Method for detecting a distant target and measuring the target distance using inelastically scattered light
Inventors
Pohl, Kenneth R. • Neglia, Christopher
Assignees
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Publication Number
US-10761189-B1
Publication Date
2020-09-01
Expiration Date
Abstract
The present invention comprises a novel approach for determining range to a target using the inelastic scattering of light from the target and/or inelastic scattering of light from molecules between the light emitting source and the target. This is a useful approach in that the range measurement is independent of the retroreflectivity or absorptivity of the target. Using this methodology allows optical detection and rangefinding of targets which by intention or otherwise cannot be detected using conventional LIDAR rangefinding.
Core Innovation
The invention measures the distance from a sensor to a target by detecting inelastically scattered light from the target and/or from an intermediate medium such as air, and determining the distance based on the time-dependence of the intensity of the detected light. Inelastically scattered light is collected in time-gated fashion so that different time-of-flight windows correspond to different spatial regions relative to the target. This approach uses the time evolution of intensity and differing spectral signatures to separate air contributions from target contributions.
A rangefinding/Raman standoff spectroscopy approach is described in which the receiver sweeps a series of time-of-flight windows that distinguish a front-of-target region, a mixed region, and a behind-target region. In the front region, primarily air Raman signatures are observed, while in the mixed region both air and target contributions are present, and in the behind-target region the air signal drops or is blocked while target-related spectral features can appear. Using these differing time dependence and spectral signatures, the system brackets or estimates the target range.
The disclosed embodiment includes time-gated detection of inelastically scattered light using a wavelength dispersive spectrometer and an intensified CCD with controlled gate delay, together with optical transmitter and receiver subsystems. A deep-UV standoff Raman configuration is described in which oxygen/nitrogen Raman peaks disappear beyond the target range while target-specific Raman features appear at the corresponding gate delay. This enables range estimation and supports optimizing acquisition for subsequent chemical detection.
Claims Coverage
The partial content includes three independent claims. Across these claims, the inventive features center on using inelastically scattered light from an intermediate medium and/or the target, distinguishing air inelastic scattering from target inelastic scattering and from elastically scattered light, and determining distance using time-dependent intensity with time-selective gating and delay variation.
Time-dependent distance from inelastically scattered light
Detecting inelastically scattered light from the target and/or from an intermediate medium such as air, and determining the distance based on the time-dependence of the intensity of the detected light.
Wavelength-selective range estimation apparatus with time-dependent signals
Using a pulsed monochromatic source, an optical transmitter subsystem to direct light toward a target, and an optical receiver subsystem with wavelength selective components to detect inelastic scattered light from the air and distinguish it from inelastic scattered light from the target and from elastically scattered light; providing a detector generating a time-dependent signal or multiplicity of signals proportional to the wavelength-selected time-dependent inelastic scattered light, and a signal processor subsystem producing an estimated distance based on the time-dependent signal.
Time-selective delay-swept range determination system with air/target discrimination
Using a pulsed monochromatic source and optical transmitter/receiver subsystems; providing an optical receiver subsystem with wavelength selective components to detect inelastic scattered light from the air and distinguish it from inelastic scattered light from the target and from elastically scattered light, and time-selective components that pass light to a detector only during selected periods of time; generating a signal or multiplicity of signals proportional to the total light falling on the detector during each period of time; varying the delay in timing of the time-selective component after the pulsed source over a multiplicity of delay times via a control subsystem; and producing an estimated distance to the target based on the measured signals for each of the multiplicity of delay times.
Overall claim coverage is grounded in detecting inelastically scattered light and converting its time dependence, implemented via wavelength selection and time-selective gating with delay sweeps, into an estimated target distance while discriminating air inelastic scattering from target inelastic scattering and from elastically scattered light.
Stated Advantages
Reduced sensitivity to target reflectivity/retroreflectivity.
Ability to detect targets not usable with conventional LIDAR.
Detect targets in contexts with weak target Raman scattering.
Enables optimizing acquisition for subsequent chemical detection.
Documented Applications
Rangefinding/Raman standoff spectroscopy for estimating the distance to a target by time-gated collection of inelastically scattered light from intermediate air molecules and/or from the target.
Supporting subsequent chemical detection by optimizing acquisition using the range estimation results.
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