Method for elimination of passive noise interference in sonar

• US 6,335,905 B1
• Filed: 12/17/1999
• Issued: 01/01/2002
• Est. Priority Date: 12/17/1999
• Status: Expired due to Term

• Current Assignee: Garmin Corporation (Garmin Limited)
• Original Assignee: Garmin Corporation (Garmin Limited)
• Inventors: Kabel, Darrin W.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US09/465,620
• Time in Patent Office: 746 Days
• Field of Search: 367/98, 367/97, 367/99
• US Class Current: 367/98
• CPC Class Codes: G01S 7/527 Extracting wanted echo signals Doppler systems G01S15/50

Abstract

A sonar depth sounder device and method for processing echo signals, reflected from objects within a body of water, utilizes a processor, a memory, a display, and a keypad connected to the processor. The receiver receives sonar signals indicative of ambient noise in an underwater environment. The processor receives an electrical signal representative of the ambient noise, and calculates a detection threshold. The detection threshold is calculated by multiplying a scaling factor times the variance of the signal indicative of the ambient noise, and adding that product to the mean of the signal indicative of the ambient noise in the underwater environment. A transmitter then excites a transducer which emits sonar pulses into a body of water, and a receiver receives reflected sonar echo signals. When the intensity of the reflected sonar echo signals is less than the detection threshold, the reflected echo signals are eliminated from processing. When, however, the amplitude of a reflected sonar signal is greater than the detection threshold, the processor causes data indicative of the reflected sonar signal to be displayed on the display. Further, the detection threshold is increased from its starting point over time to compensate for increasing a gain in the receiver of the sonar depth sounder device. Additionally, the detection threshold is periodically updated to compensate for changes in ambient noise in the underwater environment. In an alternate embodiment, after a preliminary value is determined, based upon ambient noise or predicted ambient noise, the sonar depth sounder device generates a continuous time-varying detection threshold by sampling a received echo signal and storing the samples in memory, applying a continuous time averaging technique to the sampled data, wherein sample data comprises a time varying detection threshold. That time varying detection threshold is then compared on a sample-by-sample basis with corresponding samples of the originally received data, such that the originally received data that is greater than its corresponding detection threshold sample is displayed, whereas originally received data is less than its corresponding detection threshold sample is rejected and not displayed. In a preferred embodiment, in order to display data indicative of an originally received data sample that is greater than the detection threshold, it must be part of a sequence of consecutive data samples that are greater than the corresponding detection threshold samples, wherein that sequence has an associated time that is greater than a selected time limit.

Claims

1. A sonar depth sounder device comprising:

a display;

a transmitter for generating a sonar signal toward the bottom surface of a body of water;

a receiver;

a processor connected to said transmitter and said receiver, wherein said transmitter transmits a sonar signal into said body of water, and wherein said receiver receives a corresponding echo sonar signal, wherein said echo sonar signal is sampled, and wherein a continuous time average is applied to at least a portion of the data corresponding to said samples, thereby creating a time varying detection threshold;

wherein said sonar depth sounder device further comprises a memory, and wherein data indicative of data samples received by said receiver or stored in said memory, and wherein data indicative of said data samples after said continuous time average technique has been applied to said originally received data is stored in memory;

wherein each data sample of said averaged data samples is compared with a corresponding data sample of said originally received set of data, and wherein, when a numeric value of an originally received data sample is greater than a data value associated with its corresponding averaged data sample, information indicative of said original data sample is displayed on said display;

wherein when a numeric value associated with a data sample of said originally received data is less than a corresponding data value of said averaged data, said originally received data sample is rejected, and information indicative thereof is not displayed on said display; and

wherein said processor, prior to making said comparison, applies lower and upper limits to said detection threshold.

2. The sonar depth sounder device as set forth in claim 1, wherein said lower and upper limits are based upon a preliminary established value indicative of ambient noise in said body of water.

3. The sonar depth sounder device as set forth in claim 1, wherein said preliminary determined value is based upon a user input indicative of a predicted ambient noise level in said body of water.

4. The sonar depth sounder device as set forth in claim 1, wherein each data sample of said averaged data samples is prepared with a corresponding data sample of said originally received set of data, and wherein, when each of a set of data samples corresponding to the originally received data is greater than its corresponding average data sample, and wherein, each of the said set of consecutive data samples corresponding to said originally received data has associated time which is greater than a minimum time limit, information indicative of said set of consecutive original data samples is displayed on said display.

5. The sonar depth sounder device as set forth in claim 1, wherein said continuous-time average application is accomplished with.

6. The sonar depth sounder device as set forth in claim 1, wherein said continuous-time average application is accomplished with a correlative window.

7. A method for eliminating ambient noise received by a sonar depth sounder having a display, said method comprising:

transmitting at least one sonar signal to an underwater environment;

receiving an echo sonar signal corresponding to said transmitted signal;

sampling said received echo sonar signal, resulting in a sequence of data samples;

applying a continuous time average to said sequence of data samples, thereby obtaining a detection threshold; and

applying upper and lower limits to said detection threshold.

8. The method as set forth in claim 7, further comprising:

comparing said data to which said continuous time average has been applied with said originally received sample data; and

making a determination of whether to display information indicative of said sample data based upon said comparison.

9. The method as set forth in claim 8, wherein the step of making said determination further comprises:

comparing each data sample with a corresponding data sample of said detection threshold and, when a data sample is greater than the corresponding sample in the detection threshold, then displaying information on the display indicative of said data sample.

10. The method as set forth in claim 9, wherein the step of making said determination further comprises:

comparing each data sample with a corresponding data sample of said detection threshold and, when a data sample is less than electing not to display information indicative of said data sample on said display.

11. The method as set forth in claim 8, wherein the step of making said determination further comprises:

comparing each data sample with a corresponding data sample of said detection threshold and, when a consecutive set of said data sample is greater than their corresponding said samples in said detection threshold, and wherein said consecutive set of said data samples is associated with a time that is greater than a time limit, then displaying information indicative of said consecutive set of data samples on said display.

12. The method as set forth in claim 7, wherein said method is carried out by a series of processor implemented instructions in a processor-readable medium.

13. A sonar depth sounder device comprising:

a display;

a transmitter for generating sonar signal toward the bottom surface of a body of water;

a receiver;

a processor r connected to said transmitter and said receiver, wherein said transmitter transmits a sonar signal into said body of water, and wherein said receiver receives a corresponding echo sonar signal, wherein said echo sonar signal is sampled, and wherein a continuous time average is applied to at least a portion of the data corresponding to said samples, thereby creating a time varying detection threshold, wherein said processor, prior to making said comparison, applies lower and upper limits to said detection threshold.

14. The sonar depth sounder device as set forth in claim 13, wherein said continuous-time average application is accomplished with a low pass filter implemented in a medium readable by said processor.

15. The sonar depth sounder device as set forth in claim 14, wherein said continuous-time average application is accomplished with a correlative window.

16. A sonar depth sounder device comprising:

a display;

a transmitter for generating sonar signal toward the bottom surface of a body of water;

a receiver;

a processor connected to said transmitter and said receiver, wherein said transmitter transmits a sonar signal into said body of water, and wherein said receiver receives a corresponding echo sonar signal, wherein said echo sonar signal is sampled, and wherein a continuous time average is applied to at least a portion of the data corresponding to said samples, thereby creating a time varying detection threshold, wherein said continuous-time average application is accomplished with a series of software instructions for accomplishing a low pass filter filtering operation.

17. The sonar depth sounder device as set forth in claim 16, wherein said low pass filtering operation is accomplished with a correlative window.