Proposed Calibration Algorithm Research Articles

Uncooled Thermal Camera Calibration and Optimization of the Photogrammetry Process for UAV Applications in Agriculture.

The acquisition, processing, and interpretation of thermal images from unmanned aerial vehicles (UAVs) is becoming a useful source of information for agronomic applications because of the higher temporal and spatial resolution of these products compared with those obtained from satellites. However, due to the low load capacity of the UAV they need to mount light, uncooled thermal cameras, where the microbolometer is not stabilized to a constant temperature. This makes the camera precision low for many applications. Additionally, the low contrast of the thermal images makes the photogrammetry process inaccurate, which result in large errors in the generation of orthoimages. In this research, we propose the use of new calibration algorithms, based on neural networks, which consider the sensor temperature and the digital response of the microbolometer as input data. In addition, we evaluate the use of the Wallis filter for improving the quality of the photogrammetry process using structure from motion software. With the proposed calibration algorithm, the measurement accuracy increased from 3.55 °C with the original camera configuration to 1.37 °C. The implementation of the Wallis filter increases the number of tie-point from 58,000 to 110,000 and decreases the total positing error from 7.1 m to 1.3 m.

Calibration of atmospheric density model using two-line element data

For satellites in orbits, most perturbations can be well modeled, however the inaccuracy of the atmospheric density model remains the biggest error source in orbit determination and prediction. The commonly used empirical atmospheric density models, such as Jacchia, NRLMSISE, DTM, and Russian GOST, still have a relative error of about 10%–30%. Because of the uncertainty in the atmospheric density distribution, high accuracy estimation of the atmospheric density cannot be achieved using a deterministic model. A better way to improve the accuracy is to calibrate the model with updated measurements. Twoline element (TLE) sets provide accessible orbital data, which can be used in the model calibration. In this paper, an algorithm for calibrating the atmospheric density model is developed. First, the density distribution of the atmosphere is represented by a power series expansion whose coefficients are denoted by the spherical harmonic expansions. Then, the useful historical TLE data are selected. The ballistic coefficients of the objects are estimated using the BSTAR data in TLEs, and the parameterized model is calibrated by solving a nonlinear least squares problem. Simulation results show that the prediction error is reduced using the proposed calibration algorithm.

A direct conversion transmitter with digital‐assisted DC offset and I/Q phase calibration

SummaryA direct conversion transmitter with auto‐calibration mechanism is presented in this paper. Both the carrier leakage and in‐phase/quadrature (I/Q) phase imbalance are compensated by a proposed calibration algorithm to improve transmitter's single‐sideband performance. The digital‐assisted correction circuits are implemented in a calibration feedback path to reduce the mismatches and variations, which in turn achieves properties of high linearity, high sideband, and carrier suppression ratio. The measured single‐sideband performance with calibration applied to the transmitter demonstrates an over 40 and 50‐dBc rejection on sideband and carrier signals at the desired frequency band, respectively. For linearity performance, the measured output 1‐dB compression point (OP1dB) is 9.1 dBm, while the highest voltage gain is from 4.3 to 6.2 dB. Additionally, the error vector magnitude (EVM) of −37.082 dB (< 1.4%) can be achieved under an orthogonal frequency division multiple access (OFDMA) 64 QAM‐3/4 modulated signal test. The transmitter consumes 112.7 mA under supply voltage of 3.3 V using the TSMC SiGe BiCMOS technology. Copyright © 2017 John Wiley & Sons, Ltd.

Normalized-Full-Scale-Referencing Digital-Domain Linearity Calibration for SAR ADC

This paper proposes a linearity calibration algorithm of a capacitive digital-to-analog converter (CDAC) for successive approximation register (SAR) analog-to-digital converters (ADCs) based on a normalized-full-scale of the DAC. Since the capacitor weight errors are represented as the difference between the real and ideal weights with respect to the normalized-full-scale, the calibrated digital representation of CDAC does not have gain error. A model of a 14-bit-format SAR ADC with a segmented CDAC by a bridge capacitor is simulated to demonstrate the performance of the proposed calibration algorithm. The effective number of bits (ENOB) and spurious-free dynamic range (SFDR) of the 14-bit-format ADC model are improved to 13.2 bits and 94.0 dB from 8.4 bits and 54.8 dB, respectively, at a standard deviation of a unit capacitor of 2%. The gain-error-free characteristic of the proposed linearity calibration algorithm is verified with a 2-channel time-interleaved (TI) SAR ADC model.

Analyzing and Modeling of Geo Spatial Effect on Radio Wave Propagation System Using Geospatial Technologies

The research presented in this thesis reveals the level of rightness of the recurrence Prediction systems by correlated with geospatial effect. The Geospatial technology elements split up: Geographic Information System (GIS), Remote Sensing (RS) and Global Positioning System (GPS) consolidated into this technique in light of the fact that the vast majority of the components in radio wave propagation are geographic highlights. In this exploration, ICEPAC remote arranging programming is tried in a field test completed in Tigray and Afar district. The consequence show that, the Prediction programming doesn’t put, day by day, regular and month to month topographical marvels into thought. Moreover, it doesn’t demonstrate the correct area of the radio stations. Furthermore, the new proposed ICEPAC Calibration algorithm anticipates a good Signal quality for frequencies in the vicinity of 1.5 MHz up to 30 MHz. The total result showed that Geographical Information Systems (GIS) are getting to be noticeably valuable apparatuses in accumulation, stockpiling, control and portrayal of Geo spatial information and also the RS and GIS situated Signal quality forecast can essentially enhance forecast quality contrasted with the hypothetical free space demonstration which does not consider any Geo spatial and neighborhood landscape highlights impacts.

A 12-bit, 1 MS/s SAR-ADC for a CZT-based multi-channel gamma-ray imager using a new digital calibration method

The successive approximation register-analog to digital converter (SAR-ADC) is widely used in the CdZnTe-based gamma-ray imager because of its outstanding characteristics of low power consumption, relatively high resolution, and small die size. This study proposes a digital bit-by-bit calibration method using an input ramp signal to further improve the conversion precision and power consumption of an SAR-ADC. The proposed method is based on the sub-radix-2 redundant architecture and the perturbation technique. The proposed calibration algorithm is simpler, more stable, and faster than traditional approaches. The prototype chip of the 12-bit, 1 MS/s radiation-hardened SAR-ADC has been designed and fabricated using the TSMC 0.35 μm 2P4M CMOS process. This SAR-ADC consumes 3 mW power and occupies a core area of 856× 802μm2. The digital bit-by-bit calibration algorithm is implemented via MATLAB for testing flexibility. The effective number of bits for this digitally calibrated SAR-ADC reaches 11.77 bits. The converter exhibits high conversion precision, low power consumption, and radiation-hardened design. Therefore, this SAR-ADC is suitable for multi-channel gamma-ray imager applications.

A Generally Applicable Calibration Algorithm for Digitally Reconfigurable Self-Healing RFICs

A generally applicable calibration technique for digitally reconfigurable self-healing radio frequency integrated circuits based on a hybrid of the Nelder-Mead and Hooke-Jeeves direct search algorithms is presented. The proposed algorithm is applied to the multiobjective problem of gain error and phase error minimization for a self-healing phase rotator test case. For the 8-D phase rotator calibration problem, we show that the proposed hybrid Nelder-Mead and Hooke-Jeeves calibration algorithm is capable of reducing the gain error and phase error of the phase rotator output to less than a maximum of 0.5 dB and 2°, respectively, relative to the chosen gain and phase targets. A 3-GHz self-healing phase rotator test chip was fabricated in a 45-nm silicon-on-insulator CMOS process, and the measured data were obtained to validate the performance of the proposed calibration algorithm.

Flexible calibration method for telecentric fringe projection profilometry systems.

A newly developed flexible calibration algorithm for telecentric 3D measurement systems is presented in this paper. We theoretically analyzed the similarities and differences between the telecentric and entocentric system. The telecentric system can be calibrated with the aid of the traditional 2D planar calibration method. An additional two-step refining process is proposed to improve the calibration accuracy effectively. With the calibration and refining algorithm, an affine camera can be calibrated with a reprojection error of 0.07 pixel. A projector with small field of view (FOV) is applied to achieve a full 3D reconstruction in our profilometry system. Experiments with a prototype demonstrate the validation and accuracy of the proposed calibration algorithm and system configuration. The reconstruction accuracy can achieve 5 µm with a measurement FOV of 28.43 mm×21.33 mm and a working distance of 110 mm.

All-Digital Calibration of Timing Skews for TIADCs Using the Polyphase Decomposition

This brief proposes a new all-digital calibration technique suppressing the timing mismatch effect in time-interleaved analog-to-digital converters (TIADCs) for input at any Nyquist band (NB) using the equivalent polyphase structure of the TIADC. The correction technique is simple and does not require the adaptive digital synthesis filters. The timing mismatch is estimated based on an adaptive stochastic gradient descent technique, which is a promising solution for TIADCs operating at a very fast sampling rate. The digital circuit of the proposed calibration algorithm is designed and synthesized using a 28-nm fully depleted Silicon on insulator (FD-SOI) CMOS technology for the 11-b 60-dB SNR TIADC clocked at 2.7 GHz with the input in the first four NBs. The designed circuit occupies the area of 0.05 mm2 and dissipates the total power of 41 mW.

평면형 병렬 케이블 구동 로봇에 대한 형상보정

This paper proposes a calibration algorithm for a three-degree-of-freedom (DOF) planar cable-driven parallel robot (CDPR). To evaluate the proposed algorithm, we calibrated winches and an optical tracking sensor, measured the end-effector pose using the optical tracking sensor, and calculated the accurate robot configuration using the measurement information. To conduct an accuracy test on the end-effector pose, we followed guidelines from "Manipulating industrial robots - Performance criteria and related test methods." Through the test, it is verified that the position accuracy can be improved by up to 20% for a <TEX>$2m{\times}2m$</TEX>-sized planar cable robot using the proposed calibration algorithm.

Calibration algorithm for 16-bit voltage-mode R–2R DAC

A novel calibration algorithm is presented for the 16-bit voltage-mode R–2R Digital-to-Analog converter (DAC). The proposed calibration can be realized with only some digital circuits and an additional calibrating DAC (CaliDAC) identical to the main DAC (MDAC) added. With the weighing-coefficient compressing technology (WCT) adopted, the nonlinearity of the CaliDAC can be compressed when the calibration is implemented, therefore leaving almost no effect on the output. Adopting the segment-calibration technology (SCT), the integral nonlinearity (INL) errors of the output can be calibrated segment by segment. With the proposed calibration algorithm, the INL errors in the final output can be calibrated successfully in the range of [−0.5LSB, 0.5LSB] for 16-bit voltage-mode R–2R DAC.

Improved airborne PolSAR calibration algorithm based on time-variant attitude compensation

The polarimetric synthetic aperture radar (PolSAR) usually has to be calibrated before practical application, so as to compensate for polarimetric distortion. The varying platform attitude is one of the factors causing distortion but has rarely been considered in existing polarimetric calibration algorithms. With the resolution of PolSAR systems improving and the synthetic aperture time prolonging, this factor cannot simply be ignored. The varying attitude will distort the polarimetric information by rotating the polarimetric orientation angle, and such distortion changes with azimuth time. In this article, we modified the conventional polarimetric system model to take account of the time-variant impact of the unstable platform attitude. A calibration algorithm is proposed to compensate the time-variant attitude impact on the raw return data. The proposed calibration algorithm is tested on the data collected by Institute of Electronics, Chinese Academy of Sciences P-band PolSAR system. Results show that it can achieve better performance by reducing crosstalk error than two conventional methods.

Automation of experiments at the Dubna gas-filled separator of recoil nuclei: Part II

An application developed in Builder C++ (Windows) for the offline analysis of experimental data from the spectrometer of the gas-filled separator of recoil nuclei (Flerov Laboratory of Nuclear Reactions) based on the double-sided silicon strip detector is discussed. The automatic express method developed for calibrating 48 strips of the silicon position-sensitive detector based on the three most energetic spectral lines from the natYb + 48Ca▭*Th reaction is compared to the results produced by more rigorous calibration methods. The examples of spectra for this reaction and the results of filtering for the proposed calibration algorithm are given.

Simultaneous identification of joint compliance and kinematic parameters of industrial robots

Owing to the flexibility of robot joints and links, the industrial robot can hardly achieve the specified accuracy to perform tasks when a payload is attached at its end-effector. Hence, compliance errors due to the deflections of robot joints and links should be identified and compensated as well as kinematic errors to improve the positioning accuracy of the industrial robot. Assuming the links of the robot are much stiffer than its actuated joints, compliance errors mainly come from the joint deflections. This paper presents a new algorithm for robot calibration, which simultaneously identifies joint compliance and kinematic parameters of industrial robots through a comprehensive error model consisting of kinematic errors and compliance errors. The identified parameters are used to compensate kinematic errors and compliance errors in industrial robots. The proposed calibration algorithm is implemented on a 6 degree of freedom serial robot (Hyundai YS100) to show its effectiveness.

A novel camera calibration method for fish-eye lenses using line features

Abstract. In this paper, a novel method for the fish-eye lens calibration is presented. The method required only a 2D calibration plane containing straight lines i.e., checker board pattern without a priori knowing the poses of camera with respect to the calibration plane. The image of a line obtained from fish-eye lenses is a conic section. The proposed calibration method uses raw edges, which are pixels of the image line segments, in stead of using curves obtained from fitting conic to image edges. Using raw edges is more flexible and reliable than using conic section because the result from conic fitting can be unstable. The camera model used in this work is radially symmetric model i.e., bivariate non-linear function. However, this approach can use other single view point camera models. The geometric constraint used for calibrating the camera is based on the coincidence between point and line on calibration plane. The performance of the proposed calibration algorithm was assessed using simulated and real data.

Camera Calibration Method Based on Vanishing Point

We present a camera calibration method based on vanishing point, that is, the vanishing points of two groups of parallel lines on the target plane are used to achieve camera calibration. A series of known positions points on target plane are used as the feature points, and the target images are recorded, the image coordinates of feature points are used to calculate the coordinates of vanishing point, then the matrix between feature points and camera is used to obtain internal parameters of camera. Experimental results show that the proposed calibration algorithm is correct, simple and convenient.

Development of Perez-Du Mortier Calibration Algorithm for Ground-Based Aerosol Optical Depth Measurement with Validation using SMARTS Model

Aerosols are small particles suspended in air that have wide varying spatial and temporal distributions. The concentration of aerosol in total columnar atmosphere is normally measured using aerosol optical depth (AOD). In long-term monitoring stations, accurate AOD retrieval is often difficult due to the lack of frequent calibration. To overcome this problem, a near-sea-level Langley calibration algorithm is developed using the combination of clear-sky detection model and statistical filter. It attempts to produce a dataset that consists of only homogenous and stable atmospheric condition for the Langley calibration purposes. In this paper, a radiance-based validation method is performed to further investigate the feasibility and consistency of the proposed algorithm at different location, day, and time. The algorithm is validated using SMARTS model based n DNI value. The overall results confirmed that the proposed calibration algorithm feasible and consistent for measurements taken at different sites and weather conditions.

Improvement of Polarimetric SAR Calibration Based on the Ainsworth Algorithm for Chinese Airborne PolSAR Data

It is necessary to calibrate polarimetric synthetic aperture radar (PolSAR) data in order to use the data for science applications. In this letter, we propose an improved algorithm to estimate the calibration parameters based on the Ainsworth algorithm and the Quegan algorithm. Since there is no approximation in the process of the parameter estimation, this algorithm can accurately solve all parameters, even if the crosstalk is high. To verify the effect of the proposed calibration algorithm, this letter analyzes the accuracy of the proposed algorithm with the simulated PolSAR data and Chinese airborne X-band PolSAR data. The results confirm that the proposed algorithm can provide a more stable and accurate solution to the crosstalk parameters.

Environmental-Adaptive Bias Calibration in Wireless Localization

This paper presents a simple bias calibration method in wireless localization networks. Based on measured distances between a mobile sensor node and reference beacon sensor nodes fixed at known points, the proposed method estimates the bias error. To compute the bias error accurately, an optimization problem is formulated. Through numerous experiments, the performance of the proposed calibration algorithm is evaluated.

Procedure for Measurement, Characterization, and Calibration of Active Antenna Arrays

The GEOdesic Dome Antenna is an interesting design for efficient satellite-tracking prototypes based on 45 elements active antenna arrays manufactured by the Radiation Group of the Technical University of Madrid. Extensive measurement campaign in RF laboratories and in an anechoic chamber was performed for complete calibration and characterization of those active antenna arrays, resulting in the proposal of a new efficient procedure. To accomplish the calibration procedure, the expansion of equations of the proposed calibration algorithms, based on the proposed active antenna array model and the derivation of the scattering matrix from the active element pattern, is presented. These algorithms deal with mutual coupling effect and gain and phase errors, and in general, the overall procedure leads to a significant reduction in time and costs associated to the measurements of the antenna under test and the proposed calibration algorithm. Significant measurement results from the Certified Laboratory of Tests and Standardization of Antennas (LEHA) located in the Universidad Politecnica de Madrid are presented to validate the procedure.