Doppler radar method and apparatus for measuring a projectile's muzzle velocity
First Claim
1. Doppler radar apparatus for determining the initial velocity of a projectile ejected from a muzzle, comprising:
- radar means for producing a Doppler signal indicative of movement of the projectile relative to the muzzle;
Fourier transform means for operating on a predetermined plurality of segments of the Doppler signal, each segment representing a separate time period, to produce a corresponding plurality of frequency spectrum signals;
detection means, responsive to the plurality of frequency spectrum signals, for measuring the velocity of the projectile during the time period associated with each successive segment of the Doppler signal, wherein the detection means includes comparator means for comparing each of the plurality of frequency spectrum signals with a prescribed threshold that varies with frequency and with the amount of superimposed noise, the comparator means also determining that portions of the signals exceeding the threshold result from one or more moving objects, including the projectile whose initial, muzzle velocity is being estimated; and
regression means, responsive to the projectile velocities measured by the detection means for the plurality of successive time periods, for estimating the projectile'"'"'s initial, muzzle velocity.
2 Assignments
0 Petitions
Accused Products
Abstract
A muzzle velocity chronograph method and apparatus for providing an accurate and precise measurement of the muzzle velocity of a projectile ejected from a gun.
A conventional radar Doppler signal is sampled and digitized and arranged in a succession of groups, each group representing a separate time period. A fast-Fourier transform is then computed for each group of samples, and peak frequency measurements in the transformed data are tracked from one time period to the next. These peaks indicate the velocities of the projectile of interest and any other nearby moving objects. Finally, a least mean square error curve fit and standard regression algorithm are used to deduce the projectile'"'"'s initial, muzzle velocity. The invention provides accurate muzzle velocity determinations even in circumstances where the Doppler signal contains substantial interference caused, for example, by random noise and the presence of moving fragments in the direction of the projectile.
30 Citations
29 Claims
-
1. Doppler radar apparatus for determining the initial velocity of a projectile ejected from a muzzle, comprising:
-
radar means for producing a Doppler signal indicative of movement of the projectile relative to the muzzle; Fourier transform means for operating on a predetermined plurality of segments of the Doppler signal, each segment representing a separate time period, to produce a corresponding plurality of frequency spectrum signals; detection means, responsive to the plurality of frequency spectrum signals, for measuring the velocity of the projectile during the time period associated with each successive segment of the Doppler signal, wherein the detection means includes comparator means for comparing each of the plurality of frequency spectrum signals with a prescribed threshold that varies with frequency and with the amount of superimposed noise, the comparator means also determining that portions of the signals exceeding the threshold result from one or more moving objects, including the projectile whose initial, muzzle velocity is being estimated; and regression means, responsive to the projectile velocities measured by the detection means for the plurality of successive time periods, for estimating the projectile'"'"'s initial, muzzle velocity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. Doppler radar apparatus for determining the initial velocity of a projectile ejected from a gun muzzle, comprising:
-
radar means for directing a radar signal at a projectile after it has been ejected from a gun muzzle, for receiving back a radar signal reflected from the projectile, and for producing a Doppler signal based on the reflected radar signal; analog-to-digital converter means for converting the Doppler signal to a sequence of digital words, arranged in K successive groups of N digital words each; fast-Fourier transform means for operating on the N digital words in each of the K successive groups, to produce N discrete frequency measurements for each group; comparator means for comparing each of the N discrete frequency measurements in each group with a prescribed threshold that is selected in accordance with the average value of frequency measurements for nearby frequencies, the comparator means determining that frequency measurements exceeding their respective thresholds result from one or more moving objects, including the projectile whose initial, muzzle velocity is being estimated; interpolation means for determining the weighted average of those frequency measurements determined by the comparator means to exceed their respective thresholds, to determine the average velocities of the projectile and any other moving object during the time period associated with each group of digital words; association means for associating together the particular velocity measurements in each of the successive time periods corresponding to the respective projectile and one or more additional moving objects, the association means including means for comparing each velocity measurement with velocity measurements made for previous time periods, if any; harmonic elimination means, operable during each time period, for comparing the velocity measurements of the projectile and one or more additional moving objects to each other and for discarding any velocity measurements that is harmonically related to any other velocity measurement; regression means for defining an initial velocity profile that provides the least mean square error based on the velocity measurements made by the interpolation means and association means for the plurality of successive time periods, the regression means including means for discarding any velocity measurements differing by more than a predetermined amount from the initial velocity profile and for redefining the velocity profile based on the velocity measurements remaining, the redefined velocity profile indicating the projectile'"'"'s initial, muzzle velocity; and means for disabling the apparatus from measuring the projectile'"'"'s velocity for a predetermined time period, until any ionization associated with firing of the gun has substantially dissipated.
-
-
12. Doppler radar apparatus for determining the initial velocity of a projectile ejected from a gun muzzle, comprising:
-
radar means for directing a radar signal at a projectile after it has been ejected from a gun muzzle, for receiving back a radar signal reflected from the projectile, and for producing a Doppler signal based on the reflected radar signal; analog-to-digital converter means for converting the Doppler signal to a sequence of digital words, arranged in K successive groups of N digital words each; fast-Fourier transform means for operating on the N digital words in each of the K successive groups, to produce a range of discrete frequency measurements for each group, each such range representing the frequency spectrum for a separate time segment of the Doppler signal; detection means for operating on the range of discrete frequency measurements for each of the K groups, to measure the velocity of the projectile during the time period associated with the corresponding group of N digital words, wherein the detection means includes comparator means for comparing each of the plurality of frequency measurements with a prescribed threshold that varies in accordance with the levels of frequency measurements for nearby frequencies and for determining that frequency measurements exceeding the threshold result from one or more moving objects, including the projectile whose initial, muzzle velocity is being estimated; and regression means for operating on the K successive projectile velocity measurements, to estimate the projectile'"'"'s initial, muzzle velocity. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
-
-
20. Doppler radar method for determining the initial velocity of a projectile ejected from a muzzle, comprising steps of:
-
producing a Doppler signal indicative of movement of the projectile relative to the muzzle; operating on a predetermined plurality of segments of the Doppler signal, each segment representing a separate time period, to produce a corresponding plurality of frequency spectrum signals; processing the plurality of frequency spectrum signals to measure the velocity of the projectile during the time period associated with each successive segment of the Doppler signal, wherein the step of processing includes steps of comparing each of the plurality of frequency spectrum signals with a prescribed threshold that varies with frequency and with the amount of superimposed noise, and determining that portions of the signals exceeding the threshold result from one or more moving objects, including the projectile whose initial, muzzle velocity is being estimated; and estimating the projectile'"'"'s initial, muzzle velocity based on the projectile velocities measured by the step of processing for the plurality of successive time periods. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29)
-
Specification