单框架控制力矩陀螺转子动不平衡对遥感卫星成像的影响

分析了单框架控制力矩陀螺（SGCMG）转子在高速旋转时产生的动不平衡干扰力矩引起的星体颤振角和颤振角速度对TDI CCD相机成像的影响。通过坐标变换将转子坐标系下的干扰力矩转换至星体坐标系下的干扰力矩,将卫星姿态动力学方程计算出干扰力矩引起的星体颤振角位移和颤振角速度代入TDI CCD相机成像像移补偿模型;利用TDICCD相机像点与物点对应模型的仿真系统仿真了陀螺转子在不同转速下引起星体颤振角位移和角速度对相机成像的影响;最后,利用图像对比度和互相关相似性测度分析仿真成像质量。仿真显示：SGCMG转子在转速为3 000 r/min时,横向调制传递函数为0.997,图像互相关相似性测度为0.996 1;转速为6 000 r/min时,横向调制传递函数为0.928 3,图像互相关相似性测度为0.974 8。结果表明：SGCMG转子在高速旋转过程中引起的星体颤振角位移和角速度严重影响了TDI CCD相机的成像质量,应依据颤振的影响对SGCMG实施减震措施。     

Improved spatial phase detection for profilometry using a TDI imager

Performance of a time delay and integration (TDI) imager is analogous to a drum/periphery camera. Coupled to a modulated line generating laser diode, it is possible to use a TDI imager to encode the shape profile of a rotating cylindrical object as deformed gratings in a digital image. Among the various methods for extracting the phase from a deformed grating, the spatial phase detection (SPD) method is fast and easy to use. Errors are introduced in this method if the phase gradient is high over a grating interval. Here we propose a method to reduce the phase gradient by using a TDI feature which makes it possible to record images at variable lateral magnification.     

The Brewster effect for a one-dimensional random surface

Abstract

By the use of a unitarity and reciprocity conserving theory for the scattering of p-polarized light from a one-dimensional random dielectric surface the we determine the shift in the Brewster angle toward smaller angles of incidence caused by the surface roughness, and the (non-zero) value of the reflectivity at its minimum. Both quantities may be useful in the characterization of the roughness of such surfaces.     

Measurement of water-leaving radiance on smooth water surfaces at different viewing angles using high-resolution spectroradiometer

This letter describes a method for calculating water-leaving radiance on smooth surfaces at differentangles based on Fresnel law and the polarized measurements using an ASD FS3 spectroradiometer. The spectroradiometer is mounted on a goniometer so that it views the water surface from a height of severaldecimeters at different viewing angles through a linear polarizing filter. The incident angles equal theviewing angles. The water-leaving radiance spectra acquired by other methods are compared with the polarized measurements from the smooth water surface, and the radiance spectra obtained by the proposedmethod are found to be consistent with the results of the reference methods. The current study provides another effective technique for measuring water-surface reflectance via remote sensing. Moreover, the method does not avoid the sun glint during the detection of water-leaving radiance in cases where the viewing geometric position is clear.     

The Brewster effect for a one-dimensional random surface

By the use of a unitarity and reciprocity conserving theory for the scattering of p-polarized light from a one-dimensional random dielectric surface the we determine the shift in the Brewster angle toward smaller angles of incidence caused by the surface roughness, and the (non-zero) value of the reflectivity at its minimum. Both quantities may be useful in the characterization of the roughness of such surfaces.     

A novel method for adjusting CCD camera in geometrical calibration based on a two-dimensional turntable

In order to ensure the accuracy of the collimator viewing angles in geometrical calibration of the CCD camera, a novel method for adjusting CCD camera with wide field of view based on a two-dimensional turntable was presented. The method involves two steps: the first is to adjust collimator parallel to a rotation axis of turntable by estimating a fixed point image of collimator on the CCD when the camera is orientated around this rotation axis; the second step is to adjust the camera axis parallel collimator by estimating the symmetry of point images when the camera is orientated around another rotation axis of turntable. As an example, the adjustment accuracy of the wide field of view radiometer developed by us is analyzed and discussed in the article.     

高分五号卫星多角度偏振相机最优化估计反演:角度依赖与后验误差分析

多角度偏振相机(directional polarimetric camera, DPC)随高分五号卫星已经成功发射并持续获取全球观测数据.针对DPC在陆地气溶胶反演领域的应用需求,本研究基于多参数最优化估计反演框架,引入信息量和后验误差分析工具,讨论了DPC观测信息量对角度的依赖,给出了地表和气溶胶参数的后验误差,并分析了后验误差的影响因素.研究表明:1)卫星观测信息量随观测角度个数的增加显著提升, DPC多角度观测比单角度观测的总DFS(degree of freedom for signal)平均提高了5.45; 2)气溶胶反演比地表更依赖于卫星观测几何,散射角覆盖范围越大,观测包含的气溶胶信息量越多; 3)反演参数的后验误差随观测角度个数的增加显著降低,而气溶胶模型误差对后验误差的影响并不显著.总体来说,观测误差是影响反演结果不确定性的主要因素.本研究对DPC多角度偏振观测的反演能力以及反演不确定性进行了系统的定量评估,为DPC在轨测试及反演算法开发提供参考.     

宽覆盖型光学遥感相机侧摆像移速度计算

根据宽覆盖相机的特性,分析了其侧摆成像的几何关系。建立了地面物点到相机像面的空间坐标变换关系,在此基础上,推导了基于圆地球模型的相机侧摆像移速度计算公式,并以像移失配传递函数MTFmismatch作为评价方法分析了相对像移匹配残差对像质的影响。以某宽覆盖型相机为例,计算了不同侧摆角和不同地心角条件下的像面像移速度。计算结果表明：像面各点的侧摆像移速度均不相同,且变化趋势也不相同,远地点处像移速度相对变化量最大。在侧摆角为25°且积分级数为48的条件下,像移失配传递函数的最大值为0.681。外场成像试验结果表明,积分级数控制在16级以内时的相机成像质量良好。     

Aspheric surface reconstruction for scanning interference

A simplified reconstructing method for the aspheric surface testing based on scanning interference technology is presented. The aspheric normal intersects the optical axis at different points with different angles, which is called normal congruence; a normal congruence can identify an aspheric surface. In this method, the test aspheric surface is shifted along the optical axis to scan the tested aspheric surface; meanwhile a series of interferograms and phase maps are obtained. The angles between the normal lines and the aspheric axis are obtained using the positions of zero-phase points, according to the image-forming principle of the camera. Here, Zernike polynomials are applied to analyze the phase maps and extract the zero-phase points. Finally, the absolute coordinates of the test surface is rebuilt through iterative integration. Because both the system deformation and amplification do not affect the reconstruction result, this method can avoid complicated stitching algorithm in the subaperture stitching interferometric method. Experimental results show that the method has high accuracy and reliability.     

偏振光谱的土壤湿度遥感方法实验研究

偏振探测作为一种新型遥感技术,是对传统光谱遥感探测的有益补充,为目标遥感探测提供更丰富的信息。用地物偏振光谱仪实验测量,分析土壤湿度与偏振光谱的相关性,同时研究不同观测角下的土壤表面反射光偏振光谱特性。结果表明：在土壤湿度较高的情况下,偏振光谱与土壤湿度具有一定的相关性,尤其在500～700 nm波段,湿度与偏振度呈正比关系;低湿度的情况下,偏振光谱与土壤湿度相关性不明显;此外,不同观测角对偏振光谱也有影响,如入射角固定为50°,观测角在20°～60°区间测量时,偏振度随观测角增大而增大,且观测角愈大,偏振度随湿度的变化愈显著。     

高速TDI CCD亚像元动态成像系统分析

亚像元动态成像技术是目前实现相机小型化及提高相机空间分辨率的有效方法。将亚像元动态成像技术引入高速TDICCD相机中,通过特殊设计的光学拼接方法,使相机在不影响扫描速度及不改变TDICCD器件尺寸和相机焦距的情况下,可大大提高空间分辨率。为评价该TDICCD亚像元动态成像系统的成像质量,对成像系统的调制传递函数(MTF)进行了分析,分析结果表明该TDICCD亚像元动态成像技术可以将系统的空间分辨率提高1.6倍以上。     

Restoration of TDI camera images with motion distortion and blur

Platform movement during exposure of imaging system severely degrades image quality. In the case of Time delay and integration (TDI) camera, abnormal movements cause not only image blur but also distortion, for image Point Spread Function (PSF) is space-variant. In this paper, we present a motion degradation model of TDI image, and provide a method to restore such degraded image. While a TDI camera is imaging, it outputs images row by row (or line by line) along the scanning axis, and our method processes in the same track. We firstly calculate the space-invariant PSF of each row using the movement information of the TDI camera. Then, we substitute pixels of the row and the ones of their neighbor rows together with the PSF into standard Richardson–Lucy algorithm. By deconvoluting we get the restored pixels of the row. The same operations are executed for all rows of the degraded TDI image. Finally, a restored image can be reconstructed from those restored rows. Both simulated and experimental results prove the effectiveness of our method.     

Quantitative surface normal measurement by a wavefront camera

A compact wavefront camera that allows users to quantitatively measure the intensity and wavefront at a remote object plane is reported. The camera is built from a chip-scale wavefront sensor that we previously developed. By measuring the wavefront of the image and calibrating the wavefront relationship between the image and object planes, the wavefront at the object plane can be computed and the surface normal of the object can be derived. We built a prototype camera and calibrated the wavefront relationship. In a proof-of-concept experiment, a set of concave mirrors with different focal lengths (50-200 mm), were imaged. The results agree well with their expected values. To demonstrate the application of the camera, we applied this method to measure the deformation of a microfluidic channel under pressure.     

TDI imaging and scanning moiré for online defect detection

This paper explains the application of scanning moiré in association with TDI (Time Delay and Integration) imaging for complete peripheral inspection of cylindrical objects. Based on the structured light technique, a grating pattern modulated by deformations, such as dents on the surface of a rotating cylindrical object, is recorded using a TDI camera. The illumination system consists of an intensity modulated, line generating laser diode aligned at an angle to the camera axis. By using the TDI option for recording every nth line, an online scanning moiré pattern is generated. After providing a simple explanation of the scanning moiré, the effects of object rotation speed and TDI scan speed on the fringe pattern are discussed and demonstrated. The techniques presented here offer low cost solutions to industrial machine vision tasks related to peripheral imaging and inspection of cylindrical objects.     

Calibrating the HXMT collimators using diffuse illumination

We propose a new method to calibrate the HXMT collimators by measuring the optical point spread function (PSF) of the hard X-ray modulation telescope (HXMT). The light transmission of the collimator at different viewing angles with a camera and a diffuse backlight placed behind the collimator is measured. This method is much easier to accomplish than measuring the PSF with a parallel optical beam. The experimental results are very consistent with the simulations. The PSF of the collimator of the high energy X-ray telescope on HXMT is found to be in good agreement with the design, with accuracy better than 1 arcmin.     

Decoupling error for the atmospheric correction in ocean color remote sensing algorithms

This paper studies the decoupling error associated with the atmospheric correction procedures in the ocean color remote sensing algorithms. The decoupling error is caused by the lack of proper consideration of multiple scattering between the atmospheric and ocean components. In other words, the atmosphere and ocean are not coupled properly. A vector radiative transfer model for the coupled atmosphere and ocean (CAO) system based on the successive order of scattering (SOS) method is used to study the error. The inherent optical properties (IOPs) of the ocean are provided by the most updated bio-optical models. Two wavelengths are used in the study, 412 and 555 nm. For a detector located just above the ocean interface, the decoupling errors range from 0.3% to 7% at 412 nm; and from 0.3% to 3 % at 555 nm for zenith viewing angles smaller than 70°. The decoupling errors are significantly larger for larger zenith viewing angles for this detector. For a detector at the top of the atmosphere (TOA), it is hard to separate the decoupling error from the error introduced by the diffuse transmittance. If we assume the upwelling radiance is uniform just below the ocean surface when estimating the diffuse transmittance, the decoupling errors are from ?4% to 8% for zenith viewing angles smaller than 70°; and negative decoupling errors show up at mainly large zenith viewing angles.     

Three-dimensional visualization of diffusion flame shapes under acoustic excitation using stereoscopic imaging and reconstruction technique

Stereoscopic imaging and reconstruction technique is introduced to reconstruct the flame structures that are subject to acoustic excitation. The laminar diffusion flame under investigation was created in a cylindrical tube and excited by a loudspeaker. Stereo images were taken at a shutter speed of 1/10000^th second using a ‘stereo camera’ and the depth cue of the flame structures along the camera viewing direction were then computed using machine vision methodology. By visualizing the computed three-dimensional flame models, as well as judging the corresponding attribute such as surface gradient, the understanding of the flame and acoustic wave interaction could be improved.     

Droplet transient migration and dynamic force balance mechanism on vibration-controlled micro-texture surfaces

In this paper, forced vibration was used to regulate the droplet migration, fully recording the transient migration of droplets on a micro-textured substrate under the resonance frequency by a high-speed camera. The influence of resonance frequency and dynamic migration characteristics of droplets on the solid micro-texture surface under lateral vibration were researched. The experiment demonstrates that the driving force is caused by the difference between the left and right contact angles made the droplet oscillate and migrate, and as time t increases, the left and right contact points are periodically shifted and the amplitude of migration increases. Therefore, based on the droplet migration behavior and its force balance mechanism, a spring vibration model of migration behavior of the vibrating droplet micro unit was set up to predict the complete trajectory of its migration on a solid surface. The calculation results show that the theoretical displacement is less than the experimental displacement, and the longer the time, the larger the difference. Affected by the vibration, part of the droplet permeates through the micro-texture, resulting in the droplet losing height and the contact angle becoming smaller as well. While the other part of droplet overcomes the internal surface tension to migrate.     

Bayer滤波型彩色相机调制传递函数测量方法

Bayer滤波型彩色相机广泛应用于航天遥感、空间对地观测、环境监测等领域.由于Bayer滤波片造成彩色相机相比黑白相机在像质方面进一步退化,如何对Bayer滤波型彩色相机成像性能全频段综合评价是目前亟待解决的问题.调制传递函数(MTF)是相机成像性能综合评价的关键指标,传统调制传递函数测量方法无法实现对Bayer滤波型彩色相机MTF全频段高精度测量.为了解决这个问题,本文提出了一种采用旋转刀口靶测量彩色相机调制传递函数的方法.理论方面,推导了Bayer滤波型彩色相机调制传递函数测量理论模型,仿真分析了刃函数采样率和刀口刃边倾斜角度误差对调制传递函数测量精度的影响,并给出了计算算法.实验方面,对彩色相机R,G,B三基色调制传递函数权重因子进行了实验定标,并搭建了基于条纹板和旋转刀口靶的彩色相机调制传递函数测量试验装置.采用旋转刀口靶法和条纹靶板法测量彩色相机MTF结果在耐奎斯特频率f_c处极差为0.061,在空间频率f_c/2处极差为0.043,试验结果验证了所提方法的有效性.