Method and device for measuring spectral reflectivity of plant

Abstract

The invention discloses a plant spectral reflectivity determination method and device, and relates to the field of spectral reflectivity determination, and the method comprises the following steps: obtaining an initial measurement signal of a to-be-determined plant; converting the initial measurement signal into a voltage signal to obtain a first measurement signal; performing high-pass filtering on the first measurement signal to obtain a second measurement signal; acquiring an initial excitation signal having the same frequency as the modulated light, and adding 90-degree phase shift to the initial excitation signal to obtain a first excitation signal; performing low-pass filtering on a signal obtained after multiplication of the initial excitation signal and the second measurement signal to obtain an in-phase component; performing low-pass filtering on a signal obtained after multiplication of the first excitation signal and the second measurement signal to obtain an orthogonal component; calculating a second amplitude based on the in-phase component, the quadrature component and the first amplitude; and determining the spectral reflectivity of the plant to be measured based on the second amplitude and a spectral reflectivity calibration equation. According to the invention, accurate determination of the spectral reflectivity of the plant is realized.

Description

Technical Field

[0001] The present application relates to the technical field of spectral reflectance measurement, and in particular to a method and device for measuring plant spectral reflectance. Background Art

[0002] The determination of plant spectral reflectance is an important part of modern agricultural and ecological research. It can provide key information about the nutritional status and water content of plants. By analyzing the reflectance characteristics of plants at different wavelengths, the health status of plants can be detected. For example, in the visible light band, chlorophyll is one of the main factors affecting the spectral response of plants, while healthy green vegetation usually shows a higher reflectance in the near-infrared band. When plants are attacked by diseases or lack necessary nutrients, their spectral characteristics will change. The vegetation spectral index composed of reflectance in specific bands, such as the Normalized Difference Vegetation Index (NDVI), can be used to judge the growth and development of vegetation. In addition, reflectance spectrum analysis can not only identify different vegetation types, but also evaluate vegetation coverage, which can be used to predict vegetation productivity and pest and disease conditions.

[0003] At present, the equipment based on lossless acquisition of plant spectral reflectance is mainly divided into two categories, one is passive equipment that uses sunlight as the light source, and the other is active equipment with its own light source in a specific band. Due to the limitation of sunlight, the working conditions of passive equipment are greatly affected by the external environment. Changes in light intensity and angle under natural conditions will lead to unstable measurement results, especially in outdoor environments. Factors such as cloud cover and solar altitude angle will introduce additional errors, greatly limiting the use of passive equipment. Since active equipment has its own light source and is less dependent on the external environment, it has the advantages of good real-time performance, low external interference, low cost, and a large working range. It has become one of the core equipment for obtaining crop physiological information in precision agriculture, and its application prospects are very broad.

[0004] However, since the spectral range of sunlight is very wide and the intensity is very high, the spectral bands emitted by the active light sources used by active devices are basically within the solar spectrum, which means that the photodetector module can not only receive the modulated light emitted by the active light source, but also receive sunlight, which brings troubles to the subsequent signal processing and analysis. Although existing methods also filter out most of the sunlight by adding a filter or filter in the active light source band, this will cause the attenuation of the effective signal or the phase delay of the effective signal, resulting in the final measured plant spectral reflectance being inaccurate. Summary of the invention

[0005] The purpose of this application is to provide a method and device for measuring the spectral reflectance of plants, which avoids the influence of sunlight and realizes the accurate measurement of the spectral reflectance of plants.

[0006] To achieve the above objectives, this application provides the following solutions.

[0007] In a first aspect, the present application provides a method for measuring the spectral reflectance of a plant, the method comprising: obtaining an initial measurement signal of a plant to be measured; the initial measurement signal is a current signal corresponding to the reflected light generated by the plant to be measured after being irradiated with modulated light and ambient light; converting the initial measurement signal into a voltage signal to obtain a first measurement signal; high-pass filtering the first measurement signal to obtain a second measurement signal; obtaining an initial excitation signal having the same frequency as the modulated light, adding a 90° phase shift to the initial excitation signal to obtain a first excitation signal; low-pass filtering the signal after multiplying the initial excitation signal and the second measurement signal to obtain an in-phase component; low-pass filtering the signal after multiplying the first excitation signal and the second measurement signal to obtain an orthogonal component; calculating a second amplitude based on the in-phase component, the orthogonal component and the first amplitude; the first amplitude is the amplitude of the initial excitation signal and the first excitation signal; the second amplitude is the amplitude of the second measurement signal; the amplitude of the second measurement signal is the amplitude of the reflected light; and determining the spectral reflectance of the plant to be measured based on the second amplitude and a spectral reflectance calibration equation.

[0008] In the second aspect, the present application also provides a plant spectral reflectance measuring device, which includes: an active light source module, used to emit modulated light of a specific frequency to the plant to be measured; a spectral reflectance measurement module, connected to the active light source module, and used to execute the plant spectral reflectance measuring method described in the first aspect.

[0009] According to the specific embodiments provided in this application, this application discloses the following technical effects.

[0010] In order to achieve the separation of the reflected signals of sunlight and active light, the present application performs high-pass filtering on the initial measurement signal after voltage conversion, thereby filtering out most of the DC components. At this time, the measurement signal mainly contains the reflected signal of the active light and a small amount of noise signal. In order to solve the problem of phase delay of the measurement signal caused by the filter, line, and noise interference, the present application multiplies the high-pass filtered measurement signal with the initial excitation signal of the same frequency, and multiplies the high-pass filtered measurement signal with the first excitation signal with a 90° phase shift, respectively extracting the in-phase component and the orthogonal component of the measurement signal, and accurately obtaining the actual amplitude of the measurement signal, avoiding the interference of phase delay. Finally, based on the actual amplitude of the measurement signal, the present application uses the spectral reflectance calibration equation to accurately determine the spectral reflectance of the plant to be measured, and the entire measurement process is not affected by sunlight. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0012] Figure 1 This is a flow chart of a method for measuring plant spectral reflectance provided in an embodiment of the present application.

[0013] Figure 2 This is a diagram of the internal structure of the spectral reflectance measurement module provided in an embodiment of the present application.

[0014] Figure 3 This is a module structure diagram of the plant spectral reflectance measuring device provided in an embodiment of the present application.

[0015] Figure 4 This is a front view of a plant spectral reflectance measuring device provided in an embodiment of the present application.

[0016] Figure 5 A bottom view of the plant spectral reflectance measuring device provided in an embodiment of the present application.

[0017] Explanation of symbols: active light source module-1, spectral reflectance measurement module-2, photodetector module-21, I / U conversion module-22, high-pass filter-23, lock-in amplifier module-24, microprocessor-25, key module-3, display module-4, wireless communication module-5, battery module-6, battery charging and discharging module-7, voltage-stabilized power supply module-8, connection hole-9. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0019] With the development of the times, the agricultural field has experienced a transformation from traditional chemical analysis to modern spectroscopy non-destructive testing methods. Traditional crop growth information is mainly obtained through field sampling and chemical analysis. This method has the defects of destroying plants, high cost, and inability to obtain crop physiological information on a large scale in real time, and this method is not suitable for precision agriculture online operations. At present, non-destructive testing has been widely used in the industrial field. It refers to a method that uses advanced technology and instruments to detect and identify the type, nature, quantity, shape, position, size, distribution and changes of abnormalities and defects inside and outside the object under the premise of not damaging or affecting the performance of the object being tested and not damaging the internal organization of the object being tested. In the agricultural field, the non-destructive acquisition of crop growth information has broad application prospects. Early research on plant spectral characteristics mainly relied on integrating sphere measurement under laboratory conditions. This method can accurately determine the directional hemispherical reflectivity, but the operation is complicated and not suitable for field operations. With the advancement of portable equipment, such as the emergence of handheld spectrometers, it has become feasible to quickly obtain vegetation reflectance spectra on site. This type of instrument can perform continuous wavelength scanning in the visible to short-wave infrared range (usually 350-2500nm) and ensure data accuracy through standard whiteboard correction. However, the data is redundant and very troublesome to process. In addition, calibration must be performed before each measurement. The operation is cumbersome, the equipment is large, and field operations are very inconvenient.

[0020] The purpose of this application is to provide a method and device for measuring the spectral reflectance of plants, which avoids the influence of sunlight and realizes the accurate measurement of the spectral reflectance of plants.

[0021] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0022] Example 1 like Figure 1 As shown, this embodiment provides a method for measuring plant spectral reflectance, and the specific method for measuring plant spectral reflectance is as follows.

[0023] Step S1: Acquire the initial measurement signal of the plant to be measured.

[0024] In this embodiment, the initial measurement signal is a current signal corresponding to the reflected light generated by the plant to be measured after being irradiated by modulated light and ambient light (mainly sunlight). In the subsequent process, the sunlight will be filtered out, and only the measurement signal related to the modulated light will be retained.

[0025] Step S2: converting the initial measurement signal into a voltage signal to obtain a first measurement signal.

[0026] In this embodiment, in order to facilitate subsequent calculations, the initial measurement signal in the form of current needs to be converted into a first measurement signal in the form of voltage.

[0027] Step S3: Perform high-pass filtering on the first measurement signal to obtain a second measurement signal.

[0028] In this embodiment, high-pass filtering will filter out most of the measurement signals related to sunlight, and only retain the measurement signals related to modulated light. At the same time, the phase delay caused by high-pass filtering or signal interference will also be eliminated in subsequent steps.

[0029] The expression of the second measurement signal is: ; is the second measurement signal, is the second amplitude, is the frequency, For time, For phase shift.

[0030] Step S4: obtaining an initial excitation signal having the same frequency as the modulated light, and adding a 90° phase shift to the initial excitation signal to obtain a first excitation signal.

[0031] In this embodiment, the frequencies of the modulated light, the initial excitation signal, the first excitation signal and the second measurement signal are the same; and the amplitudes of the initial excitation signal and the first excitation signal are the same.

[0032] The expression of the initial excitation signal is: ; is the initial excitation signal, is the first amplitude.

[0033] The expression of the first excitation signal is: ; is the first excitation signal.

[0034] Step S5: low-pass filtering is performed on the signal obtained by multiplying the initial excitation signal and the second measurement signal to obtain an in-phase component.

[0035] In this embodiment, the in-phase component is , the specific derivation process is as follows.

[0036]

[0037] because , then the following relationship exists.

[0038] .

[0039] The DC component obtained after low-pass filtering is , which is the measured in-phase component I .

[0040] Step S6: low-pass filtering the signal obtained by multiplying the first excitation signal and the second measurement signal to obtain an orthogonal component.

[0041] In this embodiment, the orthogonal components are , the specific derivation process is as follows.

[0042] .

[0043] because , then the above formula is as follows.

[0044]

[0045] because ,but: .

[0046] After low-pass filtering, the DC component is , which is the measured orthogonal component .

[0047] Step S7: Calculate the second amplitude based on the in-phase component, the quadrature component and the first amplitude.

[0048] In this embodiment, the first amplitude is the amplitude of the initial excitation signal and the first excitation signal, and the second amplitude is the amplitude of the second measurement signal, which is the amplitude of the reflected light. ,and , , are all known quantities, so they satisfy the following relationship.

[0049] .

[0050] After deducing the above formula, the calculation formula for the second amplitude is obtained.

[0051] .

[0052] Step S8: Determine the spectral reflectance of the plant to be measured based on the second amplitude and the spectral reflectance calibration equation.

[0053] In this embodiment, the second amplitude obtained in step S7 needs to be converted into digital form, and then it is brought into the spectral reflectance calibration equation with determined parameters for calculation, and the final calculation result is the spectral reflectance of the plant to be measured. The determination process of the spectral reflectance calibration equation is: The first step is to obtain the spectral reflectance calibration plate.

[0054] In the second step, the spectral reflectance calibration plate is irradiated with modulated light of a set frequency, and multiple sets of calibration data are read; the calibration data includes the amplitude of the reflected light and the corresponding spectral reflectance.

[0055] The third step is to obtain the spectral reflectance calibration equation based on multiple sets of calibration data using the least squares method.

[0056] In addition, since the modulated light signal in the second measurement signal of this embodiment and the initial excitation signal (or the first excitation signal with a 90° phase shift added) have the same frequency, the final result is a DC signal and a signal with twice the original frequency. Multiplication will only move the signal of the modulated frequency back to DC, and all other frequency components in the second measurement signal (mainly sunlight signals) will move to other non-zero frequencies, thereby achieving the separation of modulated light and sunlight.

[0057] Example 2 This embodiment provides a plant spectral reflectance measuring device, and the plant spectral reflectance measuring device is specifically described as follows.

[0058] The active light source module 1 is used to emit modulated light of a specific frequency to the plant to be measured. The active light source module 1 contains a light emitting diode or a laser diode.

[0059] The spectral reflectance measurement module 2 is connected to the active light source module 1 and is used to execute the plant spectral reflectance measurement method in Example 1.

[0060] like Figure 2 As shown, the spectral reflectance measurement module 2 is specifically as follows.

[0061] The photodetector module 21 is used to obtain the initial measurement signal of the plant to be measured; the initial measurement signal is the current signal corresponding to the reflected light generated by the plant to be measured after being irradiated by the modulated light and the ambient light. The photodetector module 21 contains a photodiode or a photocell.

[0062] The I / U conversion module 22 is connected to the photoelectric detector module 21 and is used to convert the initial measurement signal into a voltage signal to obtain a first measurement signal.

[0063] The high-pass filter 23 is connected to the I / U conversion module 22 and is used to perform high-pass filtering on the first measurement signal to obtain a second measurement signal.

[0064] The lock-in amplifier module 24 is connected to the high-pass filter 23, and is used to obtain an initial excitation signal with the same frequency as the modulated light, add a 90° phase shift to the initial excitation signal, and obtain a first excitation signal; low-pass filter the signal after multiplying the initial excitation signal and the second measurement signal to obtain an in-phase component; low-pass filter the signal after multiplying the first excitation signal and the second measurement signal to obtain an orthogonal component; calculate the second amplitude based on the in-phase component, the orthogonal component and the first amplitude.

[0065] The microprocessor 25 is connected to the active light source module 1 and the lock-in amplifier module 24, and is used to send a PWM signal to drive the active light source module 1 to emit modulated light of a specific frequency; based on the second amplitude and the spectral reflectance calibration equation, the spectral reflectance of the plant to be measured is determined. The lock-in amplifier module 24 is connected to the ADC interface of the microprocessor 25.

[0066] like Figure 3 As shown, the plant spectral reflectance measuring device also includes: a key module 3 connected to the I / O interface of the microprocessor 25, and used to trigger the microprocessor 25 to send a PWM signal to the active light source module 1.

[0067] The display module 4 is connected to the SPI interface of the microprocessor 25 and is used to display the spectral reflectance of the plant to be measured determined by the plant spectral reflectance measuring device.

[0068] The wireless communication module 5 is connected to the UART interface of the microprocessor 25 and is used to realize the transmission and positioning of the plant spectral reflectance measuring device and the external signal. The wireless communication module 5 is 4G+GNSS.

[0069] In addition, the plant spectral reflectance measuring device also includes: a battery module 6, a battery charging and discharging module 7 and a voltage-stabilizing power supply module 8.

[0070] The battery module 6 is connected to the battery charging and discharging module 7; the battery charging and discharging module 7 is connected to the voltage-stabilized power supply module 8; and the voltage-stabilized power supply module 8 is connected to the microprocessor 25. In actual use, the battery module 6 needs to be charged by the charging function of the battery charging and discharging module 7 first, and after the battery module 6 is fully charged, the voltage-stabilized power supply module 8 is further discharged by the discharging function of the battery charging and discharging module 7.

[0071] As a preferred embodiment, the plant spectral reflectance measuring device is Figure 4 The pistol-type structure shown in the figure includes a gun body and a handle. Figure 5As shown, an active light source module 1, a photodetector module 21 and a connecting hole 9 are sequentially arranged on the lower surface of the gun body part, the handle part is connected to the gun body part by inserting into the connecting hole 9, a display module 4 is also arranged on the upper surface of the gun body part, and the display module 4 is an OLED display screen, and the handle part is also equipped with an outward protruding button corresponding to the internal button module 3.

[0072] In summary, the present application measures the plant spectral reflectance based on the lock-in amplification technology, which can not only separate sunlight from modulated light, but also ensure that the effective signal will not be attenuated. At the same time, the plant spectral reflectance measuring device of the present application is not affected by sunlight, and can accurately measure the plant spectral reflectance under cloudy, overcast or dark conditions, expanding the use environment of plant spectral reflectance measurement.

[0073] All actions to obtain signals, information or data in this application are carried out in compliance with the relevant data protection laws and policies of the country where they are located, and with the authorization given by the owner of the corresponding device.

[0074] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0075] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for measuring plant spectral reflectance, characterized in that: The plant spectral reflectance determination method comprises: Acquire an initial measurement signal of the plant to be measured; the initial measurement signal is a current signal corresponding to the reflected light generated by the plant to be measured after being irradiated by modulated light and ambient light; Converting the initial measurement signal into a voltage signal to obtain a first measurement signal; Performing high-pass filtering on the first measurement signal to obtain a second measurement signal; Acquire an initial excitation signal having the same frequency as the modulated light, and add a 90° phase shift to the initial excitation signal to obtain a first excitation signal; Performing low-pass filtering on a signal obtained by multiplying the initial excitation signal and the second measurement signal to obtain an in-phase component; Performing low-pass filtering on a signal obtained by multiplying the first excitation signal and the second measurement signal to obtain an orthogonal component; Based on the in-phase component, the quadrature component and the first amplitude, a second amplitude is calculated; the first amplitude is the amplitude of the initial excitation signal and the first excitation signal; the second amplitude is the amplitude of the second measurement signal; the amplitude of the second measurement signal is the amplitude of the reflected light; Based on the second amplitude and the spectral reflectance calibration equation, the spectral reflectance of the plant to be measured is determined.

2. The method for measuring plant spectral reflectance according to claim 1, characterized in that: The frequencies of the modulated light, the initial excitation signal, the first excitation signal and the second measurement signal are the same; and the amplitudes of the initial excitation signal and the first excitation signal are the same.

3. The method for measuring plant spectral reflectance according to claim 2, characterized in that: The expression of the initial excitation signal is: ； In the formula, is the initial excitation signal, is the first amplitude, is the frequency, For time; The expression of the first excitation signal is: ； In the formula, is the first excitation signal; The expression of the second measurement signal is: ； In the formula, is the second measurement signal, is the second amplitude, For phase shift.

4. The method for measuring plant spectral reflectance according to claim 1, characterized in that: The in-phase component is , the orthogonal components are ; In the formula, is the first amplitude, is the second amplitude, For phase shift.

5. The method for measuring plant spectral reflectance according to claim 1, characterized in that: The calculation formula of the second amplitude is: ； In the formula, is the second amplitude, is the first amplitude, is the same direction component, are orthogonal components.

6. The method for measuring plant spectral reflectance according to claim 1, characterized in that: The determination process of the spectral reflectance calibration equation is: Obtain a spectral reflectance calibration plate; irradiating the spectral reflectance calibration plate with modulated light of a set frequency, and reading multiple sets of calibration data; the calibration data includes the amplitude of the reflected light and the corresponding spectral reflectance; Based on multiple groups of calibration data, the spectral reflectance calibration equation is obtained by using the least squares method.

7. A plant spectral reflectance measuring device, characterized in that: The plant spectral reflectance measuring device comprises: An active light source module, used for emitting modulated light of a specific frequency to the plant to be measured; A spectral reflectance measurement module is connected to the active light source module and is used to execute the plant spectral reflectance measurement method according to any one of claims 1 to 6.

8. The plant spectral reflectance measuring device according to claim 7, characterized in that: The spectral reflectance measurement module specifically includes: A photoelectric detector module is used to obtain an initial measurement signal of the plant to be measured; the initial measurement signal is a current signal corresponding to the reflected light generated by the plant to be measured after being irradiated by modulated light and ambient light; An I / U conversion module, connected to the photoelectric detector module, for converting the initial measurement signal into a voltage signal to obtain a first measurement signal; a high-pass filter, connected to the I / U conversion module, and configured to perform high-pass filtering on the first measurement signal to obtain a second measurement signal; A lock-in amplifier module, connected to the high-pass filter, used to obtain an initial excitation signal with the same frequency as the modulated light, add a 90° phase shift to the initial excitation signal to obtain a first excitation signal; perform low-pass filtering on the signal after multiplying the initial excitation signal and the second measurement signal to obtain an in-phase component; perform low-pass filtering on the signal after multiplying the first excitation signal and the second measurement signal to obtain an orthogonal component; calculate a second amplitude based on the in-phase component, the orthogonal component and the first amplitude; the first amplitude is the amplitude of the initial excitation signal and the first excitation signal; the second amplitude is the amplitude of the second measurement signal; the amplitude of the second measurement signal is the amplitude of the reflected light; A microprocessor is connected to the active light source module and the lock-in amplifier module, and is used to send a PWM signal to drive the active light source module to emit modulated light of a specific frequency; based on the second amplitude and the spectral reflectance calibration equation, the spectral reflectance of the plant to be measured is determined.

9. The plant spectral reflectance measuring device according to claim 8, characterized in that: The plant spectral reflectance measuring device also includes: A button module, connected to the I / O interface of the microprocessor, and used to trigger the microprocessor to send a PWM signal to the active light source module; A display module, connected to the SPI interface of the microprocessor, for displaying the spectral reflectance of the plant to be measured determined by the plant spectral reflectance measuring device; The wireless communication module is connected to the UART interface of the microprocessor and is used to realize the transmission and positioning of the plant spectral reflectance measuring device and external signals.

10. The plant spectral reflectance measuring device according to claim 8, characterized in that: The plant spectral reflectance measuring device also includes: a battery module, a battery charging and discharging module and a voltage-stabilizing power supply module; The battery module is connected to the battery charging and discharging module; the battery charging and discharging module is connected to the voltage-stabilizing power supply module; and the voltage-stabilizing power supply module is connected to the microprocessor.

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