阅读说明：本技术 一种基于迭代Klett的机载海洋激光雷达信号处理方法 (Airborne marine laser radar signal processing method based on iteration Klett ) 是由 陈鹏 毛志华 刘航 朱乾坤 黄海清 龚芳 于 2019-09-25 设计创作，主要内容包括：本发明公开了一种基于迭代Klett的机载海洋激光雷达信号处理方法,利用Klett法对经过背景噪声去除和距离校正的激光雷达回波信号进行处理,通过设置不同的后向散射消光对数比k获取不同的雷达衰减系数；将采集的叶绿素剖面数据代入生物光学模型,获得海水衰减系数；对比分析同一观测点生物光学模型得到衰减系数与激光雷达反演得到的雷达衰减系数,确定海水后向散射消光对数比k,进而获得更为准确的海水衰减系数。本发明的方法能够提高激光雷达反演海水衰减系数剖面的精确度。(The invention discloses an iterative Klett-based airborne marine laser radar signal processing method, wherein a laser radar echo signal subjected to background noise removal and distance correction is processed by using a Klett method, and different radar attenuation coefficients are obtained by setting different backscattering extinction log ratios k; substituting the collected chlorophyll profile data into a biological optical model to obtain a seawater attenuation coefficient; and comparing and analyzing the bio-optical model at the same observation point to obtain an attenuation coefficient and a radar attenuation coefficient obtained by laser radar inversion, and determining a seawater backscattering extinction logarithmic ratio k to further obtain a more accurate seawater attenuation coefficient. The method can improve the accuracy of the laser radar for inverting the sea water attenuation coefficient profile.)

1. An iterative Klett-based airborne marine laser radar signal processing method is characterized by comprising the following steps:

s1: respectively calculating the attenuation coefficient alpha (z) of the laser radar and the attenuation coefficient alpha of the model_model；

The specific calculation steps of the laser radar attenuation coefficient alpha (z) are as follows:

(1) preprocessing the original data of the airborne marine laser radar, including background noise removal and distance correction;

(2) determining a reference boundary, and determining a laser radar attenuation coefficient of a boundary point by using a slope method;

(3) setting an initial value of iteration times n as 0, setting an initial value of a seawater backscattering extinction logarithm ratio k as 0.6, wherein k is 0.6+0.01n, kn belongs to [0.6, 1.3], and n belongs to [0, 70 ];

(4) substituting the value of n and the value of k into the following formula to obtain the laser radar attenuation coefficient alpha (z)

Wherein S (z) is a radar range correction signal, S_m＝S(z_m)，z_mIs a boundary value, α_mIs the lidar attenuation coefficient of the boundary point;

(5) returning to the step (4) to operate when n is equal to n +1 until k is equal to 1.3, and outputting a laser radar attenuation coefficient alpha (z);

the model attenuation coefficient alpha_modelThe calculation steps are as follows:

selecting chlorophyll section data consistent with the longitude and latitude matching of the laser radar data, substituting the chlorophyll section data into the following formula to obtain the model attenuation coefficient alpha_model；

α_model＝Kd+(c-Kd)exp(-0.85cD) (2)

Kd＝0.0452+0.0494chl^0.67(3)

c＝a+b (4)

a＝1.055(0.0488+0.028chl^0.65) (5)

b＝1.7×10^-3+0.416chl^0.766(6)

Wherein Kd is a diffuse attenuation coefficient, c is a beam attenuation coefficient, a is an absorption coefficient, b is a scattering coefficient, D is a spot diameter projected to the sea surface by laser, and chl is the actually measured chlorophyll concentration.

S2: comparing radar attenuation coefficient alpha (z) with model attenuation coefficient alpha_modelFinding out the alpha_modelAnd the closest radar attenuation coefficient corresponds to the optimal k value of the water body.

2. The iterative Klett-based airborne marine lidar signal processing method according to claim 1, wherein the background noise in S1 is a signal out of the detection range of the lidar, specifically an average value of the last one hundred sampling points of each pulse signal.

3. The iterative Klett-based airborne marine lidar signal processing method according to claim 1, characterized in that the distance correction specifically is: and multiplying the echo signal at each depth by the square of the depth value, wherein the depth value comprises the height value of the airplane and the depth of the sea water.

4. The iterative Klett-based airborne marine lidar signal processing method according to claim 1, wherein the reference boundary in S1 is the maximum depth value detectable by the lidar.

Technical Field

The invention belongs to the technical field of laser radar detection, and particularly relates to an iterative Klett-based airborne marine laser radar signal processing method.

Background

The detection of ocean optical parameters has very important significance in the research fields of ocean hydrological exploration, underwater communication, ocean environment monitoring, ocean laser remote sensing and the like. Common detection means are: on-site in-situ measurement, sonar, passive remote sensing and active remote sensing. The on-site in-situ measurement accuracy is higher, but the time and the money are consumed; the sonar has good transmission performance underwater, but cannot be placed on a ship or other platforms such as an airplane and the like due to high reflectivity of a water-vapor interface; the passive remote sensing can realize global large-scale real-time observation, but only can acquire sea surface information and can not acquire sea profile information; active remote sensing, such as laser radar, has high resolution, can acquire ocean profile information, and is widely used in ocean research in recent years.

The attenuation coefficient of the seawater can be inverted by utilizing the echo signal of the laser radar and according to a laser radar equation, and the vertical distribution condition of seawater particles is obtained. But the result is usually obtained on the assumption that the logarithmic ratio k of the backscattering extinction is constant, generally assuming that k is equal to 1. When k takes different values, the results are greatly different, thereby showing that k is a key factor for the inversion of the laser radar echo signals and is also a main error source for solving the laser radar equation by the Klett method.

The backscattering extinction logarithm ratio k is related to the laser wavelength and the optical characteristics of seawater, and various characteristics of seawater are not well known at present, so that the feasibility of determining the k value by the method is low.

Disclosure of Invention

The invention aims to obtain a seawater backscattering extinction logarithmic ratio k and further obtain a more accurate seawater attenuation coefficient profile structure.

The purpose of the invention is realized by the following technical scheme:

an iterative Klett-based airborne marine laser radar signal processing method is characterized by comprising the following steps:

s1: respectively meterCalculating laser radar attenuation coefficient alpha (z) and model attenuation coefficient alpha_model；

The specific calculation steps of the laser radar attenuation coefficient alpha (z) are as follows:

(1) preprocessing the original data of the airborne marine laser radar, including background noise removal and distance correction;

(2) determining a reference boundary, and determining a laser radar attenuation coefficient of a boundary point by using a slope method;

(3) setting an initial value of iteration times n as 0, setting an initial value of a seawater backscattering extinction logarithm ratio k as 0.6, wherein k is 0.6+0.01n, kn belongs to [0.6, 1.3], and n belongs to [0, 70 ];

(4) substituting the value of n and the value of k into the following formula to obtain the laser radar attenuation coefficient alpha (z)

Wherein S (z) is a radar range correction signal, S_m＝S(z_m)，z_mIs a boundary value, α_mIs the lidar attenuation coefficient of the boundary point;

(5) returning to the step (4) to operate when n is equal to n +1 until k is equal to 1.3, and outputting a laser radar attenuation coefficient alpha (z);

the model attenuation coefficient alpha_modelThe calculation steps are as follows:

selecting chlorophyll section data consistent with the longitude and latitude matching of the laser radar data, substituting the chlorophyll section data into the following formula to obtain the model attenuation coefficient alpha_model；

α_model＝Kd+(c-Kd)exp(-0.85cD) (2)

Kd＝0.0452+0.0494chl^0.67(3)

c＝a+b (4)

a＝1.055(0.0488+0.028chl^0.65) (5)

b＝1.7×10^-3+0.416chl^0.766(6)

Wherein Kd is a diffuse attenuation coefficient, c is a beam attenuation coefficient, a is an absorption coefficient, b is a scattering coefficient, D is a spot diameter projected to the sea surface by laser, and chl is the actually measured chlorophyll concentration.

S2: comparing radar attenuation coefficient alpha (z) with model attenuation coefficient alpha_modelFinding out the alpha_modelAnd the closest radar attenuation coefficient corresponds to the optimal k value of the water body.

Further, the background noise in S1 is a signal beyond the detection range of the laser radar, specifically, an average value of the last one hundred sampling points of each pulse signal.

Further, the distance correction specifically includes: and multiplying the echo signal at each depth by the square of the depth value, wherein the depth value comprises the height value of the airplane and the depth of the sea water.

Further, the reference boundary in S1 is the maximum depth value detectable by the lidar.

The invention has the beneficial effects that:

the method is based on the iterative Klett inversion algorithm, and takes different backscattering extinction logarithmic ratios k of different water bodies into consideration, so that the radar attenuation coefficient obtained by inversion is higher in accuracy and smaller in error.

Drawings

FIG. 1 is a schematic diagram of an iterative Klett-based airborne marine laser radar signal processing method;

FIG. 2 is a comparison of the results of different k value inversions with the measured values;

FIG. 3 is an error analysis graph of the ratio of the inversion result to the measured value of the iterative Klett algorithm.

Detailed Description

The present invention is further illustrated by the following figures and specific examples, which are to be understood as illustrative only and not as limiting the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.

Compared with the conventional sea water optical parameter detection means, the method extracts the attenuation coefficient and the backscattering coefficient of the water body from the laser radar echo signal, and finds a quick and accurate inversion method, which is an important target for the research of the marine detection laser radar. At present, a common algorithm for inverting the ocean attenuation coefficient by using the laser radar echo signal is a Coliis method. The Coliis method is simple and convenient, but is only suitable for uniform water bodies, and the water bodies are mostly non-uniform water bodies in practical situations, so that the application of the Coliis method is limited. Klett proposes a Klett inversion algorithm with wide applicability on the basis of the Collis algorithm. In general, the Klett method sets a k value equal to 1 for calculation, the attenuation coefficient and the radar attenuation coefficient obtained by laser radar inversion are obtained by iteratively comparing and analyzing a biological optical model of the same observation point, and the seawater backscattering extinction logarithm ratio k is determined, so that the inversion accuracy of the seawater attenuation coefficient is improved.

As shown in fig. 1, the iterative Klett-based airborne marine laser radar signal processing method of the present invention specifically includes the following steps:

s1: respectively calculating the attenuation coefficient alpha (z) of the laser radar and the attenuation coefficient alpha of the model_model；

The specific calculation steps of the laser radar attenuation coefficient alpha (z) are as follows:

(1) preprocessing the original data of the airborne marine laser radar, including background noise removal and distance correction;

(2) determining a reference boundary, and determining a laser radar attenuation coefficient of a boundary point by using a slope method;

(3) setting an initial value of iteration times n as 0, setting an initial value of a seawater backscattering extinction logarithm ratio k as 0.6, wherein k is 0.6+0.01n, kn belongs to [0.6, 1.3], and n belongs to [0, 70 ];

(4) substituting the value of n and the value of k into the following formula to obtain the laser radar attenuation coefficient alpha (z)

Wherein S (z) is a radar range correction signal, S_m＝S(z_m)，z_mIs a boundary value, α_mIs the lidar attenuation coefficient of the boundary point;

(5) returning to the step (4) to operate when n is equal to n +1 until k is equal to 1.3, and outputting a laser radar attenuation coefficient alpha (z);

the model attenuation coefficient alpha_modelThe calculation steps are as follows:

selecting chlorophyll section data consistent with the longitude and latitude matching of the laser radar data, substituting the chlorophyll section data into the following formula to obtain the model attenuation coefficient alpha_model；

α_model＝Kd+(c-Kd)exp(-0.85cD) (2)

Kd＝0.0452+0.0494chl^0.67(3)

c＝a+b (4)

a＝1.055(0.0488+0.028chl^0.65) (5)

b＝1.7×10^-3+0.416chl^0.766(6)

Wherein Kd is a diffuse attenuation coefficient, c is a beam attenuation coefficient, a is an absorption coefficient, b is a scattering coefficient, D is a spot diameter projected to the sea surface by laser, and chl is the actually measured chlorophyll concentration.

S2: comparing radar attenuation coefficient alpha (z) with model attenuation coefficient alpha_modelFinding out the alpha_modelAnd the closest radar attenuation coefficient corresponds to the optimal k value of the water body.

Preferably, the background noise in S1 is a signal beyond the detection range of the laser radar, specifically, an average value of the last one hundred sampling points of each pulse signal.

Preferably, the distance correction specifically includes: and multiplying the echo signal at each depth by the square of the depth value, wherein the depth value comprises the height value of the airplane and the depth of the sea water.

Preferably, the reference boundary in S2 is the maximum depth value detectable by the lidar.

Fig. 2 shows a comparison result of radar attenuation coefficients obtained by setting different k values and actually measured water attenuation coefficients, different symbols represent the attenuation coefficients inverted by the laser radar, and a solid line is an in-situ measurement result. It can be seen from the graph that the attenuation coefficient of the lidar inversion varies significantly with the k value and increases with the k value. When the k value is smaller, the result has an underestimation phenomenon, but the overall trend is unchanged; when the k value is larger, the result is an overestimation phenomenon, and the radar attenuation coefficient is continuously reduced along with the increase of the depth. The result shows that k is a key factor for laser radar signal inversion and is also an important error source for a klett inversion laser radar equation. Therefore, it is very important to accurately determine the k value. The iterative Klett-based airborne marine laser radar signal processing method provided by the invention can accurately determine the k value of a research area.

In order to verify the accuracy of the relationship between the attenuation coefficient of the lidar inversion and the field measurement, error analysis was performed. Fig. 3 shows a graph of the error of the ratio of the lidar attenuation coefficient to the field measurement. It can be seen from the figure that, with the depth increasing, the ratio approaches 1 except for the invalid depth, and the relative error is within 12%, wherein the 80% error is less than 5%. The error of only 6% is larger than 10%, and the error is mainly concentrated at the depth of 17-18 m under the influence of low signal to noise ratio. Since the method of the present invention involves inverse integration, the depth is slightly larger at 3m to 5m error due to the accumulation of error. The result proves that the iterative Klett-based airborne marine laser radar signal processing method is an effective and feasible method for inverting the attenuation coefficient of the laser radar, and is higher in accuracy and smaller in error.