ISO 12233 slanted-edge method experiences errors using fast Fourier transform (FFT) in the camera modulation transfer function (MTF) measurement due to tilt angle errors in the knife-edge resulting in nonuniform sampling of the edge spread function (ESF). In order to resolve this problem, a modified slanted-edge method using nonuniform fast Fourier transform (NUFFT) for camera MTF measurement is proposed. Theoretical simulations for images with noise at a different nonuniform sampling rate of ESF are performed using the proposed modified slanted-edge method. It is shown that the proposed method successfully eliminates the error due to the nonuniform sampling of the ESF. An experimental setup for camera MTF measurement is established to verify the accuracy of the proposed method. The experiment results show that under different nonuniform sampling rates of ESF, the proposed modified slanted-edge method has improved accuracy for the camera MTF measurement compared to the ISO 12233 slanted-edge method.
In order to resolve issue of azimuth framework stability of optics-electricity system for unmanned aerial vehicle depressing, reason of azimuth platform stability depressing and noise caused by secant compensation was analyzed, which work in big pitching angle with tradition mode of measuring speed. Stabilization controlling method with big pitching angle is designed in which azimuth platform install azimuth and roll gyro which was apeaked mutual, and azimuth angle velocity of line of sight was calculated. In the end, simulate experiment validate that, azimuth platform stability controlling performance of two axes platform with big pitching angle was advanced, and influence of gyro noise on controlling performance was depressed.
In order to realize the effective detection of surface structure targets in hyperspectral images, an improved target detection algorithm was proposed in this paper presents to solve the CEM algorithm problems which the large object extraction efficiency is low .First, the image was preprocessed, including end-member extraction, SAM classification. Second, after the ship pixels were subtracted from all pixels, the correlation matrix of pure background pixels was constructed to detect ship target. Third, the biggest write region was found as sea region by mathematical morphology. Finally, the false target pixels were removed from all target pixels using the characteristics which ship targets were surrounded in seawater, so the final ship targets were selected in the end. Experimental results show that the final max ratio between the energy of detection target and the energy of background increased greatly, the target signal is enhanced and the background signal is suppressed by the improved algorithm.
The terahertz absorption spectrum of explosive materials can be measured by terahertz time domain spectroscopy operated in transmission mode. In this paper, the absorption characteristics of four explosive materials in spectral range of 0.1–3 THz are studied. It shows that even for the same materials, the spectral absorption peak value in the same measurement condition is a little different. So the measurement precision of the terahertz time domain spectroscopy is very important for the feature extraction and identification of explosive materials. This work investigates the measurement precision of terahertz time domain spectroscopy. Some factors that affect the measurement precision of the terahertz time domain spectroscopy are analyzed and discussed.
KEYWORDS: Black bodies, Terahertz radiation, Sensors, Infrared radiation, Signal detection, Temperature metrology, Millimeter wave sensors, Optical filters, Signal to noise ratio, Cryogenics
Blackbody radiation principle was the study element of detection for target radiation. Research on the test device of
blackbody terahertz radiation due to terahertz photon energy was very lower than infrared energy and achieve a high
signal to noise ratio test for THz blackbody radiation . First calculate the radiance of low temperature blackbody in the
terahertz band. Radiation power from blackbody in the terahertz detector photosensitive surface was calculated in
Cassegrain system. Second, blackbody terahertz radiation testing device was developed. The blackbody radiation was
modulated by chopper and become square wave of a specific frequency, the detector output cycle signal was received by
lock in amplifier in order to improve the radiation signal to noise ratio. Tsurupica material lenses and filters are used for
removing the blackbody infrared radiation signals. Vacuum reduced background cryogenic channel was used to
eliminate background radiation interference signals. Experimental results show the blackbody terahertz radiation testing
device can successfully achieve radiation test of blackbody in temperature range (223 ~ 323) K.
Signal to noise ratio is a fundamental performance of a image intensifier, which shows the photons
detection ability from object in low light level, and its determine detection range and image definition.
The input illuminated circular area must be 0.2mm in diameter on the photocathode, input illuminance
must be 1.02×10-4lx in signal to noise ratio value measurement of Image intensifier . So the paper study
a novel illuminance calibration method, which uses PMT photon counting detection technique. The
method can directly calibrate illuminance value of very low light sources in signal to noise ratio
measurement device of image intensifier. First, we introduce the principle of low light image intensifier
S/N tester. Secondly we research illuminance calibration method of 0.2mm in diameter on the
photocathode of image intensifier, design quasi-point low light luminometer, which adopts the photon
counting detection technique. So we research the radiation characteristic of standard light source with
2856K color temperature and calculate its output photon number, For high accuracy measurement on
quasi-point sources, vision function correction and cosine correction is made. Lastly, we research the
traceability diagram of this luminometer, which is traceable to our primary photometry metrology
standard device. The experimental results indicate the novel illuminance calibration method can
accurately directly measure illuminance of quasi-point sources. Comparing with the conventional
calibration method this novel method avoids the transfer error. The absolute illuminance calibration
uncertainty is analyzed. These analysis results are useful as a evaluating method for improving signal
to noise ratio of Image intensifier.
Detection and identification performance prediction is an important part in designing the passive
terahertz imaging system. This paper presents a novel detection and identification model of passive
terahertz imaging system for concealed extended target. In the modeling process we take into account
main factors such as radiation principle of target and background, the characteristics of atmospheric
transmission, and imaging detecting system. Firstly we research interaction principle of terahertz
radiation for object based radiation principle of low temperatures terahertz blackbody. We calculate
target and background terahertz radiation power. So target-to-background contrast is described in
different fields and ranges. Secondly, we research the effect of terahertz beam attenuation in
atmospheric environment, and choose the best terahertz atmospheric absorption frequency. So we can
account target radiation power in the surface of detector. Lastly we research passive terahertz imaging
detecting method for improving THz radiometric resolution. Due to testing target is extended, the two
dimensional real-time scanning method is adopted. So we account identification probability of passive
terahertz imaging system in different distance. The paper shows results in different distances and is
useful to design and evaluate the passive terahertz imaging system for concealed object detection and
identification.
Spectral radiation intensity measurement at ultraviolet wavelengths is important for the material composition analysis of
transient extended area light sources. Here we developed transient ultraviolet multi-spectral spectrometer which is
utilized to measure relative spectral radiation intensity distributions of remote transient as well as steady-state extended
area light sources in the wavelength range (0.22-0.40) μm. Simultaneously the device also shows different spectral
radiation intensity distribution curve of the transient radiation source along with time changes. This spectrometer consists
of mobile collimation lens, Cassegrain imaging system, grating spectrograph, high speed data acquisition system and
computer software. Since ultraviolet spectral radiation is severely absorbed in air transmission, firstly the Cassegrain
system which has high reflectance in ultraviolet wavelength range is used to image the extended area light source onto
the entrance slit of spectrograph, in order to markedly improve the light gathering power of the device. The spectrograph
uses plane blazed grating to disperse spectrums which are focalized as the focal plane for detection by ultraviolet
response enhancing array CCD detector. Secondly, to resolve spectrum acquisition problem of nanosecond transient light
sources, we adopt CCD drive technology programmed by CPLD and fixed phasic high speed data acquisition method.
Finally, the spectral distortion of the spectrograph is reduced by using non-parametric kernel regression de-noising
algorithm and convolution algorithm in order to improve the spectral resolving power of the device. So we
experimentalize for spectral radiation intensity distributions of remote transient and steady-state extended area light
sources, then the uncertainty of measurement results is analyzed.
Schmidt system is a famous optical system. The corrector equation based on the third-order aberration theory has been acknowledged all along. When the previous equation is confirmed in characteristic of the aspheric surface equation and optical design program ZEMAX, it is found that the equation of the corrector has some errors. Analyses of this problem are given. A new corrector equation is established. The new equation is confirmed seriously by the optical design program ZEMAX again, it can be deduced that the coefficient α=1/2r02, and the spherical aberration coefficient ΣS1=0. This improvement is very useful for the optical design of Schmidt system, which quickens the optimization and easily reaches the optimal design data.
Based on the third-order aberration theory, the equation expressing the relationship between the conic constant and unaberration conjugate points is obtained. The corresponding graphs illuminating the relationship between e2 and β are given. According to the equation and graphs, the analyses of convex and concave surfaces are given in detail. We not only consider the unification of all kinds of reflective testing methods, such as Hindle test, concave elliptical mirror test and Ritchey-Common test etc, but also apply the unaberrational conjugate points test to refractive surface. The auto-collimating and interferometer diagnostic methods are powerful for the manufacture of lens. Kinds of convex and concave aspheric lenses have been manufactured with the detecting methods as mentioned above.
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