Pushbroom scan cameras with linear image sensors, commonly used for Earth observation from satellites, require high attitude stability during the image acquisition. Especially noticeable are the effects of high frequency attitude variations originating from micro shocks and vibrations, produced by momentum and reaction wheels, mechanically activated coolers, steering and deployment mechanics and other reasons. The SMARTSCAN imaging concept offers high quality imaging even with moderate satellite attitude stability on a sole opto-electronic basis without any moving parts. It uses real-time recording of the actual image motion in the focal plane of the remote sensing camera during the frame acquisition and a posteriori correction of the obtained image distortions on base of the image motion record. Exceptional real-time performances with subpixel accuracy image motion measurement are provided by an innovative high-speed onboard optoelectronic correlation processor. SMARTSCAN allows therefore using smart pushbroom cameras for hyper-spectral imagers on satellites and platforms which are not specially intended for imaging missions, e.g. micro satellites. The paper gives an overview on the system concept and main technologies used (advanced optical correlator for ultra high-speed image motion tracking), it discusses the conceptual design for a smart compact space camera and it reports on airborne test results of a functional breadboard model.
Fractal approach to mathematical modelling of signals in space optical observation systems is proposed. The scannings of two-dimensional images as one-dimensional stochastic fractal processes are built on the base of Brownian motion. Integrals over trajectories of Wiener processes with different kernels are used for modeling of one-dimensional stochastic fractals and multifractals. Modelling of scannings of remotely sensed data based on formalism of integrals over Wiener stochastic process trajectories and modelling of probabilistic characteristics based on formalism of Feynman continual integrals are performed. Algorithms of multiscale detection of signals on the basis of discrete and continuous wavelet transforms are developed and applied for anomaly detection and estimation.
The information technology of remotely sensed image analysis is based on system integration of two main concepts:
diffractive optical elements (DOEs) aided multispectral preprocessing and multiscale analysis. Proposed technology
allows to: decrease the threshold of hidden signal detection; detect the signals with unknown form; improve the
performance of subpixel signal detection and estimation in case of limited resolution of sensors. Data preprocessing
method for anomaly detection on the base of DOE technology is developed. DOE-based technology is implemented and
tested. Nonparametric statistic methods for signal detection and estimation are proposed. Multiresolution image analysis
methods are applied for anomaly detection and estimation.
Onboard analysis of remotely sensed images can help in the case of real time processing of high resolution Earth images,
giving the possibility of selecting frames, containing essential information, for transmission to ground station (for
reducing the data flow). One of possible methods of frames selection is image texture analysis on base of spatial
frequencies spectrum processing. The questions of incoherent light source usage in the optoelectronic Fourier spectrum
analyser are considered. Using of incoherent light source of specific size and shape makes it possible to provide an
optimal spatial filtering of the spectrum, reduce a sensitivity to phase distortions and obtain a compact and rugged design
of the device. Special algorithm of spectrum image digitising is developed to enlarge a range of spatial frequencies to be
processed and maximise the photosensitivity. The algorithms for texture properties recognition are developed and tested
using prototype incoherent Fourier spectrum analyzer.
Hybrid optoelectronic landmark navigation is proposed as backup navigation for Low Earth Orbit satellite. Optoelectronic navigation can use earth observation camera, originally not assigned for navigation purposes. The concept of the landmark navigation system is based on the onboard optical correlator application for real time matching of the earth images and pre-recorded images of landmarks with known coordinates. The software model of image processing by optical correlator has been developed to test the system operation in simulated experiments and to estimate the expected performance. The hardware model of the joint transform optical correlator has been manufactured and tested. The model uses commercially available optoelectronic components and works with PC, which performs all digital processing and data flow control. As a result ofthe model testing, the feasibility ofthe system concept and the adequacy ofthe software model have been proved. The image processing system which calculates satellite attitude and position on the base of correlation peaks measurements has been used for simulation of optoelectronic satellite landmark navigation. In the series of simulated experiments the navigation accuracy was estimated in presence of image distortions and noise for earth observation mission.
The paper presents a concept of a smart pushbroom imaging system with compensation of attitude instability effects. The compensation is performed by active opto-mechatronic stabilization of the focal plane image motion in a closed loop system with visual feedback on base of an auxiliary matrix image sensor and an onboard optical correlator. In this way the effects of the attitude instability, vibrations and micro shocks can be neutralized, the image quality improved and the requirements to satellite attitude stability reduced. To prove the feasibility and to estimate the effectiveness of the image motion stabilization, a performance model of the smart imaging system has been developed and a simulation experiment has been carried out. The description of the performance model and the results of the simulation experiment are also given.
Information system determining the satellite navigation parameters on the base of landmark image processing is considered. The concept of the optoelectronic navigation is based on the onboard optical correlator application for real time matching of the Earth images and prerecorded images of landmarks with known coordinates. The system is suitable for the low-orbit Earth imaging missions with 3-axis attitude stabilization and can be used for backup landmark navigation, precision pointing of the imaging payload and for onboard georeferencing of the obtained images. Mathematical model of the optoelectronic landmark navigation is considered. Compact optics design, the software and hardware models of the joint transform optical correlator have been developed. Experimental results obtained by using the image processing system are represented. The effects of the current image distortions on correlator performance were investigated. In the series of simulated experiments the accuracy of images matching was estimated in presence of image distortions and noise typical for high resolution Earth observation mission. The possibility to obtain the sub-pixel accuracy of images matching in real conditions under noisy environment is shown.
Smart pushbroom imaging system (SMARTSCAN) solves the problem of image correction for satellite pushbroom cameras which are disturbed by satellite attitude instability effects. Satellite cameras with linear sensors are particularly sensitive to attitude errors, which cause considerable image distortions. A novel solution of distortions correction is presented, which is based on the real-time recording of the image motion in the focal plane of the satellite camera. This allows using such smart pushbroom cameras (multi-/hyperspectral) even on moderately stabilised satellites, e.g. small sat's, LEO comsat's. The SMARTSCAN concept uses in-situ measurements of the image motion with additional CCD-sensors in the focal plane and real-time image processing of these measurements by an onboard Joint Transform Optical Correlator. SMARTSCAN has been successfully demonstrated with breadboard models for the Optical Correlator and a Smart Pushbroom Camera at laboratory level (satellite motion simulator on base of a 5 DOF industrial robot) and by an airborne flight demonstration in July 2002. The paper describes briefly the principle of operation of the system and gives a description of the hardware model are provided. Detailed results of the airborne tests and performance analysis are given as well as detailed tests description.
The paper describes the test results of the hardware model of a smart pushbroom imaging system. The imaging system can be used on satellites with moderately attitude stability due to application of the image correction on base of the real-time image motion record by an optoelectronic image processor and auxiliary sensors in the focal plane. The tested model includes the breadboard model of a smart pushbroom camera with auxiliary sensors, the optoelectronic processor model and the image correction software. The tests have been performed on a laboratory satellite motion simulator based on a 5 DOF industrial robot. Numerical values of the image motion record accuracy and the image correction efficiency are given as well as a detailed test description.
The paper describes the design concept of an optoelectronic system for real time image motion analysis. The system is proposed to be used onboard an Earth observation satellite for the real time recording of the image motion in the focal plane of the camera. With this record available, it is possible to use pushbroom scan cameras onboard satellites with moderate attitude stability (possible geometric distortions, caused by the attitude instability, can be corrected posteirori on base of the records). New experimental results are presented, which have been derived from a real-time breadboard model of the optical processor, developed and manufactured under ESA- contract. The results of the tests are provided as well as the expected performances of a full scale system.
The concept of the small, medium resolution Earth observation camera (14 - 20 m per pixel) using a joint transform optical correlator is proposed. The camera is intended to be used as a secondary payload for low orbit, 3-axis stabilized spacecraft, including ones with moderate attitude stability. The optical correlator is used for a real-time determination of the camera pointing motion for posteriori correction of the image distortions due to attitude unstability. A wide angle lens and long assembly of the line sensors in the focal plane permit to change the view direction without need to move the satellite or camera elements. A possible layout of the optoelectronic unit is described and the results of simulated experiments, expected performances and size estimations are given.
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