Sensor Response Function Research Articles

Camera characterization for color research

AbstractIn this article we introduce a new method for estimating camera sensitivity functions from spectral power input and camera response data. We also show how the procedure can be extended to deal with camera nonlinearities. Linearization is an important part of camera characterization, and we argue that it is best to jointly fit the linearization and the sensor response functions. We compare our method with a number of others, both on synthetic data and for the characterization of a real camera. All data used in this study is available online at www.cs.sfu.ca/∼colour/data. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 152–163, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/col.10050

Analysis of Piezoelectric Sensor to Detect Flexural Waves

In this paper the electro-mechanical transfer characteristics of adhesively bonded piezoelectric sensors are investigated. Using dynamic piezoelectricity theory, Mindlin plate theory for flexural wave propagation and a multiple integral transform method, the frequency response functions of piezoelectric sensors with and without backing materials are developed and the pressure-voltage transduction functions of the sensors calculated. The corresponding simulation results show that the sensitivity of the sensors is not only dependent on the sensors' inherent features such as piezoelectric properties and geometry, but also on local characteristics of the tested structures and the admittance and impedance of the attached electrical circuit. It is also demonstrated that the simplified rigid mass sensor model can be used to successfully analyse the sensitivity of the sensor at low frequencies, but that the dynamic piezoelectric continuum model has to be used for higher frequencies, especially around the resonance frequency of the coupled sensor-structure vibration system.

Correction of a Piezoresistive Pressure Sensor Using a Microcontroller

A smart piezoresistive pressure sensor using a microcontroller is described. The microcontroller ensures temperature compensation and linearization of the sensor, as well as the data exchange. To compensate for the sensor's imperfection, approximation of the sensor inverse response function by a second-order polynomial in terms of pressure and temperature is used. The maximum measurement error with respect to the full measurement range lies within ±0.1% compared to the ideal sensor response function within the temperature range of 0–70°C.

Turbulent properties in a homogeneous tidal bottom boundary layer

Profiles of mean and turbulent velocity and vorticity in a tidal bottom boundary layer are reported. Friction velocities estimated (1) by the profile method using the time mean streamwise velocity, (2) by the eddy‐correlation method using the turbulent Reynolds stress, and (3) by the dissipation method using the turbulent kinetic energy dissipation rate ε are in good agreement. The mean streamwise velocity component exhibits two distinct log layers. In both layers, ε is inversely proportional to the distance from the bottom Z. The lower log layer occupies the bottom 3 m. In this layer, the turbulent Reynolds stress is nearly constant. The dynamics in the lower log layer are directly related to the stress induced by the seabed. The upper log layer spans 5 to 12 m above the bottom. In this layer, the turbulent Reynolds stress decreases toward the surface. The friction velocity estimated by the profile method in the upper log layer is about 1.8 times of that estimated in the lower log layer. Form drag might be important in the upper log layer. A detailed study of upstream topography is required for the bed stress estimate. The mean profile of vertical flux of spanwise vorticity is nearly uniform with Z and is at least a factor of 5 larger than the vertical divergence of turbulent Reynolds stress to which it may be compared. A new method of estimating the friction velocity is proposed that uses the vertical flux of turbulent spanwise vorticity. This is supported by the fact that the vertical eddy diffusivity for the turbulent vorticity is about equal in magnitude and vertical structure to the eddy viscosity for the turbulent momentum. The friction velocity calculated from the vorticity flux is equal to that estimated by the other three methods. Turbulent enstrophy, corrected for the sensor response function, is proportional to Z−1 for the entire water column. The relation between ε and enstrophy for high‐Reynolds‐number flows is confirmed by our observations.

Response function and analytical parameters of nitrite-selective optode membranes in absorbance and fluorescence mode

Four different nitrite-selective optode membranes were studied. Each membrane consisted of a nitrite-selective ligand and four different H +-selective chromoionophores dissolved in a plasticized poly(vinyl chloride) bulk medium. The membranes' analytical parameters differ with respect to optical spectra, dynamic range and detection limit. The unique features of each membrane are discussed and the versatility of the optical sensors based on the membranes is evaluated. The response functions of the optical sensors, derived from the changes in the absorbance and/or fluorescence of the membranes with varying nitrite concentration, are described by a theoretical model based on coextraction equilibria. The dynamic range of the sensors extended from 0.5 to 5000 mg l −1 nitrite with a detection limit of 0.24 mg l −1. The response time, τ 95, of the membranes placed in a continuous flow measuring cell was 1.2 min when changing from 0.5 mg l −1 nitrite to 0.05 mg l −1, and 3.6 min in the opposite direction. The selectivity coefficients determined by the separate solution method were: 10 −3.3 for nitrate, 10 −3.7 for chloride, 10 −3.0 for bromide, 10 −3.8 for sulphate, and 10 −5.0 for phosphate. Various applications of these optode membranes are discussed.

Instruments and methods for measuring the backward-scattering coefficient of ocean waters

The backward-scattering coefficient bb is an important optical property that plays a central role in studies of ocean-color remote sensing, suspended particle distributions, water clarity, and underwater visibility. We investigate the fixed-angle backscattering sensor approach for the application of measuring bb . Analysis shows that the sensor response to volume scattering can be expressed as the integral of the volume scattering function (VSF) over the backward angles (90 -180 degrees ) weighted by the sensor-response function. We present a procedure for determining the sensor-response function that contains all the information necessary to calibrate the sensor fully to measure the VSF at a nominal backscattering angle. It is shown that, for fixed-angle backscattering sensors,bb is most accurately estimated when the sensor-response function covers the middle range of backscattering angles, roughly 110 -160 degrees , where the shape of the VSF has the least variability. Backscattering at and near the end angles, namely, 90 degrees and 180 degrees , are least correlated with bb . We describe a variety of spectral backscattering sensors that we have developed, and we present their sensor-response functions.

Optimization of sensor response functions for colorimetry of reflective and emissive objects

This paper describes the design of color filters for a surface color measurement device. The function of the device is to return the XYZ tristimulus vector characterizing the color of the surface. The device is designed to measure emissive as well as reflective surfaces. It uses an internal set of LEDs to illuminate reflective surfaces while characterizing their color under assumed standard illuminants. In the design of the filters, we formulate a nonlinear optimization problem with the goal of minimizing error in the uniform color space CIE L*a*b*. Our optimization criteria employs a technique to retain a linear structure while approximating the true L*a*b* error. In addition, our solution is regularized to account for system noise, filter roughness, and filter implementation errors. Experimental results indicate average and worst-case device accuracy of 0.27 L*a*b* DeltaE units and 1.56 L*a*b* DeltaE units for a "system tolerance" of 0.0005.

Models and methods of determining the transient response of ion sensors: comparison with impedance spectroscopy

This paper deals with the study of models and methods for determining the transient response function of ion sensors (ion-selective electrodes, ISEs), especially in our case sodium sensors. Theoretical models have been studied, such as the Rechnitz-Hameka model, the Toth and Pungor model and the Markovic-Osborn model. The methods studied are the dipping method, which involves two separate solutions for step generation, and the injection method, which involves a carrier solution with a small sample solution. These methods are compared with a fast system realized for this purpose. Recorded data are fitted to mathematical models and the response time is determined and compared to the relaxation time obtained by impedance spectroscopy with a 1250-Schlumberger analyser. Actually, the results obtained show a very fast response time of about 50 ms for sensors based on NASICON material, which is ten times faster than those of usual sensors (Solea-Tacussel).