Longwave infrared imaging of a high-temperature, high-intensity light source

• US 9,307,156 B1
• Filed: 12/19/2013
• Issued: 04/05/2016
• Est. Priority Date: 12/19/2013
• Status: Active Grant

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Sinfield, Matthew, Lueken, Dennis M., Setlik, Brian J.
• Primary Examiner(s): Bhuiyan, Fayez
• Application Number:
  US14/134,484
• Time in Patent Office: 838 Days
• Field of Search: 348/342
• US Class Current: 1/1
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/0018 Flames, plasma or welding
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/75 by influencing optical camera components
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A neutral density (ND) filter made of an LWIR-transmissive, heat-resistant material is interposed between a longwave infrared (LWIR) imager and an entity that is highly emanative of both light and heat. According to exemplary inventive practice, the ND filter is a thermoplastic (e.g., polystyrene) sheet characterized by a thickness in the 1-2 mm range and a thermal conductivity≦0.13 W/m-K. Important parameters of the ND filter include LWIR transmittance (which depends on material and thickness) and thermal conductivity (which depends on material). The quality of the image taken of the entity is affected by the respective degrees of LWIR attenuation by, and heating up of, the ND filter. Accordingly, the material and the thickness of the ND filter are selected to optimize the image, in particular so as to avoid saturation and/or whiting-out of the image due to insufficient LWIR attenuation and/or excessive ND filter temperature.

Claims

1. An imaging method comprising:

providing an imager operable in the longwave infrared spectral region of electromagnetic radiation;

providing a neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat;

positioning said neutral density filter between said imager and an entity emanating electromagnetic radiation and heat;

imaging said entity, said imaging including using said imager and said neutral density filter, wherein said neutral density filter attenuates longwave infrared radiation emanating from said entity, said neutral density filter resists heat emanating from said entity, and said imager receives longwave infrared radiation attenuated by said neutral density filter;

wherein said neutral density filter is made of a material having a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K.

2. The imaging method of claim 1, wherein said neutral density filter is made of a thermoplastic.

3. The imaging method of claim 2, wherein said thermoplastic is polystyrene.

4. An imaging method comprising:

providing an imager operable in the longwave infrared spectral region of electromagnetic radiation;

providing a neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat;

positioning said neutral density filter between said imager and an entity emanating electromagnetic radiation and heat;

imaging said entity, said imaging including using said imager and said neutral density filter, wherein said neutral density filter attenuates longwave infrared radiation emanating from said entity, said neutral density filter resists heat emanating from said entity, and said imager receives longwave infrared radiation attenuated by said neutral density filter;

wherein said neutral density filter is made of a thermoplastic and is characterized by at least one of;

a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K;

a thickness in the range of 1 to 2 millimeters.

5. The imaging method of claim 4, wherein said neutral density filter is characterized by said thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K, and by said thickness in the range of 1 to 2 millimeters.

6. An imaging method comprising:

providing an imager operable in the longwave infrared spectral region of electromagnetic radiation;

providing a neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat;

positioning said neutral density filter between said imager and an entity emanating electromagnetic radiation and heat;

imaging said entity, said imaging including using said imager and said neutral density filter, wherein said neutral density filter attenuates longwave infrared radiation emanating from said entity, said neutral density filter resists heat emanating from said entity, and said imager receives longwave infrared radiation attenuated by said neutral density filter;

viewing an image obtained by said operating of said imager;

at least once, repeating performance of the steps of said providing of said neutral density filter, said positioning of said neutral density filter, said operating of said imager, and said viewing of said image obtained by said operating of said imager;

comparing the respective images obtained in the plural said performances of said steps;

wherein in each said performance of said steps, said neutral density filter is made of a thermoplastic having a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K.

7. An imaging method comprising:

providing an imager operable in the longwave infrared spectral region of electromagnetic radiation;

providing a neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat;

positioning said neutral density filter between said imager and an entity emanating electromagnetic radiation and heat;

imaging said entity, said imaging including using said imager and said neutral density filter, wherein said neutral density filter attenuates longwave infrared radiation emanating from said entity, said neutral density filter resists heat emanating from said entity, and said imager receives longwave infrared radiation attenuated by said neutral density filter;

viewing an image obtained by said operating of said imager;

at least once, repeating performance of the steps of said providing of said neutral density filter, said positioning of said neutral density filter, said operating of said imager, and said viewing of said image obtained by said operating of said imager;

comparing the respective images obtained in the plural said performances of said steps;

wherein in each said performance of said steps, said neutral density filter has a thickness in the range of 1 to 2 millimeters.

8. The imaging method of claim 7, wherein in each said performance of said steps, said neutral density filter is made of a thermoplastic having a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K.

9. An imaging method comprising:

providing an imager operable in the longwave infrared spectral region of electromagnetic radiation;

providing a neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat;

positioning said neutral density filter between said imager and an entity emanating electromagnetic radiation and heat;

imaging said entity, said imaging including using said imager and said neutral density filter, wherein said neutral density filter attenuates longwave infrared radiation emanating from said entity, said neutral density filter resists heat emanating from said entity, and said imager receives longwave infrared radiation attenuated by said neutral density filter;

viewing an image obtained by said operating of said imager;

at least once, repeating performance of the steps of said providing of said neutral density filter, said positioning of said neutral density filter, said operating of said imager, and said viewing of said image obtained by said operating of said imager;

comparing the respective images obtained in the plural said performances of said steps;

wherein said neutral density filter is characterized by a thickness and a material, and wherein in each said performance of said steps, said step of providing said neutral density filter includes providing a said neutral density filter that differs from said neutral density filter of at least one other said performance in terms of said material characterizing said neutral density filter, or said thickness characterizing said neutral density filter, or both said material and said thickness characterizing said neutral density filter;

wherein in each said performance of said steps, said material characterizing said neutral density filter is a thermoplastic having a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K.

10. An imaging method comprising:

providing an imager operable in the longwave infrared spectral region of electromagnetic radiation;

providing a neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat;

positioning said neutral density filter between said imager and an entity emanating electromagnetic radiation and heat;

imaging said entity, said imaging including using said imager and said neutral density filter, wherein said neutral density filter attenuates longwave infrared radiation emanating from said entity, said neutral density filter resists heat emanating from said entity, and said imager receives longwave infrared radiation attenuated by said neutral density filter;

viewing an image obtained by said operating of said imager;

at least once, repeating performance of the steps of said providing of said neutral density filter, said positioning of said neutral density filter, said operating of said imager, and said viewing of said image obtained by said operating of said imager;

comparing the respective images obtained in the plural said performances of said steps;

wherein said neutral density filter is characterized by a thickness and a material, and wherein in each said performance of said steps, said step of providing said neutral density filter includes providing a said neutral density filter that differs from said neutral density filter of at least one other said performance in terms of said material characterizing said neutral density filter, or said thickness characterizing said neutral density filter, or both said material and said thickness characterizing said neutral density filter;

wherein in each said performance of said steps, said thickness characterizing said neutral density filter is in the range of 1 to 2 millimeters.

11. The imaging method of claim 10, wherein in each said performance of said steps, said material characterizing said neutral density filter is a thermoplastic having a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K.

12. An imaging apparatus comprising a camera and a neutral density filter, said camera operable in the longwave infrared spectral region of electromagnetic radiation, said neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat, said neutral density filter positioned between said camera and said entity, wherein said imaging apparatus is capable of producing at least one image of an entity emanating electromagnetic radiation and heat, said neutral density filter attenuating longwave infrared radiation emanating from said entity and resisting heat emanating from said entity, said camera receiving longwave infrared radiation attenuated by said neutral density filter, wherein said neutral density filter is made of a material having a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K.

13. The imaging apparatus of claim 12 wherein said neutral density filter is made of a thermoplastic.

14. An imaging apparatus comprising a camera and a neutral density filter, said camera operable in the longwave infrared spectral region of electromagnetic radiation, said neutral density filter characterized by transmission of longwave infrared radiation and by resistance to heat, said neutral density filter positioned between said camera and said entity, wherein said imaging apparatus is capable of producing at least one image of an entity emanating electromagnetic radiation and heat, said neutral density filter attenuating longwave infrared radiation emanating from said entity and resisting heat emanating from said entity, said camera receiving longwave infrared radiation attenuated by said neutral density filter, wherein said neutral density filter has a thickness in the range of 1 to 2 millimeters.

15. The imaging apparatus of claim 14, wherein said neutral density filter is made of polystyrene.

16. The imaging apparatus of claim 14, wherein said neutral density filter is made of a material having a thermal conductivity of greater than zero W/m-K and less than or equal to 0.13 W/m-K.