Measurement Accuracy Of Sensors Research Articles

On-board radiometric calibration for thermal emission band of FY-3C/MERSI

ABSTRACTOn-board radiometric calibration is the most efficient method to improve the measurement accuracy of satellite-borne sensors. Chinese Medium Resolution Spectral Imager (MERSI), loaded on the Fengyun-3C (FY-3C) satellite, uses one satellite-borne fixed-temperature blackbody (BB) for its thermal emission band’s (TEB) radiometric calibration, but its optimal calibration algorithm is not determined. By using MERSI’s on-board calibration data taken on November 2013, this article investigates two algorithms of linear and semi-nonlinear calibration for MERSI TEB’s on-board radiometric calibration and finds that the linear calibration is more reasonable than semi-nonlinear calibration because linear coefficients’ variation tendency can reflect MERSI’s inherent systematic properties better. The relative difference between linear properties and inherent properties for pixel variability being 9.5%, mirror-side variability being 21.5% and scan variability being 17.8% are all smaller than those between semi-nonlinear case and inherent case. All of those suggest that the linear calibration is coincident with the inherent systematic properties. By using MERSI’s calibration data at June 2014, the performance of those two algorithms is validated by comparing the difference between inferred BB radiance LI and standard BB radiance LS (0.01%), and between inferred BB brightness temperature TI and standard BB temperature TS (0.25 K).

Characteristics of strain transfer and the reflected spectrum of a metal-coated fiber Bragg grating sensor

Previous researchers have simulated strain transfer and spectrum of normal fiber Bragg grating (FBG) sensors with a polymer coating bonded on the structure. They only considered the shear stress in a polymer coating for the simulation. However, for metal-coated FBG sensors, not only shear stress but also axial stress in the metal coating should be reflected into the calculation because its axial stiffness is no longer negligible. Thus, the author investigated the strain transfer and reflected spectra of metal-coated FBG sensors by considering both shear stress and axial stress. The strain transfer analysis involved evaluating the strain profiles along the sensor by plotting an analytical solution, and validating the evaluated profiles with the results obtained by a finite element analysis (FEA). The solution was also verified by the experiments that used aluminum-coated FBG sensors bonded on a carbon fiber reinforced polymer (CFRP) composite specimen. A transfer-matrix (T-matrix) formulation and coupled mode theory were used to simulate the reflected spectra of metal-coated FBG sensors for the evaluated strain profile. In addition, the effect of mechanical and geometric parameters of the sensor was examined. The findings revealed that the strain transfer characteristics and reflected spectra deteriorated with increases in the thickness and Young's modulus of the metal coating due to the consideration of axial stress. It is the opposite results for the normal FBG sensor with a polymer coating. Furthermore, the results also indicated that the decrease in bonding thickness resulted in improved strain transfer and signal characteristics. Moreover, a bonding length of 14mm was suitable in suppressing an asymmetric shape of the reflected spectrum and in achieving an accurate measurement. The results of the parametric study are expected to contribute to improve the measurement accuracy of metal-coated FBG sensors in actual applications. The analytical methodology can be usefully employed in the design of a metal-coated FBG sensor system.

Shared control on lunar spacecraft teleoperation rendezvous operations with large time delay

Teleoperation could be used in space on-orbit serving missions, such as object deorbits, spacecraft approaches, and automatic rendezvous and docking back-up systems. Teleoperation rendezvous and docking in lunar orbit may encounter bottlenecks for the inherent time delay in the communication link and the limited measurement accuracy of sensors. Moreover, human intervention is unsuitable in view of the partial communication coverage problem. To solve these problems, a shared control strategy for teleoperation rendezvous and docking is detailed. The control authority in lunar orbital maneuvers that involves two spacecraft as rendezvous and docking in the final phase was discussed in this paper. The predictive display model based on the relative dynamic equations is established to overcome the influence of the large time delay in communication link. We discuss and attempt to prove via consistent, ground-based simulations the relative merits of fully autonomous control mode (i.e., onboard computer-based), fully manual control (i.e., human-driven at the ground station) and shared control mode. The simulation experiments were conducted on the nine-degrees-of-freedom teleoperation rendezvous and docking simulation platform. Simulation results indicated that the shared control methods can overcome the influence of time delay effects. In addition, the docking success probability of shared control method was enhanced compared with automatic and manual modes.

The Research of the Suitability of Hydrostatic Water Level Sensor to Measure Storm Water Runoff Flow Rate with the Focus on the Influence of Sediments

Since most of the contaminants in surface waters fall with storm water runoff, it is very important to correctly describe the content of pollutants discharging with them (kilograms or tons) for a given unit of time (hour, shift, day, month or year). Measurements are complicated by the fact that the flow rate and pollutant concentration is very variable over time. The aim of the research was to determine the grain size of sweepings accumulated on the surfaces of the researched territory and to investigate the impact of storm water runoff sediments on the accuracy of measurements of water level height using the hydrostatic water level sensor. For the experiment four typical Vilnius city streets, two storm water runoff treatment plants and also the streets sweeping machine was chosen. Storm water runoff in urban areas has an abundance of sediment, therefore, studying the hydrostatic water level sensor DI 240 Diver suitability to determine storm water runoff flow rate, for the experimental studies the impact of sludge and sand for measuring accuracy was chosen. Particles with diameters ranging from 0.315 to 0.630 mm consisting the maximum weight (the average value of 24 g per 100 g of the sample) of street sweepings. Storm water runoff treatment plants sediments are approximately 60% of the smallest particles with a size of less than 0.05 mm. Particles of less than 0.25 mm consisting about 80% of sediment. During laboratory and full scale tests it was determined, that there is no significant affect of sediments on the accuracy of the hydrostatic water level sensor measurements. The average square error (standard deviation) was 0.567 cm when the measurement uncertainty was 0.0021 cm.

Design and analysis on fume exhaust system of blackbody cavity sensor for continuously measuring molten steel temperature

Fume exhaust system is the main component of the novel blackbody cavity sensor with a single layer tube, which removes the fume by gas flow along the exhaust pipe to keep the light path clean. However, the gas flow may break the conditions of blackbody cavity and results in the poor measurement accuracy. In this paper, we analyzed the influence of the gas flow on the temperature distribution of the measuring cavity, and then calculated the integrated effective emissivity of the non-isothermal cavity based on Monte-Carlo method, accordingly evaluated the sensor measurement accuracy, finally obtained the maximum allowable flow rate for various length of the exhaust pipe to meet the measurement accuracy. These results will help optimize the novel blackbody cavity sensor design and use it better for measuring the temperature of molten steel.

Effective Calibration of Low-Cost Soil Water Content Sensors.

Soil water content is a key variable for understanding and modelling ecohydrological processes. Low-cost electromagnetic sensors are increasingly being used to characterize the spatio-temporal dynamics of soil water content, despite the reduced accuracy of such sensors as compared to reference electromagnetic soil water content sensing methods such as time domain reflectometry. Here, we present an effective calibration method to improve the measurement accuracy of low-cost soil water content sensors taking the recently developed SMT100 sensor (Truebner GmbH, Neustadt, Germany) as an example. We calibrated the sensor output of more than 700 SMT100 sensors to permittivity using a standard procedure based on five reference media with a known apparent dielectric permittivity (1 < Ka < 34.8). Our results showed that a sensor-specific calibration improved the accuracy of the calibration compared to single “universal” calibration. The associated additional effort in calibrating each sensor individually is relaxed by a dedicated calibration setup that enables the calibration of large numbers of sensors in limited time while minimizing errors in the calibration process.

Research on Key Technologies of Network Centric System Distributed Target Track Fusion

To realize common tactical picture in network-centered system, this paper proposes a layered architecture for distributed information processing and a method for distributed track fusion on the basis of analyzing the characteristics of network-centered systems. Basing on the noncorrelation of three-dimensional measurement of surveillance and reconnaissance sensors under polar coordinates, it also puts forward an algorithm for evaluating track quality (TQ) using statistical decision theory. According to simulation results, the TQ value is associated with the measurement accuracy of sensors and the motion state of targets, which is well matched with the convergence process of tracking filters. Besides, the proposed algorithm has good reliability and timeliness in track quality evaluation.

Adaptive control architectures for mitigating sensor attacks in cyber-physical systems

The accuracy of sensor measurements is critical to the design of high-performance control systems since sensor uncertainties can significantly deteriorate achievable closed-loop dynamical system performance. Sensor uncertainty can arise due to low sensor quality, sensor failure or detrimental environmental conditions. For example, relatively cheap sensor suites are used for low-cost, small-scale unmanned vehicle applications that can result in inaccurate sensor measurements. Alternatively, sensor measurements can also be corrupted by malicious attacks if dynamical systems are controlled through large-scale, multilayered communication networks as is the case in cyber-physical systems. This paper presents several adaptive control architectures for stabilisation of linear dynamical systems in the presence of sensor uncertainty and sensor attacks. Specifically, we propose new and novel adaptive controllers for state-independent and state-dependent sensor uncertainties. In particular, we show that the proposed controllers guarantee asymptotic stability of the closed-loop dynamical system when the sensor uncertainties are time-invariant and uniform ultimate boundedness when the uncertainties are time-varying. We further discuss the practicality of the proposed approaches and provide several numerical examples to illustrate the efficacy of the proposed adaptive control architectures.

A Closed-Loop Operation to Improve GMR Sensor Accuracy

Giant magnetoresistance (GMR) magnetic field sensors are compact, low power, high sensitivity devices that are low cost and have very simple supporting electronics. One of the disadvantages of GMR sensors can be their nonlinearity, hysteresis, and temperature-dependent output, which can reduce measurement accuracy. This paper presents an approach to improve the measurement accuracy of GMR sensors using a closed-loop circuit, which includes the sensor, a biasing coil, and a feedback circuit. The current in the biasing coil is actively changed to ensure that the component of magnetic field along the sensitive axis of the device is held constant, so that as the external magnetic field or orientation of the GMR sensor changes, the output of GMR sensor remains stable. In this way, the external magnetic field component along the sensitive axis of the device can be calculated by measuring the current in the biasing coil surrounding the GMR sensor, regardless of the hysteresis and nonlinearly of GMR sensor. The linearity and the accuracy of magnetic field measurements using a GMR sensor are significantly improved and a hardware prototype has been constructed and tested under a reference magnetic field.

Theoretical Analysis on Strain Transfer Error of FBG Sensors Attached on Steel Structures Subjected to Fatigue Load

AbstractFibre Bragg grating (FBG) sensors have been increasingly adopted to detect the dynamic strain of structures. When the sensor is attached on the surface, adhesive material is employed to assist the installation, which leads to indirect contact of sensing fibre and the monitored structure. To correct the strain transfer error induced by the shear lag effect and improve the measurement accuracy of FBG sensors under dynamic response, strain transfer mechanism of a three‐layered testing model constituted of sensing fibre, adhesive layer and host material has been studied in this paper. Laboratory test on steel beam attached with FBG sensor under fatigue load has been projected to investigate the feasibility of the derived strain transfer formula, and numerical simulation by MATLAB has been used as a supporting tool to offer the reference dynamic strain. Based on the analysis, sensitive parameters that affect the strain transfer coefficient have been discussed to instruct the application design of FBG sensors. Results indicate that strain transfer coefficient under dynamic response is much lower than that in static state, and error modification is particularly significant; in the dynamic testing model, bonded length, shear modulus and thickness of adhesive layer are more sensitive, which should be precisely selected in practical engineering to guarantee the effective strain measurement.

A Novel Error Model of Optical Systems and an On-Orbit Calibration Method for Star Sensors

In order to improve the on-orbit measurement accuracy of star sensors, the effects of image-plane rotary error, image-plane tilt error and distortions of optical systems resulting from the on-orbit thermal environment were studied in this paper. Since these issues will affect the precision of star image point positions, in this paper, a novel measurement error model based on the traditional error model is explored. Due to the orthonormal characteristics of image-plane rotary-tilt errors and the strong nonlinearity among these error parameters, it is difficult to calibrate all the parameters simultaneously. To solve this difficulty, for the new error model, a modified two-step calibration method based on the Extended Kalman Filter (EKF) and Least Square Methods (LSM) is presented. The former one is used to calibrate the main point drift, focal length error and distortions of optical systems while the latter estimates the image-plane rotary-tilt errors. With this calibration method, the precision of star image point position influenced by the above errors is greatly improved from 15.42% to 1.389%. Finally, the simulation results demonstrate that the presented measurement error model for star sensors has higher precision. Moreover, the proposed two-step method can effectively calibrate model error parameters, and the calibration precision of on-orbit star sensors is also improved obviously.

Evaluating corrections for a horizontal offset between sensor and position data for surveys on land

When regarding evolutions in land-based, motorized sensor data collection it can be generalized that the speed of surveying, sampling rates, digital communications speed and survey resolutions have increased over the last years. Possibilities for accurate positioning have been following pace. However, a spatial offset between sensor and position data can be necessary to avoid interference with the instrument or can be the result of using a sensor array. It can also be due to practical considerations such as mounting possibilities. Unfortunately a severe degradation of positional accuracy is possible when performing corrections for a spatial offset and quantification of the induced error is quite difficult. As a consequence, the actual positional accuracy of sensor measurements is therefore often omitted or unknown, and a correction may be neglected during data processing. In this paper, accounting for a horizontal (spatial) offset is researched by examining the use of several correction methods. To evaluate the degree of loss of positional accuracy and validate several correction procedures, global navigation satellite system (GNSS) data (with real-time kinematic correction) have been simultaneously collected, using a GNSS receiver that was mounted on an all-terrain vehicle and two other receivers that were mounted near the front and end of an elongated sensor sled. The sled was connected to the towing vehicle using a flexible connection. Since the positioning systems’ horizontal accuracies were about 20 mm, it was possible to quantify the horizontal error of the predicted positions for the different correction procedures considered. The best approach for high-resolution surveys, which make use of a connection to a cart or sled that can rotate around a pivot on the towing vehicle, was researched. The strengths and weaknesses of the applied corrections were also evaluated, allowing selection of an appropriate correction for a given survey implementation.

Evaluation of the oceanographic measurement accuracy of different commercial sensors to be used on fishing gears

The aim of the paper is to assess the accuracy for physical oceanography purposes of some commercial sensors (Star-Oddi and NKE) installed on fishing boats in the Adriatic Sea. When mounted on fishing gears, they can retrieve huge amounts of daily datasets (temperature, depth and salinity), spanning a very large spatial region. The possibility to establish their accuracy would be of extreme importance for physical oceanography studies since it would be almost impossible to obtain the same amount of data by means of cruises onboard Research Vessels. Comparison tests against a calibrated CTD were performed during several surveys.Summarizing, the data collected by Star-Oddi sensors are useful only considering the data portion where a dwell time at a fixed depth permanence is longer than 50s, while those collected by NKE sensors are much more accurate for both depth and temperature and could be usefully considered for broader oceanographic purposes. The weak point of the NKE sensors is the salinity measurement. The evaluation carried out in the present study underlined the optimal conditions for the usage of the considered sensors and produced a series of offsets that might be used to enhance the accuracy of the recorded datasets.

Maximum measurement range and accuracy of SAW reflective delay line sensors.

In a surface acoustic wave (SAW) wireless sensor with a reflective delay line structure, three reflectors are often used to eliminate 2π ambiguity of phase measurement. The maximum range of the measured parameter and the maximum accuracy have recently been attracting much research attention. In this paper, an analytical formula for all the factors influencing the measurement range and accuracy of the delay line SAW sensor are deduced for the first time. The factors include: the sensor sensitivity, the topology of the delay line, the available wireless bandwidth and the allowed maximum phase measuring error of the reading system, which is easier to retrieve and more fully describes the possible noises than SNR. Additionally, many designers believe that increasing the reflector could improve accuracy continuously or realize multi-resolution measurement. However, they ignore some certain criteria that the reflector location must satisfy. The reachable maximum accuracy by every increase of a reflector is also presented. A SAW temperature sensor system using 128° YX-LiNbO3 is designed to verify the above theoretical analysis.

Linear Polarization Resistance Sensor Using the Structure as aWorking Electrode

A direct method of measuring corrosion on a structure using a micro-linear polarization resistance (mLPR) sensor is presented. The sensor includes three electrodes, where each electrode is fabricated on a flexible substrate to create a circuit consisting of gold-plated copper. The first two electrodes, or the counter and reference electrodes, are configured in an interdigitated fashion with a separation distance of 8mil. The flex cable contains a porous membrane between the pair of electrodes and the structure. A third electrode, or the working electrode makes electrical contact to the structure through a 1mil thick electrically conductive transfer tape placed between the electrode and structure. The reference and counter electrodes are electrically isolated from the working electrode and physically separated from the surface of the structure by 1mil. The flex cable can be attached to the structure through the use of adhesives or in the case of placement in a butt joint or lap joint configuration, by the joint itself. Corrosion is computed from known physical constants, by measuring the polarization resistance between the electrolytic solution and the structure. A controlled experiment using the ASTM G85 Annex 5 standard verifies the precision and accuracy of sensor measurements by comparing the estimated mass loss with witness coupons.

Mean-square errors of object positioning in rectangular coordinate system

The original method for determining object coordinates before drawing them on topographic maps in a rectangular coordinate system by sighting the angular object position by the navigation system (complex) from the mobile carrier was proposed, and mathematical expressions for the object positioning in the rectangular coordinate system were obtained in the paper. The main objective is to study the method and simplified algorithm for the location object positioning in the rectangular coordinate system, based on multiple measurements of the object sighting angle on the course from the mobile carrier. The methods and simplified algorithms for object positioning in the rectangular coordinate system, based on measurements of the search object sighting angles on the course from the mobile carrier with the motion trajectory, which provides multiple object sighting were proposed, mean-square sighting errors, caused by errors of angle sensors of the control system of the navigation system were defined, and requirements for measurement accuracy of angle sensors were determined. The obtained results prove the prospects of using the object positioning method and algorithm in navigation systems of aircraft and ground vehicles.

Dynamic consensus estimation of weighted average on directed graphs

Recent applications call for distributed weighted average estimation over sensor networks, where sensor measurement accuracy or environmental conditions need to be taken into consideration in the final consensused group decision. In this paper, we propose new dynamic consensus filter design to distributed estimate weighted average of sensors’ inputs on directed graphs. Based on recent advances in the filed, we modify the existing proportional-integral consensus filter protocol to remove the requirement of bi-directional gain exchange between neighbouring sensors, so that the algorithm works for directed graphs where bi-directional communications are not possible. To compensate for the asymmetric structure of the system introduced by such a removal, sufficient gain conditions are obtained for the filter protocols to guarantee the convergence. It is rigorously proved that the proposed filter protocol converges to the weighted average of constant inputs asymptotically, and to the weighted average of time-varying inputs with a bounded error. Simulations verify the effectiveness of the proposed protocols.

Mine Multi-sensor Maximum Likelihood Estimation Data Fusion Algorithm

After an overall consideration of the differences in the measurement accuracy of various sensors, an improved algorithm based on consensus data fusion has been proposed, the measurement accuracy of which is reflected through weight coefficient. It is indicated in simulation that this approach can effectively reduce data variation extent when there is disturbance in sensors, improving fusion accuracy and anti-interference capability. This algorithm will be applied in the data fusion of temperature sensor, gas concentration sensor in intelligent monitoring system of coal mine.

Sensor Scheduling Criterion for Space Surveillance Based on Relative Orbit Analysis

To exploit the observation effectiveness of the space surveillance network comprehensively and provide a mathematical explanation of a sensor scheduling result, the analytical sensor scheduling criterion is required. This paper presents an analytical sensor scheduling criterion of the space surveillance network based on the relative orbit analysis. A virtual chief orbit and the relative orbit elements, which are the set of orbit element differences of the real satellite relative to the virtual chief satellite, are used to describe the motion of the real satellite. Because the virtual chief orbit, which is selected under the constraint that the relative orbit radius is less than 0.3% of that of the chief orbit radius, is accurately known, the uncertainty of the relative motion will describe the uncertainty of orbit determination of the real satellite. Then one can obtain an analytical criterion derived from the covariance matrix of the relative orbit elements to measure the observation effectiveness of a sensor scheduling. This criterion is valid for the observation of the general elliptic orbit satellite with arbitrary observation data types and is expressed explicitly in terms of influencing factors, such as the sensor type, measurement accuracy, observation time, fit span, and observation geometry. The individual effectiveness and tradeoffs of these influencing factors can be explored quantitatively by this criterion. To get a clear view of how these factors individually or cooperatively affect the predicted position error, a closed-form expression of this criterion is presented under the planar orbit assumption. This simplified criterion, which is valid for the observation of near-circular orbit satellites, can provide the mathematical explanation of the traditional sensor scheduling strategies. Finally, some simple sensor scheduling strategies are analyzed based on this criterion.

Study on the influence of the response characteristics of a temperature sensor on the measurement accuracy of a water-absorption-based high-energy laser energy meter

When using water as a cooling or absorption medium for an energy meter, a temperature sensor is limited by response characteristics and cannot reflect the real-time temperature changes in the water flow. In order to improve the accuracy of measurement, we should ensure that the corresponding value of the temperature integral will be substantially independent of the effects of the sensor response time. According to the analysis of the interaction process between temperature sensor and water flow temperature field, we have established a hot physical model of the whole measurement process, and decomposed it into a superposition of a slowly varying process and a transient process, then simplified the model. Finally, a quantitative relationship between the sensor response characteristics and measurement accuracy of the high energy laser energy meter is derived. With the mandatory heat exchange method, the frequency characteristics of the temperature field meet the requirements of the frequency characteristics of a temperature sensor; as a result, the impact on measurement accuracy is eliminated. The experimental results show that this method has good effects, and it can help to improve the measurement accuracy of a high-energy laser energy meter.