UVB-visible channel apparatus and method for viewing a scene comprising terrestrial corona radiation

• US 8,781,158 B1
• Filed: 01/10/2014
• Issued: 07/15/2014
• Est. Priority Date: 01/10/2014
• Status: Active Grant

• Current Assignee: OFIL Limited
• Original Assignee: OFIL Limited
• Inventors: Frisch, Eran, Koslovsky, Odelya, Haavrahami, Reuel
• Primary Examiner(s): SHAH, UTPAL D
• Application Number:
  US14/151,885
• Time in Patent Office: 186 Days
• Field of Search: 382/100, 382/224, 382/284, 250/226, 359/350, 359/885
• US Class Current: 382/100
• CPC Class Codes: G02B 5/208 for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation
• CPC Class Codes: H04N 23/11 for generating image signals from visible and infrared light wavelengths

Abstract

A UVB-visible hybrid system and method for visualizing a scene comprising one of more terrestrial corona discharge(s) and one or more objects is disclosed. On the UVB channel, an object-devoid UVB image of at least a portion of the scene is generated using UVB light which passes though a corona-peak tuned optical filter configured to filter out sufficient non-terrestrial-corona light so that the generated UVB image is object-devoid. The object-devoid UVB image is analyzed to classify pixels thereof as corona-discharge pixels or non-corona-discharge pixels. When a derivative of the object-devoid UVB image superposed with a visible-band image of the scene is displayed on a display device, the pixels classified as corona-discharge are displayed at increased visibility, while the pixels classified as corona-discharge are displayed at decreased visibility. In some embodiments, the optical filter has an average optical density over the [290 nm, 700 nm] spectrum of at least 4.

Claims

1. A system for visualizing a scene comprising one of more terrestrial corona discharge(s) and one or more objects, the scene illuminated by non-terrestrial-corona-discharge radiation, the system comprising:

a. Ultraviolet B (UVB) image-generating apparatus configured to generate, from UVB light of the non-terrestrial-corona-discharge-radiation-illuminated scene, an object-devoid UVB image of at least an object-containing portion of the scene, the object-devoid UVB image comprising an image of the corona discharge(s) of the scene and lacking images of all of the scene objects, the UVB image-generating apparatus comprising a wavelength-dependent light filter configured to filter out sufficient non-corona UVB radiation so that generated image is object-devoid, the wavelength-dependent light filter having an optical-density OD(λ

) profile that satisfies the following conditions;

i. an average value of min [OD(λ

),10] over the range [280 nm, 700 nm] is at least x, a value of x being at least 4;

ii. for at least one wavelength in at least one range selected from the UVB corona-peak range set defined as {[281 nm, 285 nm], [292 nm, 302 nm], [308 nm, 320 nm], [334 nm, 340 nm], [351 nm, 362 nm]}, optical density OD of the filter is at most 1;

b. UVB image-processing apparatus operative to classify each pixel of the object-devoid UVB image as either a corona-discharge pixel or as a non-corona-discharge pixel and to process the object-devoid image according to the results of the pixel-classifying to generate a UVB processed image;

c. a visible-band image-generating apparatus configured to generate a visible-band image from visible light of the scene; and

d. video-display apparatus configured to display a visible band-UVB hybrid image that is a superposition of;

(i) the visible-band image or a derivative thereof; and

(ii) the UVB processed image or a derivative thereof, the UVB image-processing apparatus configured to perform the image processing so as to increase a visibility of the corona-discharge pixels and/or to decrease a visibility of the non-corona-discharge pixels.

2. The system of claim 1 wherein the UVB image-processing apparatus is configured to respond to a change in an estimated ambient level of non-corona-discharge UVB radiation by modifying a corona-discharge-classification-threshold-function of the pixels to increase the threshold-function in response to an increase in the estimated ambient level and to decrease the threshold-function in response to an estimated decrease in the ambient level.

3. The system of claim 2, configured obtain the estimated intensity of ambient non-corona-discharge UVB radiation in accordance with at least one of:

(i) an auxiliary photodetector;

(ii) location data;

(iii) time-of-day; and

(iv) weather data.

4. The system of claim 2, configured estimate the ambient level of non-corona-discharge UVB radiation by analyses of the object-devoid UVB image.

5. The system of claim 1 wherein the pixel classification is performed in accordance with detected temporal variations in the object-devoid UVB image.

6. The system of claim 1 wherein the pixel classification of a target pixel is performed in accordance with analysis of neighboring pixels.

7. The system of claim 1 wherein the pixel classification of a target pixel is performed in accordance with a brightness-thresholding algorithm.

8. The system of claim 1 wherein a value of x is at least 6.

9. The system of claim 1 wherein a value of x is at least 8.

10. The system of claim 1 wherein for at least 5 nm of wavelength over the UVB corona-peak range set, an optical density OD of the filter is at most 1.

11. The system of claim 1 wherein an average value of min [OD(λ

),10] over the range [400 nm, 700 nm] is at least y, a value of y being at least 4.

12. The system of claim 1 wherein an average value of min [OD(λ

),10] over the range [280 nm, 400 nm] is at least z, a value of z being at least 4.

13. The system of claim 1 configured to perform the image processing so as to increase a visibility of the corona-discharge pixels.

14. The system of claim 1 configured to perform the image processing so as to decrease a visibility of the non-corona-discharge pixels.

15. The system of claim 1 configured to perform the image processing so as to increase a visibility of the corona-discharge pixels and to decrease a visibility of the non-corona-discharge pixels.