# US 10,371,818 B2 · Motion compensation for dynamic imaging

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- Number: US 10,371,818 B2
- Document ID: US10371818B2
- Status: Granted
- Kind: B2
- Application number: 15/490,858
- Filed: 2017-04-18
- Published: 2018-10-18
- Granted: 2019-08-06
- Earliest claimed: 2017-04-18
- Assignees: Raytheon Company
- Applicants: Raytheon Company
- Inventors: Eran Marcus; Vitaliy M. Kaganovich
- Web page: https://patentgrep.com/patent/US10371818B2

## CPC

- G01S 7/4808: {Evaluating distance, position or velocity data}
- G01S 7/4863: Detector arrays, e.g. charge-transfer gates
- G01S 7/4865: Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak (peak detection in noise, signal conditioning G01S7/487)
- G01S 7/4876: {by removing unwanted signals (G01S7/495 takes precedence)}
- G01S 17/18: wherein range gates are used
- G01S 17/42: Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46)
- G01S 17/58: Velocity or trajectory determination systems; Sense-of-movement determination systems
- G01S 17/86: Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
- G01S 17/894: Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar
- G01S 17/933: of aircraft or spacecraft
- G06T 7/262: using transform domain methods, e.g. Fourier domain methods
- G06T 2207/10028: Range image; Depth image; 3D point clouds
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL

## Abstract

A system and method for forming an image of a target with a laser detection and ranging system. The system includes a laser transmitter and an array detector. The method includes transmitting a sequence of laser pulses; forming a plurality of point clouds, each point cloud corresponding to a respective transmitted laser pulse, each point in the point cloud corresponding to a point on a surface of the target; grouping the plurality of point clouds into a plurality of point cloud groups according to a contiguous subset of the sequence of laser pulses; forming a plurality of average point clouds, each of the average point clouds being the average of a respective group of the plurality of point cloud groups; and forming a first estimate of a six-dimensional velocity of the target, including three translational velocity components and three angular velocity components, from the plurality of average point clouds.

## Claims

### Claim 1

A method for forming an image of a target with a laser detection and ranging system comprising a laser transmitter and an array detector, the method comprising: transmitting a sequence of laser pulses; forming a plurality of point clouds, each point cloud corresponding to a respective transmitted laser pulse, each point in the point cloud corresponding to a point on a surface of the target; grouping the plurality of point clouds into a plurality of point cloud groups according to a contiguous subset of the sequence of laser pulses, each of the point clouds of each group having an index; forming a plurality of average point clouds, each of the average point clouds being the average of a respective group of the plurality of point cloud groups; forming a first estimate of a six-dimensional velocity of the target, comprising three translational velocity components and three angular velocity components, from the plurality of average point clouds; transforming each of the point clouds of a first group of the plurality of point cloud groups by a transformation proportional to the product of: the first estimate of the six-dimensional velocity, and the index of the point cloud within the first group of point clouds; forming the image of the target from the transformed point clouds; and displaying the image of the target on a display.

### Claim 2 (depends on 1)

The method of claim 1, wherein forming of each point cloud comprises: detecting, with an array detector, a plurality of ladar return photons from the corresponding laser pulse, each detection producing an electrical pulse; and
identifying, for each of the electrical pulses, a bin, of a plurality of time bins corresponding to the laser pulse, within which the electrical pulse was produced.

### Claim 3 (depends on 1)

The method of claim 1, wherein forming a first estimate of a six-dimensional velocity of the target comprises:
estimating a six dimensional transformation for approximately transforming a first average point cloud corresponding to a first group of point clouds to a second average point cloud, of the plurality of average point clouds, corresponding to a second group of point clouds;
calculating the first estimate of the six-dimensional velocity as the ratio of:
the six dimensional transformation and
a difference between:
an average time for the second group of point clouds; and
an average time for the first group of point clouds.

### Claim 4 (depends on 3)

The method of claim 3, wherein estimating a six dimensional transformation comprises estimating the six dimensional transformation with an iterative closest point (ICP) algorithm.

### Claim 5 (depends on 1)

The method of claim 1, wherein forming an average point cloud of the plurality of average point clouds comprises discarding data using coincidence processing.

### Claim 6 (depends on 5)

The method of claim 5, wherein discarding data using coincidence processing comprises:
defining a plurality of three-dimensional voxels; and
discarding data from each voxel, from among the plurality of voxels, within which a number of detected ladar return photons is less than a threshold value.

### Claim 7 (depends on 6)

The method of claim 6, wherein the threshold value is 10.

### Claim 8 (depends on 1)

The method of claim 1, further comprising,
forming a plurality of average transformed point clouds from the transformed point clouds;
forming a second estimate of the six-dimensional velocity of the target, from the plurality of average transformed point clouds; and
transforming each of the point clouds, of a second group of point clouds, of the plurality of groups of point clouds, by a transformation proportional to the product of:
the second estimate of the six-dimensional velocity, and
the index of the point cloud within the first group of point clouds.

### Claim 9

A ladar system for forming an image of a target, the system comprising: a pulsed laser transmitter configured to transmit a sequence of laser pulses; a camera comprising an array detector; a processing circuit; and a display, the camera and the processing circuit being together configured to form a plurality of point clouds, each point cloud corresponding to a respective transmitted laser pulse, each point in the point cloud corresponding to a point on a surface of the target, the processing circuit being configured to: group the plurality of point clouds into a plurality of point cloud groups according to a contiguous subset of the sequence of laser pulses, each of the point clouds of each group having an index; form a plurality of average point clouds, each of the average point clouds being the average of a respective group of the plurality of point cloud groups; form a first estimate of a six-dimensional velocity of the target, comprising three translational velocity components and three angular velocity components, from the plurality of average point clouds; and transform each of the point clouds of a first group of the plurality of point cloud groups, by a transformation proportional to the product of: the first estimate of the six-dimensional velocity, and the index of the point cloud within the first group of point clouds; form the image of the target from the transformed point clouds; and display the image of the target on the display.

### Claim 10 (depends on 9)

The system of claim 9, wherein forming each point cloud comprises: detecting, with an array detector, a plurality of ladar return photons from the corresponding laser pulse, each detection producing an electrical pulse; and
identifying, for each of the electrical pulses, a bin, of a plurality of time bins corresponding to the laser pulse, within which the electrical pulse was produced.

### Claim 11 (depends on 9)

The system of claim 9, wherein forming the first estimate of the six-dimensional velocity of the target comprises:
estimating a six dimensional transformation for approximately transforming a first average point cloud corresponding to a first group of point clouds to a second average point cloud, of the plurality of average point clouds, corresponding to a second group of point clouds;
calculating the first estimate of the six-dimensional velocity as the ratio of:
the six dimensional transformation and
a difference between:
an average time for the second group of point clouds; and
an average time for the first group of point clouds.

### Claim 12 (depends on 11)

The system of claim 11, wherein estimating a six dimensional transformation comprises estimating the six dimensional transformation with an iterative closest point (ICP) algorithm.

### Claim 13 (depends on 9)

The system of claim 9, wherein forming an average point cloud of the plurality of average point clouds comprises discarding data using coincidence processing.

### Claim 14 (depends on 13)

The system of claim 13, wherein discarding data using coincidence processing comprises:
defining a plurality of three-dimensional voxels; and
discarding data from each voxel, from among the plurality of voxels, within which a number of detected ladar return photons is less than a threshold value.

### Claim 15 (depends on 14)

The system of claim 14, wherein the threshold value is 10.

### Claim 16 (depends on 9)

The system of claim 9, wherein the processing circuit is further configured to:
form a plurality of average transformed point clouds from the transformed point clouds;
form a second estimate of the six-dimensional velocity of the target, from the plurality of average transformed point clouds; and
transform each of the point clouds, of a second group of point clouds, of the plurality of groups of point clouds, by a transformation proportional to the product of:
the second estimate of the six-dimensional velocity, and
the index of the point cloud within the first group of point clouds.