DE102007017482A1 - Spectral area analysis method for determining chlorophyll concentration, involves providing two spectral value functions for analyzing spectral areas by filters, where spectral ranges overlap each other - Google Patents

Abstract

The method involves providing two spectral value functions (6, 8) for analyzing spectral areas by filters, where the spectral ranges overlap each other. The area lies in the range between 600 nanometer and 800 nanometer and has a red edge (4) in a reflection spectrum of green vegetation. The spectral analysis is implemented by point measurement and surface measurement. The filters are arranged before a measurement lenses and detectors. Independent claims are also included for the following: (1) a device for analysis of a spectral area (2) a vegetation characterizing method for identifying vegetation characteristics (3) a vegetation characterizing system for determining chlorophyll concentration.

Description

This The invention relates to a method and a device for analysis a given spectral range, as well as a method and a System for the characterization of an existing vegetation.

at the analysis of narrow-band spectral reflection phenomena of objects, the problem is that when the narrow-band phenomenon with with sufficient accuracy, comparatively many spectrally or linearly independent Sensors needed become. Therefore become common Hyperspectral sensors (line detectors) used that gapless can capture a spectral range of 500 to 1000 nm. The spectral resolution such devices is generally between 0.5 and 5 nm.

is also a big one resolution of at least 0.5 nm needed, for example, shifts in the reflection of an object To determine a few nanometers, several measurement channels are needed to to provide the required coverage of the spectral range. Another disadvantage is that due to the required narrow-band recording the exposure times or the integration times become very long, so that only static or quasistatic measurements are carried out can. Dynamic measurements, such as metrological departure a surface with a detector, are therefore almost impossible and, if they are done be loaded with a very high noise level.

moreover The reflection phenomenon to be examined must be selected from a variety of Spectral information to be filtered out, resulting in a high processing costs means and thus also a dynamic or real-time analysis with a portable cost / benefit is not possible.

Farther there is the problem that the pure spectral analysis is explicit must be derived from the radiometric analysis data. In addition, disturbances, such as For example, different lighting conditions are filtered out.

Especially this problem exists in the analysis of vegetation characteristics by determining the change the existing chlorophyll concentration in a studied area. This chlorophyll concentration change stands in relation to a shift of the so-called red edge in the reflection spectrum of green Plants moving through the transition area from the very strong absorption bands of chlorophyll in the area of 660 nm and the absorption-free spectral range above a wavelength of 700 nm results. It is the displacement of the red edge is only a few nanometers, with the associated change the chlorophyll concentration can be pronounced. Because with the help of this Spectral data, in particular the vegetation of large-scale agricultural areas determined should, which traversed with vehicles, especially tractors be a method and a device is needed, which is a cost-effective dynamic area measurement enable.

task Therefore, it is a method and an apparatus to provide spectral analysis of a given spectral range, the static as well as dynamic determinations of the given Enable spectral range.

These Task is solved by a method for the spectral analysis of a given spectral range according to claim 1, a device for spectral analysis of a given spectral range according to claim 11, and a vegetation characterization method according to claim 22 and a vegetation characterization system according to claim 25th

This Invention is based on the knowledge that through the analysis with at least two overlapping ones Spectral value functions no longer have many narrowband independent wavelength bands comparatively long exposure times or integration times need to be recorded but it is sufficient to use broadband spectral functions.

there If one makes use of the same principle with which the human Eye is able to, with only three or four different Receptors to dissolve 10,000 different colors. This is in the human Eye even covered a spectral range of several hundred nanometers, while in the given spectral range to be investigated here only investigated a narrowband range of less than a hundred nanometers must become.

For the analysis itself become two spectral value functions analogous to the receptors of the eye set which overlap each other. This can be done for example by appropriate filters, the upstream of a detector or detectors. The of the detectors detected measurement signals then correspond to the specified spectral value functions. Particularly advantageous is an embodiment in which the overlapping each other Spectral ranges of spectral value functions the spectral range to be examined Cover with their intersection.

Around contamination of the signal by noise can, As a particularly preferred embodiment shows, the radiation power a measuring channel over the integral of the spectral value function in the range of the given Spectral range are determined. Particularly preferred is an embodiment, in which the measured signals defined by the spectral value functions be recorded statically or dynamically. These can be the Measurement signals by means of a point measurement or by area measurement be determined.

Around the inventive method perform, For example, it is particularly preferred to use a device in which a measuring head provided with at least one detector and a measuring optics is, with that over advantageously the spectral value functions defining filters that recorded measurement signals can be. The filters can be introduced alternately into the focal plane of the detector, but it is also possible to use two detectors, each preceded by a filter is. It can the filters either in front of the measuring optics or directly in front of the detector be arranged by yourself. It is also possible the filters integral with the detector or the measuring optics.

alternative can, as another preferred embodiment shows, too two measuring heads be used, which the set spectral value functions record corresponding measuring signals.

Of the Detector / detectors can preferably as photodiode single detector, diode array (line detector) and / or focal plane array.

moreover can the device of the invention a memory unit for storing the measurement signals and a possibility to communicate with a GPS device, so that the measuring signals can be determined cartographically for a surface.

Farther it is advantageous if the device according to the invention has a sensor has, which determines a radiation power of the ambient light. Thereby can Interference, the exist by different types of lighting, be eliminated.

Around the disturbing influences through different lighting possible To keep it low, it is also advantageous if, as a preferred embodiment shows, furthermore, a light source is provided, which is the one to be analyzed Area or the reflection spectrum of the object to be analyzed actively lit.

Especially It is advantageous if the device according to the invention and the method according to the invention be used in the characterization of vegetation stocks. there the spectral range to be examined is preferably in the range the so-called red edge is laid, which is the transition from strong absorption defined to non-absorption areas in the chlorophyll spectrum. Due to the location of the Rote Kante, it is possible chlorophyll concentrations to determine. The position of the red edge varies in relation to the size of the chlorophyll concentration. This is due to the fact that healthy vegetation is visible Spectral range relatively low and in the following near infrared range reflects a relatively large amount of radiation. Other surface materials, such as soil, rock or dead or non-chlorophyll vegetation, show no such distinctive difference in reflectance both areas. This circumstance can consequently serve with vegetation covered by uncovered areas to distinguish.

there it is particularly advantageous if the overlapping spectral value functions cover the range between 600 nm and 800 nm, advantageously Their cutting range is in the range between 650 and 700 nm.

Especially advantageous is an embodiment, in which the device according to the invention a vehicle, in particular a tractor, is attachable to also large-scale vegetation stocks, such as for example, arable land, to be able to determine.

Further advantages and preferred embodiments are in the subclaims, the descrip and defined in the figures.

in the The invention will be described in more detail below with reference to figures become. Here are the embodiments shown in the figures purely exemplary nature and should not be used to Restrict protection range thereupon.

It demonstrate:

1 schematically the reflection spectrum of chlorophyll with arranged therein red edge;

2 a first embodiment of the overlap of two spectral value functions in the region of the red edge;

3 a first embodiment of a device according to the invention for recording two spectral functions;

4 a second embodiment of the device according to the invention for receiving two spectral functions; and

5 A third embodiment of the device according to the invention for recording two spectral functions.

1 shows the reflection spectrum of green plants, ie the absorption spectrum of chlorophyll. Over the visible range of 400 to about 700 nm of the human eye, chlorophyll shows pronounced absorption down to one region, here by the reference numeral 2 at 550 nm, which is why plants appear green. Also shown is the end of absorption at approximately 700 nm - the so-called red edge above this wavelength-wise chlorophyll has no absorption. The red edge is indicated by the reference numeral 4 characterized.

2 shows a section of the reflection spectrum around the area of the red edge 4 from 650 to 750 nm. In addition, in 2 show which exemplary spectral regions two spectral value functions 6 and 8th cover the area of the red edge. It can clearly be seen that the red edge is preferably in the intersection region for the overlapping spectral value functions 6 and 8th lies. In this "artificial" color space spanned by the two specified spectral value functions, the fact that the spectral properties of the phenomenon to be investigated, such as the red edge, affect both measured signals defined by the spectral value functions, results in a change / shift in the spectrum Depending on the position of the spectral ranges of the spectral value functions, this can be used to deduce the exact spectral position of the red edge.

Noise contamination of the signal can be minimized by forming the integral over the spectral value function. The integration limits are chosen so that they cover the possible area in which the red edge comes to rest. Mathematically, this is determined by the following formalization: S x (λ) = k · I O (λ) · ρ (λ) · x (λ) [1] S y (λ) = k · I O (λ) · ρ (λ) · y (λ) [2] With:
S _{x / y} (λ) = spectral signal power in channel "x" (according to [1]) or "y" (according to [2])
k = constant for the detection of the electronic signal power (device function).
I _o (λ) = spectral (solar) irradiation power
ρ (λ) = spectral reflection coefficient (see Figure 1)
_{x / y} (λ) = spectral value function in channel "x" or "y" (see Figure 2)

The signal powers in the channels "x" and "y" (according to the method presented) result from the "determined" integration of λ ₁ to λ ₂ , where λ ₁ , λ ₂ are chosen so that the red edge in the of λ ₁ and λ ₂ spanned spectral range is:

By defining the relevant spectral range λ ₁ to λ ₂ for the integral, interference effects, such as ambient light fluctuations, are reduced to the spectral range around the red edge. In particular, the influence of "serene clouds" or "blue sky" is minimized or completely hidden.

There the determination of the position of the red edge on the radiation power within the channels takes an elaborate processing of the measurement results is unnecessary because the integration is already intrinsically contained in the measuring principle.

For receiving are the measuring signals defined by the spectral value function several devices conceivable. Basically, however, two measurement signals be recorded, this being realized by two measuring heads, each with a detector can be. However, it is also possible to use a single measuring head to use with a single detector, in succession, for example about different successively introduced filters, the two measurement signals can be realized. It is also possible to use a measuring head with two detectors or the filters to arrange on a detector so that two of the specified Spectral value corresponding measurement signals can be recorded. The can Devices for both a dot as well as for an area measurement be used. Basically however, that the observation of a measuring point in two channels to same time of measurement is only possible monostatically and biaxially, any other method at a time offset of the measuring points leads.

If simultaneously (two detectors) or offset in time (one detector) is measured, hangs from the specific measuring tasks. This static measurements can both be performed simultaneously and in succession. However, at dynamic measurements the dynamics of the test object with time-shifted measurements considered become.

3 shows a first preferred embodiment of the present invention, in which the measurements of the spectral value functions by means of two measuring heads 12 . 14 is carried out. The measuring heads 12 . 14 each have a detector 16 . 18 and an optic - here as lenses 20 . 22 shown on. It takes in the first measuring head 12 arranged detector 16 a first by a first Spektralwertfunktion defined measurement signal, while in the second measuring head 14 arranged detector 18 receives a second measured signal defined by a second spectral value function. For the determination of the first and the second spectral value function can be in front of the measuring heads 12 respectively. 14 filter 24 . 26 be arranged, which set the range of spectral value functions. Both measuring heads 12 . 14 focus on the same point of an object 28 , To record the spectral reflections of the object 28 In addition, active lighting units, not shown, may be present, which bring about a defined reflection. In addition, on the measuring heads 12 . 14 There may be additional sensors that analyze the ambient light.

4 shows a schematic representation of a device according to the invention for the time-shifted measurement of specified by the spectral value measurement signals. This is only a measuring head 12 with only one detector 16 again using two filters defining the spectral value functions 24 . 26 are provided, which alternately in the beam path between object to be examined 28 and detector 16 can be introduced, so that at a first time t1, the measurement signal by the first spectral value function or the first filter 24 is defined, while at a second time t2, the measurement signal by the second spectral value function or the second filter 26 is defined is recorded.

Again, both measurements are from one and the same point 28 on an object. The filter set 24 and 26 can in front of the measuring optics 20 or alternatively directly in front of the detector 16 be introduced alternately or rotate.

Another possibility of recording two spectral value functions corresponding measuring signals is in 5 shown. In this case, in the focal plane of a single measuring head 12 instead of, as in 4 shown, a detector two detectors 16 . 18 arranged. In principle, however, it is also possible to divide the beam path by means of mirrors, so that the two detectors 16 . 18 angeord at an angle to each other are net and one beam each to the detector 16 and another beam to the detector 18 is forwarded.

5 However, shows a variant without additional mirror, in which in the focal plane of the measuring optics 20 two filters 24 . 26 are arranged, the radiation in turn from two detectors 16 . 18 Will be received. In this measuring device, at a first time t1 a first measuring signal with the filter 24 from an object point 30 and a second measurement signal with the filter 26 from an object point 32 However, in order to perform an analysis again by means of overlapping spectral value functions, the object points must 30 respectively. 32 be picked up exactly with the other filter again. That is, at a second time t2 must be from the object point 32 a measuring signal with the filter 28 and from the object point 32 a measuring signal with the filter 26 be recorded. For this purpose, either the measuring head 12 or the detectors 16 . 18 be tilted by an angle α. However, it is also possible not to tilt the measuring head, but the offset between object point 30 and 32 to move altogether.

In principle, everyone would be in the 3 to 5 a dynamic measurement is possible, however, such is one with two measuring heads, as in 3 described, mechanically complex and very complex with respect to the optical adjustment and dimensional accuracy.

For dynamic measurements, therefore, the in 5 described device, since only the exposure times and durations of the two channels with the dynamic image offset must be synchronized by the object movement. This means that the direction of movement of the object must have the same orientation as the detector arrangement in the focal plane. This will be the same object point 30 at time t1 on the detector 16 and at time t2 on the detector 18 displayed.

For dynamic measurements, the in 4 However, for static measurements, the mechanical complexity is low and the synchronization of the filter closing times can be easily solved electronically by a timing of the detector cycles. In dynamic measurements, however, a mechanism must be provided that moves the entire apparatus.

If not only point measurements are to be carried out, but surface measurements can be used instead of the individual detectors shown here, a diode arrays or focal-plain arrays. For dynamic measurements, in particular with the device off 5 can be performed, the two arranged in the focal plane detectors are preferably replaced by two diode arrays having an orientation transverse to the direction of movement. Continuous movement in one direction results in a continuous image structure that analyzes the spectral range over the measured area.

This is particularly preferred in the characterization of vegetation stocks by means of the determination of the chlorophyll concentration by means of the position of the red edge. There are two different cases:
In the case of closed stands, an areal survey of the position of the red edge of the vegetation takes place. Since the position of the red edge in the spectrum correlates to a first approximation with the chlorophyll concentration, the relative concentration fluctuations can be recorded. For this it is assumed that for homogeneous crop stands the leaf geometry, the leaf scattering coefficient and the stock spread characteristics are homogeneous. Depending on the measurement results, for example, required fertilizer quantities can be adjusted.

Of the The second case of the vegetation characteristic is the open stock. This can be due to mixed signal formation from plant reflection and soil reflection the so-called normalized difference vegetation index determined be over the degree of plant cover of the field soil can be determined. The index is based on the fact that vegetation is visible Spectral range (wavelength from about 400 to 700 nm) relatively little and in the following near Infrared range (wavelength from about 700 to 1300 nm) reflects relatively much radiation.

Other Surface materials, such as soil, rock or dead or non-chlorophyll vegetation, show no such distinctive difference in reflectance both areas. This circumstance can consequently serve with vegetation covered by uncovered areas to distinguish. Dependent from the different measurement results, can also about the state of vegetation Conclusions made become. these can again as the basis for fertilization or weed control measures serve.

Especially It is advantageous if the devices also have a signal detection unit which is correlated with the recording of GPS data, whereby a mapping of the measured spectral value functions over the area possible is. In addition, it is advantageous if the irradiation power of the ambient light monitored by a sensor attached to the device becomes, whereby a normalization of the signals is possible. Furthermore, can the device also includes an active light source for measuring the spectral value functions which also allows measurements in low light conditions possible are.

Especially It is advantageous, the measurements with a vehicle or a Tractor, perform and to pair with a so-called Miniveg N-sensor. The Miniveg-N data can also be used to normalize the soil conditions, where data is also obtained from large-area agricultural land can.

Disclosed is a method and apparatus for determining a predetermined Spectral range, in particular of the spectral range around the red Edge, where the analysis of the spectral range by means of two overlapping Spectral value functions performed as well as a method and a system for the characterization of a existing vegetation.

2

Green absorption area of chlorophyll

4

Red edge

6 8th

spectral

10

cutting area

12 14

detectors

16 18

measuring channel

20 22

measurement optics

24 26

filter

28

object point

30 32

object point

Claims (26)

Method for the spectral analysis of a given spectral range, characterized in that for the analysis at least two spectral value functions are defined whose spectral ranges overlap one another. The method of claim 1, wherein the predetermined Spectral range is narrowband, in particular less than 100 nm includes. Method according to claim 1 or 2, wherein the spectral ranges the spectral value functions are broadband. Method according to one of the preceding claims, wherein the given spectral range in the range between 600 nm and 800 nm, in particular between 650 nm and 750 nm. Method according to one of the preceding claims, wherein the predetermined spectral range the red edge in the reflection spectrum from greener Vegetation includes. Method according to one of the preceding claims, wherein the radiant power according to the spectral value functions via integration is determined along the predetermined spectral range. Method according to one of the preceding claims, wherein the spectral analysis is determined statically and / or dynamically. Method according to one of the preceding claims, wherein the predetermined spectral range through a reflection to be examined is predefined on an object. Method according to one of the preceding claims, wherein the spectral analysis is performed by point measurement. Method according to one of claims 1 to 8, wherein the spectral analysis by area measurement carried out becomes. Device for analyzing a given spectral range to perform a method according to any one of the preceding claims characterized in that at least one measuring head is provided which at least one device for specifying spectral value functions which specifies two spectral value functions which overlap each other. Apparatus according to claim 11, wherein the measuring head furthermore has at least one detector and a measuring optics. Apparatus according to claim 12, wherein the measuring head has two detectors. Apparatus according to claim 11, wherein two measuring heads with each a detector and a device for specifying spectral value function are provided. Device according to one of claims 11 to 14, wherein the device for specifying spectral value functions in front of the measuring optics and / or before the at least one detector is arranged. Device according to one of claims 11 to 15, wherein the device for setting the spectral value functions by at least two filters is realized. Device according to one of claims 11 to 16, wherein the at least a detector as a photodiode single detector, diode array and / or Focal plain array is trained. Apparatus according to any one of claims 11 to 17, wherein further a memory unit is provided in which one of the at least a detector detected measurement signal can be stored. Device according to one of claims 11 to 18, wherein the device has an interface over a memory unit and / or a GPS device is responsive. Apparatus according to any one of claims 11 to 19, wherein further a sensor is provided, with which a radiation power of a Ambient light is determined. Apparatus according to any of claims 11 to 20, wherein further a light source for irradiating a region whose spectral value function is to be determined exists. Vegetation characterization method for identification a vegetation characteristic, characterized in that a the vegetation characterizing chlorophyll concentration means A method according to any one of claims 1 to 10 is determined. The method of claim 22, wherein the chlorophyll concentration exceeds the spectral position of the red edge is determined. Method according to one of claims 22 to 23, wherein a device according to one of the claims 11 to 21 is used. Vegetation characterization system for determining a chlorophyll concentration characterizing the vegetation characterized in that the chlorophyll concentration with a Device according to one of the claims 11 to 21 is determinable. Vegetation characterization system according to claim 25, wherein the system on a vehicle, in particular on a tractor, is fastened.