Interferometric signal processing

• US 7,768,442 B2
• Filed: 07/18/2006
• Issued: 08/03/2010
• Est. Priority Date: 07/18/2005
• Status: Active Grant

• Current Assignee: GroundProbe Pty Ltd. (Orica Limited)
• Original Assignee: GroundProbe Pty Ltd. (Orica Limited)
• Inventors: Reeves, Bryan, Stickley, Glen
• Primary Examiner(s): Sotomayor; John B
• Application Number:
  US11/988,821
• Publication Number:
  US 20090121921A1
• Time in Patent Office: 1,477 Days
• Field of Search: 342/28, 342/114, 342/156, 342/160, 342/179, 342/197
• US Class Current: 342/28
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 13/89 for mapping or imaging
• CPC Class Codes: G01S 7/414 Discriminating targets with respect to background clutter

Abstract

A method of error handling in a slope monitoring system that generates slope movement data from interferometric signal processing of radar images of the slope monitoring system. The error handling occurs in two steps. The movement data is corrected for changes in atmospheric conditions and disturbances are identified. It is convenient to mask the regions identified as disturbed in the display of the corrected movement data. Typical disturbances include short term disturbances, such as trucks, and long term disturbances, such as vegetation.

Claims

1. A method of error handling in interferometric signal processing for a ground based slope monitoring system including the steps of:

extracting uncorrected movement data from interferometric radar measurements;

correcting the movement data for changes in atmospheric conditions;

identifying disturbances in the corrected movement data; and

displaying the corrected movement data and regions affected by the disturbances,

wherein disturbances are identified in the movement data by detecting variations in short-term and long-term signal coherence.

2. The method of claim 1 wherein displaying regions affected by the disturbances includes masking the regions.

3. The method of claim 1 wherein the step of identifying disturbances includes identifying blocking disturbances caused by short-term blockage of the radar signal.

4. The method of claim 3 wherein the step of identifying disturbances includes identifying disturbances caused by trucks.

5. The method of claim 1 wherein the step of identifying disturbances includes identifying random disturbances caused by long-term interference.

6. The method of claim 5 wherein the step of identifying disturbances includes identifying disturbances caused by vegetation.

7. The method of claim 1 wherein the step of correcting the movement data for changes in atmospheric conditions is achieved by estimating the change in the signal speed due to changes in the refractive index of the air and the offset induced at zero range.

8. The method of claim 1 further including the step of comparing the long-term coherence of a data point to a disturbance mask threshold and classifying the data point as disturbed if the long-term coherence is less than the disturbance mask threshold.

9. The method of claim 1 further including the step of comparing a ratio of short-term coherence to long-term coherence of a data point to a blocking mask threshold and classifying the data point as blocking mask if the ratio is less than the blocking mask threshold.

17. The method of claim 1 wherein the step of correcting the movement data for changes in atmospheric conditions includes acquiring atmospheric correction data from a weather sensing module.

10. A method of atmospheric correction of movement data comprising multiple data points in a ground based slope monitoring system including the steps of:

selecting a plurality of atmospheric correction regions at different ranges;

deducing displacement data within the selected regions;

determining a search space;

calculating a cost function for a grid of points within the search space;

using a minimisation algorithm to determine a correction slope and offset; and

applying the correction slope and offset to the movement data.

11. The method of claim 10 wherein the step of a using a minimisation algorithm includes calculating local minima within the search space and using the local minima to seed a multidimensional minimisation algorithm to find true minima.

12. A method of identifying disturbances of movement data comprising multiple data points in a ground based slope monitoring system including the steps of:

determining short-term coherence for each data point;

averaging the short-term coherence to determine long-term coherence;

comparing the long-term coherence to a first threshold and masking the data point if the long-term coherence is less than the first threshold; and

comparing a ratio of the short-term coherence to the long-term coherence with a second threshold and masking the data point if the ratio is less than the second threshold.

13. The method of claim 12 further including the step of comparing signal amplitude of the data point with a sky threshold and classifying the data point as sky if the amplitude is less than the sky threshold.

14. A ground based slope monitoring system of the type comprising at least a radar module generating interferometric movement measurements of a slope further comprising an anomaly detection and correction module, the anomaly detection and correction module comprising:

an atmospheric correction module comprising a processor that corrects slope movement measurements for anomalies caused by atmospheric changes; and

a disturbance detection module comprising a processor that identifies disturbances that cause errors in the slope movement measurements by detecting variations in short-term and long-term signal coherence.

15. The ground based slope monitoring system of claim 14 comprising a video module that provides visual images of the slope.

16. The ground based slope monitoring system of claim 14 comprising a weather sensing module providing atmospheric correction data to the atmospheric correction module.