CN111024818B - Submerged plant identification method of ultrasonic sensor based on longitudinal wave sound velocity - Google Patents
Submerged plant identification method of ultrasonic sensor based on longitudinal wave sound velocity Download PDFInfo
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- CN111024818B CN111024818B CN201911372715.9A CN201911372715A CN111024818B CN 111024818 B CN111024818 B CN 111024818B CN 201911372715 A CN201911372715 A CN 201911372715A CN 111024818 B CN111024818 B CN 111024818B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
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- 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
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
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Abstract
The invention discloses a longitudinal wave sound velocity-based submerged plant identification method for an ultrasonic sensor, which comprises the following steps of: determining the echo time difference of the plant interface by using a threshold value method; identifying the echo of the soil interface through a cross-correlation function to obtain the echo time difference of the soil interface and the actual echo amplitude of the soil interface; calculating to obtain a plurality of plant thicknesses corresponding to the different plants by respectively adopting longitudinal wave sound velocities of the different plants and introducing the echo time difference of the plant interface and the echo time difference of the soil interface; calculating a plurality of corresponding transmission coefficients according to the thicknesses of the plants; deducing and obtaining a theoretical echo amplitude value of the soil interface corresponding to each plant according to the plurality of transmission coefficients and the reflection coefficient of the soil interface backing; and the plant corresponding to the theoretical echo amplitude closest to the actual echo amplitude in the plurality of theoretical echo amplitudes is the identified plant. Has the advantages of low cost; the method can be suitable for identifying submerged plants in small lakes; the image does not need to be identified, and the identification time is short.
Description
Technical Field
The invention relates to a submerged plant identification method based on a longitudinal wave sound velocity of an ultrasonic sensor.
Background
At present, submerged plants are mainly identified by generating sonar images by using image sonars and then identifying the images. The mature sonar products in the market are sonar arrays and image sonars, and are characterized by high frequency, multiple frequency bands, high resolution, far detection range, adaptability to complex environments such as deep sea and the like and high cost.
The image sonar is high in cost and long in detection range, and is not suitable for detection and identification of small lakes and submerged plants. The time of several seconds is usually needed for image recognition after one sonar image is shot, and the time is long if online recognition is to be realized.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides an ultrasonic sensor submerged plant identification method based on longitudinal wave sound velocity, which identifies submerged plants by utilizing the combination of the echo of an ultrasonic sensor and the longitudinal wave sound velocity of different plants.
A submerged plant identification method of an ultrasonic sensor based on longitudinal wave sound velocity comprises the following steps:
performing band-pass filtering on the original signal;
calculating a signal envelope;
determining an echo interval by a threshold value method according to the amplitude of the signal envelope;
determining the echo time difference of the plant interface by using a threshold value method;
identifying the echo of the soil interface through a cross-correlation function to obtain the echo time difference of the soil interface and the actual echo amplitude of the soil interface;
calculating to obtain a plurality of plant thicknesses corresponding to the different plants by respectively adopting longitudinal wave sound velocities of the different plants and introducing the echo time difference of the plant interface and the echo time difference of the soil interface;
calculating a plurality of corresponding transmission coefficients according to the thicknesses of the plants;
deducing and obtaining a theoretical echo amplitude value of the soil interface corresponding to each plant according to the plurality of transmission coefficients and the reflection coefficient of the soil interface backing;
and the plant corresponding to the theoretical echo amplitude closest to the actual echo amplitude in the plurality of theoretical echo amplitudes is the identified plant.
Furthermore, after the types of the plants are determined, the thickness of the corresponding plants can be obtained, and then the heights of the plant interface and the soil interface can be calculated.
Further, the signal envelope is found using a hilbert transform.
Further, the transducer of the ultrasonic sensor is a piezoelectric transducer.
The invention has the advantages of low cost and suitability for detecting and identifying submerged plants in small lakes. The image is not required to be identified, the identification time is short, and the online identification is favorably realized.
Drawings
FIG. 1 is a flow chart of a submerged plant identification method based on an ultrasonic sensor of longitudinal wave sound velocity;
FIG. 2 is a schematic illustration of acoustic material transmission and reflection;
fig. 3 is an echo diagram of the submerged plant identification method of the ultrasonic sensor based on the longitudinal wave sound velocity in fig. 1.
Detailed Description
The invention is described in detail below with reference to the figures and the embodiments.
As shown in fig. 1 to 3, a submerged plant identification method based on a longitudinal wave sound velocity by an ultrasonic sensor includes the following steps:
performing band-pass filtering on the original signal;
calculating a signal envelope;
determining an echo interval by a threshold value method according to the amplitude of the signal envelope;
determining the echo time difference of the plant interface by using a threshold value method;
identifying the echo of the soil interface through a cross-correlation function to obtain the echo time difference of the soil interface and the actual echo amplitude of the soil interface;
calculating to obtain a plurality of plant thicknesses corresponding to the different plants by respectively adopting longitudinal wave sound velocities of the different plants and introducing the echo time difference of the plant interface and the echo time difference of the soil interface;
calculating a plurality of corresponding transmission coefficients according to the thicknesses of the plants;
deducing and obtaining a theoretical echo amplitude value of the soil interface corresponding to each plant according to the plurality of transmission coefficients and the reflection coefficient of the soil interface backing;
and the plant corresponding to the theoretical echo amplitude closest to the actual echo amplitude in the plurality of theoretical echo amplitudes is the identified plant. After the types of the plants are determined, the thickness of the corresponding plants can be obtained, and then the heights of the plant interface and the soil interface can be calculated.
Fig. 1 shows a submerged plant identification method based on an ultrasonic sensor of longitudinal wave sound velocity by taking 3 plants as an example. The submerged plant identification method based on the longitudinal wave sound velocity for the ultrasonic sensor is not limited to the comparison by adopting 3 plants, and 2 plants can be set for comparison or more than 3 plants can be set for comparison according to needs.
As a specific embodiment, a Hilbert (Hilbert) transform is used to find the signal envelope. The transducer of the ultrasonic sensor is a piezoelectric transducer.
A beam of sound waves striking the acoustic material is reflected, absorbed and transmitted.
The reflection coefficient being equal to the reflected acoustic energy compared to the incident acoustic energy
The transmission coefficient being equal to the transmitted acoustic energy compared to the incident acoustic energy
Referring to the echoes of fig. 3, there is a series of random echoes at the front of the vegetation, which is the effect of the superposition of the constant reflections hitting the vegetation. An echo with a more obvious reflection wave amplitude is generated at a soil interface (hard interface) behind the back of the plant. The location of the soil interface (hard interface) can be determined by the reflected echo of the soil interface. Further, the height of the submerged plant and the height of the soil are accurately calculated.
According to the principle of echo time difference positioning:
the position of the plant interface can be calculated.
Specifically, hp＝t1cw，cwIs the speed of sound in water.
Height of submerged plant: dp＝t2cp. The height of the submerged plant, i.e., the distance from the soil interface to the plant interface, may also be referred to as the thickness of the submerged plant.
Distance d of transducer reached by soil interfaces＝t1cw+t2cp。
The transmission coefficient gamma and the thickness d of different plants are measured in advance through experimentspThe relationship γ ═ f (d)p) Illustrated by three different plant ABCs, the longitudinal wave sound velocities are cpA，cpB，cpC. The average reflection coefficient beta of the soil.
And determining the echo time difference t1 of the plant interface by using a threshold method. And (4) calculating a cross-correlation function with the transmitted waves to obtain the echo time difference t2 of the soil interface and the actual echo amplitude A of the soil interface.
C is respectively substituted according to t1 and t2pA，cpB，cpCThe thickness d of the plant can be calculatedpA，dpB，dpC。
Deducing theoretical echo amplitude A corresponding to the soil section according to the transmission coefficient of the plant and the reflection coefficient of the backingpA，ApB，ApC。
3 theoretical echo amplitudes ApA，ApB，ApCAnd the corresponding plant is the identified plant according to the theoretical echo amplitude value of the closest actual echo amplitude value A.
The cross-correlation function (cross-correlation algorithm) is an important method for identifying echoes, and the cross-correlation algorithm of signals is to determine the positions of echoes by comparing the degrees of similarity of transmitted waves and echoes. Specifically, the transmitted wave and the echo are subjected to cross-correlation calculation, and the peak value of the obtained cross-correlation function is the starting point of the signal. In the signal processing of the cross-correlation method, the method can well analyze the relation of two signals on time delay and obtain the propagation time of ultrasonic waves. The method utilizes the overall shape of the ultrasonic echo, and the precision of the ultrasonic wave propagation time obtained by searching the ultrasonic wave till the moment is much higher than that of a threshold method.
If there are two random signals x (t) and y (t) the mutual function can be expressed as:
the actual acquired data is discrete, so the discrete signal can be expressed as:
the time corresponding to the maximum value of the function is the time of propagation of the ultrasonic wave. The precision of the cross-correlation method measurement is improved greatly compared with the precision of the threshold value method measurement for the ultrasonic wave propagation time, and misjudgment caused by direct search of the echo signal starting point in the threshold value method is prevented. The echo is affected rather than the standard echo due to the reflection and absorption of the submerged plants, but the position of the positive reflection echo of the hard interface can be searched to the maximum extent by using a cross-correlation algorithm, so that the transit time of the hard interface can be estimated.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It should be understood by those skilled in the art that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by using equivalent alternatives or equivalent variations fall within the scope of the present invention.
Claims (4)
1. A submerged plant identification method of an ultrasonic sensor based on longitudinal wave sound velocity is characterized by comprising the following steps:
performing band-pass filtering on the original signal;
calculating a signal envelope;
determining an echo interval by a threshold value method according to the amplitude of the signal envelope;
determining the echo time difference of the plant interface by using a threshold value method;
identifying the echo of the soil interface through a cross-correlation function to obtain the echo time difference of the soil interface and the actual echo amplitude of the soil interface;
calculating to obtain a plurality of plant thicknesses corresponding to the different plants by respectively adopting longitudinal wave sound velocities of the different plants and introducing the echo time difference of the plant interface and the echo time difference of the soil interface;
calculating a plurality of corresponding transmission coefficients according to the thicknesses of the plants;
deducing and obtaining a theoretical echo amplitude value of the soil interface corresponding to each plant according to the plurality of transmission coefficients and the reflection coefficient of the soil interface backing;
and the plant corresponding to the theoretical echo amplitude closest to the actual echo amplitude in the plurality of theoretical echo amplitudes is the identified plant.
2. The method for identifying submerged plants by using an ultrasonic sensor based on the longitudinal wave sound velocity as claimed in claim 1, wherein after the type of the plant is determined, the thickness of the corresponding plant can be obtained, and then the height of the plant interface and the height of the soil interface can be calculated.
3. The longitudinal wave sound velocity-based ultrasonic sensor submerged plant identification method according to claim 1, wherein a signal envelope is obtained by using a Hilbert transform.
4. The longitudinal sonic velocity-based ultrasonic sensor submerged plant identification method according to claim 1, wherein the transducer of the ultrasonic sensor is a piezoelectric transducer.
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Citations (3)
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| CN101614819A (en) * | 2009-08-04 | 2009-12-30 | 北京师范大学 | Submerged plants in shallow water lake automatic identification technology and device |
| CN103913422A (en) * | 2014-03-03 | 2014-07-09 | 中国科学院南京地理与湖泊研究所 | Rapid monitoring method for aquatic plants in shallow lake based on HJ-CCD images |
| CN107728150A (en) * | 2017-09-26 | 2018-02-23 | 江苏省水利科学研究院 | The method for investigating lake submerged plant through water |
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| US10371816B2 (en) * | 2015-12-30 | 2019-08-06 | Aurora Borealis Dakota L.L.C. | Updating contour maps for bodies of water |
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| CN101614819A (en) * | 2009-08-04 | 2009-12-30 | 北京师范大学 | Submerged plants in shallow water lake automatic identification technology and device |
| CN103913422A (en) * | 2014-03-03 | 2014-07-09 | 中国科学院南京地理与湖泊研究所 | Rapid monitoring method for aquatic plants in shallow lake based on HJ-CCD images |
| CN107728150A (en) * | 2017-09-26 | 2018-02-23 | 江苏省水利科学研究院 | The method for investigating lake submerged plant through water |
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| Assessing the biomass and distribution of submerged aquatic vegetation using multibeam echo sounding in Lake Towada, Japan;Kazuki Abukawa 等;《Limnology》;20120703;第39-42页 * |
| 基于光谱特征的沉水植物种类识别研究;邹维娜 等;《华东师范大学学报（自然科学版）》;20140731(第4期);第132-140页 * |
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