11,128 research outputs found
System calibration method for Fourier ptychographic microscopy
Fourier ptychographic microscopy (FPM) is a recently proposed quantitative
phase imaging technique with high resolution and wide field-of-view (FOV). In
current FPM imaging platforms, systematic error sources come from the
aberrations, LED intensity fluctuation, parameter imperfections and noise,
which will severely corrupt the reconstruction results with artifacts. Although
these problems have been researched and some special methods have been proposed
respectively, there is no method to solve all of them. However, the systematic
error is a mixture of various sources in the real situation. It is difficult to
distinguish a kind of error source from another due to the similar artifacts.
To this end, we report a system calibration procedure, termed SC-FPM, based on
the simulated annealing (SA) algorithm, LED intensity correction and adaptive
step-size strategy, which involves the evaluation of an error matric at each
iteration step, followed by the re-estimation of accurate parameters. The great
performance has been achieved both in simulation and experiments. The reported
system calibration scheme improves the robustness of FPM and relaxes the
experiment conditions, which makes the FPM more pragmatic.Comment: 18 pages, 9 figure
Stent optical inspection system calibration and performance
Implantable medical devices, such as stents, have to be inspected 100% so no defective ones are implanted into a human body. In this paper, a novel optical stent inspection system is presented. By the combination of a high numerical aperture microscope, a triple illumination system, a rotational stage, and a CMOS camera, unrolled sections of the outer and inner surfaces of the stent are obtained with high resolution at high speed with a line-scan approach. In this paper, a comparison between the conventional microscope image formation and this new approach is shown. A calibration process and the investigation of the error sources that lead to inaccuracies of the critical dimension measurements are presented.Postprint (author's final draft
Image synthesis for SAR system, calibration and processor design
The Point Scattering Method of simulating radar imagery rigorously models all aspects of the imaging radar phenomena. Its computational algorithms operate on a symbolic representation of the terrain test site to calculate such parameters as range, angle of incidence, resolution cell size, etc. Empirical backscatter data and elevation data are utilized to model the terrain. Additionally, the important geometrical/propagation effects such as shadow, foreshortening, layover, and local angle of incidence are rigorously treated. Applications of radar image simulation to a proposed calibrated SAR system are highlighted: soil moisture detection and vegetation discrimination
Characterization of a dense aperture array for radio astronomy
EMBRACE@Nancay is a prototype instrument consisting of an array of 4608
densely packed antenna elements creating a fully sampled, unblocked aperture.
This technology is proposed for the Square Kilometre Array and has the
potential of providing an extremely large field of view making it the ideal
survey instrument. We describe the system,calibration procedures, and results
from the prototype.Comment: 17 pages, accepted for publication in A&
Air fluorescence measurements in the spectral range 300-420 nm using a 28.5 GeV electron beam
Measurements are reported of the yield and spectrum of fluorescence, excited
by a 28.5 GeV electron beam, in air at a range of pressures of interest to
ultra-high energy cosmic ray detectors. The wavelength range was 300 - 420 nm.
System calibration has been performed using Rayleigh scattering of a nitrogen
laser beam. In atmospheric pressure dry air at 304 K the yield is 20.8 +/- 1.6
photons per MeV.Comment: 29 pages, 10 figures. Submitted to Astroparticle Physic
Positioning and trajectory following tasks in microsystems using model free visual servoing
In this paper, we explore model free visual servoing algorithms by
experimentally evaluating their performances for various tasks
performed on a microassembly workstation developed in our lab. Model
free or so called uncalibrated visual servoing does not need the
system calibration (microscope-camera-micromanipulator) and the
model of the observed scene. It is robust to parameter changes and
disturbances. We tested its performance in point-to-point
positioning and various trajectory following tasks. Experimental
results validate the utility of model free visual servoing in
microassembly tasks
LIDAR SYSTEM CALIBRATION USING OVERLAPPING STRIPS
A LiDAR system calibration procedure estimates a set of parameters that represent biases in the system parameters and measurements. These parameters can be used to improve the quality of any subsequently-collected LiDAR data. Current LiDAR calibration techniques require full access to the system parameters and raw measurements (e.g., platform position and orientation, laser ranges, and scan-mirror angles). Unfortunately, the raw measurements are not usually available to end-users. The absence of such information is limiting the widespread adoption of LiDAR calibration activities by the end users. This research proposes alternative methods for LiDAR system calibration, without the need for the system raw measurements. The simplified method that is proposed in this paper uses the available coordinates of the LiDAR points in overlapping parallel strips to estimate biases in the system parameters and measurements (more specifically, biases in the planimetric lever-arm offset components, boresight angles, ranges, and mirror-angles). In this approach, the conventional LiDAR equation is simplified based on a few reasonable assumptions; the simplified LiDAR equation is then used to model the mathematical relationship between conjugate surface elements in overlapping parallel strips in the presence of the systematic biases. In addition, a quasi-igorous calibration method is also proposed to deal with non-parallel overlapping strips. The quasi-rigorous method can handle heading angle and elevation variations of platform trajectories since it also makes use of time-agged point cloud and trajectory position data. To illustrate the feasibility and the performance of the proposed calibration methods, experimental results from simulated and real datasets are introduced.
Evaluation of anomalies observed on film from S-190A flight system calibration test
Due to a persistent problem of scratched film from testing of the Skylab S-190A system, a series of tests were designed to identify the cause of the film scratching. The procedures followed in this test for pretest handling and packaging of the film, the makeup of the rolls for processing, and the results of the processed film evaluation are reported
Model-based vs. model-free visual servoing: A Performance evaluation in microsystems
In this paper, model-based and model-free image based visual servoing (VS) approaches are implemented on a microassembly workstation, and their regulation and tracking performances are evaluated. A precise image based VS relies on computation of the image jacobian. In the model-based visual servoing, the image Jacobian is computed via calibrating the optical system. Precisely calibrated model based VS promises better positioning and tracking performance than the model-free approach. However, in the model-free approach, optical system calibration is not required due to the dynamic Jacobian estimation, thus it has the advantage of adapting to the different operating modes
An LED-based Flasher System for VERITAS
We describe a flasher system designed for use in monitoring the gains of the
photomultiplier tubes used in the VERITAS gamma-ray telescopes. This system
uses blue light-emitting diodes (LEDs) so it can be operated at much higher
rates than a traditional laser-based system. Calibration information can be
obtained with better statistical precision with reduced loss of observing time.
The LEDs are also much less expensive than a laser. The design features of the
new system are presented, along with measurements made with a prototype mounted
on one of the VERITAS telescopes.Comment: Accepted for publication in Nuclear Instruments and Methods in
Physics Research
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