Digital passband processing of wideband modulated optical signals for enhanced imaging
An optical imaging system and method for use in a degraded visual environment is provided. A wideband modulated laser pulse is transmitted from a first location through a medium toward a target object. An input of the transmitted wideband modulated laser pulse is detected by an optical receiver. A target modulated laser pulse, reflected from the target object is detected by the optical receiver. The transmitted and reflected laser pulses are filtered by a bandpass filter, based on a predetermined modulated frequency range. The filtered transmitted and reflected laser pulses are digitized by an analog-digital converter. The digitized transmitted laser pulse is correlated with digitized reflected laser pulse by a digital matched filter, wherein the matched filter produces a passband matched filter output. A range of the target object is determined based on the matched filter output.
1. A method of imaging in degraded visual environments, wherein the method comprises:
transmitting a wideband modulated laser pulse from a first location through a medium toward a target object at a second location;
detecting a reference input of the transmitted wideband modulated laser pulse by an optical receiver;
detecting a target modulated laser pulse reflected from the target object by the optical detector;
filtering the target modulated laser pulse and the reference input with a bandpass filter, based on a predetermined modulated frequency range;
digitizing the filtered target modulated laser pulse and the reference input with an analog-digital converter;
correlating the filtered target modulated laser pulse and the filtered reference input with a digital matched filter, wherein the digital matched filter produces a passband matched filter output; and
determining a range of the target object based on the matched filter output.
2. The method of claim 1 , wherein the transmitted wideband laser pulse is in a blue-green light spectrum.
3. The method of claim 1 , wherein the wideband modulated laser pulse comprises a defined bandwidth and a defined center frequency.
4. The method of claim 3 , further comprising:
modifying the defined bandwidth of the wideband modulated laser pulse, wherein modifying a ratio of bandwidth to center frequency tunes the determined range.
5. The method of claim 3 , further comprising:
modifying the center frequency of the wideband modulated laser pulse, wherein modifying a ratio of bandwidth to center frequency tunes the determined range.
6. A system for imaging in degraded visual environments, the system comprising:
a laser, positioned to transmit a wideband modulated pulse toward a target object located within a degraded visual environment;
an optical receiver, positioned to receive one or more return pulses;
a bandpass filter, wherein the bandpass filter rejects a portion of the one or more return pulses outside a threshold modulated frequency range;
an analog-digital converter, wherein the wideband modulated pulse and the one or more return pulses are converted to a plurality of digital signals; and
a digital matched filter arranged to receive the plurality of digital signals.
7. The system of claim 6 , wherein the optical receiver receives an input from the laser comprising a signal of the wideband modulated pulse.
8. The system of claim 6 , wherein the digital matched filter correlates the wideband modulated pulse and the one or more return pulses to produce a matched filter output.
9. The system of claim 6 , wherein the digital matched filter determines a range of the target object based on the matched filter output.