CN1566928A - Measurement normalization vegetation differential index method and instrument - Google Patents

Abstract

A method for measuring normalization vegetation dispersion index and its apparatus, can quickly and conveniently measure the NDVI value in the farm crop and evaluate the nitrogen fertilizer absorption of farm crop and is important to guide the use of nitrogen fertilizer. It uses sunlight as light source and separately detects the reflection light of incident light and vegetation in two characteristic wavelength of near-infrared light and red light through four photo-detectors with spectral-response characteristic.

Description

A kind of method and instrument of measuring normalized difference vegetation index

Technical field

The invention belongs to optical instrument field, be particularly related to a kind of method and instrument of measuring normalized difference vegetation index, can measure the NDVI value of crops quickly and easily, exactly crop nitrogen fertilizer absorption situation is assessed, according to the demand of nitrogenous fertilizer being implemented variable fertilization, vital role is arranged again to instructing nitrogenous fertilizer to use the different growing stage crop.

Background technology

Applied nitrogen is the important means of increasing crop yield, in plant, nitrogen is protein, nucleic acid and chlorophyllous important component, is concerning that the cell enlargement of plant and new cell form, during the plant nitrogen stress, chlorophyll content in the blade is low, the leaf look light green, and photosynthesis also weakens thereupon, thereby the synthetic quantity of carbohydrates is reduced, cause the plant poor growth, plant is short and small.But when plant absorbing nitrogen is too much, exhibit tissue softness usually, the leaf look dark green, and cauline leaf excessive growth is remaining green when it is due to become yellow and ripe ripe late, easily falls shape, and subjects to the harm of disease worm, finally also can cause the underproduction.Because nitrogen content and the leaf color of vegetation are closely related, according to the analysis to different nitrogen content vegetation spectral reflectivity curve characteristics, discovery can be obtained the nitrogen content of vegetation by the reflectance analysis of some wavelength.The method of human portable fiber-optic spectrometer measure spectrum reflectivity such as the upright Dr.MarvinStone of university of Oklahoma, United States, carried out the research of obtaining nitrogen use efficiency NUE (nitrogen use efficiency) and nitrogenous fertilizer requirement with NDVI, and born fruit.

Normalized difference vegetation index NDVI is defined as:

$\mathrm{NDVI}=\frac{{\mathrm{\ρ}}_{\mathrm{IR}}-{\mathrm{\ρ}}_R}{{\mathrm{\ρ}}_{\mathrm{IR}}+{\mathrm{\ρ}}_R}---\left(1\right)$

ρ in the formula _RBe the vegetation reflectivity of certain infrared light characteristic wave strong point, ρ _IRReflectivity for certain ruddiness characteristic wave strong point vegetation.At present, often adopt field spectroradiometer to carry out the measurement of NDVI, this measuring method field angle is less, the daylight illumination condition is had higher requirements, and device structure complexity, weight big, be worth expensive, operating difficulties, so be difficult to promote.

Summary of the invention

The purpose of this invention is to provide a kind of new method that is used to measure normalized difference vegetation index (NDVI), in light weight according to the NDVI tester of this method design, volume is little, cost is low, simple in structure, easy to use, be suitable for producing in enormous quantities.

The principle of work of this instrument is as follows: utilize daylight to make light source, by four photodetectors with peculiar spectrum response characteristic, in near infrared and two certain wave strong points of ruddiness, respectively the reflected light of incident light and vegetation is surveyed, four parameters that record, after Analog-digital conversion, handle to obtain the NDVI value by single-chip microcomputer, the gained result is shown by LCD (LCD).If it is E that instrument records the incident optical signal of ruddiness characteristic wave strong point _R, corresponding wavelength vegetation reflected light signal is E _RR, infrared light characteristic wave strong point incident optical signal be E _IR, corresponding wavelength vegetation reflected light signal is E _IRR, then have

$R_R=K_R\frac{E_{\mathrm{RR}}}{E_R};$ $R_{\mathrm{IR}}=K_{\mathrm{IR}}\frac{E_{\mathrm{IRR}}}{E_{\mathrm{IR}}}---\left(2\right)$

K in the formula _RAnd k _IRBe proportionality constant, by the characterisitic parameter decision of optical system, photodetector and the adaptive amplifier thereof of instrument.If make k _IR=k _RK just has

$\mathrm{NDVI}=\frac{K_R\frac{E_{\mathrm{RR}}}{E_R}-K_{\mathrm{IR}}\frac{E_{\mathrm{IRR}}}{E_{\mathrm{IR}}}}{K_R\frac{E_{\mathrm{RR}}}{E_R}+K_{\mathrm{IR}}\frac{E_{\mathrm{IRR}}}{E_{\mathrm{IR}}}}=\frac{E_{\mathrm{RR}}{E}_{\mathrm{IR}}-{\mathrm{KE}}_{\mathrm{IRR}}{E}_R}{E_{\mathrm{RR}}{E}_{\mathrm{IR}}+{\mathrm{KE}}_{\mathrm{IRR}}{E}_R}---\left(3\right)$

Formula (3) shows: as long as determine that the characteristic constant undetermined of instrument is k, just can try to achieve NDVI by the signal that four photodetectors record.

The NDVI tester of realizing above-mentioned method of testing and designing, four photodetectors 1 that comprise the peculiar spectrum response characteristic, 2,3,4, optical lens 19,20, analog-digital converter 9, single-chip microcomputer 10, display 11, four spike interference filters 14,15,17,18, four spike interference filters 14,15,17,18 are divided into two groups, every group is two identical optical filters of optical characteristics, and their centre wavelength lays respectively at the near infrared (0.77-0.86 μ m) and ruddiness (the 0.65-0.68 μ m) wave band at vegetation spectral reflectivity rate of curve maximum two ends; Measure be coupled respectively before two photodetectors of the sun incident optical signal near infrared filter 14 and ruddiness optical filter 15, be provided with diffuser 12,13 before the optical filter 14,15, to reduce the influence that day angle of light causes signal amplitude; Be provided with image-forming objective lens 19,20 before two photodetectors 3,4 of measurement vegetation reflected light signal, image-forming objective lens 19,20 will be provided with near infrared filter 17 and ruddiness optical filters 18 in the middle of image-forming objective lens 19,20 and photodetector 3,4 apart from the vegetation target imaging at 1-1.5m place on the photosurface of the detector 3,4 of light.

The photodetector of above-mentioned peculiar spectrum response characteristic is made up of spike interference filter, silicon photoelectric diode and adaptive amplifier thereof etc.The interior light of passband passed through near spike interference filter only allowed centre wavelength, four spike interference filters are divided into two groups, every group is two identical optical filters of characteristic, their centre wavelength lays respectively at the near infrared (0.77-0.86 μ m) and ruddiness (the 0.65-0.68 μ m) wave band on vegetation spectral reflectivity rate of curve maximum both sides, red spectral band is vegetation chloroplast peak absorbance zone, the bandwidth of interference filter should guarantee that spectral reflectivity does not have significant change in passband, to guarantee the measuring accuracy of NDVI.Four silicon photoelectric diodes and four spike interference filters are formed two groups of photodetectors, be respectively applied for the catoptrical detection of near infrared and ruddiness two characteristic wave strong point incident lights and vegetation, the silicon photoelectric diode has higher spectrum sensitivity near infrared and ruddiness characteristic wave strong point, and its photosurface size will guarantee to have the enough large-signal output and the linearity under different daylight illumination conditions.Two photodetectors that are used for incident day optical signal detection are installed in the top of instrument, and two photodetectors that are used for the detection of vegetation reflected light are installed in the below of instrument towards vegetation.

Above-mentioned optical system comprises the receiving objective of frosted glass, diaphragm and the vegetation reflection light detector front of incident daylight signal sensor front.

The characteristic constant k undetermined of above-mentioned instrument determines, can be by trying to achieve to demarcating at the near infrared reference plate equal with ruddiness two characteristic wave strong point spectral reflectivities, and the size of reference plate should conform to the instrument investigative range.Because R _R=R _IR, formula (1) is NDVI=0 as can be known, just can obtain the computing formula of characteristic constant undetermined according to formula (3)

$K=\frac{E_{\mathrm{RR}}{E}_{\mathrm{IR}}}{E_R{E}_{\mathrm{IRR}}}---\left(4\right)$

The effect of above-mentioned analog-digital converter, single-chip microcomputer and display is the simulating signal with the adaptive amplifier output of silicon photoelectric diode, be converted to digital signal through analog-digital converter, by one-chip computer (3) calculating by formula, obtain the NDVI value and go out LCD (LCD) demonstration again.

Description of drawings

Fig. 1 is a vegetation spectral reflectance rate curve, and it can be recorded by field spectroradiometer, and A is chloroplast absorption peak zone among the figure, B is water absorption peak zone, C is the ruddiness characteristic wavelength, and D is the near infrared light characteristic wavelength, and is closely related in the vegetation spectral reflectivity and the vegetation nitrogen content of this two characteristic waves strong point;

Fig. 2 is the theory diagram of portable NDVI measuring instrument, 1 detector among the figure for the incident optical signal that is used to measure ruddiness characteristic wave strong point, 2 detectors for the vegetation reflected light signal that is used to measure ruddiness characteristic wave strong point, 3 detectors for the incident optical signal that is used to measure infrared light characteristic wave strong point, 4 detectors for the vegetation reflected light signal that is used to measure infrared light characteristic wave strong point, 5～8 is the adapter circuit of photodetector, 9 A/D (Analog-digital) converters for the band multiway analog switch, 10 is one-chip computer, 11 for being used to show the LCD of NDVI value.

Fig. 3 is portable NDVI measuring instrument structural representation, during use as shown in the figure vertically downward, 12 and 13 is the diffuser of frosted glass or opal glass, to reduce the influence that day angle of light causes signal amplitude, below this diffuser 14,15 is respective wavelength scope (650-680nm, spike interference filter 770-860nm), sun incident light with other wavelength of elimination, 1 and 2 is two identical photodetectors, to measure optical filter 12 and the ruddiness (650-680nm) of 13 correspondences and the solar irradiation intensity of near infrared light (770-860nm) characteristic wave strong point, 19 and 20 is two identical receiving objectives, design field angle (FOV), make the desired investigative range of instrument (as 1m * 1m), be imaged on the silicon photoelectric diode 3 and 4 photosurface of focal plane of lens from vegetation a distance (as 1.2m) at instrument, 17 and 18 is the interference fringe pass filter same with 14 and 15, be positioned at receiving objective 19,20 and photodetector 3, in the middle of 4, to select optical filter 17, the vegetation reflected light of 18 corresponding ruddiness (650-680nm) and near infrared light (770-860nm) characteristic wave strong point, photodetector 3 and 4 receives the reflected light of vegetation in 650-680nm and 770-860nm spectral range respectively like this, 16 is 3 1.5 volts general dry battery, it provides the energy for the NDVI instrument, 9 A/D (Analog-digital) converters for the band multiway analog switch, it is a digital signal with the analog signal conversion of 4 photodetectors, and export to single-chip microcomputer 10, the ruddiness (650-680nm) that 4 photodetectors of single-chip microcomputer 10 receptions obtain and the solar irradiation intensity and the vegetation reflective light intensity of near infrared light (770-680nm) characteristic wavelength scope, calculate the NDVI value according to formula (3), 11 is display screen, and it shows the NDVI value of single-chip microcomputer output.

Fig. 4 is the digital circuit figure of NDVI, and 21 is AT89C2051 single-chip microcomputer and display circuit, and 22 is the MAX1248 A-D converter, and 23 is LM308 photodetector and adapter circuit.

Embodiment

Vertically downward apart from 1.2 meters of vegetation canopy, its corresponding ground field range is 1m*1m with NDVI, if the sunshine that detector 1 receives is 45watts/ (m in the spectral radiance of 650-680nm wave band ²), the sunshine that detector 2 receives is 90watts/ (m in the spectral radiance of 770-860nm wave band ²), the vegetation canopy that detector 3 receives is 2.25watts/ (m in the spectral reflectance intensity of 650-680nm red spectral band ²), the vegetation canopy that detector 4 receives is 45watts/ (m in the spectral reflectance intensity of 770-860nm near-infrared band ²), can calculate this moment vegetation canopy by formula (2) so is 5% at the spectral reflectivity of red spectral band, is 50% at the spectral reflectivity of near-infrared band, the NDVI value of being calculated the vegetation canopy by formula (1) is 0.818.

Claims (2)

1. method of measuring normalized difference vegetation index, it is characterized in that: it utilizes sunshine as light source, the interference filter of two groups of near infrareds of coupling and red spectral band before four identical photodetectors, respectively the reflected light of sun incident light and vegetation is surveyed, record sun incident light and vegetation reflected light radiation signal at ruddiness and near-infrared band, these four radiation signals are changed through A-D analog-digital, and the computing formula processing of pressing normalized difference vegetation index (NDVI) by single-chip microcomputer, obtain the NDVI value, output results to LCD LCD and show.

2. NDVI testing tool of realizing the described method of claim 1 and designing, it is characterized in that: it comprises four photodetectors (1), (2), (3), (4), optical lens (19), (20), analogue-to-digital converters (9), single-chip microcomputer (10), display (11), four spike interference filters (14), (15), (17), (18); Four spike interference filters (14), (15), (17), (18) are divided into two groups, every group is two identical optical filters of optical characteristics, and their centre wavelength lays respectively at the near infrared (0.77-0.86 μ m) and ruddiness (the 0.65-0.68 μ m) wave band at vegetation spectral reflectivity rate of curve maximum two ends; Near infrared filter (14) and ruddiness optical filter (15) are coupled respectively before two photodetectors of measurement sun incident optical signal, optical filter (14), (15) preceding diffuser (12), (13) of being provided with are to reduce the influence that day angle of light causes signal amplitude; Measure preceding image-forming objective lens (19), (20) of being provided with in two photodetectors (3), (4) of vegetation reflected light signal, image-forming objective lens (19), (20) will be provided with near infrared filter (17) and ruddiness optical filter (18) in the middle of image-forming objective lens (19), (20) and photodetector (3), (4) apart from the vegetation target imaging at 1-1.5m place on the photosurface of the detector (3) of light, (4).

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