Method and apparatus for azimuth bias error correction of sequential-observer detectors

Claim 3

A method as defined in claim 1 wherein said first counter is used to find a trailing edge by inverting its operation to increment on misses and decrement on hits after a leading edge is declared, and the azimuths of sweeps during which said leading and trailing edges are declared are used to compute an apparent target center, and the apparent target center is corrected to provide a bias corrected center by subtracting a number of azimuth sweep angles equal to said threshold count from said apparent target center, and said bias corrected center is further corrected for bias error by subtracting a number of azimuth sweep angles equal to the count in said second counter during the sweep in which said leading edge was declared.

Claim 4

A method as defined in claim 2 wherein said second counter is incremented in response to misses only until a predetermined maximum count is reached.

Claim 5

A method as defined in claim 3 wherein said maximum count is greater than said threshold count.

Claim 6

A method as defined in claim 3 wherein said maximum count is greater than said threshold count by one.

Claim 7

A method as defined in claim 5 wherein said maximum count is an add number, and said second counter is incremented by only one in response to a miss when the count in said second counter is one less than sAid maximum count and said second counter would otherwise be incremented by two.

Claim 8

In a surveillance radar system having a sequential-observer detector for declaring a target leading edge upon an up-down counter reaching a predetermined threshold count as it is incremented in response to each hit, and decremented except when at a count of zero, in response to each miss in each sweep at a given range as said radar scans in azimuth, a method for the correction of azimuth bias error in declaring said leading edge comprising: counting sweeps at said given range not producing a hit until said up-down counter reaches said threshold count, each sweep counted to produce a leading edge delay count being weighted to account for a delay in declaring a leading edge of a target according to predetermined patterns of hits and misses; and reporting said count with target leading edge azimuth data for subtraction of half the number of sweep angles equal to said count from a target azimuth computed from said leading edge azimuth data.

Claim 9

In a surveillance radar system having a sequential-observer detector for declaring a target leading edge upon an up-down counter reaching a predetermined threshold count as it is incremented in response to each hit, and decremented except when at a count of zero, in response to each miss in each sweep at a given range as said radar scans in azimuth, a method for the correction of azimuth bias error in declaring said leading edge comprising: counting sweeps at said given range not producing a hit until said up-down counter reaches said threshold count, each sweep counted to produce a leading edge delay count being weighted to account for a delay in declaring a leading edge of a target according to predetermined patterns of hits and misses; and reporting said count with target leading edge azimuth data for subtraction of half the number of sweep angles equal to said count from a target azimuth computed from said leading edge azimuth data.

Claim 10

A method as defined in claim 7 wherein each count is weighted according to the following predetermined patterns: when said up-down counter is at a count not equal to zero, each sweep counted to produce said leading edge delay count has a weight of two until the total leading edge delay count reaches a maximum count, and a weight of one when the total leading edge delay count is one less than said maximum; when said up-down counter is at a count equal to zero, each sweep counted to produce said leading edge delay count has a weight of one if the total leading edge delay count is then equal to two; and when said up-down counter is at a count equal to zero and the total leading edge delay count is then not equal to two, the total leading edge delay count is reset to zero.

Claim 11

A method as defined in claim 8 wherein at the time a target leading edge is declared, said total leading edge delay count then attained is retained together with the azimuth of the sweep during which said target leading edge is declared until a target trailing edge is declared, where upon said total leading edge delay count is reported with the azimuths of sweeps during which said leading and trailing edges were declared as target data.

Claim 12

A method as defined in claim 9 wherein the target center is computed from reported target data to be the average of azimuths declared for said leading and trailing edges, less a predetermined azimuth bias equal to said threshold count in sweep angles, and less one-half said total leading edge delay count in sweep angles.

Claim 13

In a radar surveillance system, wherein binary signals are provided as quantized video returns representing hits and misses from a given range at successive azimuths as a radar transmitter-receiver sweeps in azimuth in search of a target, the combination comprising: up-down counting means for counting up in response to hits until a threshold count is reached, and down in response to misses, except when at a count of zero; storage means responsive to said up-down counting means for storing as a leading edge the azimuth of the sweep during which said threshold count is reached; and a leading edge delay counting means for determining error in declaring a leading edge of a target due to misses in the video return pattern occurring before said up-down counter reaches said threshold count by incrementing a leading edge delay count by two in response to each miss of the count of said up-down counter was not equal to zero after the last sweep at the preceding azimuth, incrementing said leading edge delay count by one in response to each miss if the count of said up-down counter was equal to zero after the last sweep at the preceding azimuth and said leading edge delay count was at the same time equal to two, and setting said leading edge delay count to zero in response to a miss if the count of said up-down counter was equal to zero after the last sweep at the preceding azimuth, And said leading edge delay count was at the same time not equal to zero.

Claim 14

In a radar surveillance system, wherein binary signals are provided as quantized video returns representing hits and misses from a given range at successive azimuths as a radar transmitter-receiver sweeps in azimuth in search of a target, the combination comprising: up-down counting means for counting up in response to hits until a threshold count is reached, and down in response to misses, except when at a count of zero; storage means responsive to said up-down counting means for storing as a leading edge the azimuth of the sweep during which said threshold count is reached; and a leading edge delay counting means for determining error in declaring a leading edge of a target due to misses in the video return pattern occurring before said up-down counter reaches said threshold count by incrementing a leading edge delay count by two in response to each miss of the count of said up-down counter was not equal to zero after the last sweep at the preceding azimuth, incrementing said leading edge delay count by one in response to each miss if the count of said up-down counter was equal to zero after the last sweep at the preceding azimuth and said leading edge delay count was at the same time equal to two, and setting said leading edge delay count to zero in response to a miss if the count of said up-down counter was equal to zero after the last sweep at the preceding azimuth, And said leading edge delay count was at the same time not equal to zero.

Claim 15

Apparatus as defined in claim 11 including: means for inverting the operation of said up-down counter to count up from zero misses and down on hits upon said leading edge azimuth being stored; means responsive to said up-down counting means for transmitting a trailing edge azimuth the azimuth of the sweep during which said threshold count is reached after said leading edge azimuth is stored; and means for transmitting simultaneously with said trailing edge azimuth said leading edge delay count and said leading edge azimuth from said leading edge delay counting means and said storage means, respectively, whereby a target center can be computed from transmitted leading and trailing edge azimuth data and corrected by said transmitted leading edge delay count.

Claim 16

Apparatus as defined in claim 12 wherein said leading edge delay counter is incremented in response to misses only until a predetermined maximum count is reached.

Claim 17

Apparatus as defined in claim 13 wherein said maximum count is greater than said threshold count.

Claim 18

Apparatus as defined in claim 13 wherein said maximum count is greater than said threshold count by one.

Claim 19

Apparatus as defined in claim 15 wherein said maximum count is an add number, and said leading edge delay counter is incremented by only one in response to a miss when the count therein is one less than said maximum count and said leading edge delay counter would otherwise be incremented by two.

Claim 20

In a surveillance radar system having an apparatus which declares a target leading edge upon an up-down counter reaching a predetermined count as it is incremented in response to each hit and decremented, except when at a count of zero, in response to each miss in each sweep at a given range as said radar scans in azimuth, and improvement for the correction of azimuth bias error comprising: first means for indicating the azimuth of a sweep when a leading edge of a target has been declared; a leading edge delay counting means counting sweeps at said given range not producing a hit, each leading edge delay count being weighted to account for delay in declaring a leading edge of a target according to predetermined patterns of hits and misses until said indicating means indicates a leading edge azimuth of a target; and means for transmitting the leading edge delay count from said counting means with said target leading edge azimuth for correction of a target azimuth derived from said leading edge azimuth.

Claim 21

In a surveillance radar system having an apparatus which declares a target leading edge upon an up-down counter reaching a predetermined count as it is incremented in response to each hit and decremented, except when at a count of zero, in response to each miss in each sweep at a given range as said radar scans in azimuth, and improvement for the correction of azimuth bias error comprising: first means for indicating the azimuth of a sweep when a leading edge of a target has been declared; a leading edge delay counting means counting sweeps at said given range not producing a hit, each leading edge delay count being weighted to account for delay in declaring a leading edge of a target according to predetermined patterns of hits and misses until said indicating means indicates a leading edge azimuth of a target; and means for transmitting the leading edge delay count from said counting means with said target leading edge azimuth for correction of a target azimuth derived from said leading edge azimuth.

Claim 22

The improvement defined in claim 17 wherein said leading edge delay counting means comprises: means for incrementing the contents thereof by two in response to a miss when said up-down counter is at a count not equal to zero, until said contents reaches a maximum of seven, and for incrementing by one in response to a miss when said up-down counter is at a count of six; means for incrementing said contents by one when said up-down counter is at a count equal to zero, if said contents is then equal to two; and means for resetting said contents to zero when said up-down counter is at a count equal to zero and said contents is then not equal to two.

Claim 23

The improvement as defined in claim 18 wherein said apparatus proceeds to search for and declare a trailing edge of a target once a leading edge has been declared, and wherein said leading edge delay counting means includes: means responsive to said first means for retaining said contents unaltered once a leading edge of a target is declared until a target trailing edge is declared; and first data transfer means for reporting said contents as a leading edge delay count upon said trailing edge being declared.

Claim 24

The improvement as defined in claim 19 including: means for counting azimuth sweeps; storage means for storing the contents of said azimuth sweep counting means when a leading edge is declared by said apparatus; second dAta transfer means for reporting as target data upon said trailing edge being declared the contents of said storage means, and the contents of said azimuth sweep counting means when said first data transfer means reports said contents of said leading edge delay counting means; and means for receiving said target data from said first and second data transfer means.

Claim 25

In a surveillance radar system having apparatus for determining the center azimuth of a target by first detecting a predetermined number of sweeps producing hits for determining the leading edge azimuth of said target, then detecting a predetermined number of sweeps producing misses for determining the trailing edge azimuth of said target, and subsequently providing a bias correction to said leading and trailing edge azimuths by subtracting a number of sweep angles equal to said predetermined number from an average of said leading and trailing edge azimuths, apparatus for the correction of error in determining the leading edge of said target comprising: first means for detecting predetermined patterns of sweeps which produce at the leading edge of said target spurious misses that cause a delay in reaching said predetermined number of hits; and second means responsive to said first means for developing for each of said patterns a compensating number substantially corresponding to the error in said average of said leading and trailing edge azimuths.

Claim 26

In a surveillance radar system having apparatus for determining the center azimuth of a target by first detecting a predetermined number of sweeps producing hits for determining the leading edge azimuth of said target, then detecting a predetermined number of sweeps producing misses for determining the trailing edge azimuth of said target, and subsequently providing a bias correction to said leading and trailing edge azimuths by subtracting a number of sweep angles equal to said predetermined number from an average of said leading and trailing edge azimuths, apparatus for the correction of error in determining the leading edge of said target comprising: first means for detecting predetermined patterns of sweeps which produce at the leading edge of said target spurious misses that cause a delay in reaching said predetermined number of hits; and second means responsive to said first means for developing for each of said patterns a compensating number substantially corresponding to the error in said average of said leading and trailing edge azimuths.

Claim 27

Apparatus as defined by claim 21 including computing means and transfer means for reporting to said computing means said compensating number along with leading and trailing edge azimuths to said computing means for determination and correction of said center azimuth of said target.