In the process of wide-band spectrum detection, interferogram acquisition of the traditional Michelson interferometer needs to follow Nyquist sampling theorem, the static performance such as high resolution of moving mirror scanning and the dynamic performance such as transient response need to meet strict requirements, which usually make the spectrometer system structure complex. Meanwhile, the interference modulation efficiency of traditional Michelson interferometer will drop sharply with the increase of optical path difference(OPD). In this way, the interference data value at the long optical path difference will be submerged by noise, which will reduce the signal-to-noise ratio of reconstructed spectrum. In order to simultaneously achieve spectrum detection with wide-band spectrum, high resolution and high signal-to-noise ratio, this paper introduces a configuration of wide-band interference spectrometer based on band-pass sampling technology. The wide-band interference spectrometer includes dispersion unit and interference modulation unit. Firstly, the dispersion unit pre-disperses the wide spectrum into continuous spectrum distributed along wavelength and divides the interference modulation signal of continuous spectrum into several interference signals of narrow-band spectrum. Secondly, the interference modulation unit carries out interference modulation on the dispersed continuous spectrum and the interferograms of every narrow-band spectrum are sampled and obtain the interferogram sequence of every narrow-band spectrum according to the band-pass sampling theorem. Finally, the spectral distribution of the detection target can be obtained by data processing and spectral superposition. The interference spectrometer provides a new idea for the development of spectral detection with wide spectral range, high resolution and high signalto- noise ratio.
To ensure the high surface accuracy and high thermal stability of space mirror, a lightweight design for the Φ514mm ULE primary mirror of a space remote sensor and flexible support structure with three-point was carried out. By further optimizing the parameters of the flexible supporting structure, the requirements of the optical index were met. The finite element model of the mirror assembly was established, and the static and dynamic characteristics of the assembly were analyzed. The results showed that the surface shape accuracy (RMS) of the mirror assembly is better than 8 nm under a load case of 1g gravity when the optical axis is level, and the first-order natural frequency of the component is 254 Hz. Finally, a mechanical test was carried out on the mirror assembly. The test results showed that the first-order frequencies of the three directions of the mirror assembly are all greater than 100 Hz , the error between the test data and the finite element analysis results does not exceed 10%. Analysis and test results showed that, the reasonable support structure design can effectively lower the change of the mirror surface shape caused by assembly stress and thermal stress, and has good dynamic performance. It is verified that the mirror and its supporting structure designed in this paper are reasonable, which provides reference and ideas for the design of flexible supporting structure of similar space mirror.
Coastal environmental elements such as bathymetry maps are of great significance to the economic and military development of each country. Spaceborne hyperspectral imager is one of the important instruments for coastal zone monitoring. Firstly, this paper systematically reviews the index system of spaceborne hyperspectral imagers, and then introduces the applications of hyperspectral remote sensing images in the retrieval of nearshore bathymetry. In order to improve the inversion accuracy, the current research status and shortcomings of fusion technology of laser active remote sensing and hyperspectral passive remote sensing are discussed. Furthermore, the index system of hyperspectral imagers is prospected based on the requirement of applications in coastal zone monitoring, which provides reference and support for the further development of hyperspectral remote sensing in coastal applications.
To minimize the assembly stress and thermal stress introduced by the support structure, and ensure the high surface accuracy and high thermal stability of space mirror. An ultra-lightweight design of secondary mirror was carried out for some space remote sensor, and three tangential bipods were used for quasi-kinematic support. Firstly, the design principle of quasi-kinematic support structure was investigated, and advantages of bipod kinematic support were analyzed from the angle of degree of freedom decoupling. Based on structure designed above, the finite element model was established. Taking surface accuracy of the mirror as optimization objectives, the integrated optimization method was adopted to extract the structural parameters with high sensitivity on the surface accuracy in the flexible support structure, and parameters optimization design was carried out. Finally, the static and dynamic characteristics of the optimized mirror assembly were analyzed. The analysis results showed that the surface shape accuracy (RMS) of the mirror assembly is better than 1 nm under a load case of 1g gravity when the optical axis is level. Surface accuracy (RMS) is better than 2 nm under the load case of 4℃ uniform temperature rise. The first-order natural frequency of the secondary mirror assembly is 587 Hz. The optimized mirror support structure can well unload the additional deformation caused by the support structure, and has good dynamic stiffness, which verifies that the designed mirror and its support structure are reasonable, and the optimization design method is reliable. This paper provides a reference and idea for the design of flexible support structure of space mirror.
Low-light stereo vision is a challenging problem because images captured in dark environment usually suffer from strong random noises. Some widely adopted algorithms, such as semiglobal matching, mainly depend on pixel-level information. The accuracy of local feature matching and disparity propagation decreases when pixels become noisy. Focusing on this problem, we proposed a matching algorithm that utilizes regional information to enhance the robustness to local noisy pixels. This algorithm is based on the framework of ADCensus feature and semiglobal matching. It extends the original algorithm in two ways. First, image segmentation information is added to solve the problem of incomplete path and improve the accuracy of cost calculation. Second, the matching cost volume is calculated with AD-SoftCensus measure that minimizes the impact of noise by changing the pattern of the census descriptor from binary to trinary. The robustness of the proposed algorithm is validated on Middlebury datasets, synthetic data, and real world data captured by a low-light camera in darkness. The results show that the proposed algorithm has better performance and higher matching rate among top-ranked algorithms on low signal-to-noise ratio data and high accuracy on the Middlebury benchmark datasets.
The influence of adhesive bonding and curing on the accuracy of mirror surface shape was analyzed to realize low-stress assembly of large aperture mirror. Firstly, based on Hooke's law, a curing shrinkage stress equation was deduced, taking deformation of the mirror and support structure into account under the boundary condition of continuous edge bond, and key parameters effecting mirror deformation were obtained. Secondly, for a 514mm ULE spectrometer primary mirror with an inserts structure mosaiced and bonded on mirror-back, an equivalent linear expansion coefficient method was used for finite element modeling. The shrinkage stress at the bond edge of mirror and the mirror surface shape were analyzed. It’s found that adhesive shrinkage has a significant effect on the mirror surface shape. Finally, the inserts structure of mirror assembly was optimized. In contrast to the non-optimum structure, the average stress of adhesive surface caused by adhesive curing shrinkage reduced from 0.28MPa to 0.18MPa, and the mirror surface shape (Root Mean Square, RMS) reduced from 0.029λ to 0.017λ. Finite element analysis results of the mirror assembly were given at last, surface shape accuracy (RMS) of mirror is 0.012λ under a load case of 1g gravity, and the first-order natural frequency of the component is 216 Hz. The obtained results showed that a suitable optimized support structure can effectively relieve adhesive curing stress, and also satisfy the design requirements for both the static and dynamic stiffness.
Large aperture static interferometer spectrometer (LASIS) use the method of push-boom to get the geometric and spectral characteristics of ground target, the particularity of principle requires the movement of satellite must be in the same direction with spectrometers detectors. Drift angle of satellite leading to abnormal image shifts in the column direction which should be perpendicular to the detector and can seriously affect the spectrum recovery precision of collected data. This paper analyzes the influence mechanism of drift angle for spectrum recovery precision. Simulation based on the actual on-orbit data analyses the effects of different drift angle of relative mean deviation and relative secondary deviation rehabilitation of the spectrum, besides the influence of spectral angle similarity. These studies have shown that, when the lateral deviation due to the drift angle on the across track is less than 0.3 pixel, the effect for the relative mean deviation of the inversive spectra will be no more than 7%. when the lateral deviation due to the drift angle on the across track is larger than one pixel, even though the resampling correction is proceeded, the restored spectral data cube still shows an relative mean error more than 10%, which seriously affect the availability of spectral data.
Trajectory prediction is essential for the maneuvering target tracking. Nowadays, one of the major challenges for precise prediction of position and velocity of one maneuvering target is the mismatching of target motion model and the movement mode the target performs. In order to solve this problem, the interacting multiple model method is proposed, which is able to adopt the current model to match the target motion mode so that the precision of prediction can be improved. One of the major problems of the interacting mult iple model methods is the selection of models for the algorithm. In this paper, such three models as constant velocity model, exponential increasing accelerat ion model, and the generalized coordinated turn model is selected. Afterwards, one simulat ion to verify the validation of the algorithm is performed, and it indicates that the interacting mult iple model methods with the specific models utilized in this paper does have the ability to track maneuvering target quite precisely.