Raytheon Company

Stephen J Schiller

Clifton Quan

John F Silny

Christopher R Koontz

James R Chow

John J Coogan

Stephanie J Lin

Randall W Zywicki

Hans P Naepflin

Yanmin Zhang

Edward Ward, Jr

Steven E Persh

A system () and method can monitor a reflectance of a mirror target that includes at least one curved mirror (M). The system () can take a first irradiance measurement of the sun (S), the first irradiance measurement representing a direct solar irradiance. The system () can take a second irradiance measurement that represents an irradiance from a reflection of the sun (S) from the mirror target plus background irradiance from a reflection of the sky from the mirror target. The system () can take a third irradiance measurement that represents the background irradiance from the reflection of the sky from the mirror target. The system () can determine a reflectance of the mirror target from the first, second, and third irradiance measurements. The system () can compare the reflectance to a specified reflectance threshold, and, upon determining that the reflectance of the mirror target is less than the specified reflectance threshold, can generate an alert signal.

Monitoring mirror reflectance using solar illumination

A method for vicarious spatial characterization of a remote sensor system. The method includes detecting, via the remote sensor system, radiation reflected from at least one body of water corresponding to a plurality of point reflector images, selecting a set of point reflector images from the plurality of point reflector images, the selected set of point reflector images corresponding to sub-pixel point reflector images, analyzing the selected set of point reflector images by executing an algorithm for fitting the point reflector images to obtain a point spread function of the remote sensor system, and determining a spatial characteristic of the remote sensor system based on the point spread function.

Vicarious calibration using solar glint over water

An apparatus and method of intersensor calibration including using a zero airmass response constant proportional to sensor absolute radiometric gain coefficients to monitor sensor radiometric stability. Tracking the ratio of zero airmass response constant values for similar bands between two sensors provides a parameter on a common radiometric scale for evaluating interoperability performance. The method includes imaging a solar signal using a mirror to create an image reference target, detecting the image reference target using a first sensor, generating a zero airmass response constant based on a ground sampling distance of the first sensor and an at-sensor radiance value, computing a radiometric gain coefficient of the first sensor using the zero airmass response constant, and comparing the radiometric gain coefficient of the first sensor to a radiometric gain coefficient of a second sensor to determine a gain ratio between the first sensor and second sensor.

Systems and methods for intersensor satellite calibration

An example method includes recording dark images on an image sensor on-board an orbital vehicle during flight, which include a first image recorded before the orbital vehicle is over a predefined location on the Earth and a second image recorded after the orbital vehicle is over the predefined location; and recording third and fourth images on the image sensor during flight based on illumination from a light source that is on-board, with the third image being recorded before the orbital vehicle is over the predefined location and the fourth image being recorded after the orbital vehicle is over the predefined location. A fifth image is recorded on the image sensor during flight while the predefined location on the Earth is visible to the image sensor. The fifth image is based on light from a ground-based calibration system. The light source is calibrated during flight based on the five images.

On-board light source calibration

A broadband calibrator assembly is provided and includes a medium/long wave infrared (MW/LW IR) assembly and multiple ultraviolet (UV)/visible and near IR (VNIR)/short wave IR (SWIR) assemblies.

Broadband calibrator from visible to long wave infrared

An angularly-dependent reflectance of a surface of an object is measured. Images are collected by a sensor at different sensor geometries and different light-source geometries. A point cloud is generated. The point cloud includes a location of a point, spectral band intensity values for the point, an azimuth and an elevation of the sensor, and an azimuth and an elevation of a light source. Raw pixel intensities of the object and surroundings of the object are converted to a surface reflectance of the object using specular array calibration (SPARC) targets. A three-dimensional (3D) location of each point in the point cloud is projected back to each image using metadata from the plurality of images, and spectral band values are assigned to each value in the point cloud, thereby resulting in a multi-angle spectral reflectance data set. A multi-angle surface-specific signature (MASS) is fitted to the multi-angle spectral reflectance data set, and the multi-angle surface-specific signature of the object and the surroundings of the object are stored into a spectral database. The spectral database is mined to find one or more of spatial and temporal anomalies in the plurality of images and patterns and correlations of the multi-angle surface-specific signature.

In-scene multi-angle surface-specific signature generation and exploitation

In an optical system, a color filter mosaic can determine first color pixel locations, second color pixel locations, and third color pixel locations in an array of sensor pixels. The optical system can capture overhead images, which can be subtracted to form a background-subtracted tri-color image of a reflection of sunlight from at least one ground-based curved mirror. A processor can scale color values at the first and second color pixel locations of the tri-color background-subtracted image. The processor can form a single-color background-subtracted image from the scaled color values at the first color pixel locations, the scaled color values at the second color pixel locations, and third color values at the third color pixel locations. The single-color background-subtracted image can correspond to a point spread function or a line spread function of the optical system.

Spatial radiometric correction of an optical system having a color filter mosaic

Geometric calibration of an imaging system is performed by recording visible control points in a calibration image whose geometric properties are known and calibration coefficients can be derived utilizing an image processing system for transforming the recorded image into a geometric distortion-free image. Described are methods and systems for vicarious geometric calibration of a remote sensor that include a processor configured to receive image data collected at a remote sensor, the image data including a plurality of image elements each associated with a respective reflective mirror from a plurality of reflective mirrors located at respective know positions, determine, for each of the plurality of reflective mirrors, an image location in the image data and determine one or more figures of merit based on the image locations and the known positions for each of the plurality of reflective mirrors.

Geometric calibration of a remote sensor

Described are methods and systems for vicarious polarimetric calibration and performance validation of a remote sensor. The system includes a plurality of reflective mirrors configured and arranged to reflect radiation from a source of radiation onto the remote sensor with accurately known polarimetric properties. Each of the reflective mirrors are located so that the target images do not overlap. The remote sensor is configured to receive the radiation reflected from the plurality of reflective mirrors and store the received radiation as image data (e.g., the image of each mirror appears as a point target). The system includes a processor configured to process the received data to provide direct calibration and performance validation for each polarimetric or spectral channel of the remote sensor. In addition, the calibration method removes all atmospheric effects except for transmittance and provides reference targets that have high polarimetric contrast, full spectrum performance and easy to deploy.

Polarimetric calibration of a remote sensor

A method and a system for vicarious characterization of a remote sensing sensor are described. The system includes a plurality of reflective mirrors configured and arranged to reflect radiation from a source of radiation onto a remotely located radiation sensor. The plurality of mirrors are spaced apart so as to obtain a plurality of distinct spot images on the remotely located radiation sensor. The system further includes a processor configured to analyze the plurality of spot images by fitting the images to obtain a point spread function of the remote sensing sensor.

Method and system for vicarious spatial characterization of a remote image sensor

A method and a system for spectral calibration of a remote sensing sensor and a synthetic target having a tunable spectral composition are described. The system or synthetic target includes a plurality of reflective mirrors arranged to reflect radiation from a source of radiation onto a remotely located radiation sensor. A first mirror in the plurality of mirrors is configured to reflect a first portion of the radiation in a first wavelength toward the remotely located radiation sensor. A second mirror in the plurality of mirrors is configured to reflect a second portion of the radiation in a second wavelength different from the first wavelength toward the remotely located radiation sensor. The first portion of the radiation and the second portion of the radiation can be selected to calibrate the remotely located radiation sensor so as to provide a quantitative spectral relationship between the radiation detected at the remotely located sensor and the radiation reflected by the plurality of mirrors.

Method and system for spectral calibration of a remote sensing sensor and a synthetic target having a tunable spectral composition

A specular array for radiometric calibration (SPARC) includes a plurality of spherical mirrors disposed upon a uniform background as at least one array of reflective points, at least two points reflecting a different intensity of directly incident sunlight. Each mirror has a radius of curvature and a diameter, the radius of curvature and the diameter providing a field of regard, the collective mirrors providing a collective minimum calibratability field of regard. Based upon the radius of curvature, the transmittance value of the sun to each mirror and from each mirror to a sensor being calibrated, the intensity of calibration light provided to the input aperture of a sensor to be calibrated within the collective minimum calibratability field of regard may be determined and used as a baseline for sensor calibration. An associated method of combined spatial and radiometric calibration is also provided.

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La Mirada, CA, United States of America

Stephen J Schiller