WO2014008842A1

WO2014008842A1 - Land-based cloud chart aberration correction method for whole sky imager

Info

Publication number: WO2014008842A1
Application number: PCT/CN2013/079004
Authority: WO
Inventors: 丁宇宇; 丁杰; 周海; 程序; 陈颖; 崔方; 曹潇; 王知嘉; 于炳霞; 谭志萍; 周强; 陈志宝
Original assignee: 国家电网公司; 中国电力科学研究院
Priority date: 2012-07-09
Filing date: 2013-07-08
Publication date: 2014-01-16
Also published as: CN103544679A; CN103544679B

Abstract

The present invention provides a land-based cloud chart aberration correction method for a whole sky imager, and relates to the technical field of photovoltaic power generation and power distribution. The method comprises the following steps: establishing a conversion function between a spherical aberration zenith angle in a land-based cloud chart and an actual zenith angle; converting the land-based cloud chart into a cloud chart of a spherical coordinates system; and converting the cloud chart of a spherical coordinates system into a cloud chart of a rectangular plane coordinate system. In the method, few parameters are required, and only a few of parameters such as a distance between a lens of a whole sky imager and a spherical lens, and a radius of the spherical lens are required; input data is simple, and it is only required to input original land-based cloud chart data for implementing the correction; and image information has no loss during the conversion.

Description

Ground cloud image distortion correction method for full sky imager

Technical field

The invention belongs to the technical field of photovoltaic power distribution and power transmission, and particularly relates to a method for correcting a ground cloud image distortion of a full sky imager. Background technique

In recent years, solar technology and applications have developed rapidly. As of 2010, the cumulative installed capacity of the world's photovoltaics is close to 40GW, with an average annual growth rate of 45% in the past decade, making it one of the fastest growing industries. However, due to the random and intermittent nature of solar power generation, the grid connection of large-scale solar power will bring shocks and challenges to the safe and stable operation of the power grid. Therefore, timely and effective monitoring and prediction of regional solar energy resources has become a key factor restricting the integration of photovoltaic power generation.

At present, an effective means for automatic monitoring of cloud-based and cloud-like conditions is ground-based cloud image observation. Ground-based cloud image observation is an atmospheric detection method for observing the local sky through a full-sky imager installed on the ground. The advantage is that it has high spatial and temporal resolution, and can obtain the total cloud amount in the sky, the cloud detail information less than 1km, and the observation frequency of the minute level. Domestic and foreign scholars have carried out certain researches on cloud recognition and radiation prediction based on ground-based cloud maps. Calbo et al. realized the identification of cloud types by extracting the features of the ground-based all-sky cloud map. Chow et al. used the TSI 440A full-sky imager to observe the San Diego region of the United States and established an intra-hour cloud prediction method based on ground-based cloud maps. Domestic scholar Zhang Yonghong et al. used wavelet packet decomposition and morphological methods to extract the edge of the foundation cloud image respectively, and used image fusion technology to obtain the optimal edge image. However, the distortion correction of the foundation cloud map and the restoration of the actual cloud map of the horizontal plane have not yet seen relevant research results.

The key to predicting the direction and speed of cloud movement is to use cloud-based maps for cloud trajectories and radiation prediction. However, because the imaging method of the full-sky imager is convex mirror imaging, and the imaging angle of view, the captured image has certain distortion, which brings difficulties to cloud computing and cloud trajectory prediction. The invention realizes the distortion correction of the ground-based cloud image by performing spherical mirror reflection distortion correction and spherical coordinate to rectangular coordinate transformation on the original ground cloud image, and provides a real and reliable data source for cloud amount calculation, regional solar energy monitoring and prediction. Summary of the invention

In order to overcome the above deficiencies of the prior art, the present invention provides a method for correcting the distortion of the foundation cloud image of the full sky imager. The required parameters are small, and only a few parameters such as the distance from the full sky imager lens to the spherical mirror and the radius of the spherical mirror are required; The calibration can be completed only by inputting the original ground cloud image data, and the image information is not lost during the conversion process.

In order to achieve the above object, the present invention adopts the following technical solutions: A method for correcting a ground cloud image distortion of a full sky imager, the method comprising the following steps:

Step 1: Establish a transfer function between the spherical distortion zenith angle and the actual zenith angle in the foundation cloud map;

Step 2: Convert the ground cloud image into a spherical coordinate system cloud image;

Step 3: Convert the spherical coordinate system cloud image into a plane rectangular coordinate system actual cloud image.

The step 1 includes the following steps:

Step 1-1: establishing an imaging distortion model of the full sky imager;

Step 1-2: Establish a conversion function between the spherical distortion zenith angle and the actual zenith angle in the ground cloud image according to the imaging distortion model.

In the imaging distortion model, the distance from the lens to the apex of the spherical mirror is calculated as /3⁄4, the mirror radius of the spherical mirror is R, and the angle between the incident point of the sky to the spherical mirror and the vertical direction at the incident point is α. ₂ , the angle of reflection of the reflected light reflected by the spherical mirror to the lens at the center of the lens is A; the center of the mirror surface of the spherical mirror is the coordinate origin 0, the horizontal direction is the c-axis, and the vertical direction For the y-axis, the mirror equation is:

x ² + y ² =R ² (1) The equation of light from the reflected light is:

+ = -c tan α _χ ·χ (2) From the equations (1) and (2), the transverse and longitudinal coordinates of the incident point (c.,}^ are: (3)

Let the angle between the incident point (c., y.) to the center of the mirror at the center of the mirror and the vertical direction be α ₃ , a _{3 is} expressed as:

= arcsin— (5)

R

The relationship between available and obtained is: 2 = 2 · ₃ + _: = 2 · arcsin_ - \- α _λ (6)

R

The simultaneous equations (6) and (3) are the conversion functions between the spherical zenith angle and the actual zenith angle in the ground-based cloud map. The transfer function can obtain the conversion function curve of the spherical distortion zenith angle. In the step 2, the spherical distortion zenith angle of each point in the ground cloud map is corrected by the conversion function to the actual zenith angle of the point, and the azimuth angle is maintained, and the ground-based cloud map to the spherical coordinate system cloud map can be realized. Conversion.

In the step 2, the image magnification at the center of the spherical coordinate system is set. Is 1, shown as:

The derivative of the distorted zenith angle, ρ ₂ is the spherical surface

The unit zenith angle corresponds to the size of the image in the coordinate system cloud image, and Α is the size of the image corresponding to the unit zenith angle in the image of the full sky imager;

By equation (7), any M, M in the spherical coordinate system cloud image is expressed as:

Cloud coordinate system

The derivative of the zenith angle of the spherical distortion at the center to the actual zenith angle;

Cloud radius spherical coordinate system at the maximum apex angle of the day all-sky imager image corresponding point radius R _max is expressed as the ratio:

^lmax Pi ^a ima.> 0 where A is the maximum actual zenith angle and is the maximum spherical distortion zenith angle.

In the step 3: the cloud in the sky is at the same height H, and the thickness of the cloud is negligible, and the zenith angle of any point on the cloud relative to the full sky imager is “ ₂ , and the zenith angle at the same height is known to be The distance between zeros is L, and L is expressed as:

L = H tan a ₂ ( 10) 艮卩: The distance from any point in the spherical coordinate system to the zero point at the same height in the plane rectangular coordinate system. Multiply the zenith angle of the point by the point from the ground. The height is obtained.

In the step 3, the image magnification ratio at the center of the actual cloud image is set in the plane rectangular coordinate system. Is 1, . Expressed as:

M, Λ ( 11 )

AL

Is the derivative of L to the actual zenith angle at the center of the actual cloud image in the plane rectangular coordinate system, p ₂ is the plane

^ΔΩ 2 people ₂₌ .

The Cartesian coordinate system is the size of the image corresponding to the unit distance in the actual cloud image, and _Pl is the size of the image corresponding to the unit zenith angle in the spherical coordinate system cloud image;

The image magnification of any point in the actual rectangular image of the plane rectangular coordinate system is expressed as:

(12)

Wherein AL, at the point L ϋ that the derivative of the actual zenith angle, plane rectangular coordinate system is at the center of the actual cloud Aa ₂ AL J ₀ zenith angle of the actual derivative L;

The ratio R _max of the maximum radius in the actual rectangular image of the plane rectangular coordinate system to the corresponding point radius in the spherical coordinate system cloud diagram is expressed as:

R _ ^L max ^P 2L _ ^L max )

Lmax ( 13)

f ^l 2max ^2 ^fl 2max VJ. Where L _max is the maximum distance of the point in the actual cloud image of the plane rectangular coordinate system from the center of the actual rectangular image of the plane rectangular coordinate system ₍

Compared with the prior art, the beneficial effects of the invention are:

1) This method requires fewer parameters, only a few of the distance from the full sky imager lens to the spherical mirror and the radius of the spherical mirror.

2) The input data is simple, only the original ground cloud image data needs to be input to complete the calibration, and the correction precision is high;

3) There is no loss of image information during the conversion process;

4) The method is simple, reliable and easy to implement. DRAWINGS

1 is a model diagram of an imaging distortion of a full sky imager in an embodiment of the present invention;

2 is a coordinate distortion diagram of a full sky imager in an embodiment of the present invention;

3 is a conversion graph of actual zenith angle and spherical distortion zenith angle in the embodiment of the present invention;

4 is a schematic diagram of actual cloud image transformation from a spherical coordinate system to a plane rectangular coordinate system in an embodiment of the present invention. detailed description

The invention will be further described in detail below with reference to the accompanying drawings.

1 to 4, a method for correcting a ground cloud image distortion of a full sky imager, the method comprising the following steps: Step 1: establishing a transfer function between a spherical distortion zenith angle and an actual zenith angle in the foundation cloud image;

The step 1 includes the following steps:

Step 1-1: establishing an imaging distortion model of the full sky imager;

x ² + y ² =R ² (1) The equation of light from the reflected light is:

Let the angle of the incident point (c., y.) to the center of the mirror at the center of the mirror and the vertical direction be a ₃ , expressed as:

= arcsin— (5)

R

The relationship between available and ^ is:

2 · ₃ + _: = 2· arcsin— + _: (6)

R The simultaneous equations (6) and (3) are the transfer functions between the spherical zenith angle and the actual zenith angle in the foundation cloud map; the transfer function curve of the spherical distortion zenith angle can be obtained from the transfer function.

In the step 2, the spherical distortion zenith angle of each point in the ground cloud map is corrected by the conversion function to the actual zenith angle of the point, and the azimuth angle is maintained, and the ground-based cloud map to the spherical coordinate system cloud map can be realized. Conversion.

The step 2 includes the following steps:

Step 2-1: Obtain the image of the foundation cloud image taken by the full sky imager and store it in the array Arrayl;

Step 2-2: Remove the sky edge and the ground part of the image, and keep the area where the zenith angle of the cloud map is less than or equal to 70°. Step 2-3: Calculate the spherical coordinate image size according to the size of the foundation cloud and equation (9), and define the corresponding size. The array variable Array2 is used as the space for storing the spherical coordinate image;

Step 2-4: Calculate the spherical zenith angle and azimuth of each pixel in Array1, obtain the actual zenith angle of the point according to equation (6), and calculate the pixel in the spherical coordinate image by using equation (8). The size of the azimuth remains unchanged during the transformation;

Step 2-5: Calculate the coordinates of the pixel in the spherical coordinate image according to the actual zenith angle and azimuth of each pixel, and write the color values of the R, G, and B channels of each pixel into the corresponding coordinates and colors in Array2. A spherical coordinate cloud map is obtained in the channel and the correspondingly sized pixels.

The step 3 includes the following steps:

Step 3-1: Calculate the actual cloud image size of the Cartesian coordinate system according to the spherical coordinate cloud size and the equation (13), and define an array variable Array3 corresponding to the size as the space for storing the actual cloud image;

Step 3-2: For each pixel in Array2, obtain the distance from the point to the center point according to equation (10), calculate the coordinates in the Cartesian coordinate system image, and calculate the pixel in the spherical coordinate image by using equation (12). The size of the azimuth remains unchanged during the transformation;

Step3: Write the color values of each channel of R, G, and B of each pixel into the corresponding coordinates, color channels, and corresponding pixel in Array3 to obtain the actual cloud image of the Cartesian coordinate system.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limited thereto. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be The invention is to be construed as being limited to the scope of the appended claims.

Claims

Rights request

A method for correcting a ground cloud image distortion of an all-sky imager, characterized in that: the method comprises the following steps:

2. The method for correcting the ground cloud image distortion of the full sky imager according to claim 1, wherein the step 1 comprises the following steps:

Step 1-1: establishing an imaging distortion model of the full sky imager;

3. The method for correcting a ground cloud image distortion of an all-sky imager according to claim 2, wherein: in the imaging distortion model, a distance from a lens to a vertex of the spherical mirror is /3⁄4, and a mirror radius of the spherical mirror is R. The angle between the incident light of the sky point to the spherical mirror and the vertical direction at the incident point is α ₂ , and the angle of the reflected light reflected by the spherical mirror to the lens at the center of the lens is A; taking the mirror center of the spherical mirror as the coordinate origin 0, the horizontal direction as the c axis, and the vertical direction as the y axis, then the mirror equation is:

x ² + y ² =R ² (1) The equation of light from the reflected light is:

_ -( 3⁄4 + = -c tan α _χ ·χ (2) From the equations (1) and (2), the transverse and longitudinal coordinates of the incident point ( , }^ are: (3)

= arcsin— (5)

R

The relationship between available and ^ is: α ₂ = 2 · α ₃ + = 2 · arc sin + ( 6 ) The simultaneous equations (6) and (3) are the transfer functions between the spherical zenith angle and the actual zenith angle in the foundation cloud map; The conversion function can obtain the conversion function curve of the spherical distortion zenith angle.

The method for correcting the ground cloud image distortion of the full sky imager according to claim 1, wherein: in the step 2, the spherical distortion zenith angle of each point in the ground cloud image is corrected to the point by a conversion function. The actual zenith angle, and maintain the azimuth unchanged, can realize the conversion of the foundation cloud map to the spherical coordinate system cloud map.

The method for correcting the ground cloud image distortion of the full sky imager according to claim 4, wherein in the step 2, the image magnification M at the center of the spherical coordinate system is set. It is 1 M. Expressed as:

The derivative of the distorted zenith angle, ρ ₂ is the spherical surface

Any MM in the spherical coordinate system cloud diagram obtained by equation (7) is expressed as:

Cloud coordinate system

Spherical coordinate system cloud radius and the maximum apex angle at day all-sky imager image corresponding point radius R _max is expressed as the ratio:

^lmax Pi ^a ima.} 0 where " ₂ is the maximum actual zenith angle, which is the maximum spherical distortion zenith angle.

The method for correcting the ground cloud image distortion of the full sky imager according to claim 1, wherein: the step 3 is that the clouds in the sky are at the same height H, and the thickness of the cloud is negligible, and any point on the cloud is imaged relative to the whole sky. Instrument The zenith angle is "," and it can be seen that the distance from the point to the same height at the zenith angle is L, which is expressed as:

The method for correcting the ground cloud image distortion of the full sky imager according to claim 6, wherein: in the step 3, the image magnification ratio at the center of the actual cloud image is set in the plane rectangular coordinate system. Is 1, . Expressed as:

The derivative of the zenith angle, ρ _2£ is the plane

The image magnification of any point in the actual rectangular image of the plane rectangular coordinate system Μ _£ , _{£ is} expressed as: among them,

The derivative of the actual zenith angle to L; the ratio R _max of the maximum radius in the actual cloud image of the plane rectangular coordinate system to the corresponding point radius in the spherical coordinate system cloud diagram is expressed as:

R, ( 13)

J ₎ where L _max is the maximum distance of the point from the center of the actual cloud image of the plane rectangular coordinate system in the actual rectangular image of the plane rectangular coordinate system.