Alignment error analysis of the snapshot imaging polarimeter.

A snapshot imaging polarimeter (SIP) system is able to reconstruct two-dimensional spatial polarization information through a single interferogram. In this system, the alignment errors of the half-wave plate (HWP) and the analyzer have a predominant impact on the accuracies of reconstructed complete Stokes parameters. A theoretical model for analyzing the alignment errors in the SIP system is presented in this paper. Based on this model, the accuracy of the reconstructed Stokes parameters has been evaluated by using different incident states of polarization. An optimum thickness of the Savart plate for alleviating the perturbation introduced by the alignment error of the HWP is found by using the condition number of the system measurement matrix as an objective function in a minimization procedure. The result shows that when the thickness of a Savart plate is 23 mm, corresponding to the condition number 2.06, the precision of the SIP system can reach to 0.21% at 1° alignment tolerance of the HWP.

[Research on the Distribution of Broad-Band Correlated Photon Spectra and the Measurement of Time-Correlation].

The correlated photon technique makes it possible to achieve a radiation calibration processing without chain transferring. The study of the spectral radiation character and time correlation of the photon is of great significance for broad-band radiometric calibration. To absolutely calibrate quantum efficiency of photoelectric detector, it is necessary to extend calibration band from single band to more bands. According to the phase-matching condition of the spontaneous parametric down-conversion, non-collinear angle formula of correlated photon in the crystal is derived. The distribution of the photon spectrum is simulated. Meanwhile, the phase-matching angle of the crystal is optimized. The photon generated by the spontaneous parameters down-conversion has a broad spectral distribution and the correlated photon wavelength is corresponding to its emission angle. Based on the result of the simulation, the experimental measurement system of the spectral distribution and time-correlation of the correlated photon is established. The spectral distribution, the time-correlation and the polarization properties of the four pair photon were measured by using this system. The experimental results show that, (1) the spectral distribution of the measurements is 633~808 nm, where the maximum spectral distribution measurement bias is 1.51 mm. The experiment result is highly consistent with theoretical ones; (2) the correlation time of four pairs correlated photon is measured, during which "three coincidence-peaks" is observed and the minimum correlation time was 0.32 ns; (3) single photon count rate along with coincidence count rate of correlated photon vary with the polarization direction of the pump as sine function. The experimental result is shown that the correlated photon pairs are ranging from the visible to near infrared band distribution, and that the spectrum has time-correlation and polarization characteristic. The research result is firstly reported at home and abroad, and the results are promising for the application of the photoelectric detector in the multi-band radiometric calibration.

[Automatic Field Calibration and Analysis of Satellite Based on Hyper-Spectral Ratio Radiometer].

With the demand of calibration technology of high frequency and high precision in terms of the optical remote sensing satellite of China, and the deficiency of the artificial work, the automatic system of hyper-spectral ratio radiometer was developed by investigation the calibration situation of domestic and abroad satellite, then the automatic calibration of satellite sensor was carried out. According to the parameters demand of field calibration and the goal of automation, the ratio radiometer was designed to measure global spectral irradiance by integrating sphere, and the diffuse spectral irradiance was measure by the shelter, so the diffuse-global ratio was calculated by these data. Simultaneity the ground radiation was measured with radiometer optical-lens and the automatic observation of atmospheric and surface radiation characteristics was achieved, In addition, the data pre-processing of real-time and remote transmission were integrated in the system. With the field test on the Dunhuang radiometric calibration sites in 2015, the radiometer worked in an ideal way, and the atmospheric optical parameters and surface reflectance data were acquired, which support the calibration of satellite sensor. The comparison with the traditional measurement was carried, the relative deviation of the surface reflectance is less than 5%, and the absolute deviation of the atmospheric parameters is less than 5% and the diffuse ratio is less than 0.015%. According to the measured data and based on irradiance-based method, the field calibration applied to the band 1~5 of Aqua MODIS, the relative deviation of band 1~4 is less than 1% while the band 57.24%, so the requirement of the automatic calibration of the satellite sensor was satisfied preliminarily.

[Stokes Parameter Detection and Precision Analysis Based on Rotating Quarter-Wave Plate].

The accuracy of the calibration reference source polarization states directly influences the precision of the polarized optical remote sensor calibration, and thus affects the inversion accuracy of the characteristics of targets. In this paper, 870 nm horizontal linear polarized light has been chosen as the tested calibration reference light, modulated by rotating quarter-wave plate(QWP). The intensity as a Fourier series of the rotation angle of the plate and its coefficients were demodulated with the Fourier transform method, Stokes parameters can be calculated with these coefficients. The mean, standard deviation, composite uncertainty and relative deviation of measured data compared with the theoretical value of the ten measurement results were presented. In order to improve the accuracy of the measurement, the correction model for the quarter-wave plate retardance deviation Δδ, fast axis angle deviation Δα and the transmission axis alignment deviation Δß of analyzing polarizer has been constructed. In this model, detection deviation of Stokes parameters is described as a function of Δδ and Δß, Δδ and Δß were determined by the function and magnitude of the deviation. Combined with quarter-wave plate fast axis angle deviation which was the result of simulation to adjust the experiment device, and then detecting the calibration reference source polarization states again. The experimental results show that, the difference between measured value and theoretical value of Stokes parameters reduced to less than 1.41% from 3.77% relative to without correction. The experiment principle, device and deviation correction model of this research can significantly improve the accuracy of detecting the polarization state of the calibration reference light source.

[Spectral scanning measurement of high-precision solar irradiance-meter].

In order to measure the radiation of the sun absolutely and retrieve the characterization of the atmosphere precisely, a high-precision solar spectral irradiance meter working in 0.4-1.0 microm band was developed. A Fèry prism was employed to disperse the incident sunlight and a closed-loop control method was adopted for spectral scanning in this solar irradiance meter. The design of spectral scanning measurement was depicted in detail. The design requirements of Fèry prism were given and spectral dispersion was achieved by single element. The trap detectors were used to ensure precise spectral measurement. According to the parameters of the trap detectors, the demands and method of temperature control were introduced. The design of spectral scanning structure was introduced, and wavelengths were positioned accurately. The requirements for parameters, stability and power supply of voice coil actuator were given and the wavelength position error of 0. 025% was achieved. Spectral scanning measurement of 0.4-1.0 microm was accomplished in outdoor experiments. A comparison was carried out with visible-short wave infrared spectrometer and auto-sunphotometer (CE318). Results indicate that absorption peak locations of spectral scanning measurement of irradiance meter are correct, and the relative deviation from CE318 measurements is less than 0.13% for all day, and the relative deviation of optical depth in visible and near infrared band is less than 2% and 5%, respectively.

Reliable quantitative detection of uric acid in urine by surface-enhanced Raman spectroscopy with endogenous internal standard.

Abnormal levels of uric acid (UA) in urine serve as warning signs for gout and metabolic cardiovascular diseases, necessitating the monitoring of UA levels for early prevention. However, the current analytical methods employed suffer from limitations in terms of inadequate suitability for home-based applications and the requirement of non-invasive procedures. In this approach, creatinine, a metabolite with a constant excretion rate, was incorporated as an endogenous internal standard (e-IS) for calibration, presenting a rapid, pretreatment-free, and accurate strategy for quantitative determination of UA concentrations. By utilizing urine creatinine as an internal reference value to calibrate the signal fluctuation of surface-enhanced Raman spectroscopy (SERS) of UA, the quantitative accuracy can be significantly improved without the need for an external internal standard. Due to the influence of the medium, UA, which carries a negative charge, is selectively adsorbed by Au@Ag nanoparticles functionalized with hexadecyltrimethylammonium chloride (CTAC) in this system. Furthermore, a highly convenient detection method was developed, which eliminates the need for pre-processing and minimizes matrix interference by simple dilution. The method was applied to the urine detection of different volunteers, and the results were highly consistent with those obtained using the UA colorimetric kit (UACK). The detection time of SERS was only 30 s, which is 50 times faster than UACK. This quantitative strategy of using urinary creatinine as an internal standard to correct the SERS intensity of uric acid is also expected to be extended to the quantitative detection needs of other biomarkers in urine.

[Research on absolute calibration of sun channel of sun photometer using laser raster scanning method].

In the present paper, a new calibration method of absolute spectral irradiance responsivity of sun channel of sun photometer was developed. A tunable laser was used as source and a standard tranfer detector, calibrated against cryogenic absolute radiometer, was used to measure laser beam power. By raster scanning of a single collimated laser beam to generate the uniform irradiance field at the plane of effective aperture stop of sun photometer, the absolute irradiance responsivity of center wavelength of the 870 nm unpolarized sun channels of sun photometer was obtained accurately. The relative spectral irradiance responsivity of corresponding channel was obtained by using lamp-monochromator system and then used to acquire the absolute spectral irradiance responsivity in the laboratory. On the basis of the above results, the top-of-the-atmosphere responsive constant V0 was obtained by integration with extraterrestrial solar spectral irradiance data. Comparing the calibration result with that from GSFC, NASA in 2009, the difference is only 3.75%. In the last, the uncertainties of calibration were evaluated and reached to 2.06%. The principle feasibility of the new method was validated.