On-line determination of sludge settling velocity for flux-based real-time control of secondary clarifiers.

The state diagram for operation of secondary clarifiers is used to design a control algorithm for the return sludge pumping and determination of the actual hydraulic capacity of the biological step of a wastewater treatment plant. On-line input for the control algorithm is derived from a sludge volume sensor and a suspended solids sensor in the form of software sensors giving values for the sludge settling characteristics - settling velocity, sludge volume index, initial settling velocity and the exponent in the Vesilind equation - allowing the control to accommodate the ever changing settling characteristics and thereby keep the suspended solids flux in the clarifiers in balance for both dry weather flows and during rain events. The control algorithm has been implemented, tested and set into normal operation on a full scale wastewater treatment plant.

Lossless light projection.

A new technique for energy-preserving phase-only light projection is demonstrated. The phase-only encoding is based on an extension of the Zernike phase-contrast method into the domain of full-range [0; 2pi ] phase modulation, breaking the usual small-phase-angle limitation. Controlling the spatial average value of the input-phase pattern and choosing appropriate phase retardation at the phase-contrast filter yield pure-phase-based image formation. Experimental results demonstrate close to 90% energy efficiency. Output intensity levels with magnitudes more than 3.5times that of the input intensity level were measured in the brightest regions of the projected images.

Surface light scattering: integrated technology and signal processing.

The miniaturization of surface-scattering instruments for measuring viscoelastic properties is investigated. The concepts are based on the use of holographic optical elements and integrated optics. Compact forms of optics that provide the necessary spatial and angular selections are devised. Four systems representing increasing levels of integration are considered. It is demonstrated that efficient signal and data processing can be achieved by evaluation of the statistics of the derivative of the instantaneous phase of the detector signal.

Laser velocimeters: lower limits to uncertainty.

Laser velocimeters based on many-particle scattering or rough surface scattering are considered. It is shown that the established lower limits to the accuracy are not fundamental limits. Both linear and nonlinear signal processing may enhance the performance. Generic schemes for the processing are presented, and limitations are discussed.

Estimating time and time-lag in time-of-flight velocimetry.

Estimating time and time-lag in time-of-flight velocimeters is investigated. Statistics of a filtered Poisson point process is given. A Maximum Likelihood Estimator is compared with suboptimum estimators in terms of robustness. For a dominating background combined spatial and temporal processing can improve the robustness compared with purely temporal processing. Schemes for the spatial filters are given.

Surface fluctuation scattering using grating heterodyne spectroscopy.

Heterodyne photon spectroscopy is used for the study of the viscoelastic properties of the liquid interface by studying light scattered from thermally generated surface fluctuations. A theory of a heterodyne apparatus based on a grating is presented, and the heterodyne condition is given in terms of the parameters of the experimental setup. Particular attention is paid to those conditions of the experiment that can cause systematic errors. An instrument function for the apparatus relating the measured output to the experimental parameters of interest is derived. It is shown that the instrument function is generally not Gaussian but that its functional form can depend strongly on the parameters of the experimental setup. In particular, it is shown that significant systematic deviations are expected from previous published analysis of the problem. This is primarily due to the nonlinear relation of the surface wave number to the frequency. An algorithm is suggested to arrive at the frequency and width parameters of the spectrum from a typical noisy experimental data set and applied to data obtained from ethanol surfaces.

Temperature profiling by Rayleigh-scattering lidar.

A lidar with high spectral resolution can be used to measure atmospheric temperature profiles according to conservative performance calculations. The technique analyzed relies on determining the temperature-dependent Rayleigh-scattering linewidth with two stabilized Michelson interferometers in parallel. From ratios of four integrated flux values from two photomultipliers, one can determine temperature profiles within a 1 K standard deviation to 5 km with 50-m height resolution in 1(1/4) min using a laser of 1-W average power and a telescope of 30-cm diam.

Estimating the spectral width of a narrowband optical signal.

Methods for estimating the spectral width of a narrowband optical signal are investigated. Spectral analysis and Fourier spectroscopy are compared. Optimum and close-to-optimum estimators are developed under the constraint of having only one photodetector.

Differential Doppler heterodyning technique.

Measuring velocity without disturbing the moving object is possible by use of the laser doppler heterodyning technique. Theoretical considerations on the doppler shift show that the antenna property of the photodetector can solve an apparent conflict between two different ways of calculating the detected doppler frequency. We found that the doppler frequency for this particular setup is independent of the direction of detection. Investigations of the signal-to-noise ratio (SNR) show that the maximum SNR-considering the optical setup-is obtained by measuring the frequency difference between two dopplershifted beams rather than by measuring the shift of a single beam by comparing it with a reference beam. Measurements seem to be in agreement with the theoretical consideration.