The space object in highly elliptical orbit is always presented as an image point on the ground-based imaging equipment so that it is difficult to resolve and identify the shape and attitude directly. In this paper a novel algorithm is presented for the estimation of spacecraft shape. The apparent magnitude model suitable for the inversion of object information such as shape and attitude is established based on the analysis of photometric characteristics. A parallel adaptive shape inversion algorithm based on UKF was designed after the achievement of dynamic equation of the nonlinear, Gaussian system involved with the influence of various dragging forces. The result of a simulation study demonstrate the viability and robustness of the new filter and its fast convergence rate. It realizes the inversion of combination shape with high accuracy, especially for the bus of cube and cylinder. Even though with sparse photometric data, it still can maintain a higher success rate of inversion.
To meet the requirements of a variety of applications, range precision is an important specification for three-dimensional laser radar systems. The proposed laser ranging systems adopt electro-optical modulation and only measures the energy of a laser pulse to obtain range, so that it can reduce many errors in comparison to conventional systems. In this paper, the principle of continuous and pulsed laser ranging systems are introduced, through simulation analysis the target of 20 m, the continuous laser ranging system can achieve a range precision of several centimeters, and the pulsed laser ranging system can achieve a rang precision of several millimeters. And by analyze their advantages and disadvantages, it can be concluded that pulsed laser ranging accuracy is higher than the continuous laser ranging systems. The pulsed laser ranging system is expected to be an alternative method for three-dimensional laser radar system requiring high range precision in many applications.
The attitude information acquisition of unresolved space objects, such as micro-nano satellites and GEO objects under the way of ground-based optical observations, is a challenge to space surveillance. In this paper, a useful method is proposed to estimate the SO attitude state according to the simulation analysis of photometric data in different attitude states. The object shape model was established and the parameters of the BRDF model were determined, then the space object photometric model was established. Furthermore, the photometric data of space objects in different states are analyzed by simulation and the regular characteristics of the photometric curves are summarized. The simulation results show that the photometric characteristics are useful for attitude inversion in a unique way. Thus, a new idea is provided for space object identification in this paper.
A dense surface reconstruction approach based on the fusion of monocular vision and three-dimensional (3-D) flash light detection and ranging (LIDAR) is proposed. The texture and geometry information can be obtained simultaneously and quickly for stationary or moving targets with the proposed method. Primarily, our 2-D/3-D fusion imaging system including cameras calibration and an intensity-range image registration algorithm is designed. Subsequently, the adaptive block intensity-range Markov random field (MRF) with optimizing weights is presented to improve the sparse range data from 3-D flash LIDAR. Then the energy function is minimized quickly by conjugate gradient algorithm for each neighborhood system instead of the whole MRF. Finally, the experiments with standard depth datasets and real 2-D/3-D images demonstrate the validity and capability of the proposed scheme.
KEYWORDS: 3D acquisition, Cameras, Image fusion, Time of flight cameras, 3D image processing, Filtering (signal processing), Error analysis, 3D modeling, Reconstruction algorithms, 3D-TOF imaging
An approach of scale-unambiguous relative pose estimation for space uncooperative targets based on the fusion of low resolution three-dimensional time-of-flight camera and monocular camera is proposed. No a priori knowledge about the targets is assumed. First, a modified range–intensity Markov random field model is presented to quickly reconstruct the range value for each feature point. Second, the scale-ambiguous relative pose estimation algorithm based on extended Kalman filter–unscented Kalman filter–particle filter combination filter is designed in vision simultaneous localization and mapping framework. Third, the overall scale factor estimation approach based on range–intensity fusion image, which takes the feature points’ range reconstruction uncertainty as measurement noise, is proposed for the final scale-unambiguous pose estimation. Finally, some simulations demonstrate the validity and capability of the proposed approach.
A dimensionality reduction method is proposed by using the second generation Bandelet transform. The redundant components of the hyperspectral cube are firstly partitioned into several subsets. Subsequently the Bandelet coefficients and the geometries flows of the hyperspectral image are generated by performing second generation Bandelet transform. In the follow step, Principal Components Analysis (PCA) is introduced to simplify the redundant data. Finally, the new reduced hyperspectral cube is reconstructed by taking inverse Bandelet transform. Some numerical simulations are made to test the validity and capability of the proposed dimensionality reduction algorithm.
Silicon photomultiplier (SiPM)-based optoelectronic mixing (OEM) is studied for the first time. The validity of SiPM-based OEM is experimentally verified. Compared with the avalanche photodiodes-based OEM, the SiPM-based OEM is less noisy and easy to realize for its low voltage operation and high responsivity.
A fusion algorithm of hyperspectral and high-resolution images based on principal component analysis (PCA) and second generation Bandelet transform is proposed. Primarily, the numerous components of the hyperspectral image are divided. Subsequently, the maximum rule is used to select the Bandelet coefficients and geometry flows of the hyperspectral image which are transformed by PCA in the following step. Finally, the fused image is reconstructed by taking inverse PCA and Bandelet transform. Some numerical simulations are made to test the validity and capability of the proposed fusion algorithm.
KEYWORDS: Semiconductor lasers, LIDAR, Transmitters, Frequency modulation, Fermium, Ranging, Modulation, Signal processing, Collimators, Signal generators
The purpose of this paper is to present the prototype of the laser diode transmitter for the laser radar based on
frequency-modulated (FM) ranging principles. It belongs to the time-of-flight measurement category. In this case, the
time-of-flight is converted to a beat frequency proportional to the range to be measured. This conversion is realized with
intensity modulation of the laser power by a linear FM continuous wave. FM ranging theory and the principle of
operation are described to show the application of FM radar principles in laser radar. The design of laser diode
illuminator and the key techniques in the transmitter are discussed, including the generation technique of the wideband
radio-frequency (RF) chirp signal, design of the transmitter module and the laser beam collimation optics. The possible
factors that may limit the performance the laser radar system are discussed.
The purpose of this paper is to introduce the application of scannerless range imaging (SRI) laser radar in the dynamic
and real-time surveillance for cooperative and uncooperative space objects. Scannerless range imaging technique enables
the capture of a full scene 3D range image in one acquisition with faster image acquisition speed. Small size, lighter
weight, reduced mechanically complex and faster acquisition speed make it more fit for space borne scenario. Laser
radar is based on frequency-modulated (FM) ranging principle that belongs to the time-of-flight (TOF) measurement
category. In this case, the time-of-flight is converted to a beat frequency proportional to the range to be measured. This
conversion is realized with intensity modulation of the laser power by a linear FM continuous wave. A summary of FM
ranging theory and its application in range imaging are introduced. The system architecture and theory of operation are
described. The key technologies of this type of scannerless range imaging laser radar in the application of surveillance
for space objects are discussed.
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