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Issue 7 ， 2015
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Standard transfer chain for radiometric calibration of optical sensing instruments with traceability in solar reflective bands
Abstract：The weakness of current radiometric calibration methods for optical remote sensing instruments was analyzed to satisfy the precision needs of quantitative remote sensing and the data fusion coming from multi satellites. A standard transfer chain for radiometric calibration of optical sensing instruments with traceability was designed by taking a space cryogenic radiometer as a primary system for radiometric reference and the sun as the light source, which includes a solar monochromator, a transfer radiometer, a solar spectral irradiance monitor and a solar diffuser,etc. In radiometric calibration, the transfer radiometer and the solar spectral irradiance monitor were calibrated firstly by using spectral radiometric standards provided by the solar monochromator. And then the solar diffuser was calibrated by using the transfer radiometer. The radiometric standard was transferred to an imaging spectrometer for an earth observing standard, so that the radiometric standard could be used for inter calibration of other remote sensing instruments on other satellites. The analysis on the radiometric calibration for the standard transfer chain shows that the uncertainty of optical sensing instruments is 0.75%. It demonstrates that the proposed method is helpful for constructing calibration networks of remote sensing covering China in space and air and provides a technology foundation for developing space data quality assurance system parallel to the ground system of primary radiometric standards.Keywords：radiometry in space;optical remote sensing instrument;remote sensing calibration;traceable benchmark- 56
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Published：2020-08-12 -
Program-controlled sun-tracking precision of spaceborne solar irradiance monitor
Abstract：To avoid the function failure of a solar irradiance monitor (SIM) caused by the pointing faults of the Digital Sun Sensor(DSS), the program-controlled sun-tracking of SIM on the FY-3(03) satellite was explored as the backup sun-tracking, and its precision was analyzed. By using the Julian day time and the satellite orbital parameters, the sun vector in orbital coordinate system, pitch angle and the yaw angle were deduced on the basis of Baseline Surface Radiation Network(BSRN)-like algorithm. The calculated results were compared to that of the satellite-given sun-pointing data, it shows that the sun vector deviations in three axes are all less than 0.1°, and the average deviations of pitch angle and yaw angle are 0.024 6° and -0.080 4° respectively. Using the program-calibrated sun-pointing data of many orbits, a sun-tracking control simulation experiment was carried out, and the results show that the pitch tracking control precision is better than 0.1°, and the yaw tracking control precision is better than 0.05°. To guarantee the on-orbit tracking precision, the pitch zero-position angle and the yaw zero-position angle were measured, and they are 80.46° and -36.96° respectively. The final analysis results show that the pitch tracking uncertainty is ±0.318° and the yaw tracking uncertainty is ±0.316°, meeting SIM sun-tracking precision requirement of ±0.5°. The proposed program-controlled sun-tracking reduces the dependence on the optical pointing devices, and improves on-orbit sun-tracking reliability.Keywords：spaceborne solar irradiance monitor;sun vector;sun-tracking;sun synchronous orbit;total solar irradiance- 54
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Published：2020-08-12 -
Simulation and suppression of solar on-orbit pollution of FY-3/MERSI onboard blackbody
Abstract：The solar on-orbit pollution of a blackbody on the FY-3/MERSI(FY_3 Medium Resolution Spectral Imager) was simulated to explore the effect of the solar on-orbit pollution on the surface source blackbody, meanwhile, the method to suppress the solar pollution was researched. The orbit of FY-3 satellite was simulated and the solar incidence angle at each point on the orbit was recorded. Then, Tracepro software was used to establish solar pollution simulation model and the relative position of the sun and the imager was used to simulate the solar pollution and analyze the pollution changes when the imager' scan mirror scanned and the satellite flied. At last, suppression methods for the solar pollution was designed based on analyzed results, and the suppression effects were verified by simulation experiments. The results show that the solar pollution of the surface source blackbody has be removed by designing a light board near the scanning mirror, by which the power of pollution radiation is less than 0.1 W, reduced by over 97%, and protects the surface source blackbody effectively. Moreover, the uniformity and stability of the surface source blackbody are improved and the calibration precision of infrared channel onboard is guaranteed.Keywords：FY-3/Medium Resolution Spectral Imager (FY-3/MERSI);surface source blackbody;solar pollution;Tracepro simulation;pollution suppression- 53
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Published：2020-08-12 -
Influence factors on SNR of TDICCD space camera
Abstract：To quantitatively assess factors affecting the Signal to Ratio(SNR)of a Time Delay Integration(TDI)CCD camera, the imaging principle and noise sources of the TDICCD space camera were researched and a SNR model was established. The effects of the radiance lightness, integration stages, line transfer frequency and the system gain(analog gain)on the SNR were analyzed. A laboratory radiation calibration system was established to simulate the on-orbit radiance conditions of the camera. The relationship between the SNR and different working parameters were verified by radiation calibration. The calibration results show that the photon shot noise, dark current noise and the fixed pattern noise play a major role in all kinds of noise. The output signal and the SNR of the camera increase with the raises of the radiance, integration stages and the system gain and decrease with the raise of the line transfer frequency. The varieties of these factors have different influences on the SNR. Specifically, when the variations of the radiance, integration stages and the line transfer frequency are respectively L times, M times and τ times, the variations of the SNR are slightly larger than L1/2 times, M1/2 times, τ-1/2 times, respectively. Moreover, the influence of the system gain on the SNR is in a relatively small range and the variation of the SNR decreases gradually with the raise of the system gain.Keywords：CCD space camera;signal-to-noise ratio;time delay integration;radiance;integration stage;line transfer frequency;system gain- 52
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Published：2020-08-12 -
Evaluation and comparison of modulation transfer function for FY-3B/C MERSI on early orbit
Abstract：In consideration of the characteristics of polar-orbiting satellites, an edge Modulation Transfer Function(MTF) test method using ice and snow targets in polar region is proposed for the China polar-orbit meteorological satellite FengYun (FY) 3-MEdium Resolution Spectral Imager (MERSI, 20 bands, with 250 m and 1 000 m resolution). It takes samples from the edge between ice block and sea to get the Point Spread Function (PSF). Then, the Fast Fourier Transform (FFT) method is used to calculate the PSF and retrieve MTF values at the Nyquist frequency point. This method is available to the most of MERSI bands. The experiment results for MTF measurement indicate that the MTFs of all bands along FY-3B/C flight direction are about 0.31 (>design index 0.27/0.25) with high spatial frequency feature quality. However, the spatial frequency feature qualities along MERSI scan direction are bad for both FY-3B and 3C satellites. The MTFs at 1.0 km resolution of FY-3B/C images are respectively approximate 0.10 and 0.12, which also show that the systematic results of FY-3C are higher than that of the FY-3B. The MTFs of FY-3B/MERSI are even just around 0.07 at 250 m resolution. This finding may be primarily attributed to 27% overlapped scanning in the original design of FY-3/MERSI imaging system to enhance the signal-to-noise ratio (SNR) of images. It suggests that the overlapped scanning should be processed in design of the next generation FY-3 atmospheric satellite.Keywords：FY-3B/C Medium Resolution Spectral Imager (MERSI);Modulation Transfer Function (MTF);overlapped scanning- 114
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Published：2020-08-12 -
Vacuum radiance temperature national standard facility for Infrared remote sensors of Chinese Fengyun meteorological satellites
Abstract：The state-of-the art of the typical national standard vacuum radiance temperature facilities for infrared remote sensing in America, Germany, and Russia were introduced. Especially, the Vacuum Radiance Temperature National Standard Facility (VRTSF) developed by National Institute of Metrology of China for calibrating the radiance temperature of Chinese Fengyun meteorological satellite was described in detail. The design scheme of the VRTSF was given and its structure and optical path were introduced. The vacuum reduced background chamber for the big aperture blackbody was built to calibrate the infrared remote sensor, and the standard value of the radiance temperature was transmitted from the standard blackbody to the customer blackbody by a Fourer Transform Infrared Radiometer(FTIR). The temperature range of the standard blackbody is from 190 K to 340 K with a diameter of 30 mm and emissivity of 0.9999 in a cavity. The uncertainty of this blackbody is 5 050 mK@300 K/10 μm. The wavelength range of the VRTSF is 1 μm to 1 000 μm and its resolution is 0.2 cm-1,which supports the requirements of lots of infrared remote sensing. The VRTSF built at the NIM China is characterized by higher uncertainty, higher spectral resolution and stronger expansibility. The temperature range of the VRTSF will expand to 100 K-500 K in future, which can meet the requirements for calibration of the most of infrared remote sensing instruments.Keywords：FY meteorological satellite;infrared remote sensing;radiance temperature;calibration blackbody;national standard- 64
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Published：2020-08-12 -
Establishment of image model for on-board space camera
Abstract：The concept of on-board imaging model for a space camera was proposed, and the method to establish the imaging model of the space camera was researched. On the basis of the solar elevation angle and the reflection of earth surface, the radiance at the entrance pupil of space camera was calculated using the MODTRAN software. Then the radiometric calibration data were analyzed and the responsibility, radiance range and the integration time for each image model were acquired. Meanwhile, the relation between the responsibility and the integration time was obtained for scroll image and standard image and the radiance ranges at each image model was calculated at every scroll angle. Finally, according to the radiance range at each image model and the maximum objective at sensor radiance from the earth surface, an imaging model table was established under the scroll angle and solar elevation angle. When the space camera worked on board, one could choose a corresponding imaging model by looking up the table and could achieve better images. The method has been used in space camera imaging for several times, high quality remote images have been acquired. The image satisfaction improves from 65% to 99.9%. According to the method, the remote image's quality has been improved obviously. The image not only includes all scene information, but also has abundant levels.Keywords：space camera;radiometric calibration;image model- 71
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Published：2020-08-12 -
Revision of solar irradiance of FY-3C/TOU
Abstract：To solve the abnormal data of Fengyun-3C/Total Ozone Unit(FY-3C/TOU) solar irradiance, an algorithm for estimating the deviation of installation parameters of TOU diffuse plate coordinate system was presented, and the deviation of solar irradiance was revised based on the adjusted parameters. The theoretical basis of this algorithm was presented, and the numerical analysis results were discussed. The algorithm assumed the deviation between the actual TOU diffuse plate coordinate system on the orbit and its ideal diffuse plate coordinate system to be expressed by an unknown transform matrix. Then, the equations with unknown parameters could be established based on the relationship between the objective value of solar irradiance and the revised FY-3C/TOU irradiance data. Furthermore, the estimated values for the unknown transfer matrix were derived numerically by solving an optimal problem. Finally, the deviation of FY-3C/TOU solar irradiance was revised by substituting the new installment parameters of the diffuse plate into the geolocation and calibration process of TOU,and the attenuation coefficient of the tracking instrument was captured. The numerical analysis results show that the maximum relative error of solar irradiance decreases from 36.5% to 2%, and the fluctuation range of relative error narrows from 27.2% to 3.2%,which revises the deviation greatly by proposed algorithm.Keywords：FY-3C satellite;Total Ozone Unit(TOU);solar irradiance;deviation correction;diffuse plate coordinate system- 67
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Published：2020-08-12 -
Spectral and radiometric calibrations for mapping satellite-1 camera
Abstract：The spectral calibration and radiometric calibration were performed for every waveband of the Mapping Satellite-1 camera to validate its spectral and radiometric performance. In spectral calibration, a collimated monochromatic light source was provided by wavelength scan using a monochrometer and a collimator. Meanwhile, the camera acquired calibration images, and then compared image's digital number and the output of calibrated standard reference detector to obtain relative spectral responsive curve by data analysis and processing. Furthermore, spectral characteristics were acquired. In radiometric calibration, the nearest emitting source method was used to perform the end to end relative and absolute radiometric calibrations with irradiating the whole aperture and the field of view. In the on-orbit inner calibration, the aged and picked up LEDs were employed as on-orbit inner calibration light sources to monitor the changes and status of focal plane detector array and its imaging electric circuit at post launch, and they were corrected in necessary conditions. Spectral calibration and radiometric calibration results indicate that all the spectral performance and radiometric performance of the Mapping Satellite-1 camera meet design requirements, non-uniformity of the camera is decreased from 1.93% to 0.22% after relative radiometric calibration. The typical Signal to Noise ratios(SNRs) of panchromatic and multispectral cameras are beyond 90 times and 180 times respectively. The compared results from the on-board inter calibration after launching and the tested data from a laboratory before launching show that radiometric responsive performance of the camera has not changed during this period, and not need to be corrected.Keywords：mapping camera;spectral calibration;radiometric calibration;on-orbit inner calibration- 69
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Published：2020-08-12 -
Discrimination and correction for solar contamination on mid-infrared band of FY-3C/VIRR
Abstract：On the basis of solar contamination phenomenon and occurrence rules of the mid-infrared channel (3.7 μm) in the Fengyun-3C/Visible and Infrared Radiometer(FY-3C/VIRR), temporal and spatial characteristics of the solar contamination were analyzed. The method to discriminate initially and correct the solar contamination data in the northern hemisphere was proposed and the effect of solar contamination on calibration coefficients and blackbody brightness temperature was evaluated quantitatively. The results show that for the mid-infrared channel (3.7 μm) in the FY-3C/VIRR, the solar contamination in the northern hemisphere caused by the sun irradiation on calibrated blackbody will appear at the solar zenith angle between 85°-118°. The daily mean absolute error of blackbody temperature is up to 4.5 K, and the maximum absolute error in a day is up to 15 K. By discrimination of the solar contamination data day by day and calculating the linear difference of calibration coefficients before and after contaminations, the effect of solar contamination on calibration coefficients can be corrected initially.- 104
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Published：2020-08-12 -
Applications and development of radiation calibration in orbit based on space monochromator
Abstract：The dispersion principle of common used monochromators is described. The optical constructs of several kinds of reflective and horizontal imaging systems are introduced and their wavelength calibration and energy calibration methods are given. The application status of current remote sensing instruments boarding on different monochromators is illustrated, such as the applications of the Moderate Resolution Imaging Spectroradiometer(MODIS),Solar Spectrometer(SOLSPEC), Solar Backscatter Ultraviolet Spectrometer(SBUV), Ultrariolet Ozone Vertical Profile Probe(UOVPP-SBUS) and TRUTHS task from European Space Agency(ESA) to radiation measurement, spectral calibration and absolute calibration. Finally, it discusses the possible developing trends and application prospects of space monochromators and points out that the absolute calibration system by taking the sun as the light source and combining a space monochromator with a cryogenic absolute radiometer is one of the most promising trends in the future.Keywords：Monochromator;cryogenic absolute radiometer;spectral calibration;absolute calibration;space remote sensing- 54
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Published：2020-08-12 -
Cross-calibration of VIRR/FY-3A split-window channels with AIRS/AQUA and IASI/METOP-A data
Abstract：Some practical applications indicate that there is calibration deviation in the on-orbit radiometric calibration of the two split-window channels(IR4,~10.8 μm;IR5,~12.0 μm) on the Visible and Infrared Radiometer(VIRR) mounted in FY-3A. Therefore, this paper applies high-spectral convolution method to implementation of the cross radiometric calibration for the two spilt-window channels of VIRR/FY-3A based on the observation data from the Infrared Atmospheric Sounding Interferometer/METOP-A(IASI/METOP-A)and the Atmospheric Infrared Sounder/AQUA(AIRS/AQUA). According to the characteristics of the satellite orbit, the Arctic region (60°N-90°N,180°W-180°E) was chosen as the research area, and June, September, December 2010 and March 2011 were selected as the research satellite orbit spectral response functions of the 4th and 5th channels of VIRR/FY-3A. Then, the Planck blackbody radiation formula was used to achieve the conversion between radiation value and brightness temperature. On the basis on the corresponding matching conditions, the matching observation points between the 4th and 5th channesl of VIRR/FY-3A and AIRS/AQUA, the 4th and 5th channels of VIRR/FY-3A and IASI/METOP-A were extracted, respectively. Finally, the regression of matching observation point pairs was analyzed to obtain the cross radiometric calibration coefficients. The experimental results show that the proposed high-spectral convolution method with IASI/METOP-A and AIRS/AQUA for the cross calibration has the same calibration results. By using IASI/METOP-A and AIRS/AQUA as the standard, the brightness temperature biases for the 4th channel of VIRR/FY-3A are 2.39 K and 2.06 K; and those for the 5th channel of VIRR/FY-3A are 0.59 K and 0.44 K. This work indicates that calibration deviation is related to the brightness temperature.Keywords：Visible and Infrared Radiometer/FY-3A;split-window channel;Atmospheric Infrared Sounder/AQUA;Infrared Atmospheric Sounding Inter ferometer/METOP-A;cross-calibration;high-spectral convolution method- 77
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Published：2020-08-12 -
Precise measurement of voltages in space cryogenic radiation temperature system
Abstract：To implement the temperature measurement of a cavity in the space cryogenic radiometer based on a temperature resistance, the measuring accuracy and measuring stability of the electronic system in the radiometer was researched. By taking the scheme design and device selection into account, a new precise voltage measuring system was proposed based on an ultralow noise accuracy voltage reference source(LTZ1000), a four wire germanium resistance(GR1400-AA)and a 24 bit analog to digital converter(24 bit AD). Then, the noise ratio for the entire system was calculated in theory, and the temperature characteristics and the amplitude frequency response of the system were simulated by using TINA-TI. Finally, the experiment on measuring temperature accuracy and long-term stability for this system was performed at the 77 K constant temperature environment. The experimental results show that the actual sampling voltage of germanium resistance is within 100 μV, and the long-term stability is lowered to 1×10-5. Moreover, the temperature measurement accuracy of system is less than 4 mK, meanwhile, the temperature stability is up to 1×10-5. So, the proposed precise temperature measurement system basically meets the needs of space cryogenic radiometer for long-term stability and measurement accuracy.Keywords：cryogenic radiometer;germanium resistance;voltage measurement;reference source with high accuracy;24 bit Analog to Digital converter- 89
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Published：2020-08-12 -
FY-3C/MERSI caliration for solar band using multi-reflectance stable targets
Abstract：The calibration accuracy of solar bands for Fengyun-3C/Moderate Resolution spectral Imager(FY-3C/MERSI) from January 2014 to October 2014 is assessed based on multi-reflectance stable targets, such as deserts and salt lakes with different reflectances in a globe. In combination of ground surface and atmospheric parameters of Moderate Resolution Imaging Spectroradiometer(MODIS) products and the atmospheric radiation transfer model, the band reflectances of the satellite when it transits into the pupil are calculated and then they are taken as the reference true values for validation of the absolute radiation calibration accuracy. The validation experiments on radiation calibration accuracy of the FY-3C/MERSI for reflective solar bands are performed for the dates mentioned above. The results show that the calibration accuracy of most solar bands of FY-3C/MERSI is different for the targets with different reflectances. For some bands, the calibration accuracy is lower for larger reflectance targets, and higher for lower reflectance targets. For other bands, the calibration accuracy is lower for larger and lower reflectance targets, and higher for targets with moderate reflectances. Bands 1~4, 9~11, 15~16 and band 19 of FY-3C/MERSI can maintain a calibration accuracy of 5% during one year after its launching. The time series of the calibration accuracy of each band show that the variation of the calibration accuracy for the whole study period is within 5% except for the blue band and the water vapor absorption bands,. It concludes that it is effectively to acquire a good knowledge of the radiometric calibration accuracy over a wider dynamic range for FY-3C/MERSI by using the deserts and salt Lakes simultaneously.Keywords：radiometric calibration;FY-3C/Moderate Resolution Spectral Imager (MERSI);stable target;solar band- 91
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Published：2020-08-12 -
Development and applications of intercalibration for satellite optical instruments
Abstract：The on-orbit intercalibration between satellite instruments is the central method to ensure the reliability,consistency and the continuity of observation data. The calibration uncertainty of 2% has been achieved combined with high-accuracy reference on-orbit instruments. This paper introduces the concepts and significance of the intercalibration and emphasizes which is a main way to correct the relative deviation of radiation calibration between instruments. It gives the basis conditions to complete the intercalibration and discusses the existing difficulties. Then, the realized process of the intercalibration is summed up such as the data collocating, filtering, correcting, reference changing and accuracy analyzing, and the effect factors on the calibration accuracy are analyzed.Moreover, it describes the current intercalibration methods for satellite optical remote sensing and needed conditions and summarizes the uncertainty of different intercalibration methods under different conditions for post-launch radiometric calibration of satellite remote sensors. In the end, this paper introduces a few international organizations and some ongoing joint campaigns with focusing on instrument calibration and validation, which shows the recent advance of research on the SI intercalibration in orbit.- 82
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Published：2020-08-12 -
Fast non-uniformity correction for high dynamic infrared radiometric system
Abstract：Several different integration time steps are often required for a high dynamic infrared radiometric system, therefore, its non-uniformity is usually corrected one by one. As there are different correction coefficients in different time, this paper proposes a new non-uniformity correction method based on blackbody calibration method and integration time calibration method.The method obtains nonlinear correction coefficients of all integration time in whole dynamic ranges only by two integration time steps and two calibration temperature points, meanwhile keeping correction accuracy, reducing measuring temperature points and correction time. The verifying experiments for the proposed method are performed by using a Φ400 mm ground-based infrared radiometric system.The results show that the uniformity has reduced from 3.78% to 0.24% by using the proposed method. In addition, the result at 4 ms integration time illustrates that this method has a higher precision. Moreover, it greatly reduces the required equipment and correction time,and is characterized by good real-time performance and suitable for field measurements.Keywords：cooled infrared detector;radiometry;Dynamic range;integration time;non-uniformity correction- 53
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Published：2020-08-12 -
Application of laser displacement sensor to free-form surface measurement
Abstract：By taking a point displacement laser as an object, this paper researches the application of the sensor to free-form surface measurement. In consideration of the measurement error of the laser displacement sensor due to the inclination of the measuring point, a quantifiable inclination error model was proposed to improve the measuring accuracy. On the basis of the principle of direct-point laser triangulation start, the geometric relationship of the laser light paths was analyzed. According to the shift of convergent light spot centroid, the inclination error model was derived. Following that, the laser displacement sensor was calibrated with a high precision laser interferometer and a sine bar, the measured data by the laser displacement sensor were compensated by the error model, and the measurement accuracy was significantly improved. Finally, the experimental measurement on an aspheric lens surface was performed, the free-form surface inclination measuring point was calculated and the measurement data were corrected by the proposed model. Experimental results show that inclination quantization error model has controlled the measurement error of the laser displacement sensor by less than 10 μm, which meets the requirements of the free surface measurements by laser displacement sensors.Keywords：laser displacement sensor;free-form surface measurement;non-contact measurement;triangulation measurement;error compensation- 65
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Published：2020-08-12 -
Active laser detection of cat's eye effect for space-based off-axis three mirror optical system
Abstract：The cat's eye effect of a space-based Off-axis Three Mirror (OTM) system was analyzed by using the ray tracing method. The effects of image tilt, views of field and the defocus of the OTM system on the echo efficiency and beam divergence angle of cat's eye retro-reflection were given. Then, it pointed out that the image tilt size of the OTM system is a main factor to produce cat's eye echo wave. A threshold method was proposed to actively detect the cat's eye signals, then the influence of diffuse reflection from a target on the detection of cat's eye signals was analyzed by combining the high order cosine scattering mode. The minimum laser pulse energy requirements for 20 km to 120 km detection range under different transmissive beam qualities were given theoretically. The simulation results show that when the beam divergence entire angle is 0.3 mrad, the minimum laser pulse energy requirements at the detection distances of 50 km and 120 km are 0.7 mJ and 3.1 mJ, respectively. Finally, an experiment was carried out to verify the feasibility of the active detection of OTM systems with the cat's eye effects.Keywords：active laser detection;cat's eye effect;off-axis three mirror system;retro-reflection characteristics;ray tracing- 63
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Published：2020-08-12 -
Characterization of freeform optical surfaces based on surface slope
Abstract：This paper focuses on the optical freeform surface model in optical design of freeform optical surfaces. Based on the model of conventional Gaussian Radial Basis Function(RBF), a model of Gaussian Radial Basis Function based on slope (Gaussian RBF-BS) was proposed by improving the distribution of basis function and changing the shape factor of basis function. The different types of freeform surfaces were fitted and compared by using models of Gaussian RBF-BS, Gaussian RBF and Zernike polynomials. The results demonstrate that the surface fitting ability of the proposed model is stronger than those of the conventional Gaussian RBF model by 1-2 orders, and it has a stronger surface characteristic ability. Then, the proposed model was used to design a Three Mirror Anastigmat(TMA) system, where the average Modulation Transfer Function(MTF) in whole field of view has reached over 80%. As compared with that of the conventional model based on the RBF, the proposed model enhances the aberration balance ability and improves the image quality of the system. Further analysis indicates that RBF-BS model is much suitable for the characterization of the freeform surface with significant asymmetry and local variation. It is expected to be applied to the design of optical systems with large off-axis magnitudes and fields of view.Keywords：freeform optical surface;surface fitting;surface slope;Gaussian radial basis function;Zernike polynomial- 49
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Published：2020-08-12 -
Design of spectrometer in color measuring spectrophotometer
Abstract：According to the application demands of a color measuring spectrophotometer, the spectrometer composed of an optical system, a photoelectric receiving system and relevant circuits was proposed in a modular design to improve its facilitate design, alignment and test. As the spectrophotometer is a non-imaging optical instrument, every optical module was connected by optical fibers. The application requirements of the spectrophotometer were analyzed, its specifications were put forward, and spherical aberration and coma aberration were well corrected. A way to eliminate the secondary diffraction spectrum with an optical filter was analyzed in detail and the contradiction of unmatched numerical apertures between fiber optics and spectrometer was solved. A spectrometer with a dimension of 130 mm×90 mm×45 mm was established, and experimental test shows that the spectrometer achieves a spectral resolution of 2 nm in the whole band with the slit width of 50 μm. The spectrometer wavelength is calibrated and the accuracy is less than 0.2 nm. The entire band of the spectrometer uses 401 pixels, which meets the design requirements of the wavelength interval of 1 nm. The spectrometer with flexible fiber optics and electronic circuit is convenient for the layout of whole instrument, disassembly of modules and the individual test of the spectrometer, which lays a good foundation for the development and test of the whole spectrophotometer.Keywords：optical design;color measuring spectrophotometer;modular design;Spectrometer;second order diffractive spectrum- 55
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Published：2020-08-12 -
Identification of rotational center in remote angular-velocity measurement with spatial filtering
Abstract：To determine the direction of a rotational speed and to calculate the value of the rotational speed in remote angular-velocity measurement with the spatial filtering technique, it is necessary to exactly identify the location zone of measured-object rotation center. Therefore, a method of determining the rotation center based on Double Differential Spatial Filtering Sensor (DDSFS) was proposed according to the principle of spatial filtering velocimetry. The DDSFS constructed by multiple photovoltaic cells consists of two Differential Spatial Filters (DSFs), which outputed two quasi-sinusoidal signals with the central frequencies of f1 and f2. By moving the DDSFS, a coefficient j could be calculated by using two groups of central frequencies before and after moving the DDSFS. Then, the location zone of the rotational center could be distinguished depending on the sign of the coefficient j and the relative relation between f1 and f2. The achieved results show that j<0 represents the location zone of the imaged rotation center O' to be between DSF1 and DSF2, and that j>0 with f1>f2 indicates the location zone of the imaged rotation center O' to be below the DDSFS, and that j>0 with f1<f2 indicates O' to be above the DDSFS. The proposed method can be employed to determine the rotational center of solid body, and the location of whirling center in multiphase fluid with solid, liquid or gaseous substances when the rotation speed is relative stable.Keywords：differential spatial filter;double differential spatial filtering sensor;rotation center;location identification;remote angular measurement- 40
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Published：2020-08-12 -
Design and fabrication of broadband holographic ion beam etching gratings
Abstract：A broadband holographic ion beam etching grating with three different blazed angles was designed and fabricated on the same substrate. A new divisional design method for the broadband holographic ion beam etching grating was proposed and the design parameters for the grating were optimized. A reactive ion beam etching equipment was used in the pattern transfer of photosensitive resist and the divided and stepped ion beam etching technology was used in the experiment. Finally, a broadband holographic ion beam etching grating with a diameter of 60 mm×60 mm worked at 200-900 nm was fabricated on a K9 substrate, which has the same phase but three different blazed angles of 9°,18° and 29° on different areas. The experimental results show that the lowest and the highest diffraction efficiencies of holographic ion beam etching grating are higher than 30% and 50%, respectively in the broadband of 200-900 nm, which is well in agreements with that of the theoretical calculation and meets the design requirements. As compared with other fabricating methods for grating, the proposed method is characterized by controllable groove shapes, larger sizes and to be easy for bulk fabrication.Keywords：holographic grating;broadband grating;ion beam etching;etching simulation- 70
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Published：2020-08-12 -
Effects of low level laser irradiation on cell cycle and intracellular calcium concentration of osteoblastic cells under mechanical strain
Abstract：The cycle strain was exerted on osteoblastic cells, and the changes of cell cycle and intracellular calcium concentration of osteoblastic MG-63 cells under a mechanical stretching were explored and the effect of Low Level Laser Irradiation (LLLI) on the changed rule was revealed. Firstly, MG-63 cells were divided into 3 groups: control group, strain group and LLLI-strain group, and the cell cycles of these MG-63 cells were measured by a flow cytometry (FCM). Then, the MG-63 cells were divided into 2 groups: strain group and LLLI-strain group, and their intracellular calcium concentration was measured by the FCM and a fluorescent indicator fluo-3/AM at 0,5,15,30 and 60 min under the stretching. However, the LLLI-strain group would receive LLLI for 1 min after the stretching. Experimental results indicate that strain groups present higher proliferation indexes as compared to the control group. The laser-strain groups present higher proliferation index than other two groups. For laser-strain group, the concentration of the intracellular calcium ion increases gently, but that in strain group has increased drastically. It concludes that the LLLI promotes the proliferation of MG-63 cells under the stretching, and it may be achieved by regulating the changed rhythm of concentration of the intracellular Ca2+.Keywords：orthodontics;low-level-laser-irradiation (LLLI);osteoblastic cell;strain;proliferation;concentration of intracellular calcium ion- 76
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Published：2020-08-12 -
Temperature characteristics of quality factor of silicon micromachined gyroscope under high-vacuum environment
Abstract：The influence mechanism of temperature on the quality factor of a Silicon Micromachined Gyroscope (SMG) under a high-vacuum environment was analyzed. The complex frequency model of thermoelastic damping and the temperature characteristics of silicon were presented. Then, the theoretical model of temperature characteristic of quality factor was set up, and the the simulation analysis and experimental verification were performed. The temperature coefficient of quality factor is -9.76×10-3/℃ at a normal temperature with a theoretical calculation. The ANSYS was used to simulate the temperature coefficient of quality factor, and the simulation result is -9.96×10-3/℃. The temperature experiment for quality factor was carried out, and the temperature coefficient of quality factor is -9.02×10-3/℃, which is different from the theoretical calculation by 8.20%. The analytical results demonstrate that the theoretical model of temperature characteristic of quality factor in the high-vacuum environment provides theoretical basis for temperature compensation of the SMG and gives a guidance for optimization design of the SMG.Keywords：silicon micromachined gyroscope;quality factor;temperature characteristic;Thermoelastic damping;high vacuum- 50
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Published：2020-08-12 -
Self-sensing piezoelectric micro-gripper
Abstract：A self-sensing method was utilized to acquire the finger displacement and gripping force of a piezoelectric micro-gripper without micro-displacement and micro-force sensors. As the surface of piezoelectric ceramic wafer will generate free charges when it deforms under the external voltage and external force, a self-sensing method based on integral charges was proposed for sensing the finger displacement and gripping force. According to Jan G. Smits's piezoelectric cantilever bending deformation theory, the self-sensing formulas of the finger displacement and gripping force were derived, namely, the free charges on the surface of the piezoelectric ceramic wafer were used to represent the finger displacement and gripping force. Then an integral circuit was designed to acquire the surface free charges. The balance condition of self-sensing circuit was derived, which was that the product of the equivalent capacitance and leakage resistance of the piezoelectric crystals should be equal to that of the integrating capacitor and balancing resistor. Self-sensing experimental results indicate that the maximum error of modified self-sensing displacement is 0.78 μm for the finger displacement of 31.59 μm. The maximum error of modified self-sensing gripping force is 0.24 mN for the gripping force of 35.91 mN. Those experimental results show that the proposed self-sensing method is effective to detect the finger displacement and the gripping force.Keywords：piezoelectric micro-gripper;finger displacement;gripping force;self-sensing;integral charge- 55
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Published：2020-08-12 -
Influence of adhesive thickness on surface deformation of mirror supported by three-point mount
Abstract：By taking the mirror supported by a three-point mount used in a 45 nm immersed lithographic objective lens for a research object, a support structure model with the three-point mount by adhesive connection was established to determine the influence of adhesive thickness on surface deformation of the mirror supported by the three-point mount. The mirror surface deformation distribution due to gravity was analyzed, and the effect of different adhesive thicknesses on surface deformation was discussed through analytical expressions. Then, a finite element model of "block-layer-mirror" was established. The deformation of mirror surface was simulated for different adhesive thicknesses. The simulation results show that the Root Mean Square(RMS) values of mirror surface deformation first decrease and then increase with the increasing adhesive thickness, and it reaches a minimum of 1.25 nm when the adhesive thickness is about 280 μm. Finally, surface deformation changes of the mirror caused by the three-point support were tested through an experiment while adhesive thicknesses were 200 μm, 280 μm and 400 μm. Experiment results show that surface deformation of the mirror is in agreement with simulation result, which verifies the validity of simulation results.Keywords：opto-mechanical system;mirror;three-point mount;surface deformation;adhesive;Finite Element Model(FEM)- 63
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Published：2020-08-12 -
Performance and experiments of particle rotation driven by swirl
Abstract：How to generate a swirl and how to drive the particle movement by the swirl were analyzed. Then, a mechanics model of particles in the swirl was established. By taking the micro-level particles(microns to hundred microns)as examples, the characteristics of the rotary flow field generated by two ejecting micro tubes which were parallel placed and the force condition and movement characteristics of the particles in the rotary flow field were analyzed. The influences of different particle sizes, shapes and changed positions on the rotation performance of the particles were discussed, and an experiment was performed to verify the feasibility of swirl method. The analysis and experiments show that the swirl can be generated by two ejecting micro tubes which were parallel placed. And the swirl can drive the micro particles to rotate in the flow field stablely. The movement characteristics of the particles in the flow field are dependent on the flow parameters and particle shapes, particle sizes and the eccentricity. When the eccentric of initial position and the revolution of the particles are reduced, it will be conducive to capturing and adjusting the attitudes of particles. Even though the particle parameters are changed,the method still can drive the particle rotated in stability by reasonable matching these parameters.Keywords：swirl driving;particle rotation;flow injection;folw field parameter- 78
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Published：2020-08-12 -
Regulation and mechanism of edge chipping for Si3N4 ceramics worked by sliding loads
Abstract：A single diamond grit scratching test system was built to explore the damage mechanism and the edge chipping characteristics of Si3N4 ceramics. The effects of damage stations, cutting depths, cutting velocities and grit wears on the edge chipping of the Si3N4 ceramic were compared. A 3D laser measurement microscope was used to observe the geometric morphology of edge chipping and the Scanning Electric Microscopy (SEM) was taken to analyze the damage mechanisms of edge chipping. The results show that exit edge chipping is the main damage for ceramics. The cutting depths, cutting velocities and grit wears would affect the edge chipping obviously. The medical section curve of exit edge chipping has obvious staircase fractal characteristics, which could be explained well by percolation theory and the crack propagation principle of least resistance. The damage mechanism for entry edge chipping is mainly transgranular fracture, the damage mechanical for exit edge chipping is mainly intergranular fracture, and the interior edge chipping is engendered by eradicating and cutting.Keywords：sliding load;engineering ceramics;Si3N4 ceramics;edge chipping;single diamond grit scratching;percolation- 43
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Published：2020-08-12 -
Grinding force and specific grinding energy of high speed grinding of 9CrWMn cold work die steel
Abstract：The high speed grinding mechanism for 9CrWMn cold work die steel was analyzed, and DEFORM software was used to simulate the grinding force in high speed grinding processing of 9CrWMn cold work die steel.A series of high speed grinding experiments were conducted on a Computer Numerical Control(CNC) high speed grinding machine (BLOHM PROFIMAT MT-408) to measure grinding forces on line under different working conditions. It demonstrates that as the workpiece feed rate increases, the grinding forces especially the normal force increase nearly 45%. Both normal and tangential forces decrease with going up the wheel velocity and the normal force decreases nearly 33%. The cut depth has a larger effect on the grinding forces, especially the normal grinding force increases nearly 100%.The influence of processing parameters on the specific grinding energy was investigated. It shows that with increasing grinding depth and workpiece feed rate, specific grinding energy decreases obviously, in accordance with the size effect in grinding process.Moreover, with increasing the wheel velocity, the specific grinding energy increases. At last, the microtopographies of a workpiece surface before and after high speed grinding were compared. The experimental results are well consistent with simulation analysis results.Keywords：high speed grinding;cold work die steel 9CrWMn;grinding force;specific grinding energy;measurement on line- 81
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Published：2020-08-12 -
Nanostructure machining by AFM probe combined with continuous laser
Abstract：To obtain the nanostructure with stable morphology and a smallest possible size, a nanostructure machining system is established by an Atomic Force Microscopic(AFM) probe combined with a continuous laser. With this method, the study focuses on the near-field enhancement theoretical analysis and simulation when the continuous laser irradiates the AFM probe and the machining performance of this system. Firstly, based on the mechanism of surface plasmon(SP), the Factor of Enhancement Field(FEF), temperature field and the thermal expansion on the probe tip are researched. A nanostructure machining system is set up based on the optical fiber probe to guide the laser to irradiate on the AFM probe. At last, the polyethylene(PE) is chosen as a sample to do the experiment. Experimental results indicate that the size of the processed nanodot is about 200 nm and that of the nanowire is about 30-40 nm. This method shows the proposed probe has simple-structure and inexpensive-cost and could achieve nanostructure machining.Keywords：nanostructure;Atomic Force Microscopy(AFM) probe;continuous laser;machining;near-field enhancement- 75
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Published：2020-08-12 -
Estimation and improvement for fitting accuracy of instantaneous parabolic reflector in FAST
Abstract：According to the working principle of the active reflector surface in Five-hundred-meter Aperture Spherical radio Telescope (FAST) and its structure dimension, the fitting accuracy of instantaneous parabolic reflector for the FAST was researched based on analysis of the dynamic surface accuracy of reflector element. Firstly, a reflector element was selected as research object, its calculating formulas taking the mechanism movement into account were deduced from a joint to solve dynamic surface accuracy. Then, by taking 19 reflector elements from different regions for examples, the characteristics under 9 initial surface types were analyzed correspondingly. Finally, based on the dynamic characteristics of reflector element, the fitting accuracy estimation methods of instantaneous parabolic surface were proposed, including mechanical surface precision and semi-optical path difference surface accuracy with feeding lighting function. Furthermore, two improved measures for surface accuracy were given, and they were enlarging joint controlling area to next joint target ring of parabolic surface border, and offsetting the outer ring joint targets by 4 mm to the sphere center and also moving center targets by 4 mm to reserve direction. Results demonstrate that the panel with surface accuracy RMS 2 mm is a preferential selection for initial surface type of reflector element. After changing control strategy, the mechanical surface accuracy increases to RMS 3.938 mm, better than the index RMS 5 mm, Meanwhile, the semi-optical path difference surface accuracy reaches to RMS 0.629 mm. This research has important significance for ensuring reflector element initial surface type and adjusting fitting accuracy of the instantaneous parabolic reflector.Keywords：Five-hundred-meter Aperture Spherical radio Telescope(FAST);reflector element;initial surface;dynamic surface;surface accura cy;instantaneous parabolic reflector;fitting accuracy- 108
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Published：2020-08-12 -
Calibration of seeker's pointing error based on model linearization and least square estimation
Abstract：To reduce and eliminate the effects of pendulum frame processing, assembly error, sensor error on the pointing accuracy of a double pendulum frame seeker, a new pointing error calibration method was introduced through model linearization and least square estimation method. The kinematic equations of the system were built according to the kinematics of the double pendulum frame seeker and each error term affecting the pointing accuracy. Then, the kinematic equations were reconstructed to establish the linear equation from the vector of control input to the actual pointing vector. Finally, according to the step-solving ideas, the least square method was used to obtain the mapping matrix from the vector of control input to the actual pointing vector and to implement the pointing calibration. The experiment results show that after calibration the means of the yaw angle error and pitch angle error have reduced from the original 92.63 "and 75.94" to 2.86 "and 2.85", respectively,and the standard deviations have also reduced from 95.01 "and 77.44" to 11.11 "and 11.15", respectively. The results demonstrate that the proposed calibration algorithm has high accuracy and good stability in the working space of the light of sight of the seeker, and can be conveniently applied. This method also is able to be widely used in pointing error calibration in various types of optoelectronic devices.Keywords：seeker;pointing accuracy;least square estimation;calibration of pointing error;model linearization- 52
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Published：2020-08-12 -
Clutter suppression of infrared image based on three-component low-rank matrix decomposition
Abstract：To solve the infrared target detection problems caused by low contrast, weak target signals and background clutter interference, a clutter suppression method based on three-component low-rank matrix decomposition model was proposed combined with the sparse representation theory. Firstly, the three components, including target, background and noise, in a infrared image were described respectively to obtain the three-component low-rank matrix decomposition model. Then, an over-complete dictionary for modeling a small target was constructed by using two-dimensional Gaussian model. The three-component low-rank matrix decomposition model was used to decompose the block reset image data into the background, noise and target components. Finally, the target component was processed by thresholding to obtain a reconstructed image with protruded infrared targets and to complete the clutter suppression. The experiments under three conditions demonstrate that the proposed method has increased the local signal to noise ratio of image more than 2 times, and the background suppression factor has increased more than 15% as compared with that of the classical methods. It con cludes that the proposed method not only suppresses the background clutter, improves the signal-to-noise ratio of the infrared image effectively but also has strong robustness against the noise interference.Keywords：infrared image;clutter suppression;three-component low-rank matrix decomposition;sparse representation- 50
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Published：2020-08-12 -
Joint estimation of DOA and Doppler frequency by SQP
Abstract：To estimate the Direction of Arrival (DOA) and Doppler frequency in array signal processing accurately and quickly, a joint spectrum estimation method based on maximum likelihood algorithm and Sequence Quadratic Program(SQP)was presented. With this method, a space-time signal model was used to construct a generalized array manifold matrix containing the information of DOAs and Doppler frequency based on the Hankel matrix, the joint spectrum was fitted using maximum likelihood algorithm, so that the joint parameter estimation was converted to multidimensional nonlinear function optimization. Then, the SQP algorithm was used to solve and optimize the maximum likelihood function and to obtain the estimation of DOAs and Doppler frequency. Finally, the simulation results were compared with the SQP method, differential evolution method, genetic method and quantum particle swarm optimization method. Experimental results indicate that the Root Mean Square Error(RMSE) of DOAs and Doppler frequency estimation are 0.2636°and 0.0076 rad respectively under the condition of estimating two signal sources with 0 dB for SNR. It satisfies the requirements of design of joint parameter estimation method in the array signal processing.Keywords：space-time signal model;Direction of Arrival(DOA);Doppler frequency;Sequence Quadratic Program(SQP);maximum likelihood estimation- 46
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Published：2020-08-12 -
Image blind deblurring with half-quadratic penalty method
Abstract：As existing image blind deblurring algorithms have larger and more complex computing, this paper proposes a new image blind deblurring algorithm based on half-quadratic penalty method, and verifies the feasibility of the algorithm by experiments. It formulates the optimization function by using the higher-order partial derivatives of image noise and the hyper-Laplacian priors of image gradients, then uses an efficient optimization scheme that alternates between PSF and latent image estimation to solve the proposed formula. As the fast Fourier transform has been used in iterative processing, the computing time is reduced greatly, and the restoration effects are improved. An debluring experimental is performed on an image with pixel levels of 1×106 and the results demonstrate that the proposed method is more robust and more computationally efficiency than that of current blind deblurring algorithm and its computing time has been reduced by about 60%. The algorithm provides a new way for blind deblurring of video images in real time.Keywords：image processing;half-quadratic penalty;blind deblurring;iteration method;Point Spread Function(PSF)- 49
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Published：2020-08-12 -
Probabilistic model single target tracking framework for video surveillance system
Abstract：According to characteristics of video surveillance and strong mobility of tracking targets, a novel target tracking framework based on a probability model was proposed. The current standard particle filtering target algorithm was improved based on a target appearance model, a systemic dynamic model, and a systemic observation model. Firstly, the target appearance model was established by taking the distribution of human eye cell into account to improve its resistance capability for partial occlusion of local occlusion. Then, the systemic dynamic model based on the adaptive target movement was built to improve the robustness of tracking framework for the fast moving target. Finally, the systemic observation model with online update was established to prevent the tracking shift when the target faced the occlusion, illumination changes, severe deformation, etc., effectively. Experimental results show that the proposed algorithm achieves 98% of correct tracking rate, and the average tracking error is less than 6 pixels. The proposed method satisfies the video surveillance system require ments for stabilization, reliability, higher precision, less computing cost, as well as strong anti-jamming.Keywords：video surveillance;probabilistic model;target tracking;appearance model;online update- 43
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Published：2020-08-12 -
Image dark channel prior haze removal based on minimum filtering and guided filtering
Abstract：When a hazed image is processed by dark prior haze removal method, it should take the elimination of white halo on the depth-edge and the reduction of time consuming for modifying the transmittance into account. In order to eliminate the white halo on the depth-edge and to reduce the time consuming for modifying the transmittance, this article fully analyzes the advantages and disadvantages of minimum filtering and guide filtering in modifying transmittance, respectively. A new method in combination with the minimum filtering and the guide filtering is adopted to modify the transmittance, by which their advantages are taken and the inadequacies are made up. As compared with the traditional method, it not only eliminates the white halo but also reduces the processing time significantly. In addition, this paper improves the poor result of traditional dark prior method with a sky area in the hazy image. According to the bright-white features of the pixels in the sky area, the pixels with color values similar to that of the airlight are viewed as the sky area pixels. Then these pixels are processed to maintain their original color values and to eliminate the color distortion and jump existing in the sky area effectively. Thus, the visual effect of whole defogging restored image could be improved.Keywords：image haze removal;dark primary;transmittance;depth-edge;minimum filtering;guided filtering- 86
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Published：2020-08-12 -
Moving object image segmentation by dynamic multi-objective optimization
Abstract：The single objective and multi-objective optimization methods are usually adopted to segment the moving objects in community background images. However, these methods can not adapt to the dynamic change of the objects effectively. In this paper, a dynamic multi-objective optimization image segmentation method is proposed. The method makes use of the time and environment dynamic changes as dynamic factors, and takes the advantages of the K-Means and Fuzzy C-Means (FCM) clustering algorithms to construct the multi-objective function. In addition, the Dynamic Multi-objective Particle Swarm Optimization (DMPSO) algorithm is also embedded in the method, and background difference method is used to define environmental change rules to implement dynamic multi-objective image segmentation. The simulation results based on the DMPSO algorithm are compared with that of K-Means and FCM algorithms. The results show that the dynamic multi-objective optimization has made the Pareto optimal solution set evenly distributed as compared with single target segmentation algorithm, the accuracy of image segmentation reaches 95%, and the recognition accuracy reaches 90%. For the high recognition capability, the algorithm satisfies the accurate identification of moving objects under the determined background.Keywords：image segmentation;image clustering;moving object;dynamic multi-objective optimization;particle swarm algorithm- 86
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Published：2020-08-12
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