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The iterative (with constant "lidar ratio") and the general recursive (with variable "lidar ratio") algorithms have been used to backscattering lidar data. The data have been collected in the Lidar Center in Thessalonica, Greece. The vertical profiles of backscatter coefficient retrieved with these two algorithms differ slightly. The vertical profile of "lidar ratio" for the laser wavelength 532 nm, depending on the day or time of the day, changes its values but doesn't reveal any essential structure. The wavelength 355 nm seems to be more "sensitive" and shows some structure for "lidar ratio". Most probably these structures are due to the presence of different aerosol layers. From vertical backscatter coefficients, both 355 nm and 532 nm, at least, two aerosol layers can be differentiated.

Both marine and urban aerosols, which differ in their origin and chemical composition, are subjected to strong dynamic processes in the coastal areas, especially over strongly urbanised areas. The simultanteous presence of both types of aerosols leads to their effective mixing due to the action of winds and convection. This work presents examples of interactions of the two types of aerosols and the impact of the dynamic atmospheric processes on migration of aerosol masses, at two locations in Athens and Kolobrzeg.

This paper presents results of a study of aerosol pollution distribution and dynamics measured by lidar observations over the city of Athens. The seasonal dynamics of vertical changes in the backscattering coefficient, extinction coefficient and lidar ratio for lower troposphere has been determined.

Vertical profiles of aerosol extinction and "lidar ratios" of the lower troposphere in Thessalonica have been measured with two -wavelengths lidar. The extinction profile for the wavelength 355 nm seem to be insensitive for the time of the day. The profile for 532 nm has its maximum intensity at about 7 am, then decreases and increases during the afternoon and the evening. The vertical profiles of "lidar ratio" are structured for 355 nm but for 532 nm, are almost constant. It has been concluded that, at least, two different kinds of aerosols contribute to the observed profiles: one sensitive (532 nm) and a second one, insensitive for the changes in solar radiation (355 nm) during the day. Both, extinction and "lidar ratios" are characterized by high values for the wavelength 355 nm.

The paper gives a general inversion algorithm for lidar's data derivation and profiles of the extinction coefficient, backscattering coefficient and lidar ratio for the lower troposphere. To the best of our knowledge these are the first results obtained with this algorithm.

A novel backscattering lidar inversion procedure is presented. This method consists of two steps: the first one is the determination of a preliminary vertical profile of the unit volume extinction coefficient by the iterative Klett's method, and the second one is the determination of the vertical profile of unit volume backscattering coefficient from the previous step --using the relationship between (alpha) (r) and (beta) (r) -- which is given by two independent solutions for both variables. The calculation of the vertical profile of the 'lidar ratio' [determined as: (beta) (r)/(alpha) (r) is automatic ]. The proposed method is applied, in a preliminary case, to several backscatter lidar signals, obtained by a two wavelength backscattering lidar system in Greece. The proposed procedure can be applied for each wavelength of a multiwavelength backscattering lidar system, independently -- which means that the unit volume extinction and backscatterer profile of the atmosphere can be spectrally resolved. The general case of this procedure has not been applied yet, to a computer simulation, while this work is still in progress.

We present a sensor for the continuous detection of fluorescent emissions from fluids. The sensor utilizes a patented optical fiber detection system to allow separation of the excitation and emission light without the need for optical filters, has a wide working range and has applications in process control, flow tracing and monitoring. The construction, principles and experimental results of the fiber sensor will be given. The authors have also developed a novel test for total toxicity of aquatic systems, the product of which is fluorescent, enabling the proposal of a rapid, continuous and low cost toxicity measurement system. The biochemistry of the test is easily adapted for all types of aquatic environment and expected pollution levels. Results for several heavy metal and organic contaminants, performed under laboratory conditions, are also presented.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper a multiwavelength (355, 532, and 1064 nm) lidar sounding across a stack plume has been computer simulated. The lidar data were then inverted using four different procedures proposed by: Klett, Evans, Potter and Grabowski. Results of these inversions were dependent on both: dust particle size dispersion and mass concentration. It has been shown that Grabowski's iterative procedure retrieves a plume dust concentration profile with a reasonable accuracy and seem to be (as it does not require assumption on a backscatter- extinction ratio) advantageous to others.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

If a fluorogenic compound, such as fluorescein diacetate, is added to a water solution containing living cells it becomes hydrolyzed by intracellular esterases into a fluorochrome whose fluorescence can be used to monitor the cytoplasmic pH and the cytoplasmic viscosity of the cells. In this paper we have used this technique to measure the effects of different concentrations of Co2+ and Cd2+ ions on the cytoplasmic pH and the cytoplasmic viscosity of a single cell culture. Our results indicate that the observed decrease in the efficiency of the intracellular hydrolyzation of fluorogenic substances in the presence of different concentrations of heavy metals could be caused by both a decrease in the cytoplasmic pH and an increase in the cytoplasmic viscosity. A decrease in cytoplasmic pH would decrease the effectiveness of the intracellular enzymes, whereas an increase in cytoplasmic viscosity would decrease diffusion which would also reduce the effectiveness of the reaction. The dependence of the reciprocal of the cytoplasmic viscosity on the concentration of these metals correlates well with published results on their toxicity.

Preliminary results are presented for an optical fibre toxicity sensor for on-line monitoring of toxic effluents. The rate of hydrolysis of Fluorescein Diacatete, by living micro-organisms, is proportional to their metabolic rate, producing fluorescein, which fluoresces at 512 nm. The time dependence of fluorescent emission is related to the metabolic rate of the organisms which is affected by toxic substances. Fluorescence is monitored using a stripped core 1mm diamter optical fibre, by excitation at 470 nm using blue LEDs.

Toxicity testing using fluorogenic compounds offers a number of advantages. These include a small sample volume, low cost, rapidity, and applicability to both a micro-organism monoculture and a biocenosis. The method relies on measuring the rate of enzymatic intracellular conversion of a fluorogenic substrate into a fluorochrome. We show how the rate of conversion depends on the substrate concentration, the biomass concentration and pH. We also show how the method can be used to measure the toxicities of several different toxicants, to study antagonistic and synergistic effects of different metal combinations and to study inhibition mechanisms. We then show that it is also possible to measure the cytoplasmic viscosity by exciting the fluorescein molecules in the cytoplasm with polarized light and measuring the polarization of the emitted fluorescence.

— Absorption and fluorescence polarization spectra, as well as absolute fluorescence quantum yields, and lifetimes of phycobiliproteins separated from intact phycobilisomes of Porphyridium cruentum, Nostoc sp. and Fremyella diplosiphon were measured. Two different types of phycoerythrin, in addition to phycocyanin and allophycocyanin, were separated from both Porphyridium cruentum and Nostoc sp. phycobilisomes. They were distinguishable by the shape of their absorption spectra, values of fluorescence quantum yields and their limiting polarization. Phycobilisomes of Fremyella diplosiphon had a type of phycoerythrin that was different from the above kinds. By the use of fluorescence quantum yields and lifetime data, the values of natural lifetimes, the decadic molar extinction coefficients, as well as Forster's critical distances R0 for excitation energy transfer, between phycobiliproteins in phycobilisomes, were estimated. The values obtained of Forster's critical distances indicate that for most efficient energy transfer from phycoerythrin to allophycocyanin, the outer layers of Porphyridium cruentum and Nostoc sp. phycobilisomes should be composed of bangiophycean, phycoerythrin and cyanophytan phycoerythrin-II respectively.

The absorption and circular dichroism (CD) spectra of allophycocyanin II in the trimer and monomer (dissociated) forms were resolved into four and two components, respectively. The short-wavelength region of the visible spectra was approximated by a chimera of Lorentzian- and Gaussian-shaped bands having a bandwidth of ca. 65 nm. The rest of the bands have a pure Gaussian form. The characteristic 652-nm band in the absorption spectrum (656 nm in the CD spectrum) is shown to arise from exciton interaction between two fluorescent phycocyanobilin chromophores.

An optical fibre sensor is presented for the continuous measurement of fluorescent emissions from a fluid sample. The sensor employs a novel patented waveguiding system to allow separation of the excitation and emission wavelengths without optical filtering, has a working range of eight decades with fluorescein and is both chemically and physically robust. The device has applications in process control, flow tracing and environmental monitoring. The authors have developed a novel biochemical toxicity assay technique that produces a fluorescent indication of overall toxicity levels and this assay can be interfaced to the optical fibre sensor to form a rapid online toxicity monitoring device. The assay can be applied to any environment as the test organism is variable. Details of the sensor and aspects of the optical theory are presented together with the results of initial laboratory tests both of the sensor device and the toxicity assay technique.