FIELD OF THE INVENTION

The present invention generally relates to a system and method for gas cloud detection and, in particular, to a system and method of detecting obscuration of a camera window in gas and chemical imaging cameras.

DESCRIPTION OF THE RELATED TECHNOLOGY

Spectral imaging systems and methods have applications in a variety of fields. Spectral imaging systems and methods obtain a spectral image of a scene in one or more regions of the electromagnetic spectrum to detect phenomena, identify material compositions or characterize processes. The spectral image of the scene can be represented as a three-dimensional data cube where two axes of the cube represent two spatial dimensions of the scene and a third axis of the data cube represents spectral information of the scene in different wavelength regions. The data cube can be processed using mathematical methods to obtain information about the scene. Some of the existing spectral imaging systems generate the data cube by scanning the scene in the spatial domain (e.g., by moving a slit across the horizontal dimensions of the scene) and/or spectral domain (e.g., by scanning a wavelength dispersive element to obtain images of the scene in different spectral regions). Such scanning approaches acquire only a portion of the full data cube at a time. These portions of the full data cube are stored and then later processed to generate a full data cube.

SUMMARY

The systems, methods and devices of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

Various examples of imaging systems comprising an optical window and with capabilities to determine if the optical window is obscured (e.g., to detect objects on or in front of the window that may introduce obscuration that may degrade operation of the system) are described herein such as the examples enumerated below:

Example 1: An example of an infrared (IR) imaging system comprising:a housing;an optical window disposed on the housing;an optical detector system disposed within the housing; anda plurality of spatially and spectrally distinct optical channels that transfer incident IR radiation from the optical window to the optical detector system, wherein a first optical channel out of the plurality of optical channels has a focus distance that is closer to the optical window than at least some of the other optical channels of the plurality of optical channels to detect whether the optical window is obscured.

Example 2: The IR imaging system of Example 1, wherein the first optical channel out of the plurality of optical channels has a focus less than 2 meters and other optical channels of the plurality of optical channels have a focus of greater than 10 meters.

Example 3: The IR imaging system of any one of Examples 1 to 2, wherein the first optical channel out of the plurality of optical channels has a focus less than 2 meters and other optical channels of the plurality of optical channels have a focus of greater than 20 meters.

Example 4: The IR imaging system of any one of Examples 1 to 3, wherein the first optical channel out of the plurality of optical channels has a focus less than 2 meters and other optical channels of the plurality of optical channels have a focus of greater than 30 meters.

Example 5: The IR imaging system of any one of Examples 1 to 4, wherein the first optical channel out of the plurality of optical channels has a focus of 1 meter or less and other optical channels of the plurality of optical channels have a focus of greater than 10 meters.

Example 6: The IR imaging system of any one of Examples 1 to 5, wherein the first optical channel out of the plurality of optical channels has a focus of 1 meter or less and other optical channels of the plurality of optical channels have a focus of greater than 20 meters.

Example 7: The IR imaging system of any one of Examples 1 to 6, wherein the first optical channel out of the plurality of optical channels has a focus of 1 meter or less and other optical channels of the plurality of optical channels have a focus of greater than 30 meters.

Example 8: The IR imaging system of any one of Examples 1 to 7, wherein at least some of the other optical channels of the plurality of optical channels have focus distances at least 5 meters greater than the focus distance of the first optical channel.

Example 9: The IR imaging system of any one of Examples 1 to 8, wherein at least some of the other optical channels of the plurality of optical channels have focus distances at least 10 meters greater than the focus distance of the first optical channel.

Example 10: The IR imaging system of any one of Examples 1 to 9, wherein at least some of the other optical channels of the plurality of optical channels have focus distances at least 20 meters greater than the focus distance of the first optical channel.

Example 11: The IR imaging system of any one of Examples 1 to 10, wherein the first optical channel out of the plurality of optical channels has a focus distance of 1 meter or less.

Example 12: The IR imaging system of any one of Examples 1 to 11, wherein the first optical channel out of the plurality of optical channels has a focus distance of 2 meter or less.

Example 13: The IR imaging system of any one of Examples 1 to 12, wherein the first optical channel and the other optical channels include imaging lenses for imaging objects onto the optical detector system, said imaging lenses having focal lengths.

Example 14: The IR imaging system of any one of Examples 1 to 13, wherein the focal lengths for lenses in the other optical channels exceed the focal length for the first optical channel.

Example 15: The IR imaging system of any one of Examples 1 to 14, wherein the focal lengths for lenses in the other optical channels exceed the focal length for the first optical channel by at least 2×.

Example 16: The IR imaging system of any one of Examples 1 to 15, wherein the focal lengths for lenses in the other optical channels exceed the focal length for the first optical channel by at least 5×.

Example 17: The IR imaging system of any one of Examples 1 to 16, wherein the first optical channel is in focus at the optical window to detect whether the optical window is obscured.

Example 18: The IR imaging system of any one of Examples 1 to 17, wherein the first optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the first optical channel extends between a depth of the optical window and approximately 1 meter beyond the optical window.

Example 19: The IR imaging system of any one of Examples 1 to 18, wherein the first optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the first optical channel extends between a depth of the optical window and approximately 50 cm beyond the optical window.

Example 20: The IR imaging system of any one of Examples 1 to 19, wherein the first optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the first optical channel extends between a depth of the optical window and approximately 20 cm beyond the optical window.

Example 21: The IR imaging system of any one of Examples 1 to 20, wherein the first optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the first optical channel extends between a depth of the optical window and approximately 10 cm beyond the optical window.

Example 22: The IR imaging system of any one of Examples 1 to 21, further comprising:a processing unit comprising processing electronics configured to process image data from the first optical channel to detect whether the optical window is obscured.

Example 23: The IR imaging system of any one of Examples 1 to 22, wherein the processing unit is configured to evaluate how much of the image data is in focus to detect whether the optical window is obscured.

Example 24: The IR imaging system of any one of Examples 1 to 23, wherein the processing unit is configured to evaluate the contrast of the image data to detect whether the optical window is obscured.

Example 25: The IR imaging system of any one of Examples 1 to 24, wherein the processing unit is configured to perform edge enhancement of the image data.

Example 26: The IR imaging system of any one of Examples 1 to 25, wherein the processing unit is configured to perform edge detection of the image data.

Example 27: The IR imaging system of any one of Examples 1 to 26, wherein the processing unit is configured to perform normalization of the image data.

Example 28: The IR imaging system of any one of Examples 1 to 27, wherein the normalization of the image data comprises scaling the image data.

Example 29: The IR imaging system of any one of Examples 1 to 28, wherein the normalization of the image data comprises subtracting from the image data.

Example 30: The IR imaging system of any one of Examples 1 to 29, wherein the processing unit is configured to evaluate whether image data exceeds a threshold to determine whether the optical window is obscured.

Example 31: The IR imaging system of any one of Examples 1 to 30, wherein a second optical channel out of the plurality of optical channels has a focus distance that is closer to the optical window than at least some of the other optical channels of the plurality of optical channels to detect whether the optical window is obscured.

Example 32: The IR imaging system of Example 31, wherein the second optical channel out of the plurality of optical channels has a focus less than 2 meters and other optical channels of the plurality of optical channels have a focus of greater than 10 meters.

Example 33: The IR imaging system of any one of Examples 1 to 32, wherein the second optical channel out of the plurality of optical channels has a focus less than 2 meters and other optical channels of the plurality of optical channels have a focus of greater than 20 meters.

Example 34: The IR imaging system of any one of Examples 1 to 33, wherein the second optical channel out of the plurality of optical channels has a focus less than 2 meters and other optical channels of the plurality of optical channels have a focus of greater than 30 meters.

Example 35: The IR imaging system of any one of Examples 1 to 34, wherein the second optical channel out of the plurality of optical channels has a focus of 1 meter or less and other optical channels of the plurality of optical channels have a focus of greater than 10 meters.

Example 36: The IR imaging system of any one of Examples 1 to 35, wherein the second optical channel out of the plurality of optical channels has a focus of 1 meter or less and other optical channels of the plurality of optical channels have a focus of greater than 20 meters.

Example 37: The IR imaging system of any one of Examples 1 to 36, wherein the second optical channel out of the plurality of optical channels has a focus of 1 meter or less and other optical channels of the plurality of optical channels have a focus of greater than 30 meters.

Example 38: The IR imaging system of any one of Examples 1 to 37, wherein at least some of the other optical channels of the plurality of optical channels have focus distances at least 5 meters greater than the focus distance of the second optical channel.

Example 39: The IR imaging system of any one of Examples 1 to 38, wherein at least some of the other optical channels of the plurality of optical channels have focus distances at least 10 meters greater than the focus distance of the second optical channel.

Example 40: The IR imaging system of any one of Examples 1 to 39, wherein at least some of the other optical channels of the plurality of optical channels have focus distances at least 20 meters greater than the focus distance of the second optical channel.

Example 41: The IR imaging system of any one of Examples 1 to 40, wherein the second optical channel out of the plurality of optical channels has a focus distance of 1 meter or less.

Example 42: The IR imaging system of any one of Examples 1 to 41, wherein the second optical channel out of the plurality of optical channels has a focus distance of 2 meter or less.

Example 43: The IR imaging system of any one of Examples 1 to 42, wherein the second optical channel and the other optical channels include imaging lenses for imaging objects onto the optical detector system, said imaging lenses having focal lengths.

Example 44: The IR imaging system of any one of Examples 1 to 43, wherein the focal lengths for lenses in the other optical channels exceed the focal length for the second optical channel.

Example 45: The IR imaging system of any one of Examples 1 to 44, wherein the focal lengths for lenses in the other optical channels exceed the focal length for the second optical channel by at least 2×.

Example 46: The IR imaging system of any one of Examples 1 to 45, wherein the focal lengths for lenses in the other optical channels exceed the focal length for the second optical channel by at least 5×.

Example 47: The IR imaging system of any one of Examples 1 to 46, wherein a second optical channel out of the plurality of optical channels is in focus at the optical window to detect whether the optical window is obscured.

Example 48: The IR imaging system of any one of Examples 1 to 47, wherein the second optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the second optical channel extends between a depth of the optical window and approximately 1 meter beyond the optical window.

Example 49: The IR imaging system of any one of Examples 1 to 48, wherein the second optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the second optical channel extends between a depth of the optical window and approximately 50 cm beyond the optical window.

Example 50: The IR imaging system of any one of Examples 1 to 49, wherein the second optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the second optical channel extends between a depth of the optical window and approximately 20 cm beyond the optical window.

Example 51: The IR imaging system of any one of Examples 1 to 50, wherein the second optical channel has a depth of field over which the optical channel is substantially in focus and wherein the depth of field of the second optical channel extends between a depth of the optical window and approximately 10 cm beyond the optical window.

Example 52: The IR imaging system of any one of Examples 1 to 51, wherein the processing unit is configured to process image data from the second optical channel to detect whether the optical window is obscured.

Example 53: The IR imaging system of any one of Examples 1 to 52, wherein the processing unit is configured to evaluate how much of the image data from the second optical channel is in focus to detect whether the optical window is obscured.

Example 54: The IR imaging system of any one of Examples 1 to 53, wherein the processing unit is configured to evaluate the contrast of the image data from the second optical channel to detect whether the optical window is obscured.

Example 55: The IR imaging system of any one of Examples 1 to 54, wherein the processing unit is configured to perform edge enhancement of the image data from the second optical channel.

Example 56: The IR imaging system of any one of Examples 1 to 55, wherein the processing unit is configured to perform edge detection of the image data from the second optical channel.

Example 57: The IR imaging system of any one of Examples 1 to 56, wherein the processing unit is configured to perform normalization of the image data from the second optical channel.

Example 58: The IR imaging system of any one of Examples 1 to 57, wherein the normalization of the image data comprises scaling the image data from the second optical channel.

Example 59: The IR imaging system of any one of Examples 1 to 58, wherein the normalization of the image data comprises subtracting from the image data from the second optical channel.

Example 60: The IR imaging system of any one of Examples 1 to 59, wherein the processing unit is configured to evaluate whether image data from the second optical channel exceeds a threshold to determine whether the optical window is obscured.

Example 61: The IR imaging system of any one of Examples 1 to 60, wherein a plurality of the optical channels are in focus at optical infinity to detect a target species.

Example 62: The IR imaging system of any one of Examples 1 to 61, wherein a plurality of the optical channels are in focus at a distance of at least 10 meters to detect a target species.

Example 63: The IR imaging system of any one of Examples 1 to 62, wherein a plurality of the optical channels are in focus at a distance of at least 20 meters to detect a target species.

Example 64: The IR imaging system of any one of Examples 1 to 63, wherein the processing unit is further configured to process image data from the plurality of optical channels to detect the target species.

Example 65: The IR imaging system of any one of Examples 1 to 64, wherein the optical detector system comprises a plurality of optical detectors, each of which is associated with a respective one of the optical channels.

Example 66: The IR imaging system of any one of Examples 1 to 65, wherein the optical detector system comprises at least one optical detector having a plurality of regions, each of the regions being associated with a respective one of the optical channels.

Example 67: The IR imaging system of any one of Examples 1 to 66, wherein:a second optical channel out of the plurality of optical channels is in focus at the optical window; andthe processing unit is configured to process image data from the first and second optical channels to detect whether the optical window is obscured.

Example 68: The IR imaging system of any one of Examples 1 to 67, wherein the processing unit is configured to:compare image data from the first and second optical channels to detect whether the optical window is obscured.

Example 69: The IR imaging system of any one of Examples 1 to 68, wherein comparing the first and second images comprises comparing the first and second images and using differences between the first and second images caused by parallax to determine whether the optical window is obscured.

Example 70: The IR imaging system of any one of Examples 1 to 69, wherein comparing the first and second images comprises performing a correlation of the first and second images.

Example 71: The IR imaging system of any one of Examples 1 to 70, wherein the first and second optical channels are spatially distinct in a given direction and wherein processing unit is configured to:comparing image data from the first and second optical channels at a plurality of offsets along the given direction to detect whether the optical window is obscured.

Example 72: The IR imaging system of any one of Examples 1 to 71, wherein the processing unit is configured to enhance edges in the image data from the two optical channels.

Example 73: The IR imaging system of any one of Examples 1 to 72, wherein the processing unit is configured to apply an unsharp mask to the image data from the two optical channels.

Example 74: The IR imaging system of any one of Examples 1 to 73, wherein the processing unit is configured to subtract at least one reference image from the image data from the two optical channels.

Example 75: The IR imaging system of any one of Examples 1 to 74, wherein the processing unit is configured to detect edges in the image data from the two optical channels.

Example 76: The IR imaging system of any one of Examples 1 to 75, wherein the processing unit is configured to apply an edge detection mask to the image data from the two optical channels.

Example 77: The IR imaging system of any one of Examples 1 to 76, wherein the processing unit is configured to apply Sobel filter to the image data from the two optical channels.

Example 78: The IR imaging system of any one of Examples 1 to 77, wherein the processing unit is configured to apply Sobel filter to the image data from the two optical channels to create first and second gradient images.

Example 79: The IR imaging system of any one of Examples 1 to 78, wherein the processing unit is configured to normalize the first and second gradient images.

Example 80: The IR imaging system of any one of Examples 1 to 79, wherein the processing unit is configured to cross-correlate the first and second gradient images to detect whether the optical window is obscured.

Example 81: The IR imaging system of any one of Examples 1 to 80, wherein the window is embedded in the housing or is in an opening in the housing.

Example 82: The IR imaging system of any one of Examples 1 to 81, wherein the IR imaging system is configured to compensate for effects of attenuation due to the window being obscured.

Example 83: The IR imaging system of any one of Examples 1 to 82, wherein said IR imaging system is configured to perform spectral analysis on images to detect target species and is configured to compensate for effects of attenuation due to the window being obscured on said spectral analysis.

Example 84: The IR imaging system of any one of Examples 1 to 83, wherein said IR imaging system is configured to perform spectral analysis on images to detect target species and is configured to deemphasize one or more frames of infrared image data from the other optical channels of the plurality of optical channels in the determination of the presence of a target species.

Example 85: An example of an infrared (IR) imaging system for imaging a target species in a scene, the IR imaging system comprising:an optical window;a first camera system configured to acquire infrared image data of the scene through the optical window;a second camera system focused closer to the optical window than the first camera system; anda processing unit containing a processor configured to:analyze the infrared image data from the first camera system to detect the target species based on the infrared image data; andanalyze image data from the second camera system to determine that the optical window is obscured based on the image data from the second camera system.

Example 86: The IR imaging system of Example 85, wherein the first and second camera system comprise first and second optical channels that are spatially and spectrally distinct.

Example 87: The IR imaging system of any one of Examples 85 to 86, wherein said processing unit is configured to provide a window obscuration alert after determining that the optical window is obscured.

Example 88: The IR imaging system of any one of Examples 85 to 87, wherein the processing unit is configured to receive the window obscuration alert and, in response, to adjust the infrared image data from the first camera system in compensation for the obscuration of the optical window.

Example 89: The IR imaging system of any one of Examples 85 to 88, wherein the processing unit is configured to receive the window obscuration alert and, in response, to disable analysis of the infrared image data from the first camera system.

Example 90: The IR imaging system of any one of Examples 85 to 89, wherein the processing unit is configured to receive the window obscuration alert and, in response, deemphasize one or more frames of infrared image data from the first camera system in the determination of the presence of a target species.

Example 91: The IR imaging system of any one of Examples 85 to 90, wherein the IR imaging system is configured to compensate for effects of attenuation due to the window being obscured.

Example 92: The IR imaging system of any one of Examples 85 to 91, wherein said IR imaging system is configured to perform spectral analysis on images to detect target species and is configured to compensate for effects of attenuation due to the window being obscured on said spectral analysis.

Example 93: The IR imaging system of any one of Examples 85 to 92, wherein the processing unit is configured to provide the window obscuration alert to a user.

Example 94: The IR imaging system of any one of Examples 85 to 93, wherein the IR imaging system further comprises:an optical focal plane array (FPA) divided into portions; anda plurality of lens assemblies, each lens assembly configured to focus light from the scene onto a different one of the portions of the FPA.

Example 95: The IR imaging system of any one of Examples 85 to 94, wherein:the first camera system is formed from a plurality of the lens assemblies and a plurality of the portions of the FPA; andthe second camera system is formed from one of the lens assemblies and one of the portions of the FPA.

Example 96: The IR imaging system of any one of Examples 85 to 95, wherein:the first camera system is formed from a plurality of the lens assemblies and a plurality of the portions of the FPA; andthe second camera system is formed from two of the lens assemblies and two of the portions of the FPA.

Example 97: The IR imaging system of any one of Examples 85 to 96, wherein:the first camera system is formed from a plurality of the lens assemblies and a plurality of the portions of the FPA; andthe second camera system is formed from two of the lens assemblies and two of the portions of the FPA, wherein the two lens assemblies and the two portions of the FPA that form the second camera system comprise adjacent lens assemblies and adjacent portions of the FPA.

Example 98: The IR imaging system of any one of Examples 85 to 97, wherein the IR imaging system further comprises:a plurality of optical focal plane arrays (FPA); anda plurality of lenses, different lenses configured to focus light from the scene onto a different ones of FPAs.

Example 99: The IR imaging system of any one of Examples 85 to 98, wherein the IR imaging system further comprises:a plurality of optical focal plane arrays (FPA); anda plurality of lens assemblies, different lens assemblies configured to focus light from the scene onto a different ones of FPAs.

Example 100: The IR imaging system of any one of Examples 85 to 99, wherein the processing unit is configured to evaluate how much of the image data is in focus to detect whether the optical window is obscured.

Example 101: The IR imaging system of any one of Examples 85 to 100, wherein the processing unit is configured to evaluate the contrast of the image data to detect whether the optical window is obscured.

Example 102: The IR imaging system of any one of Examples 85 to 101, wherein the processing unit is configured to perform edge enhancement of the image data.

Example 103: The IR imaging system of any one of Examples 85 to 102, wherein the processing unit is configured to perform edge detection of the image data.

Example 104: The IR imaging system of any one of Examples 85 to 103, wherein the processing unit is configured to perform normalization of the image data.

Example 105: The IR imaging system of any one of Examples 85 to 104, wherein the normalization of the image data comprises scaling the image data.

Example 106: The IR imaging system of any one of Examples 85 to 105, wherein the normalization of the image data comprises subtracting from the image data.

Example 107: The IR imaging system of any one of Examples 85 to 106, wherein the processing unit is configured to evaluate whether image data exceeds a threshold to determine whether the optical window is obscured.

Example 108: The IR imaging system of any one of Examples 85 to 107, wherein analyzing image data from the second camera system comprises:analyzing image data from first and second optical channels of the second camera system to detect whether the optical window is obscured.

Example 109: The IR imaging system of any one of Examples 85 to 108, wherein the processing unit is configured to:compare image data from the first and second optical channels to detect whether the optical window is obscured.

Example 110: The IR imaging system of any one of Examples 85 to 109, wherein comparing the first and second images comprises comparing the first and second images and using differences between the first and second images caused by parallax to determine whether the optical window is obscured.

Example 111: The IR imaging system of any one of Examples 85 to 110, wherein comparing the first and second images comprises performing a correlation of the first and second images.

Example 112: The IR imaging system of any one of Examples 85 to 111, wherein the first and second optical channels are spatially distinct in a given direction and wherein processing unit is configured to:comparing image data from the first and second optical channels at a plurality of offsets along the given direction to detect whether the optical window is obscured.

Example 113: The IR imaging system of any one of Examples 85 to 112, wherein the processing unit is configured to enhance edges in the image data from the first and second optical channels.

Example 114: The IR imaging system of any one of Examples 85 to 113, wherein the processing unit is configured to subtract at least one reference image from the image data from the first and second optical channels.

Example 115: The IR imaging system of any one of Examples 85 to 114, wherein the processing unit is configured to detect edges in the image data from the first and second optical channels.

Example 116: The IR imaging system of any one of Examples 85 to 115, wherein the processing unit is configured to apply an edge detection mask to the image data from the first and second optical channels.

Example 117: The IR imaging system of any one of Examples 85 to 116, wherein the processing unit containing the processor is configured to determine that the optical window is obscured based on the image data from the second camera system by:receiving a first image from a first portion of the FPA;receiving a second image from a second portion of the FPA;transforming the first and second images into respective first and second gradient images;determining that the gradient images have gradient values that exceed a first predetermined threshold;providing the window obscuration alert after determining that the gradient values exceed the first predetermined threshold.

Example 118: The IR imaging system of any one of Examples 85 to 117, wherein the processing unit containing the processor is configured to determine that the optical window is obscured based on the image data from the second camera system by:receiving a first image from a first portion of the FPA;receiving a second image from a second portion of the FPA;transforming the first and second images into respective first and second gradient images;determining that the first and second gradient images have a cross-correlation value that exceeds a first predetermined threshold; andproviding the window obscuration alert after determining that the cross-correlation value exceeds the first predetermined threshold.

Example 119: The IR imaging system of any one of Examples 85 to 118, wherein the processing unit containing the processor is configured to determine that the optical window is obscured based on the image data from the second camera system by:receiving a first image from a first portion of the FPA;receiving a second image from a second portion of the FPA;transforming the first and second images into respective first and second gradient images;determining that the gradient images have gradient values that exceed a first predetermined threshold;cross-correlating the first and second gradient images;determining that the first and second gradient images have a cross-correlation value that exceeds a second predetermined threshold; andproviding the window obscuration alert after determining that the gradient values exceed the first predetermined threshold and the cross-correlation value exceeds the second predetermined threshold.

Example 120: The IR imaging system of any one of Examples 85 to 119, wherein:determining that the first and second gradient images have a cross-correlation value that exceeds a second predetermined threshold comprises:determining a plurality of cross-correlation values, each being associated with a different alignment of the first and second gradient images; anddetermining that at least one cross-correlation value in the plurality of cross-correlation values exceeds the second predetermined threshold.

Example 121: The IR imaging system of any one of Examples 85 to 120, wherein:determining that the first and second gradient images have a cross-correlation value that exceeds a second predetermined threshold comprises:determining a plurality of cross-correlation values, each being associated with a different alignment of the first and second gradient images;identifying a first cross-correlation value in the plurality of cross-correlation values;subtracting the first cross-correlation value from each of the cross-correlation values in the plurality of cross-correlation values;after subtracting the first cross-correlation value, identifying a second cross-correlation value in the plurality of cross-correlation values; anddetermining that the second cross-correlation value exceeds the second predetermined threshold.

Example 122: The IR imaging system of any one of Examples 85 to 121, wherein transforming the first and second images into respective first and second gradient images comprises applying a Sobel filter to the first and second images.

Example 123: The IR imaging system of any one of Examples 85 to 122, wherein transforming the first and second images into respective first and second gradient images comprises applying a Sobel filter to the first and second images and removing values from the gradient images that fall below a predetermined threshold.

Example 124: The IR imaging system of any one of Examples 85 to 123, wherein, prior to cross-correlating the first and second gradient images, the processing unit is configured to normalize each of the gradient images.

Example 125: The IR imaging system of any one of Examples 85 to 124, wherein, prior to cross-correlating the first and second gradient images, the processing unit is configured to normalize each of the gradient images by, for each gradient image, subtracting a median value from each gradient image and dividing each gradient image by a standard deviation value.

Example 126: The IR imaging system of any one of Examples 85 to 125, wherein, prior to cross-correlating the first and second gradient images, the processing unit is configured to normalize each of the gradient images.

Example 127: The IR imaging system of any one of Examples 85 to 126, wherein, prior to transforming the first and second images into respective first and second gradient images, the processing unit is configured to subtract a first reference image from the first image and subtract a second reference image from the second image.

Example 128: The IR imaging system of any one of Examples 85 to 127, wherein the second camera system is focused within 1 meter of the optical window.

Example 129: The IR imaging system of any one of Examples 85 to 128, wherein the second camera system is focused within 2 meters of the optical window.

Example 130: The IR imaging system of any one of Examples 85 to 129, wherein the second camera system is focused on the optical window.

Example 131: The IR imaging system of any one of Examples 85 to 130, wherein the first camera system is focused at a distance of at least 10 meters.

Example 132: The IR imaging system of any one of Examples 85 to 131, wherein the first camera system is focused at a distance of at least 20 meters.

Example 133: The IR imaging system of any one of Examples 85 to 132, wherein the first camera system is focused at a distance of at least 25 meters.

Example 134: The IR imaging system of any one of Examples 85 to 133, wherein the first and second camera systems have respective imaging lenses having respective focal lengths, and the focal length for the first camera is 2 times as large as the focal length for the second camera.

Example 135: The IR imaging system of any one of Examples 85 to 134, wherein the first and second camera systems have respective imaging lenses having respective focal lengths, and the focal length for the first camera is 5 times as large as the focal length for the second camera.

Example 136: An example of a method of detecting whether an optical window in an IR imaging system is obscured, the IR imaging system comprising processing circuitry and a plurality of spatially and spectrally distinct optical channels, each optical channel including a set of lenses that focus incident IR light on a respective portion of an optical detector system, the method comprising:with the processing circuitry, receiving a first image from a first optical channel in the plurality of optical channels;with the processing circuitry, receiving a second image from a second optical channel in the plurality of optical channels; andwith the processing circuitry, analyzing the first and second images to detect whether the optical window is obscured.

Example 137: The method of Example 136, wherein the first and second images are in focus at the depth of the optical window.

Example 138: The method of any one of Examples 136 to 137, wherein analyzing the first and second images comprises, with the processing circuitry, comparing the first and second images to identify whether the optical window is obscured.

Example 139: The method of any one of Examples 136 to 138, wherein analyzing the first and second images comprises, with the processing circuitry, comparing the first and second images and using differences between the first and second images caused by parallax to determine whether the optical window is obscured.

Example 140: The method of any one of Examples 136 to 139, wherein analyzing the first and second images comprises evaluating how much of the images are in focus to detect whether the optical window is obscured.

Example 141: The method of any one of Examples 136 to 140, wherein analyzing the first and second images comprises evaluating the contrast of the images to detect whether the optical window is obscured.

Example 142: The method of any one of Examples 136 to 141, further comprising performing edge enhancement.

Example 143: The method of any one of Examples 136 to 142, further comprising performing edge detection.

Example 144: The method of any one of Examples 136 to 143, further comprising normalizing image data.

Example 145: The method of any one of Examples 136 to 144, wherein the normalizing comprises scaling image data.

Example 146: The method of any one of Examples 136 to 145, wherein the normalizing comprises subtracting from image data.

Example 147: The method of any one of Examples 136 to 146, wherein analyzing the first and second images comprises performing a correlation of the first and second images.

Example 148: The method of any one of Examples 136 to 147, wherein analyzing the first and second images comprises comparing image data from the first and second images at a plurality of offsets along the given direction to detect whether the optical window is obscured.

Example 149: The method of any one of Examples 136 to 148, wherein analyzing the first and second images comprises evaluating whether image data exceeds a threshold to determine whether the optical window is obscured.

Example 150: The method of any one of Examples 136 to 149, wherein analyzing the first and second images comprises, with the processing circuitry, applying an unsharp mask to the first and second images.

Example 151: The method of any one of Examples 136 to 150, further comprising:with the processing circuitry, subtracting a first reference image from the first image and subtracting a second reference image from the second image.

Example 152: The method of any one of Examples 136 to 151, further comprising:with the processing circuitry, detecting edges in the first and second images.

Example 153: The method of any one of Examples 136 to 152, further comprising:with the processing circuitry, applying a Sobel filter to the first and second images.

Example 154: The method of any one of Examples 136 to 153, further comprising:with the processing circuitry, applying a Sobel filter to the first and second images to create respective first and second gradient images.

Example 155: The method of any one of Examples 136 to 154, further comprising:with the processing circuitry, normalizing the first and second gradient images.

Example 156: The method of any one of Examples 136 to 155, further comprising:with the processing circuitry, cross-correlating the first and second gradient images.

Example 157: The method of any one of Examples 136 to 156, further comprising:with the processing circuitry, determining that at least one cross-correlation between the first and second gradient images exceeds a first window obscuration threshold and that the first and second gradient images exceed a second window obscuration threshold and, in response, providing an alert that the optical window is obscured.

Example 158: The method of any one of Examples 136 to 157, further comprising detecting a target species based on image data from said plurality of spatially and spectrally distinct optical channels.

Example 159: The method of any one of Examples 136 to 158, further comprising performing spectral analysis to detect said target species.

Example 160: The method of any one of Examples 136 to 159, further comprising adjusting image data from the plurality of optical channels to compensate for effects of attenuation due to the window being obscured.

Example 161: The method of any one of Examples 136 to 160, further comprising de-emphasizing one or more frames of image data from the plurality of optical channels in the determination of the presence of a target species.

Example 162: The method of any one of Examples 136 to 161, further comprising sending an alert when the window is obscured.

Any of Examples 1 to 162 can include any of the features described above (for example, any of the features in Examples 1 to 162).

Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.

