Optics: measuring and testing – Standard – Surface standard
Reexamination Certificate
1999-04-28
2001-02-20
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Standard
Surface standard
C356S243100, C250S252100, C342S165000
Reexamination Certificate
active
06191851
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally related to high-resolution satellite and aircraft image acquisition technology. More specifically, the present invention is an apparatus and method for calibrating image acquisition systems for the purpose of extracting increased information from remotely sensed images.
BACKGROUND OF THE INVENTION
In agricultural applications, remote image sensing is the technology of choice for gathering timely, frequent, and cost efficient information about soil and crop status. However, remote image acquisition systems such as the new generation of high-resolution satellite and aircraft imaging systems must be calibrated, for example with respect to reflectance or thermal radiance. Imaging sensors such as scanners, cameras, or line arrays are used in these image acquisition systems to image target fields from elevated positions. The imaging data is typically digitized for later analysis. Calibration of remote or downward viewing image acquisition systems permits the application of quantitative models to the remotely sensed images and makes the data comparable between spatially separated fields and through time in order to extract useful information from the images. Without calibration, the information from remotely sensed images is typically limited to showing relative changes or anomalies concerning the imaged field. Currently, the only available calibration target on the market consists of a set of six cloth-backed panels from TRACOR which costs $60,000. These panels are difficult to handle, require intensive effort to lay out in a field, are easily damaged, and cannot remain in the field, but instead must be gathered up after the calibration exposure is completed. Deployment requires significant labor costs when sites are remote or when images must be acquired frequently.
Accordingly, there is a need in the art of remote image acquisition technology to provide inexpensive, portable, and robust calibration targets which are easily deployable in or near fields to be imaged and provide optical and thermal imagery characteristics for calibrating remote or downward viewing image acquisition systems used in agricultural and other applications. Currently, no such product is available.
SUMMARY OF THE INVENTION
The present invention is an apparatus and method for calibrating a downward viewing image acquisition system. The apparatus comprises a calibration panel with calibrative material of known reflectivity. The calibrative material coats the panel surface or is pulled across its surface or pulled across its frame so as to maintain a consistent reflectivity and/or emissivity. A housing is provided which protects the calibration panel from the deteriorative effects of natural elements. The housing alternately exposes the calibration panel to the downward viewing image acquisition system as a calibration exposure and covers the calibration panel after the calibration exposure. The housing is rotatable, allowing the panel to be properly aligned with the anticipated travel path of the downward viewing image acquisition system.
Exposing and covering the calibration panel is achieved automatically by an actuator onboard the housing. The actuator is triggered by a radio signal or timer signal which indicates when to expose and cover the calibration panel. Radio signals used to trigger the actuator control may come from any source, but will typically emanate from satellites or overflying aircraft. Timer signals come from an onboard timer which may be synchronized to a global positioning satellite clock signal or a radio clock signal.
The housing additionally contains at least one environmental sensor and an actuator control. The actuator control comprises a micro-processor which determines if panel deployment is safe under existing environmental conditions, and if so, operates to control the actuator in deployment of the panel. The microprocessor is also programmed to control panel deployment in response to radio commands or preset time settings. Protection of the calibration panel reflective surface is a main advantage of the present invention and greatly reduces the possibility of damage from environmental elements such as rain, wind, or agricultural practices.
An object of the present invention is to provide a low cost calibration target which can be left in place adjacent to or in the field of interest which permits automatic calibration of a downward viewing image acquisition system. Advantages of the present invention include inexpensive, portable, and robust calibration targets which permit easy and automatic deployment in or near locations to be imaged and provide optical and thermal imagery characteristics for calibrating the data received from remote or downward viewing image acquisition systems used in agricultural and other applications.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.
REFERENCES:
patent: 4830504 (1989-05-01), Frohardt et al.
patent: 5311191 (1994-05-01), Scannapieco
patent: 5311272 (1994-05-01), Daniels et al .
patent: 5672866 (1997-09-01), Messina
Downs Janelle L.
Kirkham Randy R.
Perry Eileen M.
Battelle (Memorial Institute)
May Stephen R.
Nguyen Sang H.
Pham Hoa Q.
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