A novel correlation technique, the robust phase correlation (RPC), is introduced which amplifies the signal-to-noise ratio of the DPIV cross-correlation to produce velocity estimations that are accurate and robust to a variety of image conditions. Specifically, this estimator shows substantial resilience against additive background noise non-uniform illumination and thermal noise effects. In addition, the RPC is able to substantially reduce bias errors and peak locking in the presence of high shear and rotational motion in comparison with standard cross-correlation algorithms. The success of this technique relies upon an analytical decomposition of the DPIV signal-to-noise ratio, which is then applied as a spectral filter in a novel implementation of the generalized cross-correlation (GCC). The RPC also utilizes advanced windowing techniques to attenuate Fourier-based errors. Because of the GCC filtering, the application of windowing in the RPC is not susceptible to the effects of additive background noise that commonly causes errors for windowed cross-correlation estimation. The RPC estimator is validated using both artificial images and experimental data to demonstrate its enhanced measurement capabilities.
Outstanding Paper Awards 2009
Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believes that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal.
The current breadth of topical areas that are covered by MST has made it advisable to expand the recognition of excellent publications. Hence, since 2005 the Editorial Board have presented 'Outstanding Paper Awards' in four subject categories: Fluid Mechanics; Measurement Science; Precision Measurements; and Sensors and Sensing Systems. This year also saw the introduction of a new category—Optical and Laser-based Techniques.
For full details please see the Editorial.
Fluid mechanics
Precision measurement
A nanonewton force facility, based on a disk-pendulum with electrostatic stiffness reduction and electrostatic force compensation, for the measurement of horizontal forces in the range below 1 µN, is presented. It consists of a measuring system and an identical reference system. Recent experiments with the nanonewton force facility have achieved agreement between an electrostatic force and a gravitational force of 80 nN with an uncertainty of less than 3%. A novel method for measurements of the air (vacuum) permittivity at zero frequencies by means of the nanonewton force facility is presented. First measurements in air show a permittivity of the air ε ≈ 8.71 × 10−12 F m−1 with an uncertainty of 3%. From a theoretical analysis, it follows that this method can be used for the measurement of the vacuum permittivity ε0 at zero frequencies with a relative uncertainty of about 10−5. The precise measurement of the vacuum permittivity ε0 for an electrostatic field would be another test for the correctness of Maxwell's equations.
Sensors and sensing systems
A new compact optical refractometer is presented to improve the measurement of the refractive index of seawater. These measurements are useful in oceanography to calculate density and salinity of oceans from empirical relations. This refractometer shows a lower temperature dependence and obtains a better absolute accuracy on salinity compared to the conductivity sensors which are used nowadays to assess seawater salinity. Tests and calibrations have been made in a temperature-stabilized seawater tank. They show that the prototype is capable of measuring seawater refractive index with a resolution of about ±4 × 10−7, equivalent to a salinity resolution of ±2 × 10−3 g kg−1.
Measurement science
This paper describes the traceability chain for photovoltaic devices and the measurement methods employed to perform the various transfer steps. The measurement uncertainties are analysed in detail based on the accreditation of the European Solar Test Installation (ESTI) for the calibration of photovoltaic devices. The various contributions to the overall uncertainty are critically analysed for various traceability chain options. A major contribution is the uncertainty in the calibration of the primary reference device. The overall measurement uncertainty is reduced using the ESTI reference cell set compared to the traceability from the world photovoltaic scale. For the maximum power of photovoltaic modules, the expanded combined uncertainty is reduced from ±2.6% to below ±2%. Recommendations are made on the scope for further reduction of uncertainty and for the best calibration strategy for various PV technologies.
Optical and laser-based techniques
Optical fibre probing is widely applied to measurements in gas–liquid two-phase flows. We have already developed and reported a four-tip optical fibre probe (F-TOP) for millimetre-size bubbles/droplets, and a single-tip optical fibre probe (S-TOP equipped with a wedge-shaped tip) for sub-millimetre-size bubbles/droplets. However, it is difficult to measure micrometre-size bubbles/droplets by S-TOP. The main purpose of the present study was to develop a new type of optical fibre probe micro-fabricated by a femtosecond pulse laser (Fs-TOP). First, we confirmed the performance of the new probe by examining millimetre- and sub-millimetre-size droplets; the results from the Fs-TOP were compared with those obtained from the visualization of the droplets by high-speed video camera, and showed satisfactory agreement. In addition, we demonstrated the measurement of velocities and chord lengths of micrometre-size droplets (about 50 µm in diameter) using the Fs-TOP and compared them with those from the S-TOP to clarify the limits and strengths of each type of probe.
Previous winners
2008, 2007, 2006