Method for phase unwrapping using confidence-based rework

Patent metadata

Field	Value
Publication number	US-9964640-B2
Application number	US-201113304945-A
Country	US
Kind code	B2
Filing date	Nov 28, 2011
Priority date	Nov 28, 2011
Publication date	May 8, 2018
Grant date	May 8, 2018

Abstract

A method, executed by one or more computers, for unwrapping phase wrapped data including a plurality of nodes. The method includes: selecting a root node from the plurality of nodes to start unwrapping ( 102 ); selecting next nodes to be unwrapped, from the neighbor nodes of the root node; dynamically calculating a confidence factor for each node being unwrapped ( 104 ); when a closed loop wherein one node can be unwrapped from either of two previously unwrapped nodes is encountered and an unwrapped value predicted by each of the prior nodes of the two nodes are different during unwrapping, comparing calculated confidence factors for the two previously unwrapped nodes ( 106 ); using the compared confidence factors of the two previously unwrapped nodes to determine which one of the two nodes is an erroneous node ( 108 ); and reprocessing the erroneous node to correct a previous unwrapping error ( 112 ).

First claim

What is claimed is:

1. A method, executed by a radar system, for unwrapping phase wrapped distance measurement data of a radar return signal, the method comprising:
transmitting a radio frequency (RF) signal toward a target;
receiving a return signal reflected from the target;
detecting from the return signal a plurality of pixel locations of a geometry of the target as a plurality of phase wrapped nodes;
selecting a root node from the plurality of nodes;
determining neighbor nodes of the root node from the plurality of pixel locations of the geometry of the target;
selecting next nodes to be unwrapped, from the neighbor nodes of the root node;
starting to unwrap said next nodes;
dynamically calculating a confidence factor for each node being unwrapped;
when a closed loop wherein a current node can be unwrapped from either of two previously unwrapped nodes is encountered and unwrapped values for the current node predicted based on each of the two previously unwrapped nodes are different, comparing calculated confidence factors for the current node based on the two previously unwrapped nodes;
using the compared confidence factors of the current node to determine which one of the two previously unwrapped nodes is an erroneous node;
reprocessing the erroneous node to correct a previous unwrapping error to generate unwrapped data, the unwrapped data representing pixel values of the geometry of the target;
converting the generated unwrapped data to distance measurement data for the target; and
transmitting the distance measurement data to be displayed on a display.

2. The method of claim 1 , wherein a node with a lower confidence factor is determined to be the erroneous node, based on the compared confidence factors.

3. The method of claim 1 , wherein the phase wrapped distance measurement data is radar distance measurement data, the method further comprising receiving the phase wrapped radar distance measurement data from a radar.

4. The method of claim 1 , further comprising propagating the confidence factor from a node of the two previously unwrapped nodes, which results in a highest confidence factor.

5. The method of claim 1 , wherein the selecting next nodes to be unwrapped uses a breadth-first node exploration method, wherein a queue of nodes to be unwrapped is established, the next node is read from the queue and is unwrapped based on its already processed neighbor nodes, and wherein wrapped nodes are added to a back of the queue and the process continues until a desired number of the nodes are unwrapped.

6. The method of claim 1 , further comprising augmenting each node with a slope X and a covariance P estimate; and propagating a slope estimation of an augmented node with the confidence factor of the augmented node to a next node.

7. The method of claim 6 , wherein the propagating a slope estimation is based on calculating the following:
X′=X+K ( Z−HX ), and
P ′=(1 /F )( I−KH ) P,

where, X′ is a slope of a next node, P′ is a covariance of the next node, F is a constant, H is an element orientation, Z is the unwrapped value of the next node, and:
K=PH′/ ( F+HPH′ [2×1]),

where, H′ is the element orientation of the next node, and I is an identity matrix.

8. The method of claim 6 , wherein the confidence factor of the next node is calculated by multiplying the confidence factor of the augmented node by a confidence factor of the unwrapping process for the next node.

9. The method of claim 8 , wherein the confidence factor of the unwrapping process for the next node is determined based on a predetermined look up table and a prediction error for the augmented node.

10. A method, executed by a radar system, for unwrapping phase wrapped distance measurement data of a radar return signal, the method comprising:
transmitting a radio frequency (RF) signal toward a target;
receiving a return signal reflected from the target;
detecting from the return signal a plurality of pixel locations of a geometry of the target as a plurality of phase wrapped nodes;
selecting a root node from the plurality of nodes;
generating a list of unwrappable nodes neighboring the selected root node from the plurality of pixel locations of the geometry of the target;
unwrapping a current node selected from the generated list;
generating a confidence factor for the unwrapped current node;
checking whether the unwrapped current node has multiple predecessor nodes;
when there are multiple predecessor nodes, comparing unwrapped values of the current node based on the predecessor nodes leading to the multiple predecessor nodes;
when there are no multiple predecessor nodes, adding the current node to the list of unwrappable nodes neighboring the current node;
when there is no match from the comparison of the unwrapped values, comparing confidence factors of the current node based on the predecessor nodes;
determining an erroneous node based on the comparison of the confidence factors;
reprocessing the erroneous node to correct a previous unwrapping error;
when there is a match from the comparison of the unwrapped values, adding the current node to the list of unwrappable nodes to generate unwrapped data, the unwrapped data representing pixel values of the geometry of the target;
converting the generated unwrapped data to distance measurement data for the target; and
transmitting the distance measurement data to be displayed on a display.

11. The method of claim 10 , wherein the unwrapping of the current node includes generating an unwrapped value, and determining a state including a slope.

12. The method of claim 10 , wherein a node with a lower confidence factor is determined to be the erroneous node, based on the compared confidence factors.

13. The method of claim 10 , further comprising augmenting each node with a slope X and a covariance P estimate; and propagating a slope estimation of an augmented node with the confidence factor of the augmented node to a next node.

14. The method of claim 13 , wherein the propagating a slope estimation is based on calculating the following:
X′=X+K ( Z−HX ), and
P ′=(1 /F )( I−KH ) P,

where, X′ is a slope of a next node, P′ is a covariance of the next node, F is a constant, H is an element orientation, Z is the unwrapped value of the next node, and:
K=PH′/ ( F+HPH′ [2×1]),

where, H′ is the element orientation of the next node, and I is an identity matrix.

15. The method of claim 10 , wherein the confidence factor of unwrapping a next node in the generated list is determined based on a predetermined look up table and a prediction error for the current node.

Assignees

• Lucas Morrison R
• Raytheon Co

Inventors

• Lucas Morrison R

Classifications

• G01S13/9035 Primary

  Physics · mapped topic

• G01S13/90

  using synthetic aperture techniques {, e.g. synthetic aperture radar [SAR] techniques} · CPC title

• G01S13/9023

  combined with interferometric techniques · CPC title

• G01S13/904 Primary

  SAR modes · CPC title