CN101813774B - Method for measuring diameter of plant underground roots by using ground penetrating radar - Google Patents

Abstract

The invention provides a method for measuring the diameter of a plant's underground root using a ground-penetrating radar, comprising the following steps: obtaining the specific position of the plant's underground root to be measured by scanning the ground-penetrating radar, and generating corresponding reflection waveform scanning data; Select a waveform diagram of a reflected wave directly above the central position of the underground root of the plant to be measured; according to the waveform diagram, extract a time parameter ΔT therefrom, and then obtain the diameter of the underground root of the plant to be measured, the time The parameter ΔT represents the time point from the first arrival of the reflected wave when the electromagnetic wave emitted by the radar reaches the root-top surface to the end of the delay point of the reflected wave on the root-bottom surface. The characteristics and advantages of the present invention are: it can accurately and quantitatively measure the diameter of the underground root of the plant through the ground penetrating radar, and the obtained measurement result has a strong correlation with the actual diameter of the underground root of the plant.

Description

A Method of Measuring the Diameter of Underground Roots of Plants Using Ground Penetrating Radar

technical field

The invention relates to a method for measuring the diameter of underground roots of plants, in particular to a method for measuring the diameter of underground roots of plants by using ground penetrating radar.

Background technique

The root system plays an important role in the plant ecosystem. It can not only help plants obtain basic soil resources (such as water and nutrients) during growth and development, but also an important organ to support and fix the plant body. In addition, the contribution of the root system to the carbon cycle in the ecosystem is also indispensable, accounting for about 20% to 40% of the total forest carbon, and the root system is also the main driving force of soil respiration in the rhizosphere environment. Recently, research on the role of plant roots in global climate change has shown that the biomass of thick roots (Biomass, the total amount of organic matter (dry weight) existing in a unit area at a certain time, usually expressed in kg/ ^m2 ) will increase with the increase of CO ₂ concentration, which also proves that thick roots can absorb and store excess CO ₂ in the rhizosphere environment for a long time. With the recognition of the important role of plant roots in ecosystems and global climate change, in order to better understand the role of roots, geobiochemical cycle processes and global changes, it is urgent to understand the parameters related to roots, such as Root size, biomass, distribution range, structure and three-dimensional structure, etc. However, in the process of root system research, it is difficult to observe and sample the roots of plants, resulting in insufficient and limited methods for quantitative estimation of root system parameters. Therefore, it is particularly important to seek new methods and techniques that can accurately estimate root system parameters in ecological research.

Ground Penetrating Radar (GPR), also known as ground penetrating radar, is a geophysical technology used to detect the distribution characteristics of underground targets. The basic composition of ground penetrating radar is shown in Figure 1. Its principle is mainly to use the characteristic that electromagnetic waves will reflect differently when encountering two material interfaces with different dielectric constants, and realize the detection and detection by analyzing and processing the reflected signals. target detection. Different dielectric constants of different media form an electrical interface, which is the condition for the reflection of electromagnetic waves during underground propagation. During detection, the high-frequency electromagnetic wave generated by the radar transmitter 1 is sent from the ground into the ground through the transmitting antenna 11 in the form of a wide-band short pulse, and returns to the ground after being reflected by the stratum 2 or the underground target body 3, and is received by the receiving antenna 12. Data sampling and data processing are carried out in the machine. When the electromagnetic wave propagates in the underground medium, its propagation path, electromagnetic field strength and waveform will change to varying degrees with the change of the electric properties, geometric shape and other factors of the medium it passes through. Therefore, the target depth, medium structure, properties and spatial distribution characteristics can be explained according to the time delay, shape and spectrum characteristics of the echo signal.

However, the use of ground penetrating radar to study root distribution is still limited to qualitative mapping to a large extent, and quantitative research has not yet achieved complete success. Moreover, this type of research is currently limited to drawing lateral roots with a root diameter greater than 20 mm, and cannot identify fine roots with a root diameter less than 20 mm.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for measuring the diameter of underground roots of plants by using ground penetrating radar, so as to reduce or avoid the problems mentioned above.

Specifically, the present invention provides a method for measuring the diameter of underground roots of plants by using ground-penetrating radar. The actual diameter of has a strong correlation.

In order to solve the problems of the technologies described above, the present invention proposes a method for utilizing ground penetrating radar to measure the diameter of plant underground roots, said method comprising the steps of:

A. Obtain the specific position of the underground root of the plant to be measured by scanning the ground penetrating radar, and generate corresponding reflection waveform scanning data;

B. Select a waveform diagram of a reflected wave directly above the central position of the underground root of the plant to be measured;

C, extract a time parameter ΔT therefrom according to the waveform diagram, and this time parameter ΔT represents that the electromagnetic wave emitted from the radar arrives at the root top surface when the reflected wave first arrives at the time point and ends at the delay point of the root bottom surface reflected wave;

D. Obtain the diameter of the underground root of the plant to be measured by the formula D=K×ΔT, wherein, D is the diameter of the underground root of the plant to be measured, and K is the range of the underground root measured by the ground penetrating radar in this area A characteristic constant corresponding to .

Preferably, the measurement method of the characteristic constant K is:

Excavating the actually measured plant underground roots, measuring the diameter D ₁ of the actually measured plant underground roots, the actually measured plant underground roots are located in the same area as the above-mentioned plant underground roots to be measured;

Obtain the time parameter ΔT ₁ of the actually measured underground root of the plant through the above steps AC;

The characteristic constant K is obtained by the formula K=D ₁ /ΔT ₁ .

Preferably, the ground penetrating radar uses a 2GHz frequency antenna to measure the diameter of the underground root of the plant.

The characteristics and advantages of the present invention are: it can accurately and quantitatively measure the diameter of the underground root of the plant through the ground penetrating radar, and the obtained measurement result has a strong correlation with the actual diameter of the underground root of the plant.

Description of drawings

The following drawings are only intended to illustrate and explain the present invention schematically, and do not limit the scope of the present invention. in,

Figure 1 shows the measurement principle diagram of ground penetrating radar;

Figure 2 shows a schematic diagram of the waveform comparison of radar reflected waves at different frequencies;

Figure 3 shows a schematic diagram of a typical monopulse ground penetrating radar scanning waveform of an underground target;

What Fig. 4 shows is a waveform diagram of the reflected wave directly above the central position of the underground root of the measured plant;

What Fig. 5 shows is the correlation diagram between the time parameter ΔT obtained by detecting the underground roots at different depths and the actual root diameter;

Fig. 6 shows the relationship between the estimated root diameter value and the actual root diameter by using the time parameter ΔT obtained from detecting another group of root diameters and the characteristic constant K obtained in Fig. 5 .

Detailed ways

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation manners of the present invention will now be described with reference to the accompanying drawings. Wherein, the same parts adopt the same reference numerals.

Embodiment 1 Measuring method

Theoretically speaking, the ability of GPR to identify the root diameter is related to the resolution of GPR. Resolution is a very important parameter to measure the detection effect of ground penetrating radar, which is defined as the ability to distinguish the smallest anomaly. The resolution of ground penetrating radar is closely related to the transmission frequency of the radar antenna. The higher the frequency, the shorter the wavelength and the stronger the resolution.

As shown in Figure 2, for a dielectric layer with a certain thickness underground, A-D-G in the figure represent the waveform records in the dielectric roof at high, medium and low frequencies (corresponding frequencies are 2GHz, 900MHz, 500MHz respectively); B-E-H Respectively represent the waveform records in the dielectric bottom plate at 2GHz, 900MHz, and 500MHz frequencies; C-F-I represent the composite records in the top plate and bottom plate at 2GHz, 900MHz, and 500MHz frequencies, respectively. It can be seen from the figure that for a 2GHz high-frequency antenna, the waveforms of the top and bottom plates can be well distinguished, thereby identifying the thickness of the dielectric layer. As the frequency of the antenna decreases and the wavelength increases, the waveforms of the top and bottom plates of the dielectric layer will interfere constructively or destructively, and the thickness of the dielectric layer cannot be distinguished. Therefore, for the three selected antenna frequencies of 2GHz, 900MHz and 500MHz, the 2GHz frequency antenna has the strongest ability to identify small objects. Therefore, in the present invention, we think that the 2GHz frequency antenna is most likely to distinguish the root diameter size.

In addition, in the present invention, in order to accurately measure the biomass of plant underground roots, what adopt is the ground-penetrating radar data measurement mode of one-dimensional form, that is, to a given measuring point position of plant underground roots ( _xi , y _i ), the waveform A( _xi , _yi , t) of a single pulse reflected wave is recorded by Ground Penetrating Radar (GPR), as shown in Figure 3, which shows a typical underground target Schematic diagram of monopulse ground penetrating radar scanning waveform. The only variable in the waveform is time. In the subsequent description of the present invention, the data obtained by such scanning is referred to as reflection waveform scanning data.

The reflection waveform scanning data obtained from Figure 3 is a kind of unprocessed data. It can be seen from the figure that the reflection amplitude of the target is much smaller than the air-ground reflection amplitude (ie, the ground direct wave). In order to obtain the real target object The air-ground reflection wave in Figure 3 can be considered as a kind of background clutter, which usually covers the reflection characteristics of the target and must be removed in data processing in order to highlight the characteristics of the target and facilitate data interpretation . Generally, the wave form of the reflected wave after background clutter is removed is similar to that shown in FIG. 4 .

In a specific embodiment of the present invention, before using ground penetrating radar to measure the diameter of the plant's underground root, the specific position of the plant's underground root that needs to be measured can be obtained by scanning the ground penetrating radar at first, after that, select a place to be measured A waveform diagram of a reflected wave directly above the center of the plant's underground root is shown in Figure 4. The waveform in the figure has been processed for clutter removal, and the ground reflection wave is suppressed, highlighting the reflection characteristics of the root target. For the method of locating underground objects through ground penetrating radar, please refer to "Study on Automatic Target Detection and Positioning of Ground Penetrating Radar in Shallow Ground", authors Zhang Chuncheng, Zhou Zhengou, Journal of Electronics and Information Technology, July 2005, Volume 27, Issue 7, Issue 1065 - 1068 pages, the entirety of which is incorporated by reference in this patent.

According to the waveform diagram shown in Figure 4, a time parameter ΔT can be extracted from it to analyze the relationship between it and the diameter of each root. ΔT represents the first arrival of the reflected wave when the electromagnetic wave emitted from the radar reaches the top surface of the root. From the time point to the end of the delay point of the reflected wave on the root bottom surface, the research shows that this time parameter is related to the diameter of the root, and the time parameter ΔT has nothing to do with the depth of the root.

Although the definition of the above-mentioned time parameter ΔT is described with reference to the waveform diagram (FIG. 4) that has undergone clutter removal processing, those skilled in the art should understand that using unprocessed waveform data similar to that shown in FIG. 3 is also The above-mentioned time parameter ΔT can be extracted, but as mentioned above, due to the existence of background clutter, the reflection characteristics of underground roots may be covered up, so that the extraction of parameters is difficult. Therefore, the original data is usually Some processing to obtain the desired parameter values is advisable and does not affect the accuracy of the data.

Finally, the diameter D of the measured underground root of the plant is obtained according to the following formula:

D＝K×ΔT

Among them, K is a constant corresponding to the underground root measured by the ground penetrating radar within the scope of the region, which is called the characteristic constant here. In the same area, the characteristic constant K corresponding to the underground root of the same plant is the same; and even for the same plant, in different areas, due to the reasons of climate and soil quality, the characteristic constant K corresponding to the underground root is also very different. may be different; of course, if it is different regions and different types of plants, the characteristic constant K corresponding to the underground roots is basically difficult to be the same. However, for a large-scale geophysics, a certain region, such as Although there are various plants growing in the Mongolian grassland area, the plant species are relatively single, and the climate and soil quality are basically the same. Therefore, in the process of measuring the diameter of underground roots of large-scale plants, it can also be determined that The characteristic constant K corresponding to the underground roots of plants is basically the same.

It should be noted that the most fundamental aspect of the method disclosed in the present invention for measuring the diameter of underground roots of plants by using ground penetrating radar is to propose a time parameter ΔT, which can effectively estimate the diameter of a single root. The prior art documents quoted in this embodiment are used to explain that the determination of the underground root position before the above-mentioned time parameter ΔT is not the invention point of the present invention, so this patent uses its full text as a reference to make the description concise and clear. It is beneficial to the understanding of those skilled in the art, and the content of related technologies is fully disclosed by the source of the cited prior art. Based on the above references, those skilled in the art can learn these technical contents without any creative effort.

Embodiment 2 Measurement characteristic constant K

As can be seen from Example 1, in the method for measuring the diameter of the underground root according to the present invention, the diameter D of the underground root of the plant is proportional to the time parameter ΔT, therefore, the corresponding value of the underground root of a certain plant in a certain area can be obtained by the following method The characteristic constant K, and then obtain the diameter of the underground root of the plant in the area. The specific method is as follows:

Dig out the underground root measured in Example 1, measure the diameter D ₁ of the excavated underground root, and calculate the specific time parameter ΔT ₁ of the actually measured plant underground root according to the method in Example 1 , the characteristic constant K=D ₁ /ΔT ₁ corresponding to the underground root can be obtained.

That is to say, in the present invention, construct a ground penetrating radar to detect a time parameter ΔT of the diameter of plant's underground root, this time parameter is proportional to the diameter of plant's underground root, therefore, can be by actually measuring the plant's underground root The diameter obtains the characteristic constant K corresponding to the underground roots of plants in this area.

Since for the same area, it can be determined that the characteristic constant K corresponding to the underground roots of plants in this area is basically the same, therefore, if the underground roots of plants in this area are measured point by point using ground penetrating radar, then The change in diameter of the underground root along its growth direction can be obtained.

Example 3 verification test

Referring to FIG. 5 , this embodiment shows the correlation diagram between the time parameter ΔT obtained by detecting underground roots at different depths and the actual root diameter, wherein the frequency of the corresponding radar wave is 2 GHz.

As shown in Figure 5, the correlation analysis results of the time parameter ΔT and the actual root diameter show that there is a very significant correlation between ΔT and the actual root diameter, the value of the determination coefficient ^R2 is 0.868, and the root mean square error ( RMSE) is 3.816mm.

What Fig. 6 shows is the relationship diagram between the estimated root diameter value and its actual root diameter obtained by using the time parameter ΔT obtained by detecting another group of root diameters and the characteristic constant K obtained in Fig. 5, as shown in Fig. 6, from The similarity between the estimated root diameter value and the measured root diameter value of the radar antenna measurement data at 2GHz frequency: the coefficient of determination R ² value is 0.857, and the root mean square error (RMSE) is 3.527mm.

It can be seen that it is more effective to measure the root diameter by using the 2GHz GPR antenna system, and the estimation accuracy of a single root diameter is quite high.

In the method for measuring the diameter of underground roots of plants using ground penetrating radar provided by the present invention, a time parameter ΔT is proposed. Using the time parameter ΔT can effectively estimate the diameter of a single root, using the high-resolution nature of the high-frequency antenna, giving full play to the advantages of the 2GHz frequency antenna, extracting from the detected record information that is directly related to the root diameter The time parameter ΔT; secondly, the GPR root diameter estimation model was constructed using the time parameter ΔT as an independent variable, and the test results of the model reached a high accuracy; the rationality and effectiveness of the new method were verified.

In summary, the following conclusions can be drawn from the above description:

(1) The higher the frequency of the radar antenna, the stronger the ability to identify shallow small target reflectors. Therefore, among the three frequency antennas, the 2GHz frequency radar antenna has the best effect in identifying root diameter information;

(2) The time parameter ΔT extracted from the detection data of the 2GHz frequency antenna has nothing to do with the root depth, and can be directly used to estimate the size of the root diameter.

However, it must be noted that the root diameter estimation model has higher requirements on the frequency of the radar antenna, and at the same time, the high attenuation of the high-frequency antenna signal limits the depth of radar detection. For example, the radar system with a 2GHz frequency antenna in this paper can be used to detect depth Tree roots that are not very deep (eg 60cm or less).

Those skilled in the art should understand that although the present invention is described in terms of multiple embodiments, not each embodiment only includes an independent technical solution. The description in the description is only for the sake of clarity, and those skilled in the art should understand the description as a whole, and understand the present invention by considering the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments scope of protection.

The above descriptions are only illustrative specific implementations of the present invention, and are not intended to limit the scope of the present invention. Any equivalent changes, modifications and combinations made by those skilled in the art without departing from the concept and principle of the present invention shall fall within the protection scope of the present invention.

Claims (2)

1. a method utilizing ground penetrating radar to measure the diameter of plant underground root, is characterized in that, described method comprises the steps: A. Obtain the specific position of the underground root of the plant to be measured by scanning the ground penetrating radar, and generate corresponding reflection waveform scanning data; B. Select a waveform diagram of a reflected wave directly above the central position of the underground root of the plant to be measured; C, extract a time parameter ΔT therefrom according to the waveform diagram, and this time parameter ΔT represents that the electromagnetic wave emitted from the radar arrives at the root top surface when the reflected wave first arrives at the time point and ends at the delay point of the root bottom surface reflected wave; D. Obtain the diameter of the underground root of the plant to be measured by the formula D=K×ΔT, wherein, D is the diameter of the underground root of the plant to be measured, and K is the range of the underground root measured by the ground penetrating radar in this area A characteristic constant corresponding to ; The measuring method of described characteristic constant K is: Excavating the actually measured plant underground roots, measuring the diameter D ₁ of the actually measured plant underground roots, the actually measured plant underground roots are located in the same area as the above-mentioned plant underground roots to be measured; Obtain the time parameter ΔT ₁ of the actually measured underground root of the plant through the above steps AC; The characteristic constant K is obtained by the formula K=D ₁ /ΔT ₁ . 2. the method for utilizing ground-penetrating radar to measure the diameter of plant's underground root according to claim 1, is characterized in that, described ground-penetrating radar utilizes the frequency antenna of 2GHz to measure the diameter of described plant's underground root.

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