Electro-optic system for crosswind measurement
View Patent ↗An electro-optic system, e.g., mounted to a weapon, measures down range winds and a range-to-target for compensating the ballistic hit point. The system may include an optical light source, collimated to generate a laser spot on the target. The system may include a wind measurement receiver that captures laser light scattered from the target. The captured light may be modulated by atmospheric scintillation eddies, producing optical patterns which change in time and move with the crosswind. These patterns may be analyzed by a processor using covariance techniques in either the time-domain or the frequency-domain to determine path-integrated crosswinds and associated errors. Ranging is done by measuring the time of flight of the laser pulse to the target collecting the scattered signal from the target. Compensated ballistic hit point, measurement errors and other data may be displayed on a micro-display digital eyepiece, or projected onto the direct view optics (DVO) of a riflescope so as to be overlaid in real-time on the optical image of the target.
1. A system encased in a housing comprising:
an optical transmitter;
an optical receiver;
a display device; and
a processor controller programmed to:
receive optical signals from a single aperture in the optical receiver that are representative of light transmitted by the optical transmitter to a target and scattered back from a target,
process the received optical signals obtained via the single aperture to measure: an average frequency of signal fluctuations caused by scintillation fades proportional to the crosswind speed, a range to the target, and a refractive index structure parameter, and
calculate a path-weighted average crosswind and an offset aim point based on the average frequency of signal fluctuations caused by the scintillation fades proportional to the crosswind, the range, and the refractive index structure parameter,
wherein the offset aim point is displayed to a user via the display device.
2. The system of claim 1 , wherein the system is mounted on one of: a rifle, gun, tripod, archer's bow and a crossbow.
3. The system of claim 2 , wherein the optical transmitter produces a dual divergence laser beam including:
a narrow divergence beam to illuminate the target in daytime, and
a larger divergence beam to illuminate the target during nighttime.
4. The system of claim 3 , wherein the narrow divergence beam produces a laser spot whose diameter is substantially 150 micro-radians or less.
5. The system of claim 1 , further comprising a riflescope with direct view optics (DVO), wherein the display device comprises a symbology projector which projects said offset aim point as an overlay on the target image viewed through the DVO.
6. The system of claim 5 , wherein the symbology projector is mounted in-line with the riflescope.
7. The system of claim 5 , wherein the symbology projector comprises an LCOS chip.
8. A system encased in a housing comprising:
an optical transmitter;
an optical receiver;
a display device; and
a processor controller programmed to:
receive optical signals from a single aperture in the optical receiver that are representative of light transmitted by the optical transmitter to a target and scattered back from a target,
process the received optical signals obtained via the single aperture to measure: an average frequency of signal fluctuations caused by scintillation fades proportional to the crosswind speed, a range to the target, and a refractive index structure parameter, and
calculate a path-weighted average crosswind and an offset aim point based on the average frequency of signal fluctuations caused by the scintillation fades proportional to the crosswind, the range, and the refractive index structure parameter,
wherein the offset aim point is displayed to a user via the display device,
wherein the optical receiver comprises a wind measurement channel including the single aperture,
wherein light from the laser beam, which is reflected from the target and travels back toward the system via said wind measurement channel, is detected by a digital imaging sensor to measure energy fluctuations in the reflected light incident on the single aperture, and
wherein a value of the measured average frequency is derived based on a number of zero-crossings associated with the measured energy fluctuations, said value being used along with the measured values of range and the refractive index structure parameter to calculate a corresponding magnitude of a crosswind.
9. The system of claim 8 , wherein said digital imaging sensor comprises a CMOS camera.
10. The system of claim 9 , wherein the single aperture of the wind measurement has a diameter that is substantially 60 millimeters or less.
11. The system of claim 8 , wherein the refractive index structure is calculated by:
detecting a centroid of the time-varying laser spot over multiple frames detected by said digital imaging sensor;
tracking a position of the centroid as a function of time; and
computing a variance of the tracked centroid position.
12. The system of claim 8 , wherein the processor is programmed to:
obtain repeated measurements of the frequency of signal fluctuations over a given time span;
calculate respective crosswind magnitudes for the repeated measurements; and
determine the path-weighted average crosswind by averaging the calculated magnitudes.
13. The system of claim 12 ,
wherein the processor is further programmed to calculate a confidence metric representing the accuracy of the determined path-weighted average crosswind based on a variance of the repeated measurements, and
wherein the display device outputs data indicative of the value of the confidence metric.
14. The system of claim 8 , wherein the processor is further programmed to determine a crosswind direction by:
detecting a time-varying laser spot over multiple frames by said digital imaging sensor;
in each of the frames, dividing said laser spot into left and right halves and summing the pixel signals in each of the left and right halves to obtain left-half and right-half time-varying signals; and
calculating a time delay of a cross-covariance between the left-half and right-half time-varying signals to determine crosswind direction.