CN110703277B - Method for inverting forest canopy aggregation index based on full-waveform laser radar data - Google Patents

Method for inverting forest canopy aggregation index based on full-waveform laser radar data Download PDF

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CN110703277B
CN110703277B CN201910997906.8A CN201910997906A CN110703277B CN 110703277 B CN110703277 B CN 110703277B CN 201910997906 A CN201910997906 A CN 201910997906A CN 110703277 B CN110703277 B CN 110703277B
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崔磊
焦子锑
孙梅
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Beijing Normal University
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    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
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Abstract

The invention relates to a method for inverting forest canopy aggregation indexes based on full-waveform laser radar data, and belongs to the technical field of spatial information. Firstly, taking the ratio of ground echo energy to total echo energy as the clearance fraction of a forest canopy of a laser radar observation area; then, calculating to obtain the vertical clearance distribution of the forest canopy of the observation area of the laser radar based on a radiation transmission model only considering single scattering about the laser radar, and further calculating the canopy clearance fraction of tree crown branch and leaf elements in a random distribution state according to the result; and finally, taking the obtained canopy gap fraction of the tree crown branch and leaf elements in the random distribution state and the obtained gap fraction in the non-random distribution state as input, and solving the forest canopy aggregation index based on the beer law. By utilizing the method, the inversion of the high-resolution forest canopy aggregation index can be realized. The method has important research significance and application value in the field of researching forest vegetation quantitative remote sensing.

Description

Method for inverting forest canopy aggregation index based on full-waveform laser radar data
One, the technical field
The invention relates to a method for inverting forest canopy aggregation indexes based on full-waveform laser radar data, and belongs to the technical field of spatial information.
Second, background Art
The aggregation index describes the spatial distribution pattern of the leaves and is an important input parameter in modeling of ecological, hydrological and surface processes. It also has important significance in remote sensing related applications, for example, it is a necessary parameter for estimating the true leaf area index; the estimation accuracy of the net primary productivity and the total primary productivity can be improved, etc.
Currently, many methods of inverting vegetation index based on ground and satellite observation data are developed. The ground observation method mainly comprises the following steps: (1) digital hemisphere photography; (2) a plant canopy analyzer; (3) a multiband vegetation imager; these methods are widely used for validation of satellite aggregation index products. However, ground observation is limited by time, labor cost, and the like, and it is difficult to realize wide-range application. Satellite observations provide an effective means for inversion of aggregate indices on a regional and global scale. However, the current method for estimating the aggregation index based on satellite observation data has certain limitations, such as hot spot and cold spot reflectivity constructed by using different BRDF models and observation data uncertainty introduced by different satellite sensor data. In addition, the resolution of the existing multi-angle optical satellite sensor is low, and the aggregation index product produced based on the data sources cannot meet the requirements of the existing fine model application.
With the development of lidar technology, a large amount of high-resolution lidar data is acquired from airborne and satellite platforms. The acquired lidar data contains detailed vegetation three-dimensional structural information, and the information has the potential of estimating regional or global scale forest canopy aggregation indexes. According to different data recording results, the laser radar data is divided into two types, namely discrete laser radar data and full-waveform laser radar data. Discrete lidar data, also known as point cloud data, is the result of recording the location of the point of contact of the emitting laser with an object (e.g., a tree top, branches, lower layers, and the ground). However, this data is not suitable for application to inversion of the aggregation index because of the lower dot density, which makes it impossible to record smaller gap variations in the canopy. Full-waveform lidar data records the echo signal of a physical laser pulse, and compared with discrete lidar data, the full-waveform lidar data records the echo signal of the whole vegetation canopy contact, and can cover more canopy gap information. Therefore, it has great potential in inverting the aggregation index.
In the research, a method for inverting the forest canopy aggregation index based on full-waveform laser radar data is developed, and the method makes full use of three-dimensional information of a vegetation canopy structure. Firstly, representing the clearance rate of a vegetation canopy by utilizing the ratio of ground echo to canopy echo energy; secondly, deducing the vertical gap distribution of the canopy by using a radiation transmission model which only considers single scattering and is related to the laser radar, wherein the vertical gap distribution result is further used for calculating the gap rate of the corresponding canopy branch and leaf elements in a random distribution state; and finally, taking the obtained canopy gap fraction of the tree crown branch and leaf elements in the random distribution state and the obtained gap fraction in the non-random distribution state as input, and solving the forest canopy aggregation index based on the beer law. The field actual measurement data verification shows that the inversion of the forest canopy aggregation index based on the full-waveform laser radar data can be realized. The invention provides a full-waveform laser radar data acquisition region or global scale high resolution CI based method, which can improve the precision of related application in the field of remote sensing and can be used as reference data to verify medium resolution aggregation index products. The applications represent the application value of the patent.
Third, the invention
The purpose is as follows: the invention aims to develop a method for inverting forest canopy aggregation indexes based on full-waveform laser radar data. The full-waveform laser radar data records more canopy gap information and has the characteristics of wide data range coverage and high resolution. The full-waveform laser radar data combined with the method provided by the invention can realize the production of regional or global scale high-resolution aggregation index products.
The technical scheme is as follows: the invention relates to a method for inverting forest canopy aggregation index based on full-waveform laser radar data, which comprises the following specific steps:
step S10: acquiring ground echo signals in full-waveform laser radar data, and then obtaining clearance fraction P of forest canopy in observation area of laser radar sensor based on acquired ground echo signals and total echo signalsH(LPR)；
Step S11: taking the emission energy and the return energy of the laser radar sensor as input data, and solving the vertical gap distribution of the forest canopy of the observation area of the laser radar sensor based on a radiation transmission model which only considers single scattering and is related to the laser radar; then, the obtained vertical gap distribution data is used as input to obtain the canopy gap fraction P under the state that the forest canopy branch and leaf elements in the corresponding observation area are randomly distributedr；
Step S12: the gap fraction P of canopy branch and leaf elements in a random distribution staterAnd gap fraction P in a non-random distributionHAs an input, the forest canopy aggregation index is found based on beer's law.
In an embodiment of the present invention, the specific implementation steps of step S10 are as follows:
step S101: taking original echo data received by a laser radar sensor as input, and carrying out denoising processing on the original echo waveform data by a Gaussian filtering method;
step S102: the filtered echo data is used as input, and the echo energy E hitting the ground is calculated by a Gaussian decomposition methodg. Ground echo energyAmount (E)g) Is the result of the last waveform integration after gaussian decomposition, the mathematical expression is as follows:
Figure GDA0003318346740000021
in the formula (1), LiIn order to record the echo energy received at the moment i, GroBeg and GroEnd are the initial position and the end position of the ground echo;
step S103: by ground echo energy EgAnd total echo energy EtAs input, calculating a penetration index LPR of the satellite-borne laser radar, and using the penetration index LPR as a clearance fraction of a forest canopy of an observation area of the laser radar, wherein the calculation formula is as follows:
Figure GDA0003318346740000022
total echo energy EtBased on the result of waveform integration from the signal beginning to the signal end of the denoised waveform, the calculation formula is as follows,
Figure GDA0003318346740000023
in equation (3), SigBeg and SigEnd are the start position and end position of the echo.
In an embodiment of the present invention, the specific implementation steps of step S11 are as follows:
step S111: a radiation transmission model that considers only a single scatter with respect to lidar is:
Ln＝En[1-exp(-k*LAIn)]ω， (4)
in the formula (4), ω is a scattering coefficient, k is an extinction coefficient, and LnThe echo energy reflected by the recording layer n, received by the lidar sensor, EnFor recording the laser radar sensor emission energy received by layer n, where EnThe expression of (a) is as follows:
En+1＝exp(-k*LAIn-1)En， (5)
the relation of the transmission energy of the laser radar between the continuous recording layers can be obtained by combining the formula (4) and the formula (5):
Figure GDA0003318346740000031
based on equation (6), a vertical distribution PRE of laser emission energy over the entire lidar observation area can be derived, and PRE can be expressed as:
Figure GDA0003318346740000032
the summation operation of the energy distribution PRE can be expressed as follows:
Figure GDA0003318346740000033
e in formula (8)nIs the ground echo energy, and the expression is:
Figure GDA0003318346740000034
l in formula (9)nIs ground echo energy, rgIs the ground reflectivity of the lidar pulse, simultaneous equations (8) and (9) can be derived as follows:
Figure GDA0003318346740000035
step S112: with initial emission energy E of the lidar sensor0Total received energy
Figure GDA0003318346740000036
And ground reflectivity rgAs input, can be obtained from equation (10)Obtaining a single scattering coefficient omega of the vegetation canopy;
step S113: with the transmitted energy E of the lidar sensor0Recorded receive echo successive energy (L)0,L1,…,Ln-1) And a scattering coefficient omega as input, and the vertical distribution (E) of the laser radar emission energy of the observation area can be obtained according to the formula (7)0,E1,…,EN)；
Step S114: transmittance T of space between two continuous recording layersnVertical distribution of energy (E) can be transmitted by lidar0,E1,…,EN) The calculation formula is as follows:
Figure GDA0003318346740000041
step S115: by calculating the vertical distribution (E) of the laser radar transmitted energy0,E1,…,EN) As input, the transmittance profile (T) of the forest canopy in the observation area of the laser radar can be obtained according to the formula (11)1,T2,…,Tn)；
Step S116: the calculation formula of the clearance rate of the canopy elements in the random distribution state is as follows:
Figure GDA0003318346740000042
wherein H is the vertical height; t isiIs the transmittance of the base layer i, which is the vertical space between two consecutive recording instants of the lidar sensor; l _ bottom is the ground location;
step S117: to calculate the vertical distribution (T) of the laser radar transmitted energy obtained1,T2,…,Tn) As input, the clearance ratio P under the state that the elements of the branches and leaves of the canopy are randomly distributed can be obtained according to the formula (12)r。
In an embodiment of the present invention, the specific implementation steps of step S12 are as follows:
step S121: the expression of beer's law is:
Figure GDA0003318346740000043
wherein P (theta) is the gap fraction of the forest canopy when the sunlight incidence direction is theta, G (theta) is the projection coefficient of the canopy and represents the projection of the unit leaf area on the ground when the sunlight incidence angle is theta, L is the leaf area index, and omega is the concentration index;
step S122: when the canopy branches and leaves are randomly distributed, the omega is 1, then the formula (13) is
Figure GDA0003318346740000044
The calculation formula of the aggregation index can be obtained by combining the formulas (13) and (14), and the expression is as follows:
Figure GDA0003318346740000045
in the formula, PH(LPR) is the gap fraction of forest canopy branch and leaf elements in a non-random distribution state, PrThe gap fraction of forest canopy branch and leaf elements in a random distribution state is shown.
The advantages and the effects are as follows: the invention relates to a method for inverting forest canopy aggregation indexes based on full-waveform laser radar data. The invention provides a method for inverting forest canopy aggregation indexes based on full-waveform laser radar data by utilizing vegetation structure three-dimensional information contained in the full-waveform laser radar data and combining a radiation transmission model. The method has clear logic, simple and clear method and strong adaptability, and the newly invented algorithm is expected to be used as a business algorithm for producing the aggregation indexes by satellite-borne and airborne laser radar data, and has important research significance for improving the resolution of regional or global scale aggregation index products.
Description of the drawings
FIG. 1 is a schematic flow diagram of the process of the present invention.
FIG. 2 is a schematic diagram of a full-waveform lidar data observation.
Fig. 3 is a graph of algorithm verification results.
Fifth, detailed description of the invention
The invention relates to a method for inverting forest canopy aggregation index based on full-waveform laser radar data, which comprises the following specific implementation steps (as shown in figure 1):
step S10: acquiring ground echo signals in full-waveform laser radar data, and then obtaining clearance fraction P of forest canopy in observation area of laser radar sensor based on acquired ground echo signals and total echo signalsH(LPR)；
Step S11: taking the transmitting energy and the returning energy of the laser radar sensor as input data, and solving the vertical gap distribution of the forest canopy of the observation area of the laser radar sensor based on a radiation transmission model only considering single scattering about the laser radar (as shown in figure 2); then, the obtained vertical gap distribution data is used as input to obtain the canopy gap fraction P under the state that the forest canopy branch and leaf elements in the corresponding observation area are randomly distributedr；
Step S12: the gap fraction P of canopy branch and leaf elements in a random distribution staterAnd gap fraction P in a non-random distributionHAs input, the forest canopy aggregation index is obtained based on beer's law
In an embodiment of the present invention, the specific implementation steps of step S10 are as follows:
step S101: taking original echo data received by a laser radar as input, and carrying out denoising processing on the original echo waveform data by a Gaussian filtering method;
step S102: the filtered echo data is used as input, and the echo energy E hitting the ground is calculated by a Gaussian decomposition methodg(ii) a Ground echo energy (E)g) Is the result of the last waveform integration after gaussian decomposition, the mathematical expression is as follows:
Figure GDA0003318346740000051
in the formula (1), LiIn order to record the echo energy received at the moment i, GroBeg and GroEnd are the initial position and the end position of the ground echo;
step S103: by ground echo energy EgAnd total echo energy EtAs input, calculating a penetration index LPR of the satellite-borne laser radar, and using the penetration index LPR as a gap fraction of a forest canopy of an observation area of the laser radar, wherein the calculation formula is as follows:
Figure GDA0003318346740000052
total echo energy EtBased on the result of waveform integration from signal start to signal end of the denoised waveform, the calculation formula is as follows:
Figure GDA0003318346740000053
in equation (3), SigBeg and SigEnd are the start position and end position of the echo.
In an embodiment of the present invention, the specific implementation steps of step S11 are as follows:
step S111: a radiation transmission model that considers only a single scatter with respect to lidar is:
Ln＝En[1-exp(-k*LAIn)]ω， (4)
in the formula (4), ω is a scattering coefficient, k is an extinction coefficient, and LnIs the echo energy received by the lidar sensor reflected by the recording layer n, EnFor recording the laser radar sensor emission energy received by layer n, where EnThe expression of (a) is as follows:
En+1＝exp(-k*LAIn-1)En， (5)
the relation of the transmission energy of the laser radar between the continuous recording layers can be obtained by combining the formula (4) and the formula (5):
Figure GDA0003318346740000061
based on equation (6), a vertical distribution PRE of the laser emission energy over the entire lidar observation area can be derived, and PRE can be expressed as:
Figure GDA0003318346740000062
the summation operation of the energy distribution PRE can be expressed as follows:
Figure GDA0003318346740000063
e in formula (8)nIs the ground echo energy, and the expression is:
Figure GDA0003318346740000064
l in formula (9)nIs ground echo energy, rgIs the ground reflectivity of the lidar pulse, simultaneous equations (8) and (9) can be derived as follows:
Figure GDA0003318346740000065
step S112: with initial emission energy E of the lidar sensor0Total received energy
Figure GDA0003318346740000066
And ground reflectivity rgAs input, the single scattering coefficient ω of the vegetation canopy can be obtained according to the formula (10);
step S113: with the transmitted energy E of the lidar sensor0Recorded receive echo successive energy (L)0,L1,…,Ln-1) And a scattering coefficient omega as input, and the vertical distribution (E) of the laser radar emission energy of the observation area can be obtained according to the formula (7)0,E1,…,En)；
Step S114: transmittance T of space between two continuous recording layersnVertical distribution of energy (E) can be transmitted by lidar0,E1,…,En) The calculation formula is as follows:
Figure GDA0003318346740000067
step S115: by calculating the vertical distribution (E) of the laser radar transmitted energy0,E1,…,En) As input, the transmittance profile (T) of the forest canopy in the observation area of the laser radar can be obtained according to the formula (11)1,T2,…,Tn)；
Step S116: the calculation formula of the clearance rate of canopy branches and leaves in the random distribution state is as follows:
Figure GDA0003318346740000074
wherein H is the vertical height; t isiIs the transmittance of the base layer i, which is the vertical space between two consecutive recording instants of the lidar sensor; l _ bottom is the ground location;
step S117: to calculate the vertical distribution (T) of the laser radar transmitted energy obtained1,T2,…,Tn) As input, the clearance ratio P under the state that the elements of the branches and leaves of the canopy are randomly distributed can be obtained according to the formula (12)r。
In an embodiment of the present invention, the specific implementation steps of step S12 are as follows:
step S121: the expression of beer's law is:
Figure GDA0003318346740000071
wherein P (theta) is the gap fraction of the forest canopy when the sunlight incidence direction is theta, G (theta) is the projection coefficient of the canopy and represents the projection of the unit leaf area on the ground when the sunlight incidence angle is theta, L is the leaf area index, and omega is the concentration index;
step S122: when the canopy branches and leaves are randomly distributed, the omega is 1, then the formula (13) is
Figure GDA0003318346740000072
The calculation formula of the aggregation index can be obtained by combining the formulas (13) and (14), and the expression is as follows:
Figure GDA0003318346740000073
in the formula, PHThe gap fraction, P, of canopy branch and leaf elements in a non-random distribution staterThe forest canopy gap fraction of canopy branch and leaf elements in a random distribution state is obtained.
Example 1:
on an associative ThinkStation desktop computer provided with an Intel E3-1220@3.1GHz/8M dual-core processor, a matlab programming language is used as an implementation tool for implementing case embodiments; in this embodiment, taking satellite-borne GLAS full-waveform lidar data as an example, the aggregation index is calculated according to the implementation flow of the method shown in fig. 1; then, the aggregation index result actually measured in the field is used for verifying the algorithm provided by the invention.
FIG. 3 is a scatter diagram comparing ground measured data with the result of aggregation index inverted based on the method of the present invention, and it can be seen from the diagram that the application results of the method proposed by the present invention in coniferous forest, commingled forest and broadleaf forest all show better consistency with the ground observation results, and the decision coefficient reaches 0.63; furthermore, the root mean square error of the fit is also only 0.09. According to the comparison and verification, the method for inverting the forest canopy aggregation index based on the full-waveform laser radar data can accurately invert the forest canopy aggregation index by using the full-waveform laser radar data.

Claims (4)

1. A method for inverting forest canopy aggregation indexes based on full-waveform laser radar data comprises the following steps:
step S10: acquiring ground echo signals in full-waveform laser radar data, and then obtaining clearance fraction P of forest canopy in observation area of laser radar sensor based on acquired ground echo signals and total echo signalsH(LPR)；
Step S11: taking the emission energy and the return energy of the laser radar sensor as input data, and solving the vertical gap distribution of the forest canopy of the observation area of the laser radar sensor based on a radiation transmission model only considering single scattering about the laser radar; then, the obtained vertical gap distribution data is used as input to obtain the canopy gap fraction P under the state that the forest canopy branch and leaf elements in the corresponding observation area are randomly distributedr；
Step S12: the gap fraction P of canopy branch and leaf elements in a random distribution staterAnd gap fraction P in a non-random distributionHAs an input, the forest canopy aggregation index is found based on beer's law.
2. The method for inverting forest canopy gather index based on full waveform lidar data of claim 1, wherein: the specific implementation steps of step S10 are as follows:
step S101: taking original echo data received by a laser radar sensor as input, and carrying out denoising processing on the original echo waveform data by a Gaussian filtering method;
step S102: the filtered echo data is used as input, and the echo energy E hitting the ground is calculated by a Gaussian decomposition methodg(ii) a Ground echo energy (E)g) Is the result of the last waveform integration after gaussian decomposition, the mathematical expression is as follows:
Figure FDA0003318346730000011
in the formula (1), LiIn order to record the echo energy received at the moment i, GroBeg and GroEnd are the initial position and the end position of the ground echo;
step S103: by ground echo energy EgAnd total echo energy EtAs input, calculating a penetration index LPR of the satellite-borne laser radar, and using the penetration index LPR as a gap fraction of a forest canopy of an observation area of the laser radar, wherein the calculation formula is as follows:
Figure FDA0003318346730000012
total echo energy EtBased on the result of waveform integration from signal start to signal end of the denoised waveform, the calculation formula is as follows:
Figure FDA0003318346730000013
in equation (3), SigBeg and SigEnd are the start position and end position of the echo.
3. The method for inverting forest canopy gather index based on full waveform lidar data of claim 1, wherein: the specific implementation steps of step S11 are as follows:
step S111: a radiation transmission model that considers only a single scatter with respect to lidar is:
Ln＝En[1-exp(-k*LAIn)]ω， (4)
in the formula (4), ω is a scattering coefficient, k is an extinction coefficient, and LnThe echo energy reflected by the recording layer n, received by the lidar sensor, EnFor recording the laser radar sensor emission energy received by layer n, where EnThe expression of (a) is as follows:
En+1＝exp(-k*LAIn-1)En， (5)
the relation of the transmission energy of the laser radar between the continuous recording layers can be obtained by combining the formula (4) and the formula (5):
Figure FDA0003318346730000021
based on equation (6), a vertical distribution PRE of laser emission energy over the entire lidar observation area can be derived, and PRE can be expressed as:
Figure FDA0003318346730000022
the summation operation of the energy distribution PRE can be expressed as follows:
Figure FDA0003318346730000023
e in formula (8)nIs the ground echo energy, and the expression is:
Figure FDA0003318346730000024
l in formula (9)nIs ground echo energy, rgIs the ground reflectivity of the lidar pulse, simultaneous equations (8) and (9) can be derived as follows:
Figure FDA0003318346730000025
step S112: with initial emission energy E of the lidar sensor0Total received energy
Figure FDA0003318346730000026
And ground surfaceRefractive index rgAs input, the single scattering coefficient ω of the vegetation canopy can be obtained according to the formula (10);
step S113: with the transmitted energy E of the lidar sensor0Recorded receive echo successive energy (L)0,L1,…,Ln-1) And a scattering coefficient omega as input, and the vertical distribution (E) of the laser radar emission energy of the observation area can be obtained according to the formula (7)0,E1,…,En)；
Step S114: transmittance T of space between two continuous recording layersnVertical distribution of energy (E) can be transmitted by lidar0,E1,…,En) The calculation formula is as follows:
Figure FDA0003318346730000031
step S115: by calculating the vertical distribution (E) of the laser radar transmitted energy0,E1,…,En) As input, the transmittance profile (T) of the forest canopy in the observation area of the laser radar can be obtained according to the formula (11)1,T2,…,Tn)；
Step S116: the clearance rate calculation formula under the state that the canopy branches and leaves are randomly distributed is as follows:
Figure FDA0003318346730000032
wherein H is the vertical height; t isiIs the transmittance of the base layer i, which is the vertical space between two consecutive recording instants of the lidar sensor; l _ bottom is the ground location;
step S117: to calculate the vertical distribution (T) of the laser radar transmitted energy obtained1,T2,…,Tn) As input, the clearance ratio P under the state that the elements of the branches and leaves of the canopy are randomly distributed can be obtained according to the formula (12)r。
4. The method for inverting forest canopy gather index based on full waveform lidar data of claim 1, wherein: the specific implementation steps of step S12 are as follows:
step S121: the expression of beer's law is:
Figure FDA0003318346730000033
wherein P (theta) is the gap fraction of the forest canopy when the sunlight incidence direction is theta, G (theta) is the projection coefficient of the canopy and represents the projection of the unit leaf area on the ground when the sunlight incidence angle is theta, L is the leaf area index, and omega is the concentration index;
step S122: when the canopy branches and leaves are randomly distributed, the omega is 1, then the formula (13) is
Figure FDA0003318346730000034
The calculation formula of the aggregation index can be obtained by combining the formulas (13) and (14), and the expression is as follows:
Figure FDA0003318346730000035
in the formula, PHIs the gap fraction, P, of forest canopy branch and leaf elements in a non-random distribution staterThe forest canopy gap fraction is the forest canopy gap fraction of the forest canopy branch and leaf elements in a random distribution state.
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