially with a specific attenuation coefficient. Conditions needed to obtain these results include averaging over long enough time intervals, a uniformly distributed seismic network, and a good distribution of far‐field noise sources. We also show that the estimated attenuation coefficient corresponds to the interstation and not the noise‐source‐to‐receiver structure.

An Empirical Expression to Estimate Specific Attenuation Coefficient due to fog at Frequencies from 100 to 300GHz

A simple expression is presented to quickly estimate specific attenuation coefficient due to fog within the ranges of 100~300GHz and -8~20°C based on the Rayleigh approximation which is not very convenient. To evaluate the expression’s estimation performance, the Pearson correlation coefficient (PCC) and maximal absolute value of the relative errors (MAVRE) are calculated. The maximum value of PCC is 1 and it reflects the fitting performance of an empirical expression. MAVRE denotes the largest deviation between a set of estimated values and corresponding theoretical values. Calculations show the PCC and MAVRE of the proposed expression are 0.99985 and 4.162%, respectively. Furthermore, a comparison analysis shows that the new expression has much better estimation performance than other two empirical expressions: the modified Mao expression and the Zhao expression.

Underwater light field determined by water constituents in highly turbid water: the case of Taihu lake

The relationships between optical properties and water constituents in highly turbid productive water were studied on the basis of the multiple bio-optical measurements and samplings of water constituents made during five cruises from 2006 to 2008 in Taihu lake. Taihu lake is a high dynamic ratio [(square root of area)/depth] inland shallow lake. The spatial and temporal variation of water constituents and optical properties is significant. The inorganic suspended matter (ISM) has become the primary constituent in Taihu lake: its average percentage can reach 65.21%. The concentration of ISM is highly correlated to the optical properties in Taihu lake due to the sediment resuspension. Consequently, the ISM can be taken into account as an important optically-active constituent in Taihu lake. Resuspended sediments also lead to a poor correlation between scattering optical property and chlorophyll-a concentration (C Chl-a ). However, empirical relationship between the C Chl-a and phytoplankton absorption coefficient at 675 nm is still valid when the package effect is removed. The parameters of linear equation in the present study have slight temporal variation, especially for the relationship between inherent optical properties (IOPs) and concentration of total suspended matter (TSM). The relationship between apparent optical property (AOP) (diffuse attenuation coefficient of particle, K dbio ) and ISM has been examined as well. The K dbio is strongly affected by ISM, and correlates to it with linear function. The difference between specific diffuse attenuation coefficients of organic [K * dOSM (l)] and inorganic [K * dISM (l)] particles is significant. K * dOSM (l) includes the absorption property of chlorophyll-a (chl-a) at 675 nm, which is much higher than that of K * dISM (l). This indicates that the attenuation ability of OSM is stronger than that of ISM although the K dbio induced by large concentration of ISM is bigger than the K dbio induced by small concentration of OSM. Overall, the knowledge of the bio-optical properties obtained in this study extends our understanding of water optics and can be used to predict the optical properties via water constituent concentration, regardless of measurement type ( in situ or simulated by hydrodynamic model).

Study of the loss of the H 11 mode in a modified circular waveguide in a wide frequency range

The specific attenuation coefficient of the hybrid HE 11 mode in a modified circular waveguide is calculated using a method developed earlier. Calculations are performed in a wide frequency range for a number of waveguide diameters. Combinations of the parameters of modified waveguides providing a substantial decrease in the specific attenuation as compared to that in an empty waveguide are determined.

SU-E-I-105: Optimizing Bomb Squad X-Ray Systems for Incidental Human Exposures.

A current terrorist tactic involves strapping an explosive device to a live victim. Technicians wishing to x-ray the device need to use appropriate exposures to create clear images while mitigating incidental health problems for the live victim. This project involves characterizing and optimizing a popular radiographic system in the explosive investigation community, both for general use and, more specifically, for generating x-rays with a human subject in the beam path. This project seeks to minimize the dose to a victim incidentally located in the beam path, while maximizing image quality, thereby allowing appropriate image evaluation to neutralize the explosive threat. Image quality and dose optimization begins with characterization of the x-ray source. The source in this study is an XRS-3, a portable device developed by Golden Engineering, which nominally produces a 270 kVp beam. Characterization of the beam involves verifying the actual kVp, as well as determining the average energy of the beam with various amounts of filtration added to the beam path. The kVp was verified using a noninvasive technique, utilizing the measurement of the dose attenuation through lead and then modeling the energy dependent attenuation curve of the lead using specific mass attenuation coefficients and parameters suggested by Joseph (Joseph, P.M., Med. Phys. Vol. 2, July/Aug1975; 201-207) in order to calculate the kVp through linear regression. The average energy of an unfiltered beam was 52 keV, and increases through adding various combinations of Cu and brass filters to a maximum value of 121 keV with 3 mm copper + 3 mm brass filtration. The calculated kVp was 290 kV. The average energies using filtration fall within the diagnostic range. The kVp fits well within the manufacturer's specifications of 15% deviation. Optimization can be accomplished with these parameters. University of Oklahoma Health Sciences Center- Department of Radiological Sciences.

Retrieval of Three-Dimensional Raindrop Size Distribution Using X-Band Polarimetric Radar Data

Abstract An improved algorithm based on the self-consistent principle for rain attenuation correction of reflectivity ZH and differential reflectivity ZDR are presented for X-band radar. The proposed algorithm calculates the optimum coefficients for the relation between the specific attenuation coefficient and the specific differential phase, every 1 km along a slant range. The attenuation-corrected ZDR is calculated from reflectivity at horizontal polarization and from reflectivity at vertical polarization after attenuation correction. The improved rain attenuation correction algorithm is applied to the range–height indicator (RHI) scans as well as the plan position indicator (PPI) volume scan data observed by X-band wavelength (MP-X) radar, as operated by the National Research Institute for Earth Science and Disaster Prevention (NIED) in Japan. The corrected ZH and ZDR values are in good agreement with those calculated from the drop size distribution (DSD) measured by disdrometers. The two governing parameters of a normalized gamma DSD, normalized number concentration NW, and drop median diameter D0 are estimated from the corrected ZH and ZDR, and specific differential phase KDP values based on the “constrained-gamma” method. The method is applied to PPI and RHI data of a typhoon rainband to retrieve the three-dimensional distribution of DSD. The retrieved DSD parameters show reasonable agreement with disdrometer data. The present results demonstrate that high-quality correction and retrieval DSDs can be derived from X-band polarimetric radar data.

Observations of OM/OC and specific attenuation coefficients (SAC) in ambient fine PM at a rural site in central Ontario, Canada

Abstract. Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in central Ontario during an intensive study in 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. The concentrations are compared to the organic aerosol mass concentration (OM) measured with an Aerodyne C-ToF Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (basp) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC=basp/EC) are derived. Proportionality of the POC mass with the oxygen mass in the aerosols estimated from the AMS offers a potential means to estimate OM/OC from thermal measurements only. The mean SAC for the study is 3.8±0.3 m2 g−1. It is found that the SAC is independent of or decrease with increasing particle mass loading, depending on whether or not the data are separated between aerosols dominated by more recent anthropogenic input and aerosols dominated by longer residence time or biogenic components. There is no evidence to support an enhancement of light absorption by the condensation of secondary material to particles, suggesting that present model simulations built on such an assumption may overestimate atmospheric warming by BC.

Optical properties and optical constituents of the Faroe Islands shelf and off-shelf waters, North East Atlantic

The study comprises a data set of CTD, optical properties—K 0(PAR), c p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005. Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C) and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K 0(PAR), beam attenuation c p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K 0(PAR) was governed by Chl a, shown by a high (r 2 = 0.64) Chl a–K 0(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient $$ K_{0}^{*} \left( {\text{PAR}} \right) $$ of 0.056 (m2 mg−1 Chl a) and a Chl a specific beam attenuation ( $$ c_{\text{p}}^{*} $$ ) of 0.27 (m2 mg−1 Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained in early spring, and Chl a concentrations were low ~0.5 mg Chl a m−3. Spring bloom Chl a are about 10 mg Chl a m−3 and estimations showed that shelf K 0(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete data set is enclosed.

Specific attenuation coefficients of optically active substances and their contribution to the underwater ultraviolet and visible light climate in shallow lakes and ponds

Sunlight penetration through the water column is controlled by the amount and kind of materials dissolved and suspended in the water. Understanding UV penetration in its complexity is essential for the prediction of the impact of UV radiation on aquatic ecosystems. However, only limited data are available on the penetration of UVR into shallow waters rich in inorganic suspended solids and chromophoric dissolved organic matter (CDOM). The same is true for the specific attenuation coefficients of light-absorbing components at the UV waveband. This study analyses the role of CDOM, algal-free suspended solids and algae in the formation of underwater UVR and PAR climate in 30 water bodies from clear gravel pit lakes trough the shallow Lake Balaton to turbid soda pans. Irradiance-depth profiles were obtained at 305, 313, 320 nm (UV-B), 340, 380, 395 nm (UV-A) and 400–700 nm (PAR) with a Biospherical PUV-2500 radiometer. Vertical attenuation coefficients (K d) were calculated. Water samples were taken for the laboratory measurement of the concentration of light-absorbing components: algae as chlorophyll a (CHL), chromophoric dissolved organic matter as colour (CDOM), and algal-free suspended solids (TSS-Alg) parallel with the in situ light measurements. Specific attenuation coefficient values were calculated by multiple regression analysis (n = 140). The obtained specific UV attenuation coefficient values of CHL, CDOM and TSS-Alg made it possible to establish light attenuation at different wavelengths based on the knowledge of the concentration of these light-absorbing components.

Variability in factors causing light attenuation in Lake Victoria

Summary1. The major optical components controlling the attenuation of photosynthetic available radiation in nearshore areas of Lake Victoria (Uganda and Kenya) were examined and their impact compared. It was found that chromophoric dissolved organic matter and tripton play a dominating role in many nearshore areas, indicating that the coastal areas of Lake Victoria cannot be considered as Case I waters.2. Concentrations of chromophoric dissolved organic matter declined with distance from the coast in an exponential manner indicating dilution and degradation of terrestrial sources of organic matter rather than in situ production. The importance of tripton was found to follow a similar pattern, while the relative importance of phytoplankton biomass in overall attenuation of photosynthetic available radiation was found to increase with distance from the coast. A specific attenuation coefficient for phytoplankton biomass was determined (0.019 m2 mg Chl a−1).3. Using a light limitation approach based on carrying capacity, it was possible to map areas that are closer to being light limited. Light limitation appears to occur throughout most bays and some coastal areas receiving catchment waters. This spatial information, geographically referenced to bathymetric and catchment conditions, was utilized to understand the importance of environmental conditions in limiting phytoplankton biomass.

Estimation of Effective Rain Height at 29 GHz at Amritsar (Tropical Region)

The effect of precipitation present in the path of Earth-space communication links, in terms of fading of the signal, is well known. The calculation of fade margin required for 99.99% of the time availability of such links requires the knowledge of various location-specific meteorological parameters, amongst which rain height is prominent. This paper presents results from measurements conducted at Amritsar during a single rain event that took place on September 19, 2005, using a zenith-pointing Dicke-type radiometer at 29 GHz in the form of sky noise temperature. The output of the radiometer along with rain rate, derived from colocated tipping-bucket rain gauge, has been used to obtain a formula relating zenith path attenuation and rain rate. Further, the values of zenith path attenuation and rain rate along with specific attenuation coefficients a and b to obtain effective rain height. It was found that rain height cannot be taken as constant as it is dependent on rain rate. The average rain height during the event was estimated to be 3.54 km with root mean square error of 3.0 km

ACCLIMATION OFEMILIANIA HUXLEYI(PRYMNESIOPHYCEAE) TO PHOTON FLUX DENSITY1

Growth rate, pigment composition, and noninvasive chlafluorescence parameters were assessed for a noncalcifying strain of the prymnesiophyteEmiliania huxleyiLohman grown at 50, 100, 200, and 800 μmol photons·m−2·s−1.Emiliania huxleyigrown at high photon flux density (PFD) was characterized by increased specific growth rates, 0.82 d−1for high PFD grown cells compared with 0.38 d−1for low PFD grown cells, and higherin vivochlaspecific attenuation coefficients that were most likely due to a decreased pigment package, consistent with the observed decrease in cellular photosynthetic pigment content. High PFD growth conditions also induced a 2.5‐fold increase in the pool of the xanthophyll cycle pigments diadinoxanthin and diatoxanthin responsible for dissipation of excess energy. Dark‐adapted maximal photochemical efficiency (Fv/Fm) remained constant at around 0.58 for cells grown over the range of PFDs, and therefore the observed decline, from 0.57 to 0.33, in the PSII maximum efficiency in the light‐adapted state, (Fv′/Fm′), with increasing growth PFD was due to increased dissipation of excess energy, most likely via the xanthophyll cycle and not due to photoinhibition. The PSII operating efficiency (Fq′/Fm′) decreased from 0.48 to 0.21 with increasing growth PFD due to both saturation of photochemistry and an increase in nonphotochemical quenching. The changes in the physiological parameters with growth PFD enableE. huxleyito maximize rates of photosynthesis under subsaturating conditions and protect the photosynthetic apparatus from excess energy while supporting higher saturating rates of photosynthesis under saturating PFDs.

A simple empirical optical model for simulating light attenuation variability in a partially mixed estuary

Representation of the subsurface light field is a crucial component of pelagic ecosystem and water quality models. Modeling the light field in estuaries is a particularly complicated problem due to the significant influence of high concentrations of dissolved and particulate matter that are derived from both terrestrial and estuarine sources. The goal of this study was to develop a relatively simple but effective way to model light attenuation variability in a turbuid estuary (Chesapeake Bay, United States) in a coupled physical-biological model. We adopted a simple, nonspectral empirical approach. Surface water quality data (salinity was used as a proxy of chromophoric dissolved organic matter [CDOM]) and light measurements from the Chesapeake Bay Program were used to determine the absorption coefficients in a linear attenuation model using regression methods. This model predicts Kc (specific attenuation due to phytoplankton/chlorophylla [chla]), Kt (specific attenuation due to total suspended solids), and Ks (a function of specific attenuation coefficients of CDOM in relation to salinity). The Bay-wide fitted relation between the light attenuation coefficient and water quality concentrations gives generally good estimates of total light attenuation, Kd. The direct inclusion of salinity in the relationship has one disadvantage: it can yield negative values for Kd at high salinities. We developed two separate models for two different salinity regimes. This approach, in addition to solving the negative Kd problem, also accounts for some changes in specific light absorption by chla, seston (nonphytoplankton particulate matter), and CDOM that apparently occur in different salinity regimes in Chesapeake Bay. The resulting model predicts the statistical characteristics (i.e., the mean and variance) of Kd quite accurately in most regions of Chesapeake Bay. We also discuss in this paper the feasibility and caveats of using Kd converted from Secchi depth in the empirical method.

Retrieval of wheat leaf area index using price approach based on inversion of canopy reflectance model

This paper reports estimation of the Leaf Area Index (LAI) of wheat crop from IRS-LISS-III data using Price (1993) approach. Empirical approach for LAI estimation with different NDVI estimation procedures viz. radiance, apparent reflectance and dark object subtraction (DOS) based atmospheric correction were also evaluated. Validation of LAI retrieval and NDVI normalizations were carried out using field level measurements of crop LAI and spectral property using canopy analyzer and spectro-radiometer, respectively over selected fields in Bhopal District, Madhya Pradesh. It was observed that empirical relations are sensitive to the NDVI estimation approach and DOS method performed better as compared to other two approaches. It was also observed that LAI estimation from Price algorithm is sensitive to the crop attenuation coefficients. Crop specific attenuation coefficients reported in literature for Indian cultivars gave higher accuracy. The root mean square (RMS) error of 0.77 for LAI estimation was achieved using above described approach.

Frequency-domain wave equation and its time-domain solutions in attenuating media.

Our purpose in this paper is to describe the wave propagation in media whose attenuation obeys a frequency power law. To achieve this, a frequency-domain wave equation was developed using previously derived causal dispersion relations. An inverse space and time Fourier transform of the solution to this algebraic equation results in a time-domain solution. It is shown that this solution satisfies the convolutional time-domain wave equation proposed by Szabo [J. Acoust. Soc. Am. 96, 491-500 (1994)]. The form of the convolutional loss operator contained in this wave equation is obtained. Solutions representing the propagation of both plane sinusoidal and transient waves propagating in media with specific power law attenuation coefficients are investigated as special cases of our solution. Using our solution, comparisons are made for transient one-dimensional propagation in a medium whose attenuation is proportional to frequency with recently obtained numerical solutions of Szabo's equation. These show good agreement.

Spatial and temporal patterns of light attenuation among lakes of the Mackenzie Delta

SUMMARY 1. The seasonal dynamics of light attenuation, and the relative roles of total suspended solids (TSS), dissolved organic carbon (DOC) and chlorophyll as light attenuators among two sets of lakes in the Mackenzie Delta, were assessed during the open‐water periods of 1998 and 1999.2. The first set consisted of 40 spatially discrete lakes where the frequency of flooding with river water was controlled by sill height (‘sill‐set lakes’). The second set consisted of a chain of six lakes connected to a main river channel (frequently flooded, all with same frequency), but where riverine influence was controlled by the distance from the channel connection point (‘chain‐set lakes’).3. As the flooding frequency of lakes decreased (sill‐set), and as the distance from the channel connection point increased (chain‐set), lake water became increasingly transparent and the stability (decreasing temporal variability) of underwater light increased.4. The effect of flooding on transparency was greater in years with a high minimum summer water level. However, the effect of river flooding on lake water transparency was damped more by an increase in the frequency and duration of flooding than by an increase in distance from the channel connection point.5. The index of scattering was linearly related to TSS over the common range of concentrations in both sets of lakes. The specific attenuation coefficient for TSS (and scattering) increased substantially from the most turbid to the most transparent waters.6. During the summer, DOC provided an approximate index of water colour in the sill‐set lakes but not in the chain‐set lakes, where the gradient of DOC ran counter to the gradient of water colour. The specific attenuation coefficient for water colour was roughly constant among both sets of lakes.7. Calculations of partial attenuation show that, during the spring flood peak, TSS is the dominant attenuator among most lakes, other than those with high sills or positioned far from channel connection points. During the lengthy summer period of open water, however, water colour appeared to be the most important light attenuator among almost all of the lakes in the central delta, with chlorophyll a of only minor importance.8. Lakes of the Mackenzie Delta may be quite sensitive to changes in climate and ultraviolet‐b (UV‐b) radiation in the circumpolar arctic because of the role of DOC as an attenuator of photosynthetically active radiation and UV‐b irradiance and as an energy source for microbial foodwebs in this system.

Development of an improved optical transmission technique for black carbon (BC) analysis

A new optical transmission technique for black carbon (BC) analysis was developed to minimize interferences due to scattering effects in filter samples. A standard thermal analysis method (VDI, 1999) is used to link light attenuation by the filter samples to elemental carbon (EC) concentration. Scattering effects are minimized by immersion of the filters in oil of a similar refractive index, as is often done for microscopy purposes. Light attenuation was measured using both a white light source and a red LED of 650 nm. The usual increase in overestimation of BC concentrations with decreasing BC amount in filter samples was found considerably reduced. Some effects of BC properties (e.g. fractal dimension, microstructure and size distribution) on the specific attenuation coefficient B ATN, however, are still present for the treated samples. B ATN was found close to 1 m 2 g −1 for dry-dispersed industrial BC and 7 m 2 g −1 for nebulized BC. Good agreement was found between the oil immersion, integrating sphere and a polar photometer technique and Mie calculations. The average specific attenuation coefficient of ambient samples in oil varied between 7 and 11 m 2 g −1 for white light and 6 and 9 m 2 g −1 for red light (LED). B ATN was found to have much less site variation for the treated than for the untreated samples. The oil immersion technique improved also the correlation with thermally analyzed EC. This new immersion technique therefore presents a considerable improvement over conventional optical transmission techniques and may therefore serve as a simple, fast and cost-effective alternative to thermal methods.

Factors affecting clarity of freshwater lakes in Brandenburg, Germany

In the German State Brandenburg, water clarity and the concentrations of the water quality components chlorophyll a, seston and gelbstoff were measured in 27 lakes. Correlation analysis showed, that spectral beam attenuation at 662 and 514 nm was mainly dependent on changes in chlorophyll a concentrations. In the UV-channel at 360 nm, beam attenuation depended mostly on gelbstoff. Multiple linear regression provided a direct model of beam attenuation at 514 nm with the inputs of inorganic seston, chlorophyll a and gelbstoff. The specific beam attenuation coefficients were comparable to other natural waters around the world. An inverse model is presented, from which gelbstoff and chlorophyll a could be predicted with some accuracy from the inputs of beam attenuation coefficients at 514 and 360 nm. However, it became obvious that biological variability put major constraints on the predictive capacity of both the direct and the inverse model. Furthermore, we observed a good correspondence of Secchi depth and the inverse of beam attenuation at 514 nm. The predictions of Secchi depth and chlorophyll a concentration from the inverse model were assessed in perspective of using this instrument instead of laborious chemical analysis for future trophic status classification according to LAWA (Länderarbeitsgemeinschaft Wasser). Predictions of trophic status were principally good when using calibrated models, however, quality of classification critically depended on predictions of chlorophyll a.