Infrared laser illuminated imaging systems and methods

• US 7,541,588 B2
• Filed: 07/12/2005
• Issued: 06/02/2009
• Est. Priority Date: 07/12/2005
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Roberts, David E., Tabirian, Anna M., Thompson, Arthur B., Stanley, Douglas P., King, Carl S.
• Primary Examiner(s): Porta; David P
• Assistant Examiner(s): Malevic; Djura
• Application Number:
  US11/179,856
• Publication Number:
  US 20070221849A1
• Time in Patent Office: 1,421 Days
• Field of Search: 250/341.1, 356/4.01
• US Class Current: 250/341.1
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/486 Receivers

Abstract

Systems and methods for long range recognition and identification of objects and targets, and, more particularly, to long range imaging systems that include the use of mid-wave infrared laser illumination technology are provided. In particular, mid-wave infrared laser illuminated imaging systems and methods are disclosed for addressing, among other things, the problems associated with long range, day or night observations of targets through various obscurants (e.g., fog, haze, rain, smoke). Such systems may be configured to operate in either a single, active illumination mode or in a dual, active/passive mode.

Claims

1. A system for observing an object at an extended distance, the system comprising:

a range receiever for determining a distance to the object, wherein said range receiver comprises a mid-wave infrared detector configured to (a) measure a time-of-flight of one or more pulses occurring prior to collecting imaging data and provide updates to the measurement of distance during the collection of imaging data to dynamically adjust to changes in the distance to the object being imaged, (b) independently measure the distance to the object while imaging it and provide updates to the measurement of distance during the collection of imaging data dynamically adjust to changes in the distance to the object being imaged;

a laser for illuminating the object with a signal (a) from within a mid-wave infrared spectral region in a 3 to 5 micron wavelength range, (b) having wavelength outputs that match peaks of mid-infrared atmospheric transmission windows of 3 to 5 microns, (c) with high pulse energies that permit imaging at an extended distance; and

(d) that operates in Q-switched regime to provide high energy illumination pulses of short duration for gated imaging;

a mid-wave imaging camera, capable of operating in a dual-imaging mode, for collecting imaging data of the object in the mid-wave infrared spectral region in both a mid-wave infrared laser-illuminated imaging mode and a mid-wave infrared thermal imaging mode, wherein said mid-wave imaging camera is configured for;

in the mid-wave infrared laser-illuminated imaging mode, capturing imaging data during a time interval when signals emitted by said laser and reflected by the object are incident upon said camera based on the distance as determined by range receiver, and

in the mid-wave infrared thermal imaging mode, capturing mid-wave infrared thermal imaging data and detecting a thermal contrast of a target scene caused by differences in emissivity and temperature of objects of the target scene, and

a controller for coordinating operations associated with the laser, a sequencing of the laser output with the range receiver, the mid-wave imaging camera, an image processing module, and a display device, wherein the controller coordinates the operations of the mid-wave imaging camera to capture both (a) imaging data that is responsive to illumination of the object by the signals provided by laser in the mid-wave infrared laser-illuminated imaging mode of operation and (b) imaging data associated with the object in the mid-wave infrared thermal imaging mode of operation that is independent of illumination of the object by the signals provided by the laser in the mid-wave infrared laser-illuminated imaging mode of operation.

2. The system of claim 1, wherein said laser is at least one of a pulsed Ho:

BYF laser, or a pulsed Ho;

YLF laser, wherein said laser (a) has a wavelength output of about 3.9 microns that matches a highest tranmission in the mid-infrared atmospheric transmission window of 3 to 5 microns;

(b) produces high pulse energies that permit imaging at an extended distance; and

(c) operates in a Q-switched regime to provide high energy illumination pulses of short duration for gated imaging.

3. The system of claim 1, wherein said laser is at least one of a frequency doubled CO₂ laser or a Nd:

YAG laser in combination with a nonlinear crystal for shifting the wavelength of for shifting the wavelength of the output signal (a) with outputs that match peaks in the mid-infrared atmospheric transmission window of 4 to 5 microns and 3 to 4 microns respectively, and (b) produces high peak power illumination pulses that permit imaging at and extended distance.

4. The system of claim 1, wherein said camera is a gated InSb or HgCdTe camera having a focal plane array, with a readout integrated circuit capable of intergration times in low-gain mode for passive imaging that are longer than the intergration times in a high-gain mode for gated active imaging.

5. The system of claim 1, wherein said controller is capable comprises an interface and timing electronics that include pulse generators and digital delay timers configured for (a) coordinating a sequencing of the laser output with the range receiver and the gating of the mid-wave imaging camera to collect individual imaging frames, (b) providing dynamic adjustment of the range gate delay based on updated real-time target range measurements from the range finder by automatically walking the range gate out in distance when an object of interest moves or when the system scans across a scene with objects at various distances in line of sight.

6. The system of claim 5 further comprising a display device capable of (a) displaying the image of the object that is concurrently comprised of imagery data collected while in both the mid-wave infrared laser-illuminated imaging and mid-wave infrared thermal imaging modes of operation, and (b) visually distinguishing through the use of color extent to which each feature in the image is based on imagery data collected in the mid-wave infrared laser-illuminated imaging mode of operation versus being based on imagery data collected in the mid-wave infrared thermal imaging mode of operation.