CN105469391B - A kind of cloud shadow detection method and system - Google Patents

A kind of cloud shadow detection method and system Download PDF

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Publication number
CN105469391B
CN105469391B CN201510792310.6A CN201510792310A CN105469391B CN 105469391 B CN105469391 B CN 105469391B CN 201510792310 A CN201510792310 A CN 201510792310A CN 105469391 B CN105469391 B CN 105469391B
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cloud
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point
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CN105469391A (en
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辛晓洲
李彬
张海龙
李映夏
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Institute of Remote Sensing and Digital Earth of CAS
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Institute of Remote Sensing and Digital Earth of CAS
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/0002—Inspection of images, e.g. flaw detection
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/10—Image acquisition modality
    • G06T2207/10032—Satellite or aerial image; Remote sensing

Abstract

The present invention relates to a kind of cloud shadow detection method and system, this method to include：Any cloud pixel in cloud atlas picture is chosen, obtains the position of shade and the height value of the cloud pixel of the cloud pixel in the position of the upright projection of horizontal earth's surface, the cloud pixel in horizontal earth's surface, and establish the linear equation of light；Cloud atlas is obtained as the altitude data of corresponding earth's surface, the altitude data is transformed under space coordinates；The coordinate of match point is obtained, the coordinate of the match point is the position of cloud pixel shadow spots；The position of each cloud pixel shadow spots in cloud atlas picture is obtained, so as to obtain the position of cloud shade.The present invention provides a kind of cloud shadow detection method and system, by cloud detection and obtain cloud altitude data, it is geometric process by the procedural abstraction that cloud is projected on relief surface, and binding geometry calculates the position of cloud shade under MODEL OVER COMPLEX TOPOGRAPHY, it disclosure satisfy that the needs that cloud shadow positions are calculated under MODEL OVER COMPLEX TOPOGRAPHY, improve the accuracy of cloud shadow Detection.

Description

A kind of cloud shadow detection method and system
Technical field
The present invention relates to remote sensing technology field, more particularly to a kind of cloud shadow detection method and system.
Background technology
With the continuous improvement of satellite image resolution ratio, influence of the cloud 3D effects to radiative invesion precision is more and more obvious. Therefore, it is that surface radiation is estimated under the conditions of the skies to carry out certain amendment on the basis of the one-dimensional radiative transmission mode to cloud 3D effects The effective ways of calculation.In this course, cloud shade calculating and detection become earth's surface solar radiation estimation an important ring Section, can improve the accuracy of radiative invesion to a certain extent.
Prior art medium cloud shadow Detection mainly utilizes analysis of spectrum threshold, or method of geometry is utilized on the basis of cloud detection To calculate, the detection of cloud shade is more difficult than cloud detection.If relying on spectral detection merely, although proving effective sometimes, Inevitably other dark earth's surfaces are obscured with earth's surface, and such as topographic shadowing and wetland, while it is not very that can miss some yet Dark shadow region and the region by cloud block.Hutchison etc. by Reflectivity for Growing Season etc. to carrying out spectral detection merely Cloud Shadow recognition method analyzed after think, as a rule there are large error, then propose that one kind is based on geometry The recognition methods of relation, i.e., can be with the case where knowing solar zenith angle and azimuth, and the height and edge extent of cloud The position of shade is predicted according to geometric projection, its effect is better than spectroscopic methodology.Luo etc. also utilizes method of geometry and calculates cloud shade Position, but do not account for orographic factor.Zhu etc. make use of Landsat band4 in cloud shaded side reflectivity in Fmask methods It is low, and high specific of shade peripheral reflection rate, possible cloud shade is differentiated using the morphological transformation method of Flood-fill.
The content of the invention
The technical problems to be solved by the invention are：The existing method using geometrical relationship detection cloud shade is not suitable for Complicated orographic condition, testing result are inaccurate.
In order to solve the above technical problems, one aspect of the present invention proposes a kind of cloud shadow detection method method, this method bag Include：
Any cloud pixel in cloud atlas picture is chosen, obtains cloud pixel in the position of the upright projection of horizontal earth's surface, the cloud The position of shade of the pixel in horizontal earth's surface and the height value of the cloud pixel, and establish the linear equation of light；
Cloud atlas is obtained as the altitude data of corresponding earth's surface, the altitude data is transformed under space coordinates；
The seat of match point is obtained according to the linear equation of the coordinate of each point, height value and the light in the altitude data Mark, the coordinate of the match point is the position of cloud pixel shadow spots；
The position of each cloud pixel shadow spots in cloud atlas picture is obtained, so as to obtain the position of cloud shade.
Alternatively, the linear equation of the light is：
Wherein, (Xshadow,Yshadow) be shade of the cloud pixel in horizontal earth's surface position, (Xnadir,Ynadir) be The position of upright projection of the cloud pixel in horizontal earth's surface, h are the height value of the cloud pixel, and (X, Y, Z) sits for spatial point Mark, Z is height value.
Alternatively, according to the linear equation acquisition of the coordinate of each point, height value and the light in the altitude data Coordinate with point, including：
The light is obtained according to the linear equation of the coordinate of each point, height value and the light in the altitude data The intersection point of linear equation earth's surface corresponding with the cloud pixel；
If the intersection point uniquely determines, the intersection point is match point；
If the number of the intersection point to be multiple, selects in each intersection point height value highest and minimum with light distance Intersection point be match point.
Alternatively, the altitude data is transformed into space and sat by the acquisition cloud atlas as the altitude data of corresponding earth's surface Under mark system, including：
Cloud atlas is obtained as the elevation minimum of each point in corresponding earth's surface, respectively by the elevation of each point in the cloud atlas picture Subtract the elevation minimum；
By the cloud atlas as the height value of each point in corresponding earth's surface divided by the resolution ratio of the cloud atlas picture, by the elevation Data are transformed under space coordinates.
Alternatively, the linear equation according to the coordinate of each point, height value and the light in the altitude data obtains The intersection point of the linear equation earth's surface corresponding with the cloud pixel of the light is taken, including：
Bring the coordinate of each point and height value in the altitude data into the following formula, obtain the linear equation of the light The intersection point of earth's surface corresponding with the cloud pixel；
Wherein, s is default error range.
Alternatively, if the number of the intersection point is multiple, select in each intersection point height value highest and with it is described The minimum intersection point of light distance is match point, including：
The height value of each point minimum is obtained in the intersection point, the height value of the intersection point is subtracted into the minimum elevation Value；
The intersection point that the difference of the height value and the minimum height value that obtain the intersection point is more than twice of elevation resolution ratio is made For new intersection point, and the selection new intersection point minimum with light distance is match point from the new intersection point.
Alternatively, the selection from the new intersection point new intersection point minimum with light distance is match point, Including：
2 points chosen in each new intersection point neighborhood form a plane with the point, obtain the plane and the light Intersection point is as plane light intersection point；
Distance of each new intersection point with corresponding plane light intersection point is obtained, selects the minimum new friendship of the distance Point is match point.
On the other hand, the invention also provides a kind of cloud shadow Detection system, the system include：
The linear equation of light establishes unit, for choosing any cloud pixel in cloud atlas picture, obtains cloud pixel in level The position of the shade of the position of the upright projection of earth's surface, the cloud pixel in horizontal earth's surface and the height value of the cloud pixel, And establish the linear equation of light；
Altitude data converting unit, for obtaining altitude data of the cloud atlas as corresponding earth's surface, the altitude data is turned Change under space coordinates；
Cloud pixel shadow spots position acquisition unit, for according to the coordinate of each point, height value and institute in the altitude data The linear equation for stating light obtains the coordinate of match point, and the coordinate of the match point is the position of cloud pixel shadow spots；
Cloud shadow positions acquiring unit, for the position of each cloud pixel shadow spots in obtaining in cloud atlas picture, so as to obtain The position of cloud shade.
Alternatively, the linear equation of the light is：
Wherein, (Xshadow,Yshadow) be shade of the cloud pixel in horizontal earth's surface position, (Xnadir,Ynadir) be The position of upright projection of the cloud pixel in horizontal earth's surface, h are the height value of the cloud pixel, and (X, Y, Z) sits for spatial point Mark, Z is height value.
Further, the altitude data converting unit, for obtain cloud atlas as each point in corresponding earth's surface elevation most Low value, subtracts the elevation minimum by the elevation of each point in the cloud atlas picture respectively；
By the cloud atlas as the height value of each point in corresponding earth's surface divided by the resolution ratio of the cloud atlas picture, by the elevation Data are transformed under space coordinates.
The present invention provides a kind of cloud shadow detection method and system, by cloud detection and obtains cloud altitude data, cloud is thrown Shadow is geometric process in the procedural abstraction of relief surface, and binding geometry calculates the position of cloud shade under MODEL OVER COMPLEX TOPOGRAPHY, It disclosure satisfy that the needs that cloud shadow positions are calculated under MODEL OVER COMPLEX TOPOGRAPHY, improve the accuracy of cloud shadow Detection.
Brief description of the drawings
The features and advantages of the present invention can be more clearly understood by reference to attached drawing, attached drawing is schematically without that should manage Solve to carry out any restrictions to the present invention, in the accompanying drawings：
Fig. 1 shows the flow diagram of the cloud shadow detection method of one embodiment of the invention；
Fig. 2 shows that light projects the geometric representation of complicated landform；
Fig. 3 shows a width cloud atlas picture；
Fig. 4 shows transformed altitude data；
Fig. 5 shows the structure diagram of the cloud shadow Detection system of one embodiment of the invention.
Embodiment
Below in conjunction with attached drawing, embodiments of the present invention is described in detail.
Fig. 1 shows the flow diagram of the cloud shadow detection method of one embodiment of the invention.As shown in Figure 1, the party Method includes：
S1：Any cloud pixel in cloud atlas picture is chosen, obtains cloud pixel in the position of the upright projection of horizontal earth's surface, described The position of shade of the cloud pixel in horizontal earth's surface and the height value of the cloud pixel, and establish the linear equation of light；
S2：Cloud atlas is obtained as the altitude data of corresponding earth's surface, the altitude data is transformed under space coordinates；
S3：Match point is obtained according to the linear equation of the coordinate of each point, height value and the light in the altitude data Coordinate, the coordinate of the match point is the position of cloud pixel shadow spots；
S4：The position of each cloud pixel shadow spots in cloud atlas picture is obtained, so as to obtain the position of cloud shade.
The cloud shadow detection method of the present embodiment, by cloud detection and obtains cloud altitude data, cloud is projected on rough ground The procedural abstraction of table is geometric process, and binding geometry calculates the position of cloud shade under MODEL OVER COMPLEX TOPOGRAPHY, disclosure satisfy that The needs of cloud shadow positions are calculated under MODEL OVER COMPLEX TOPOGRAPHY, improve the accuracy of cloud shadow Detection.
In practical applications, it is position by obtaining the shade of the locus of cloud pixel, cloud pixel in horizontal earth's surface Put and obtain the linear equation of light to the height value of the cloud pixel and the related geometry derivation of equation.
In an optional embodiment, the linear equation of the light is：
Wherein, (Xshadow,Yshadow) be shade of the cloud pixel in horizontal earth's surface position, (Xnadir,Ynadir) be The position of upright projection of the cloud pixel in horizontal earth's surface, h are the height value of the cloud pixel, and (X, Y, Z) sits for spatial point Mark, Z is height value.
Further, obtained according to the linear equation of the coordinate of each point, height value and the light in the altitude data The coordinate of match point, including：
The light is obtained according to the linear equation of the coordinate of each point, height value and the light in the altitude data The intersection point of linear equation earth's surface corresponding with the cloud pixel；
If the intersection point uniquely determines, the intersection point is match point；
If the number of the intersection point to be multiple, selects in each intersection point height value highest and minimum with light distance Intersection point be match point.
Fig. 2 shows that light projects the geometric representation of complicated landform.Fig. 3 shows a width cloud atlas picture, describes cloud Detect data.
Light is irradiated to by the present embodiment through cloud pixel to be formed the procedural abstraction of shade and in alignment passes through in slope surface One face and intersect at a point with the face or some.Position where the intersection point that they are formed is cloud pixel institute in slope surface The shadow spots position of formation.Pass through the physical location of cloud pixel and the shadow positions and correspondence of the horizontal earth's surface being calculated Cloud pixel height can obtain the space line equation for representing this light, then the coordinate in hillside fields and height value are substituted into the party It is the position that can obtain the cloud pixel in corresponding slope surface that journey, which finds match point,.Obtain the position of each cloud pixel shadow spots in cloud atlas picture Put, so as to obtain the position of cloud shade.
Because actual light can be blocked by the high slope surface of elevation first, and abstract calculating process can include all straight lines The point passed through, if thus the intersection point number to be multiple, select in each intersection point height value highest and with the light away from It is match point from minimum intersection point.
Further, the altitude data is transformed into space by the acquisition cloud atlas as the altitude data of corresponding earth's surface Under coordinate system, including：
Cloud atlas is obtained as the elevation minimum of each point in corresponding earth's surface, respectively by the elevation of each point in the cloud atlas picture Subtract the elevation minimum；
Zpi=Zi-Zmin
Wherein, Zmin represents elevation minimum, and i represents each point numbering, and Zi is the original height value of i points, and Zpi is " flat for i points Height value after platform "；
By the cloud atlas as the height value of each point in corresponding earth's surface divided by the resolution ratio of the cloud atlas picture, by the elevation Data are transformed under space coordinates；
Zsi=Zpi/d
Wherein, d represents the resolution ratio (unit of cloud atlas picture：Rice), Zsi represents the height value after i points " coordinate system ".
Fig. 4 shows transformed altitude data, and the height value of transformed altitude data is to be adapted to coordinate-system Lattice point numerical value.
Alternatively, the linear equation according to the coordinate of each point, height value and the light in the altitude data obtains The intersection point of the linear equation earth's surface corresponding with the cloud pixel of the light is taken, including：
Bring the coordinate of each point and height value in the altitude data into the following formula, obtain the linear equation of the light The intersection point of earth's surface corresponding with the cloud pixel；
Wherein, s is default error range.
During calculation is asked, since coordinate is integer value, certain error range need to be set.
In practical applications, s is incrementally increased to 0.06 by 0.01, is calculated, obtained as error range successively State the public solution of four formula, the intersection point of the linear equation earth's surface corresponding with the cloud pixel as light；Preferably, if intersection point Quantity between 2 and 6 when, stop iteration, determine intersection point；Secondary selection of land, if number of intersections is between 7-15, stops iteration, determines Intersection point；
Error range s is smaller, and obtained intersection point number is fewer.Especially, if failing to obtain when s is between 0.01-0.06 Intersection point, then be set to 0.07-0.09 by s, repeats the above process, until obtaining intersection point.
Alternatively, if the number of the intersection point is multiple, select in each intersection point height value highest and with it is described The minimum intersection point of light distance is match point, including：
The height value of each point minimum is obtained in the intersection point, the height value of the intersection point is subtracted into the minimum elevation Value；
The intersection point that the difference of the height value and the minimum height value that obtain the intersection point is more than twice of elevation resolution ratio is made For new intersection point, and the selection new intersection point minimum with light distance is match point from the new intersection point.
Alternatively, the selection from the new intersection point new intersection point minimum with light distance is match point, Including：
2 points chosen in each new intersection point neighborhood form a plane with the point, obtain the plane and the light Intersection point is as plane light intersection point；
Distance of each new intersection point with corresponding plane light intersection point is obtained, selects the minimum new friendship of the distance Point is match point.
Especially, 2 points chosen in each new intersection point 3*3 neighborhoods form a plane, Calculation Plane and light with the point Intersection point as plane light intersection point, further calculate the distance D of each new intersection point and plane light intersection point；
After calculating one by one, the new intersection point for choosing D value minimums is match point.
Fig. 5 shows the structure diagram of the cloud shadow Detection system of one embodiment of the invention.As shown in figure 5, this is System includes：
The linear equation of light establishes unit 51, for choosing any cloud pixel in cloud atlas picture, obtains cloud pixel in water The position of the shade of the position of the upright projection of level land table, the cloud pixel in horizontal earth's surface and the height of the cloud pixel Value, and establish the linear equation of light；
Altitude data converting unit 52, for obtaining altitude data of the cloud atlas as corresponding earth's surface, by the altitude data It is transformed under space coordinates；
Cloud pixel shadow spots position acquisition unit 53, for according to the coordinate of each point in the altitude data, height value and The linear equation of the light obtains the coordinate of match point, and the coordinate of the match point is the position of cloud pixel shadow spots；
Cloud shadow positions acquiring unit 54, for the position of each cloud pixel shadow spots in obtaining in cloud atlas picture, so as to obtain Take the position of cloud shade.
Alternatively, the linear equation of the light is：
Wherein, (Xshadow,Yshadow) be shade of the cloud pixel in horizontal earth's surface position, (Xnadir,Ynadir) be The position of upright projection of the cloud pixel in horizontal earth's surface, h are the height value of the cloud pixel, and (X, Y, Z) sits for spatial point Mark, Z is height value.
Further, the altitude data converting unit, for obtain cloud atlas as each point in corresponding earth's surface elevation most Low value, subtracts the elevation minimum by the elevation of each point in the cloud atlas picture respectively；
By the cloud atlas as the height value of each point in corresponding earth's surface divided by the resolution ratio of the cloud atlas picture, by the elevation Data are transformed under space coordinates.
Cloud shadow Detection system described in the present embodiment can be used for performing above method embodiment, its principle and technology effect Seemingly, details are not described herein again for fruit.
Cloud shadow detection method provided by the invention and system, by cloud detection and obtain cloud altitude data, cloud are projected It is geometric process in the procedural abstraction of relief surface, and binding geometry calculates the position of cloud shade under MODEL OVER COMPLEX TOPOGRAPHY, energy Enough meet the needs that cloud shadow positions are calculated under MODEL OVER COMPLEX TOPOGRAPHY, improve the accuracy of cloud shadow Detection.
Although being described in conjunction with the accompanying embodiments of the present invention, those skilled in the art can not depart from this hair Various modifications and variations are made in the case of bright spirit and scope, such modifications and variations are each fallen within by appended claims Within limited range.

Claims (10)

  1. A kind of 1. cloud shadow detection method, it is characterised in that including：
    Any cloud pixel in cloud atlas picture is chosen, obtains cloud pixel in the position of the upright projection of horizontal earth's surface, the cloud pixel The position of shade in horizontal earth's surface and the height value of the cloud pixel, and establish the linear equation of light；
    Cloud atlas is obtained as the altitude data of corresponding earth's surface, the altitude data is transformed under space coordinates；
    The coordinate of match point is obtained according to the linear equation of the coordinate of each point, height value and the light in the altitude data, The coordinate of the match point is the position of cloud pixel shadow spots；
    The position of each cloud pixel shadow spots in cloud atlas picture is obtained, so as to obtain the position of cloud shade.
  2. 2. cloud shadow detection method according to claim 1, it is characterised in that the linear equation of the light is：
    <mrow> <mfrac> <mrow> <mi>X</mi> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>Y</mi> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>Z</mi> <mo>-</mo> <mi>h</mi> </mrow> <mi>h</mi> </mfrac> <mo>,</mo> </mrow>
    Wherein, (Xshadow,Yshadow) be shade of the cloud pixel in horizontal earth's surface position, (Xnadir,Ynadir) it is described For cloud pixel in the position of the upright projection of horizontal earth's surface, h is the height value of the cloud pixel, and (X, Y, Z) is space point coordinates, Z For height value.
  3. 3. cloud shadow detection method according to claim 2, it is characterised in that according to the seat of each point in the altitude data The linear equation of mark, height value and the light obtains the coordinate of match point, including：
    The straight line of the light is obtained according to the linear equation of the coordinate of each point, height value and the light in the altitude data The intersection point of equation earth's surface corresponding with the cloud pixel；
    If the intersection point uniquely determines, the intersection point is match point；
    If the number of the intersection point is multiple, height value highest and the friendship minimum with light distance in each intersection point are selected Point is match point.
  4. 4. cloud shadow detection method according to claim 1, it is characterised in that the acquisition cloud atlas is as corresponding earth's surface Altitude data, the altitude data is transformed under space coordinates, including：
    Cloud atlas is obtained as the elevation minimum of each point in corresponding earth's surface, respectively subtracts the elevation of each point in the cloud atlas picture The elevation minimum；
    By the cloud atlas as the height value of each point in corresponding earth's surface divided by the resolution ratio of the cloud atlas picture, by the altitude data It is transformed under space coordinates.
  5. 5. cloud shadow detection method according to claim 3, it is characterised in that described according to each point in the altitude data Coordinate, the linear equation of height value and the light obtain the linear equation earth's surface corresponding with the cloud pixel of the light Intersection point, including：
    Bring the coordinate of each point and height value in the altitude data into the following formula, obtain linear equation and the institute of the light State the intersection point of the corresponding earth's surface of cloud pixel；
    <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mfrac> <mrow> <mi>X</mi> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>+</mo> <mi>s</mi> <mo>&amp;GreaterEqual;</mo> <mfrac> <mrow> <mi>Y</mi> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>,</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mfrac> <mrow> <mi>X</mi> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>-</mo> <mi>s</mi> <mo>&amp;le;</mo> <mfrac> <mrow> <mi>Y</mi> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>,</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mfrac> <mrow> <mi>Y</mi> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>&amp;le;</mo> <mfrac> <mrow> <mi>Z</mi> <mo>-</mo> <mi>h</mi> </mrow> <mi>h</mi> </mfrac> <mo>+</mo> <mi>s</mi> <mo>,</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mfrac> <mrow> <mi>Y</mi> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>&amp;GreaterEqual;</mo> <mfrac> <mrow> <mi>Z</mi> <mo>-</mo> <mi>h</mi> </mrow> <mi>h</mi> </mfrac> <mo>-</mo> <mi>s</mi> <mo>,</mo> </mrow> </mtd> </mtr> </mtable> </mfenced>
    Wherein, s is default error range.
  6. 6. cloud shadow detection method according to claim 5, it is characterised in that if the number of the intersection point is more It is a, then select height value highest in each intersection point and the intersection point minimum with light distance is match point, including：
    The height value of each point minimum is obtained in the intersection point, the height value of the intersection point is subtracted into the minimum height value；
    The difference of the height value and the minimum height value that obtain the intersection point is more than the intersection point of twice of elevation resolution ratio as new Intersection point, and the selection new intersection point minimum with light distance is match point from the new intersection point.
  7. 7. cloud shadow detection method according to claim 6, it is characterised in that it is described from the new intersection point selection with The minimum new intersection point of the light distance is match point, including：
    2 points chosen in each new intersection point neighborhood form a plane with the new intersection point, obtain the plane and the light The intersection point of line is as plane light intersection point；
    Obtain distance of each new intersection point with corresponding plane light intersection point, select the minimum new intersection point of the distance for Match point.
  8. A kind of 8. cloud shadow Detection system, it is characterised in that including：
    The linear equation of light establishes unit, for choosing any cloud pixel in cloud atlas picture, obtains cloud pixel in horizontal earth's surface Upright projection the position of shade and the height value of the cloud pixel in horizontal earth's surface of position, the cloud pixel, and build The linear equation of vertical light；
    Altitude data converting unit, for obtaining altitude data of the cloud atlas as corresponding earth's surface, the altitude data is transformed into Under space coordinates；
    Cloud pixel shadow spots position acquisition unit, for according to the coordinate of each point, height value and the light in the altitude data The linear equation of line obtains the coordinate of match point, and the coordinate of the match point is the position of cloud pixel shadow spots；
    Cloud shadow positions acquiring unit, for the position of each cloud pixel shadow spots in obtaining in cloud atlas picture, so as to obtain cloud the moon The position of shadow.
  9. 9. cloud shadow Detection system according to claim 8, it is characterised in that the linear equation of the light is：
    <mrow> <mfrac> <mrow> <mi>X</mi> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>X</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>X</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>Y</mi> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>Y</mi> <mrow> <mi>n</mi> <mi>a</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>Y</mi> <mrow> <mi>s</mi> <mi>h</mi> <mi>a</mi> <mi>d</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>Z</mi> <mo>-</mo> <mi>h</mi> </mrow> <mi>h</mi> </mfrac> <mo>,</mo> </mrow>
    Wherein, (Xshadow,Yshadow) be shade of the cloud pixel in horizontal earth's surface position, (Xnadir,Ynadir) it is described For cloud pixel in the position of the upright projection of horizontal earth's surface, h is the height value of the cloud pixel, and (X, Y, Z) is space point coordinates, Z For height value.
  10. 10. cloud shadow Detection system according to claim 8, it is characterised in that
    Further, the altitude data converting unit, for obtaining elevation minimum of the cloud atlas as each point in corresponding earth's surface, The elevation of each point in the cloud atlas picture is subtracted into the elevation minimum respectively；
    By the cloud atlas as the height value of each point in corresponding earth's surface divided by the resolution ratio of the cloud atlas picture, by the altitude data It is transformed under space coordinates.
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