US-12618647-B2 - Laser pulse shape detection using frequency characterization

US12618647B2US 12618647 B2US12618647 B2US 12618647B2US-12618647-B2

Abstract

A method includes receiving a plurality of laser pulses as a pulse train on a plurality of imaging sensor pixels in an array of pixels. For each pixel in the array of pixels, the method includes receiving a respective one of the laser pulse trains, and scanning the pixels response across a range of frequencies with a bandpass filter to determine pulse shape characteristics of the respective one of the laser pulse trains. The method includes filtering out all of the laser pulse trains that do not fit a predetermined pulse shape characteristic for a true target designation pulse train, and physically adjusting trajectory of a physical resource toward a target based on location on the imaging sensor of one or more pixels receiving a laser pulse train that fits the predetermined pulse shape characteristic for the true target designation pulse train.

Inventors

Robert D. Rutkiewicz

Assignees

SIMMONDS PRECISION PRODUCTS, INC.

Dates

Publication Date: 20260505
Application Date: 20230217

Claims (11)

1 . A method comprising: determining a pulse repetition frequency (PRF) of a train of pulses generated by a laser designator; coordinating a capture of a sequence of images with the PRF so as to capture a single pulse of the train of pulses within each of the sequence of images captured, the images captured, via an imaging sensor with a two-dimensional array of pixels, each located at a corresponding pixel location within the two-dimensional array of pixels; globally configuring band-pass filtering, by an ROIC, of temporal signals generated by each of the two-dimensional array of pixels for each of the sequence of images captured, thereby generating filtered pulse data; determining a temporal pulse shape corresponding to each of the two-dimensional array of pixels using the filtered pulse data obtained for the sequence of images captured; identifying one or more pixels the two-dimensional array of pixels corresponding to a predetermined temporal pulse shape characteristic of a true target; and physically adjusting trajectory of a guided munition toward the true target based on the pixel locations of the one or more pixels having the predetermined temporal pulse shape characteristic of the true target.
2 . The method as recited in claim 1 , further comprising: globally configuring intensity thresholding, by the ROIC, of the temporal signals generated by each of the two-dimensional array of pixels during the sequence of images captured.
3 . The method as recited in claim 1 , further comprising: reading in the filtered pulse data from the ROIC for each of the sequence of images captured.
4 . The method as recited in claim 1 , wherein the sequence of images are captured at a frequency on the order of 1 KHz.
5 . The method as recited in claim 1 , wherein globally configuring band-pass filtering, by an ROIC, of temporal signals generated by each of the two-dimensional array of pixels during the sequence of images captured includes changing a center frequency of the band-pass filtering for each of the sequence of temporal windows of image capture.
6 . A system comprising: an imaging sensor with a two-dimensional array of pixels, each located at a corresponding pixel location within the two-dimensional array of pixels; a read out integrated circuit (ROIC) including globally configurable band-pass filtering of temporal signals generated by each of the two-dimensional array of pixels during a capture of an image, thereby generating filtered pulse data; and a processor operatively connected to the ROIC, wherein the processor includes machine readable instructions configured to cause the processor to: control settings of the ROIC to globally configure the band-pass filtering of the temporal signals generated by each of the two-dimensional array of pixels during each of a sequence of images captured, each of the sequence of images captured timed to permit capture of a single pulse of a train of pulses generated by a laser designator; determine a temporal pulse shape corresponding to each of the two-dimensional array of pixels using the filtered pulse data obtained for the sequence of images captured; identify one or more pixels of the two-dimensional array of pixels corresponding to a predetermined temporal pulse shape characteristic of a true target; and output control signals for physically adjusting trajectory of a guided munition toward the true target based on the pixel locations of the one or more pixels having the predetermined temporal pulse shape characteristic of the true target.
7 . The system as recited in claim 6 , further comprising the guided munition, wherein the imaging senor, the ROIC, and the processor are onboard the guided munition.
8 . The system as recited in claim 7 , further comprising optics aligned to focus images of a scene and laser pulse trains onto the array of pixels.
9 . The system as recited in claim 6 , wherein the ROIC includes globally configurable intensity thresholding of the temporal signals generated by each of the two-dimensional array of pixels during a temporal window of image capture, and the machine readable instructions are further configured to cause the processor to control settings of the ROIC to globally configure the intensity thresholding of the temporal signals generated by each of the two-dimensional array of pixels during each of a sequence of images captured.
10 . The system as recited in claim 9 , wherein the machine readable instructions are configured to cause the processor to read in the filtered pulse data from the ROIC for each of the sequence of images captured.
11 . The system as recited in claim 10 , wherein the machine readable instructions are configured to cause the processor to cause the ROIC to change a center frequency of the band-pass filtering for each of the sequence of images captured.

Description

BACKGROUND 1. Field The present disclosure relates to laser pulse detection, and more particularly to laser pulse detection such as for use in laser designation and laser guidance for guided munitions or the like. 2. Description of Related Art Typical laser targeting systems use timing to differentiate between a laser designator reflection pulses reflected from an intended target, and laser decoy or confuser pulses, similar to the timing used in LIDAR systems. Additionally, there can be scattered reflections of the designator laser that are from the target's environment, and the tracking system must be able to distinguish between the true intended reflection from the designated target and the scattered environmental reflections of the designator laser. Typical semi-active laser (SAL) tracking systems use high time resolution, on the order of 100 MHz, to characterize the pulse shape of received signals to help filter out environmental reflection of the designator laser as well as filtering out decoy or confuser pulses. However, typical SAL tracking systems do not provide images of the target or its environs. SWIR (short wave infrared) imaging sensors can be used in trackers to provide images of the target and its environs, and can be used for pulse detection within the sensor's field of view. But the typical SWIR sensor does not have the capability to achieve the 100 MHz time resolution needed to distinguish pulse shapes. There is a need to differentiate laser pulse returns without high-speed time resolution, e.g. for SWIR imaging sensors. For instance, something equivalent to about 10 nanosecond time resolution and about 10 feet (3.048 meters) spatial resolution is needed. The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved systems and methods for improved laser pulse detection and discrimination. This disclosure provides a solution for this need. SUMMARY A method includes receiving a plurality of laser pulse data from multiple light pulses as a capture from points in space having different pulse shapes and intensities returned from a designator pulse train onto a plurality of imaging sensor pixels in an array of pixels. For each pixel in the array of pixels over time receiving a light pulse, the method includes scanning over time a center frequency of a bandpass filter to determine a frequency signature corresponding to pulse shape characteristics reflecting from different objects and surfaces. The method includes filtering out all of the pixels with pulse data that do not fit a predetermined frequency signature corresponding to pulse shape characteristic for a true target designation laser pulse return capture. One or more pixels that are not filtered out, which do fit the pulse shape characteristic for the true target designation light pulse return capture, are designated as target return pixels. The method includes physically adjusting trajectory of a physical resource toward a target based on location on the imaging sensor of the target return pixels. The method can include, in addition to scanning the center frequency of a bandpass filter, setting a minimum pulse size threshold for each pixel in the array of pixels. Determining a frequency signature can include applying the minimum pulse size threshold together with using frequency data from pixel response of changing the frequencies setting of a bandpass filter. Determining a frequency signature can include determining rising edge speed, pulse width, and/or pulse height. The method can include generating image data using the imaging pixels in the array of pixels, and using the image data to help discriminate between true target designation light pulse shapes and false light pulse shapes for physically adjusting trajectory of the physical resource. The method can include for the target return pixels, using detection timing to lock into a pulse repetition frequency (PFR) of the true target designation pulse train. Receiving a plurality of laser pulse data can be performed at a frequency on the order of 1 KHz. Scanning over time can include changing the center frequency of the bandpass filter for each subsequent pulse within the laser pulse train. The method can include providing pulse frequency signature data corresponding to shape data, pulse intensity data, and pulse spatial location data for physically adjusting trajectory of the physical resource toward the target. A system includes an imaging sensor with a two-dimensional array of pixels. A read out integrated circuit (ROIC) including pulse detection logic and an image capture logic is operatively connected to the array of pixels for pulse detection and imaging capture. A processor is operatively connected to the ROIC. The processor includes machine readable instructions configured to cause the processor to: control settings of the ROIC to globally change the pulse detection intensity and pulse bandpass frequ