THERMAL IMAGING INCLUDING AN EXTENDED SHORT WAVE INFRARED LIGHT SOURCE TO IDENTIFY AN OBJECT

An infrared imaging system includes a detector configured to detect wavelengths in a first infrared wavelength band and a second infrared wavelength band, shorter than the first infrared wavelength band, a light source configured to output light in the second infrared wavelength band to an object, and an identify circuit configured to identify the object based on spectral characteristics of light returned from the object detected by the detector. The second infrared wavelength band is an extended short wavelength infrared band.

BACKGROUND

Field

The present disclosure relates to imaging in using a specific wavelength in the extended short wave infrared band and identify the object based on optical characteristics from being illuminated by the extended short wave infrared band.

Description of the Related Art

Different infrared wavelength bands are used for different purposes. For example, infrared detectors include those for a near infrared (NIR) wavelength band (0.75 μm to 1.4 μm), for a short wavelength infrared (SWIR) wavelength band (1.4 to 3 μm), for a mid wavelength infrared (MWIR) wavelength band (3.0 to 5.0 μm) is, and for a long wavelength infrared (LWIR) wavelength band (8.0 to 12 μm) is. Typically, SWIR imaging systems image in the wavelength band of 1.4 to 2.0 μm and extended SWIR (eSWIR) imaging systems image in the wavelength band of 2.0 to 3.0 μm. In general, infrared imaging up to 2.5 μm images reflected light from an object and infrared imaging above 3.0 μm images emitted light from an object.

SUMMARY

One or more embodiments is directed to an infrared imaging system, including a detector configured to detect wavelengths in a first infrared wavelength band and a second infrared wavelength band, shorter than the first infrared wavelength band, wherein the second infrared wavelength band is an extended short wavelength infrared band, a light source configured to output light in the second infrared wavelength band to an object, and an identify circuit configured to identify the object based on spectral characteristics of light returned from the object detected by the detector.

One or more embodiments is directed to a method of detecting an infrared image, including providing a detector for detecting a thermal image of an object, the detector configured to detect wavelengths in a first infrared wavelength band, the detector having a field of view, illuminating at least a portion of the object with a second infrared wavelength band, shorter than the first infrared wavelength band, and identifying the object based on spectral characteristics of light returned from the object detected by the detector.

The scope of the present disclosure is best understood from the following detailed description of exemplary embodiments when read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

Analyzing reflected illumination for MWIR or LWIR imaging to identify an object is typically not effective, given the poor reflectance at these wavelengths. However, in accordance with embodiments, by using a camera that can detect in both the MWIR or LWIR and the eSWIR wavelength bands, identifying an object based on reflection at a specific wavelength of the eSWIR wavelength band may be used to identify objects imaged using higher wavelength band systems may be realized. In other words, an imaging system according to embodiments may be used to image both emissive heat and reflected light. Additionally, as disclosed in U.S. application Ser. No. 18/600,232, filed Mar. 8, 2024, and entitled “THERMAL IMAGING INCLUDING AN EXTENDED SHORT WAVE INFRARED LIGHT SOURCE,” incorporated herein by reference for all purposes, the eSWIR may be used generally to target the object as well as using a specific wavelength of the eSWIR to identify the object.

Thus, one or more embodiments are directed to detecting a specific wavelength that can be reflected by the object, that is readable by thermal imaging systems having a particular spectral response, but not readily detected by other thermal imaging systems and is outside the spectral region to be used to detect the thermal image, and identifying the object based on an intensity of the specific wavelength or spectral characteristics (spectra) of specific light reflected by the object. Other embodiments are directed to identifying an object based on absorption of the eSWIR that increases the emissive heat emitted therefrom. Finally, other embodiments are directed to using either identification technique and further illuminating the object to increase the emissive heat emitted therefrom.

As shown inFIG.1, an imaging system100according to an embodiment includes a camera system110having broadband thermal camera20for detection in the LWIR (and/or MWIR) and eSWIR range and a light source30that emits light in the eSWIR range. As a particular example of such a broadband thermal camera20includes an uncooled LWIR bolometer manufactured by LightPath Technologies®, e.g., the Multispectral Infrared Camera MANTIS™.

An identify circuit25for determining whether an amount of light reflected by an object in a particular portion of the eSWIR range exceeds a threshold and identify or classify the object based on whether the threshold is exceeded or not. In particular, if the threshold is exceeded, the object is identified. Details of such detection are disclosed, e.g., in Wiley, L. et al., “Target discrimination in the extended SWIR (eSWIR) band (2-2.5 μm) compared to Vis, NIR, and SWIR in degraded visual environments” Proc. SPIE 12106, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing XXXIII, 1210606 (27 May 2022).

In particular, in order to identify a friend or one's own objects, these objects may have at least a portion thereof painted with a paint that has a distinctive spectral signature. By utilizing the infrared, and specifically the region of the infrared not commonly used (2-3 um), that adversaries would not use and such painting would not be apparent from visual inspection of the objects.

Alternatively or additionally, friendly objects, e.g., vehicles, soldiers and devices, may be provided with reflectors that reflect only a very specific wavelength, e.g., 2.7 um, that is not conventionally imaged, but that can be imaged with a camera that is specifically sensitive to that wavelength. By having a selective reflector such as a retroreflector cube, or array of such corner cubes, one can use a laser at that exact wavelength and scan an area looking for that exact reflection, in order to identify a friendly object.

A control circuit35for controlling the light source may be used to control illumination of light output by the light source30to illuminate a portion of an object to be imaged by the camera20. The control circuit35may scan the light output by the light source30to illuminate an entirety of a field of view of the camera20or may scan the light output by the light source30to illuminate subsets of the object sequentially. Alternatively or additionally, the control circuit35may control scanning based on a position of the object. Alternatively or additionally, the control circuit35may control a wavelength to be output by the light source30and/or an intensity to be output by the light source30to pulse the light output by the light source30. The control circuit may also be in communication with the camera20to synchronize detection of the light with the output of the light source30. The control circuit35may be provided in the housing40, incorporated with the thermal camera20, or remote therefrom but in communication with the light source30and/or the camera20.

The imaging system100illustrates that the camera20and the light source30may be integrated in a single housing40. Alternatively, as shown inFIG.2, an imaging system100amay include the light source30in a separate housing50from the thermal camera20and may include additional optics60to generate a holographic image to be reflected from an object. For example, the optics60may include a first mirror62to direct light from the light source30to a collimating reflector64, which collimates light onto a holographic grating66, which reflects light onto a reticle image hologram68to output the holographic images. The optics60may also be included in the housing40. Such holographic sights are known, e.g., in U.S. Pat. No. 6,490,060 B1, which is hereby incorporated by reference in its entirety for all purposes. Again, the control circuit35may be provided in the housing50, incorporated with the thermal camera20, or remote therefrom, but in communication with, the light source30.

When serving as a sight, e.g., on a gun, the light source30is collimated and aligned together with the camera20so that the light source can be used to target the gun, while seeing the laser spot reflected together with the thermal image. An example of using either configuration is shown inFIG.3. As may be seen therein, the imaging system100(or100a) illuminates an object with eSWIR illumination output from the light source30, as indicated by the solid line. This eSWIR illumination is reflected by the object back to the imaging system100, as indicated by the dashed line. The imaging system100also images the thermal image from the object, as indicated by the wavy lines. Thus, the reflection from an object may serve both as a sight and, based on an intensity of light or spectra of specific light received by the camera, to identify the object.

The exact wavelength to be output by the light source30depends on the spectral response of the camera20. For example, the Multispectral Infrared Camera MANTIS™ has a spectral response as shown inFIG.4. As may be seen therein, in the eSWIR region, this particular camera has a peak response around 2.3 μm. Response shown inFIG.4is a typical spectral response, however, peak wavelengths may vary +/−0.5 μm. Therefore, a light source30outputting this wavelength may be used in conjunction with this particular camera20. The light source30may be a gallium antimonide (GaSb) laser. Alternatively or additionally, the light source30may be a high-power light source emitting light in the range of 2-3 um to illuminate the environment surrounding the object such that a dual band or multispectral detector can image both the light reflected from the surrounding environment and the thermal image.

As may be seen inFIG.5, when such a laser is used as the light source30with this particular camera20, the camera20may detect both a thermal image and the reflected light at the same time. The reflected light may be used both as a sight and to identify the object.

Alternatively, if the friendly object includes at least a portion thereof that absorbs highly in the eSWIR, the increased emittance from the object may be used to identify the object. Thus, the reflected light may still be used for targeting and an increase in emittance may be used to identify the object.

Thus, instead of relying on the reflective characteristics of a material to identify an object, the object may be made of a material or including a portion that absorbs the eSWIR light This is in particular the case with some plastics, illumination from the light source, e.g., a pulsed laser, at a wavelength of 2 um or 2.3 um (or other wavelengths in the eSWIR range) gets absorbed by the plastic, heating it up to increase the thermal radiation emitted therefrom, sometimes within seconds. Thus, a thermal imaging camera20can better image the object as well as identify the object as friendly when in absorbs such illumination.

With this method, by heating up or marking an object that otherwise might not be generating enough heat to be detected by the thermal camera30, allows existing other thermal cameras that are limited to the detection of standard LWIR and\or MWIR wavebands, to better image an object that otherwise might not be hot enough to be imaged.

In yet another embodiment, an imaging system200includes a camera system210including the thermal camera20and the identify circuit25, without the light source30and the control circuit35, and a light source130that are not at a same location as each other or as an object. As may be seen inFIG.6, again, instead of light source being on camera system210, the light source130is incorporated in or attached to a device310, e.g., a device worn by or carried by a person, a vehicle, e.g., an unmanned aerial vehicle, and so forth, different from the object, to serve as a laser designator to illuminate the object. In other words, the light source130is at a location separate from both the camera20and the object, e.g., a person may illuminate the object for detection by a thermal camera remote from the person, e.g., in a vehicle or used by another person, or the light source may be in a vehicle to light up the object for the detection by one or more thermal cameras not on the vehicle.

In another embodiment, the illumination system may include two light sources, co-aligned, output from a common aperture. For example, a first light source, e.g., a 2-2.5 um laser, may be used to identify a reflective sample, while a high-power laser in another wavelength (such as a CO2 laser at 10.6 μm), is used to heat up the object, so that a standard thermal camera can better image the object. This method allows to heat up an object that is reflective in the range of the first laser, but absorbs the wavelength of the second laser. As may be seen inFIG.7, an imaging system300includes a camera system310, which includes the thermal camera20, the identify circuit25, the first light source30, the control circuit35, and a second light source70. The second light source70may output illumination in response to the identify circuit25identifying the object.

In yet another embodiment, as shown inFIG.8, an imaging system400may include the first and/or second light source may be in a device410remote from the camera system and the object. In the imaging system400, a camera system410includes the thermal camera20and the identify circuit25, without the light source30and the control circuit35, and/or without the second light source70. A device510includes a first light source130and/or a second light source170. When the device510includes the second light source170, a communication link between the identify circuit25in the camera system410and the device510is provided to control the second light source170.

The present disclosure is not limited to only the above-described embodiments, which are merely exemplary. It will be appreciated by those skilled in the art that the disclosed systems and/or methods can be embodied in other specific forms without departing from the spirit of the disclosure or essential characteristics thereof. In some instances, as would be apparent to one of skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise indicated. The presently disclosed embodiments are therefore considered to be illustrative and not restrictive. The disclosure is not exhaustive and should not be interpreted as limiting the claimed invention to the specific disclosed embodiments. In view of the present disclosure, one of skill in the art will understand that modifications and variations are possible in light of the above teachings or may be acquired from practicing of the disclosure. The scope of the invention is indicated by the appended claims, rather than the foregoing description.