Image navigation and registration accuracy improvement using parametric systematic error correction

Abstract

A novel Parametric Systematic Error Correction (ParSEC) system is disclosed which provides improved system accuracy for image navigation and registration (INR). This system may be employed in any suitable imaging system and, more specifically, to all imaging systems that exhibit systematic distortion. The ParSEC system may be employed to any such system regardless of sensing type (remote or in situ) or imaging media (photon or charged particle) and is further applicable to corrected imaging of any celestial body currently detectable to remove distortion and systematic error from the imaging system employed. The ParSEC system of the instant invention comprises a software algorithm that generates at least about 12 correction coefficients for each of the INR system measurements such as stars, visible landmarks, infrared (IR) landmarks and earth edges. An iterative estimation algorithm such as, for example, least squares or Kalman filters may be employed to determine the at least about 12 correction coefficients from each set of measurement residuals. The improved image products provide more accurate weather forecasting such as wind velocity and temperature.

Description

I. FIELD OF THE INVENTION[0001]This invention relates to methods and systems for making global observations of the earth and, more particularly, to image navigation and registration (INR) systems. More particularly, the present invention is directed to methods, apparatus and systems that provide real time coverage of at least 70% of the observable earth surface to improve the accuracy of INR systems.II. BACKGROUND OF THE INVENTION[0002]It is known that spacecraft, aircraft and satellites must accurately determine absolute orientation (i.e., roll, pitch and yaw) to realign their onboard attitude control system (ACS) and correct for instrument drift and buildup of errors affecting accurate and precise attitude determination. Attitude control is of particular importance in aircraft to maintain a stable operating environment, in surveillance satellites to track another object in space, and in remote imaging satellites to provide precise earth imaging and reconnaissance.[0003]In the west...

AI Technical Summary

Benefits of technology

[0038]Yet another object of this invention is to eliminate the effects of systematic errors in INR systems without requiring costly engineering directed to discovering and correcting actual sources of errors.

[0039]Yet again another object of this invention is to provide an improved INR system that provides accuracy of the coastline fixed grid overlays to better match the coastlines in the actual earth images taken by a camera on a moving satellite.

[0041]Yet again another object of this invention is to provide an improved INR system that corrects the East-West and North-South location of the actual star, visible landmark, IR landmark and earth edges resulting in improved orbit and attitude determination.

[0042]Again another object of this invention is to apply an algorithm to INR systems that corrects the location of the raw visible imagery pixels to better match the fixed coastline overlay grid and achieve more accurate geo-location and image products.

[0043]A further object of this invention is to provide a correcting algorithm which employs IR landmarks to accurately determine the location of the raw IR imagery pixels in order to better match the fixed coastline overlay grid in image products.

[0045]These and other objects of the instant invention are accomplished generally speaking by providing an improved INR method and system for imaging systems that exhibit systematic distortion comprising employing a novel algorithm system that effects improved accuracy of INR. The novel algorithm system of the instant invention employs a ParSEC system comprising at least about twelve (12) correction coefficients in either constant or time varying values for each of the INR systems measured, including those relating to stars, visible landmarks, IR landmarks and earth edges. The at least about 12 coefficients are determined on a case-by-case basis and, for example, could include at least about 12 coefficients where at least one coefficient is zero providing for a net number of coefficients to be employed in the system of the instant invention that numerically is less than 12. The at least about 12 coefficients are determined by an iterative estimation algorithm from each set of the measured residuals. The measured residuals are defined as the difference between the actual measurement of East-West and North-South coordinates from imagery data and the predicted East-West and North-South coordinates based on orbit and attitude solution. The at least 12 coefficients are applied for each set of measurements to correct the measured residuals which result in, for example, improved orbit and attitude determination process and remapping of raw image pixels to better match the fixed coastline grid to the actual coastline in the user's image products. Examples of such users' products include high rate information transmission (HRIT) and low rate information transmission (LRIT). These improved image products are found to provide inter alia more accurate weather forecasting with regard to wind velocity and temperature.

Problems solved by technology

The star tracker equipment required to detect the faint star light and maintain the star tables may be costly.

However, Ring's design concept provides coarse attitude accuracy using radar signals not suitable for applications requiring greater accuracy, such as remote imaging or surveillance satellites.

Although Ring provides accurate attitude determination employing laser communication links, it potentially represents a very complex and costly system.

However, it is found that multiple antenna GPS systems provide relatively coarse attitude accuracy on the order of 1 mille radiant at best and therefore may not be used in applications requiring greater accuracy, such as in remote imaging satellites or surveillance satellites.

Techniques such as these and existing interferometric GPS attitude determination methods employing multiple antennas are complex, expensive and provide only coarse information with milliradian accuracy.

In practice, SRSO operations are rarely used because coverage of other areas is too important to be neglected for long periods of time.

Moreover, significant earth based events that occur during lapses in coverage of a particular region may be missed.

Furthermore, phenomena that may occur a night can only be seen in the infrared channels which have a much coarser spatial resolution than the visible channel and otherwise are subject to the same limitations that are inherent in a scanning system.

GOES satellites provide a system that is optimized for monitoring cloud motion, but is far less suitable for observing other GEO physical events.

Color, enhancing the contrast and visibility of the earth's surface background, may actually detract from cloud visibility in a scene.

Moreover, adding color may triple the amount of information and thus the size of a digitized image, which creates a burden on the transmission demands for the broadcast portion of the satellite system.

Furthermore, observations of significant but perhaps transient phenomena that occur in time scales of seconds or minutes (such as volcanoes, lightening strikes or meteors) may be late or not observed at all.

Also, in other systems for example, “video” style loops created from successive images having relatively coarse temporal resolution may lack the continuity needed to provide truly reliable information if cloud movements between image samples are much greater than a pixel dimension.

These effects may have adverse impact on the fidelity of any “image” created to represent the state of the earth at a given moment, but particularly to attempts to build animations using successive co-registered scanned images of a given area.

As presently recognized, the system proposed by Hughes was deficient in both its camera resources and communication systems infrastructure with regard to the following three attributes.

The system proposed by Hughes did not provide real-time images as a result of the delay between frames.

Another deficiency was that real-time images cannot be distributed in real time, due to the interval between frames and the slow data rate, as well as the single point data reception and distribution facility.

Furthermore, the system proposed by Hughes was deficient in its inability to provide hemispheric (full disk images) in real time.

This limitation is due to the limited telemetry channel capacity, limited camera design and the time required to create a composite full disk image.

In this technique, every geographic scene element is sampled 128 times, which increases the signal-to-noise level.

However, communication satellites are relatively unstable platforms.

With a single pixel integration time on the order of milliseconds, spacecraft movement during the accumulation of over 100 samples may degrade the spatial resolution within any one scene element.

The continuity of successive observations will thus be compromised and degrade “seamless” coverage by an amount proportional to the velocities of the objects causing the shapes to apparently change.

Furthermore, the significance of obtaining real-time night images or the mechanisms needed to obtain the images was never appreciated and thus not realized.

As presently recognized, limitations of the GATES system are that neither live images nor night imaging is possible.

A limitation common to the Hughes proposed system, the MITRE system and the GATES system is that none of the systems appreciate the interrelationship between providing a real-time continuous monitoring capability of the entire earth that is accessible from a geostationary earth orbit while providing high-resolution images.

In part, the limitation with all of the devices is that none of the devices would be able to reliably provide the “watchdog” high resolution imaging function that would provide a remote user with valuable real-time data of dynamic situations occurring at or near the earth's surface.

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