External calibration methods for radar polarimeters

2021 ◽  
pp. 45-52
Author(s):  
Evgeny L. Shoshin
Keyword(s):  
Experimental Studies ◽  
Mueller Matrix ◽  
Polarization Modulation ◽  
Laboratory Sample ◽  
External Calibration ◽  
Dynamic Switching ◽  
Calibration Methods

Methods of external calibration of radar polarimeters are considered. Algorithms for evaluating elements of the Mueller matrix and eliminating distortions introduced by the polarimeter are presented. The article describes the design of a radar reflector with electrically controlled polarization properties that can imitate the properties of two and three-sided reflectors and non-reciprocal reflectors. The analysis of the mode of dynamic switching of the scattering characteristics of the reflector used for calibration by the method of polarization modulation of scattered signals is performed. The results of experimental studies of a laboratory sample of a radar reflector with controlled characteristics are presented. The results obtained can be used in radar.

scholarly journals IMU-Based Online Kinematic Calibration of Robot Manipulator

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Guanglong Du ◽  
Ping Zhang
Keyword(s):  
Kalman Filter ◽  
Robot Manipulator ◽  
Experimental Studies ◽  
Estimation Method ◽  
Kinematic Parameter ◽  
Corner Detection ◽  
Measurement Unit ◽  
Robot Calibration ◽  
Self Calibration ◽  
Calibration Methods

Robot calibration is a useful diagnostic method for improving the positioning accuracy in robot production and maintenance. An online robot self-calibration method based on inertial measurement unit (IMU) is presented in this paper. The method requires that the IMU is rigidly attached to the robot manipulator, which makes it possible to obtain the orientation of the manipulator with the orientation of the IMU in real time. This paper proposed an efficient approach which incorporates Factored Quaternion Algorithm (FQA) and Kalman Filter (KF) to estimate the orientation of the IMU. Then, an Extended Kalman Filter (EKF) is used to estimate kinematic parameter errors. Using this proposed orientation estimation method will result in improved reliability and accuracy in determining the orientation of the manipulator. Compared with the existing vision-based self-calibration methods, the great advantage of this method is that it does not need the complex steps, such as camera calibration, images capture, and corner detection, which make the robot calibration procedure more autonomous in a dynamic manufacturing environment. Experimental studies on a GOOGOL GRB3016 robot show that this method has better accuracy, convenience, and effectiveness than vision-based methods.

scholarly journals A Preliminary Study of Three-Point Onboard External Calibration for Tracking Radiometric Stability and Accuracy

2019 ◽  
Vol 11 (23) ◽  
pp. 2790 ◽  
Author(s):  
Mustafa Aksoy ◽  
Paul E. Racette
Keyword(s):  
Data Processing ◽  
Temporal Stability ◽  
Measurement Data ◽  
Absolute Calibration ◽  
Calibration Error ◽  
Validation Data ◽  
External Calibration ◽  
Calibration Methods ◽  
Preliminary Study ◽  
The Impact

Absolute calibration of radiometers is usually implemented onboard using one hot and one cold external calibration targets. However, two-point calibration methods are unable to differentiate calibration drifts and associated errors from fluctuations in receiver gain and offset. Furthermore, they are inadequate to characterize temporal calibration stability of radiometers. In this paper, a preliminary study with linear radiometer systems has been presented to show that onboard external three-point calibration offers the means to quantify calibration drifts in the radiometer systems, and characterize associated errors as well as temporal stability in Earth and space measurements. Radiometers with three external calibration reference targets operating two data processing paths: i.e., (1) measurement path and (2) calibration validation path have been introduced. In the calibration validation data processing path, measurements of one known calibration target is calibrated using the other two calibration references, and temporal calibration stability and possible calibration temperature drifts are analyzed. In the measurement data processing path, the impact of the calibration drifts on Earth and space measurements is quantified and bounded by an upper limit. This two-path analysis is performed through calibration error analysis (CEA) diagrams introduced in this paper.

External calibration methods for geosynchronous ultraviolet-visible hyperspectral instrument

2021 ◽  
Vol 29 (3) ◽  
pp. 484-492
Author(s):  
Cheng-guang CUI ◽  
◽  
Ling LI ◽  
Yun-fei LI ◽  
Yong-xiang GUO ◽  
...  
Keyword(s):  
External Calibration ◽  
Calibration Methods

Precise wavelength determination of the 4s24p 2P3/2 - 2P1/2 transition in Mo11+ and Ru13+ ions

2021 ◽  
Author(s):  
Yajing Li ◽  
Yintao Wang ◽  
Junyu Fan ◽  
Ran Si ◽  
Jiguang Li ◽  
...  
Keyword(s):  
Electron Beam ◽  
Ion Trap ◽  
Dipole Transition ◽  
Experimental Uncertainty ◽  
External Calibration ◽  
Direct Observations ◽  
Electron Beam Ion Trap ◽  
Calibration Methods ◽  
Highly Charged Ion

Abstract The 4s24p 2P3/2 – 2P1/2 magnetic dipole transition in Ga-like ions is interested in developing of high precise highly charged ion clock [Phys. Rev. A, 99, 02213(2019)]. In this work, we present direct observations of the transition in Mo11+ and Ru13+ ions at an electron beam ion trap. Internal and external calibration methods are used for determining the wavelength of the Mo11+ and Ru13+ lines, respectively. Both measurements reach precision levels of a few ppm. Compared with the available values, the current results significantly improve the experimental uncertainty.

A new method for internal calibration of left ventricular cineangiography

1977 ◽  
Vol 232 (4) ◽  
pp. H434-H436
Author(s):  
M. M. Laks ◽  
D. Garner ◽  
J. Beazell ◽  
J. Piscatelli
Keyword(s):  
Balloon Catheter ◽  
Left Ventricular ◽  
External Calibration ◽  
X Ray ◽  
Inflated Balloon ◽  
Internal Calibration ◽  
Calibration Methods ◽  
Calibration Object ◽  
Specific Orientation

Previous methods of internal calibration for cineangiography have made use of reference objects such as catheters or wires of known length or diameter. Such devices have either insufficient X-ray resolution, or require a specific orientation within the ventricle which is difficult to confirm. External calibration methods, while eliminating these errors, can only estimate actual position of the left ventricle. The use of a Swan-Ganz balloon catheter as a calibration object diminishes these problems. When positioned within the left ventrical and filled with a radiopaque medium, the balloon is of sufficient size and density to avoid errors induced by previously employed objects. The inflated balloon geometry is simple and reproducible. The use of this internal calibration catheter markedly diminishes major sources of errors in the determination of ventriculograms for both dogs and humans.

A SELF-CALIBRATION METHOD FOR ARTICULATED ARM COORDINATE MEASURING MACHINES

2016 ◽  
Vol 40 (4) ◽  
pp. 645-655 ◽  
Author(s):  
Guanbin Gao ◽  
Jing Na ◽  
Xing Wu ◽  
Yu Guo
Keyword(s):  
Simulated Annealing Algorithm ◽  
Structural Parameters ◽  
Kinematic Model ◽  
Experimental Studies ◽  
Calibration Method ◽  
Constructive Method ◽  
Movement Trajectory ◽  
Coordinate Measuring Machines ◽  
Self Calibration ◽  
Calibration Methods

To improve the accuracy of articulated arm coordinate measuring machines (AACMM) and simplify the calibration process, an improved self-calibration method was proposed. Unlike the traditional calibration methods, which need external expensive precision instruments and elaborate setups, the proposed self-calibration method only requires a gauge to assist the data acquisition operation. By designing a movement trajectory of the AACMM, a series of joint angles can be obtained to form overdetermined equations based on the kinematic model of the AACMM. Therefore, the structural parameters of the AACMM can be obtained by solving the equations. Consequently, the calibration can be achieved by solving these equations. The coefficient matrix of the equations was further analyzed to simplify the equations, and a constructive method was presented to identify the structural parameters by solving the simplified equations with a modified simulated annealing algorithm, in which an optimized search strategy was applied to improve the robustness and efficiency. Experimental studies on an AACMM validate the convenience and effectiveness of the proposed AACMM self-calibration approach.

Comparison of different calibration methods for Mueller matrix microscopy of cells

2021 ◽  
Vol 60 (5) ◽  
pp. 1380
Author(s):  
Ruoyu Meng ◽  
Zhenhua Chen ◽  
Xingjian Wang ◽  
Yudi Liu ◽  
Honghui He ◽  
...  
Keyword(s):  
Mueller Matrix ◽  
Calibration Methods

scholarly journals Error Analysis and Calibration Improvement of the Imaging Section in a Mueller Matrix Microscope

2020 ◽  
Vol 10 (13) ◽  
pp. 4422
Author(s):  
Jiewei Yu ◽  
Xuemin Cheng ◽  
Maolin Li
Keyword(s):  
Maximum Error ◽  
Coefficient Matrix ◽  
Mueller Matrix ◽  
Quarter Wave Plate ◽  
Source Analysis ◽  
Matrix Elements ◽  
Standard Samples ◽  
Comparison Results ◽  
Calibration Methods ◽  
The Matrix

Currently, there are various calibration methods available to reduce the errors caused by the polarizing section of a dual-rotating-retarder polarimeter. Although these methods have high measurement accuracy, their robustness must be improved and the influence of the imaging section needs be discussed when they are applied in Mueller matrix microscopes. In this paper, a method of error source analysis and element calibration for the Mueller matrix microscope is proposed by using error transform coefficient matrices to account for the polarizing effect of the imaging section. Using Taylor expansion, an approximate linear relationship is established between the sources of errors and the Mueller matrix elements of the measured sample. From this relationship, error magnification coefficient matrices are calculated to determine the specific parameter errors in both the polarizing and imaging sections. Furthermore, elements in the fourth row or column of the error magnification coefficient matrix are especially important for the imaging section. The measurement and simulation results for an air sample and a quarter-wave plate sample as the standard samples, as well as a Daphnia organism sample with complex internal structure, are investigated and discussed. Furthermore, the comparison results reveal the effect of the imaging section on the birefringence characteristics of the Mueller matrix. With the proposed method, the maximum error can be reduced to be less than 0.01 for all the matrix elements and for the amplitude parameter of birefringence, even when the two system parameters a 2 and a 3 of the rotating mechanical part deviate from the default.

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