Based on microscopic imaging, optical systems can effectively detect defects on the surface of laser gyro reflector without causing damage. However, the minimum detection size is limited by the resolution of the microscopic imaging system. To detect submicron-level defects on laser gyro reflector substrate, a surface scanning dual-source scattering measurement scheme based on scattering measurement technology is proposed. Utilizing the Finite Difference Time Domain (FDTD) method and the detection scheme, an electromagnetic scattering model of the laser gyro reflector substrate is established to simulate the characteristics of defects and the distribution of electromagnetic fields. An experimental platform for surface scanning dual-source scattering measurement is established, and polystyrene latex (PSL) spheres with a diameter of 200nm are deposited on the surface of the laser gyro reflector substrate to verify the effectiveness of the proposed method. Scattering imaging experiments in both bright and dark fields are conducted on the USAF 1951 standard resolution plate to obtain the directional characteristics of dark field scattering. Additionally, standard-sized rectangular line patterns, dots, and checkerboard patterns of 1-10μm are fabricated using reactive ion beam etching to create defect samples of photomask patterns, and scattering imaging experiments are conducted on these samples to obtain the detection distribution of bright field patterns. The results indicate that the system can achieve a detection resolution better than 175nm. This method provides a reference for the detection of substrate in inertial guidance systems.
In recent decades, polarization imaging has garnered much interest and research focus, due to its wide range of applications in the fields of atmospheric remote sensing, astronomy, biomedical and target detection, etc. Linear division-of-focal plane (DoFP) polarimeters deploying metal wire grid micro-polarization array as the polarization state analyzer (PSA) possess the capacity to capture polarization properties of the scene target during a single snapshot and benefit from their rugged and compact designs. However, these systems acquire the polarization measurements through spatial modulation and inevitably lead to spatial resolution loss, which cause instantaneous field of view (IFOV) errors and degradation of polarimetric accuracy. In response to this challenge, various interpolation/demosaicking methods tailored to DoFP imaging to fill the missing polarization information have emerged in recent years. This survey aims to explore these methods and briefly describe their effectiveness in enhancing the image restoration performance, highlighting their advantages and disadvantages. Lastly, according to current progress, some suggestions are made for high accuracy polarimetric measurements, especially for polarization remote sensing applications at different scales.
The reasonable design of the dynamic range of spaceborne remote sensor is the basic guarantee for its effective observation in-orbit, but the complex radiation characteristics of the earth-atmosphere system and other factors have brought some1 challenges to its design. Aiming at the Polarized Scanning Atmospheric Corrector (PSAC) on board Huanjing-2A/B(HJ-2A/B) satellite, the dynamic range of apparent radiance observed by PSAC is analyzed and obtained according to its detection target and band setting, based on the method of statistics of historical data of remote sensors such as Moderate-resolution Imaging Spectroradiometer (MODIS), considering the complex radiation characteristics of earth atmosphere system and scale effect. In order to meet the requirements of dynamic range design and ensure better radiation resolution, PSAC designed four gear adjustable electronic gain (relative gain is 1,2,3,4), and carried out the system radiation response gain adjustment and dynamic range test under laboratory conditions. The statistical results of on orbit observation data of PSAC show that the design results of its dynamic range meet the needs of on-orbit observation application, and lay a foundation for the retrieval of atmospheric and aerosol parameters and the realization of atmospheric correction objectives.
The simultaneous imaging polarization camera (SIPC) is an instrument for simultaneous polarization measurement using a three-beam splitter prism. Due to the large number of polarizing devices in the SIPC, the parameters and responses of the polarizing devices are different, which causes the measurement matrix of the instrument to deviate from the ideal value. In order to ensure the polarization measurement accuracy of the SIPC, effective polarization calibration is required. In this paper, a standard linearly polarized light source is used to calibrate the SIPC. Firstly, the measurement matrix of the instrument is calibrated by using the linear polarization calibration source, and then the calibration parameters are obtained by fitting Fourier coefficients with least squares. Finally, the polarization measurement accuracy of the SIPC is verified by calibration experiments. The results show that the polarization measurement accuracy of the SIPC is better than 4% after polarization calibration.
Data preprocessing of the Polarized Scanning Atmospheric Corrector (PSAC) onboard HuanjingJianzai-2(HJ-2)A/B satellites is a key step for further applications. Based on the principles and characteristics of PSAC sensor, this paper elaborates on the methods and procedures of its data preprocessing including parameters quality supervision, data precorrection, calibration implementation and geolocation, etc. The results show that the data preprocessing from the original data to the L1 product is accurate and effective after preliminary analysis and evaluation, which can be used for subsequent atmospheric parameters retrieval and atmospheric correction applications.
To obtain high accuracy polarization observation information is highly expecting in aerosol parameter retrieval and atmosphere environment research. In this paper, we described a space-borne multispectral polarized scanning atmospheric corrector (PSAC), which can provide extremely high polarimetric accuracy. And we use wavelet-based denoising method to improve the stability of PSAC measurement results by reducing internal noise. The result shows that the STD of DOLP difference between PSAC measurement value and theoretical value is significantly reduced, reached 5%~10% in the requirement DOLP difference accuracy 0.5%, the proposed threshold function can increase the evaluation accuracy stability of instrument polarization and reduce the uncertainty, also, the measurement results of PSAC inflight improved as well.
In order to meet the application requirements of a space borne polarizing radiometer infrared band, a high-precision on-orbit temperature control scheme for the infrared detector combining active temperature control and passive temperature control is proposed. The infrared detector is installed on the heat sink copper block, and the temperature of heat sink copper block is controlled at -20°C~-30°C through the method of auxiliary cold plate + heat pipe thermal conduction. Combined with the infrared detector built-in three-level thermoelectric cooler, the photosensitive surface temperature of the infrared detector is cooled to below -60°C by a method of constant current driving. In order to ensure the measurement accuracy of infrared radiation polarization, the short-term temperature fluctuation of the photosensitive surface of the infrared detector is required to be less than 0.03°C/s. This article has designed the infrared detector temperature control scheme verification test, and actually measured the stability of infrared detector temperature and dark current. The results of the simulation and tests show that the range of infrared detector heat sink temperature is - 25±5°C, the range of infrared detector photosensitive surface temperature is -65°C ~ -75°C,the rate of short-term temperature change of the infrared detector photo-sensitive surface is better than 0.01°C/s, and the dark current fluctuation is less than 1.3pA. Satisfying the on-orbit high-precision polarization measurement requirements.
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