Low-noise switched integration amplifier for low-photon flux radiometry.

A photodetector signal-to-noise ratio (SNR) over 1000 is one of the prerequisites to realizing the correlated photon radiometric benchmark with a relative standard uncertainty of 0.3% (k=1). To improve the SNR for low-photon flux detection, a switched integration amplifier (SIA) is designed to achieve a noise equivalent current of a fA level. A wide spectrum and low-photon flux measurement facility are built to evaluate the SNR at a photon rate of 108 s -1 within the spectral range of 350-1000 nm. SNRs of the SIA-based Si photodetector are shown to be greater than 1000 at representative wavelengths.

Calibration of the degree of linear polarization measurements of the polarized Sun-sky radiometer based on the POLBOX system.

Polarization observation of sky radiation is the frontier approach to improve the remote sensing of atmospheric components, e.g., aerosol and clouds. The polarization calibration of the ground-based Sun-sky radiometer is the basis for obtaining accurate degree of linear polarization (DOLP) measurement. In this paper, a DOLP calibration method based on a laboratory polarized light source (POLBOX) is introduced in detail. Combined with the CE318-DP Sun-sky polarized radiometer, a calibration scheme for DOLP measurement is established for the spectral range of 440-1640 nm. Based on the calibration results of the Sun-sky radiometer observation network, the polarization calibration coefficient and the DOLP calibration residual are analyzed statistically. The results show that the DOLP residual of the calibration scheme is about 0.0012, and thus it can be estimated that the final DOLP calibration accuracy of this method is about 0.005. Finally, it is verified that the accuracy of the calibration results is in accordance with the expected results by comparing the simulated DOLP with the vector radiative transfer calculations.

[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.