CN111578907B - Estimation method for observable extreme satellites and the like of small celestial bodies near the earth - Google Patents
Estimation method for observable extreme satellites and the like of small celestial bodies near the earth Download PDFInfo
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Abstract
The application discloses an estimation method for observable limit satellites and the like of a small celestial body near the earth, which comprises the following steps: a CCD image containing background stars is shot at an observation night, and the exposure time is TR(ii) a Establishing a mapping relation between the shot CCD image and a corresponding area of the star catalogue through star map matching, then selecting a fixed star target, and knowing that the sight star of the fixed star is M through the star catalogueR(ii) a Calculating the luminous flux Intensity of the sidereal target from the captured CCD imageRTypical unsaturated sidereal image full width at half maximum value is FWHMRThe radius of the star image target area is r; m of extreme stars observable according to small celestial bodies near the earthOSpeed V of motion of small celestial body near the groundOEquivalent exposure time TOCalculating the expression of the relation to obtain MO、VOAnd TOThe motion speed V of the objectODetermined equivalent exposure time TOAnd substituting the obtained data into the calculated relation model to obtain the observable limit satellites and the like of the small celestial bodies near the earth estimated under the condition.
Description
Technical Field
The application belongs to the technical field of astronomical observation, and particularly relates to an estimation method for observing extreme satellites and the like by using small celestial bodies near the earth.
Background
The astronomical observation work aiming at the small celestial bodies of the solar system is of great significance for researching the origin and evolution of the solar system, the detection of the small celestial bodies near the earth and planets outside the system, deep space navigation and other fields. As part of the solar celestial body, the small celestial body in the near field is of great interest because of the threat to the earth and human civilization, and in recent years, events in which the small celestial body hits the earth have frequently occurred, such as meteorite hit in russian car jabeck on 2 and 15 days 2013, and Mars fire star hit in Yunnan province Daizhiqing on 10 and 4 days 2017. The high-precision celestial body measurement and observation of the small solar celestial body, especially the small near-earth celestial body, is facilitated, the operation orbit of the small celestial body is monitored, and the potential threat of the small near-earth celestial body impacting the earth can be responded to by sufficient response time of human beings; and the acquisition of the high-precision small celestial body orbit theory has very important significance for further implementing a small planet detection plan and acquiring space resources by human beings.
The acquisition of the high-precision small celestial body orbit theory needs to carry out long-period multi-epoch celestial body measurement observation on the small celestial body. At present, the development mode of the work is mainly based on the ground large-scale optical telescope to find the sky in a patrolling way, and the subsequent follow-up observation is developed by combining a joint survey network consisting of ground small-caliber optical telescopes in the global range. The small celestial body in the near ground moves relative to the fixed star, so that the observation efficiency of the astronomical telescope on the targets is improved, high-quality observation data of the small celestial body in the near ground is obtained, the observable limit satellites of the small celestial body in the near ground and the like need to be estimated, and the relation between the movement speed of the small celestial body in the near ground, the exposure time and the limit satellites and the like needs to be analyzed. The traditional estimation method for the extreme stars and the like needs to acquire information such as CCD noise, station sky light background, atmospheric transmittance and the like as calculation parameters, the information needs to be acquired by using a special instrument or a professional measurement method, the atmospheric conditions at different observation nights are different, and the information such as the extreme stars which can be observed by moving celestial bodies at the observation nights is difficult to conveniently and accurately acquire.
Therefore, it is necessary to provide an estimation method for observing extreme satellites and the like by using a small celestial body in the near field.
Disclosure of Invention
An object of the present application is to provide a new technical solution of an estimation method for observable extreme stars and the like.
According to one aspect of the present application, there is provided a method for estimating near-earth celestial observable extreme stars, etc., comprising the steps of:
a CCD image containing background stars is shot at an observation night, and the exposure time is TR；
Establishing a mapping relation between the shot CCD image and a corresponding area of the star catalogue through star map matching, then selecting a fixed star target, and knowing that the sight star of the fixed star is M through the star catalogueR；
Calculating the luminous flux Intensity of the sidereal target from the captured CCD imageRTypical unsaturated sidereal image full width at half maximum value is FWHMRThe radius of the star image target area is r;
setting the detection requirements of the star-like objectsThreshold SNR of lowest signal-to-noise ratioLCorresponding to the lowest luminous flux of the detectable star image
In the formula StdBgdCalculating the number of pixels in the area for the standard deviation of the target background of the star image and N for the luminous flux of the star image;
m of extreme stars observable according to small celestial bodies near the earthOSpeed V of motion of small celestial body near the groundOEquivalent exposure time TOThe expression of the relationship:
calculating to obtain MO、VOAnd TOIn the relation model of (1), wherein VRFor small celestial bodies near the ground during the exposure time TRThe fastest moving speed of the inner observable limit;
the moving speed V of the small celestial body close to the ground of the targetODetermined equivalent exposure time TOAnd substituting the estimated observable limit satellites and the like of the small celestial bodies near the earth under the condition into the calculated relation model.
Alternatively, SNRLTaking the value of 3.
Optionally, a calculation formula of the number N of pixels in the star image luminous flux calculation area is as follows:
N＝π×r2
wherein r has a value in the range of 1.25 XFWHMR≤r≤2×FWHMR.
Optionally, the fastest moving speed V of the observable limit of the small celestial body near the groundRIs calculated by the formula
K is a pixel scale of a telescope used for observation; and in the single CCD exposure time TRThe moving distance of the small celestial body is equal to FWHMR。
Optionally, the number of the preset number of images is calculated by: exposure time of a single image
The minimum number of images taken is
Light flux of moving target of single image with integer
And the condition integrity needs to be satisfieds>NoisereadWherein NoisereadIs the readout noise when the camera exposure time is T.
The method has the technical effects that by utilizing a relative measurement method, the relationship between the observable limit satellites of the moving celestial body and the like and the moving speed and the exposure time of the celestial body can be conveniently and effectively analyzed and estimated by combining the luminosity and the full width at half maximum (FWHM) of the fixed stars in the CCD image data of the evacuated celestial body obtained at night and the information such as the minimum signal-to-noise ratio of the detectable target in the CCD image, and the observable limit satellites of the moving celestial body at night can be estimated.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application.
In the drawings:
FIG. 1 is a schematic illustration of a calculation region in some embodiments of the present application;
fig. 2 is a relationship between the extreme observation stars and the like of the celestial body 1 in application example 1 of the present application, the speed of the celestial body movement, and the equivalent exposure time.
Detailed Description
Embodiments of the present application will be described in detail with reference to the drawings and examples, so that how to implement technical means to solve technical problems and achieve technical effects of the present application can be fully understood and implemented.
The application provides an estimation method for observable limit satellites and the like of a small celestial body in the near field, which comprises the following steps of:
a CCD image containing background stars is shot at an observation night, and the exposure time is TR；
Establishing a mapping relation between the shot CCD image and a corresponding area of the star catalogue through star map matching, then selecting a fixed star target, and knowing that the sight star of the fixed star is M through the star catalogueR；
Calculating the luminous flux INtensity of the sidereal target from the captured CCD imageRTypical unsaturated sidereal image full width at half maximum value is FWHMRThe radius of the star image target area is r;
setting minimum signal-to-noise ratio threshold SNR required by star image target detectionLCorresponding to the lowest luminous flux of the detectable star image
In the formula StdBgdCalculating the number of pixels in the area for the standard deviation of the background of the star image target and N for the luminous flux of the star image target;
m of extreme stars observable according to small celestial bodies near the earthOSpeed V of motion of small celestial body near the groundOEquivalent exposure time TOThe expression of the relationship:
calculating to obtain MO、VOAnd TOIn the relation model of (1), wherein VRFor small celestial bodies near the ground during the exposure time TRThe fastest moving speed of the inner observable limit;
the moving speed V of the small celestial body close to the ground of the targetODetermined equivalent exposure time TOAnd substituting the estimated observation limit sight stars and the like of the small celestial bodies near the earth under the condition into the obtained relation model. VoCan be inquired through a small celestial body calendar.
When V isO≤VRThe small celestial body near the ground moves slowly, and long exposure is directly carried out according to the mode of observing fixed stars, and the exposure time is TO；
When V isO>VRThe moving speed of the small celestial body near the ground is high, and the equivalent exposure time is T by shooting the superposition of a preset number of imagesOThe observation effect of (1).
The method can conveniently and effectively analyze and estimate the relationship between the observable limit satellites of the moving celestial body and the like and the moving speed and the exposure time of the celestial body and estimate the observable limit satellites of the moving celestial body at night by utilizing a relative measurement method and combining the luminosity and full width at half maximum (FWHM) of the fixed stars in the CCD image data of the evacuated celestial body obtained at night and the information such as the minimum signal-to-noise ratio of the detectable target in the CCD image.
In the method, the measurement and calculation of the sight stars and the like can be estimated through luminous flux, and for two observation target stars A and B, the two observation target stars A and B have the following relationship in the same CCD observation image:
wherein M isAFor viewing the stars, etc., of object A, MBTo observe the stars, etc., of object BALuminous flux of object A, IntensityBThe light flux of the object B.
The following formula is adopted to calculate the signal-to-noise ratio of the planets:
wherein Intensity is star image luminous flux, StdBgdAnd calculating the number of area pixels for the standard deviation of the star image background, and N is the star image luminous flux. The background calculation region is shown in fig. 1, and represents a region in which the planet background calculation is performed outside the effective region of the star image, that is, outside a circle with radius R and inside a circle with radius R (a custom value); further, in order to reduce errors, setting P, and taking R < P < R; background calculation regionDomains are in the range of P and R; further, P is greater than R5 pixels and R is greater than P8 pixels. The star image luminous flux calculation area is as shown in fig. 2, and the star image luminous flux calculation area is selected according to the effective radius r of the star image, so that N is pi × r2. The calculation of the star image luminous flux subtracts the star image background.
The lowest signal-to-noise ratio satisfying the star image target detection requirement is assumed to be SNRLThen the minimum luminous flux corresponding to the detectable star image is IntensityL。
In a single CCD exposure time TRIn, the celestial body movement distance is equal to the typical FWHMRWhen the moving speed of the celestial body corresponding to the extreme sight star is VR。
Wherein K is the pixel scale of the telescope used for observation.
The observable extreme stars M of the moving celestial body obtained by the formulas 1) -4)OWith the speed V of the motion of the moving celestial bodyOEquivalent exposure time TOThe expression of the relationship is:
thereby enabling the establishment of MO、VOAnd TOThe relationship model of (1).
When V isO≤VRThe method indicates that the moving target moves slowly, can directly carry out long exposure according to the mode of observing fixed stars, and can directly carry out single-width long exposure according to the mode of observing fixed stars, and the exposure time is TO。
When V isO>VRThe moving speed of the moving object is high, and the equivalent exposure time needs to be achieved by overlapping a plurality of imagesIs TOThe observation effect of (1). At this time, the exposure time of a single image
The minimum number of images to be captured is
Luminous flux of single image moving target
And the condition integrity needs to be satisfieds>oisereadWherein NoisereadIs the readout noise when the camera exposure time is T. As will be understood by those skilled in the art, in astronomy, TOAnd T is a common custom value, divisible into an integer.
Application example 1:
and on 6, 2 and 2019, a 1m telescope of a Yunnan astronomical stage is used, the CCD image containing the background fixed star obtained by observing night on the same day is used for calculating related parameters, the relation between the observable limit sight stars of the moving celestial bodies and the like and the moving speed and the equivalent exposure time of the celestial bodies is further analyzed and calculated, and finally the observable limit sight stars of the small celestial bodies close to the ground are estimated. The key parameters in the CCD image used are shown in table 1. The relationship between the observable limit satellites of the small near-earth celestial bodies obtained by calculation and analysis, the motion speed of the celestial bodies and the equivalent exposure time is shown in figure 2. The result shows that the limit sight star of the target can be observed to be 18.58 by observing a small celestial body (celestial body 1) with the movement speed of 0.0273arcsec/s by using a 1m telescope of a Yunnan astronomical stage, and the exposure time required by a single image is not less than 40 seconds. If the movement speed of the small celestial body (celestial body 2) is increased by 1 time to be 0.0546arcsec/s, the limit sight star of the observable small celestial body target at the moment is 17.82, the equivalent exposure time is 40 seconds, and not less than two CCD images with the exposure time of 20 seconds need to be shot.
Table 1: key parameter in single background fixed star CCD image of 6, month and 2 days in 2019
As used in the specification and claims, certain terms are used to refer to particular components or methods. As one skilled in the art will appreciate, different regions may refer to a component by different names. The present specification and claims do not intend to distinguish between components that differ in name but not in name. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. "substantially" means within an acceptable error range, and a person skilled in the art can solve the technical problem within a certain error range to substantially achieve the technical effect. The description which follows is a preferred embodiment of the present application, but is made for the purpose of illustrating the general principles of the application and not for the purpose of limiting the scope of the application. The protection scope of the present application shall be subject to the definitions of the appended claims.
It is also noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a good or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such good or system. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a commodity or system that includes the element.
While the foregoing description shows and describes several preferred embodiments of the invention, it is to be understood, as noted above, that the invention is not limited to the forms disclosed herein, but is not to be construed as excluding other embodiments and is capable of use in various other combinations, modifications, and environments and is capable of changes within the scope of the inventive concept as expressed herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. A method for estimating observable extreme satellites and the like of a small celestial body near the earth is characterized by comprising the following steps of:
a CCD image containing background stars is shot at an observation night, and the exposure time is TR；
Establishing a mapping relation between the shot CCD image and a corresponding area of the star catalogue through star map matching, then selecting a fixed star target, and knowing that the sight star of the fixed star is M through the star catalogueR；
Calculating the luminous flux Intensity of the sidereal target from the captured CCD imageRTypical unsaturated sidereal image full width at half maximum value is FWHMRThe radius of the star image target area is r;
setting minimum signal-to-noise ratio threshold SNR required by star image target detectionLCorresponding to the lowest luminous flux of the detectable star image
In the formula StdBgdCalculating the number of pixels in the area for the standard deviation of the target background of the star image and N for the luminous flux of the star image;
m of extreme stars observable according to small celestial bodies near the earthOSpeed V of motion of small celestial body near the groundOEquivalent exposure time TOThe expression of the relationship:
calculating to obtain MO、VOAnd TOIn the relation model of (1), wherein VRFor small celestial bodies near the ground during the exposure time TRThe fastest moving speed of the inner observable limit;
the moving speed V of the small celestial body close to the ground of the targetODetermined equivalent exposure time TOSubstituting the estimated observable extreme satellites and the like of the small terrestrial celestial bodies under the condition into the calculated relation model;
when V isO≤VRThe small celestial body near the ground moves slowly, and long exposure is directly carried out according To a mode of observing a fixed star, wherein the exposure time is To;
when V isO＞VRThe moving speed of the small celestial body near the ground is high, and the equivalent exposure time is T after the preset number of images are shot and overlappedOThe observation effect of (1).
2. The method of estimating small celestial near-earth observable extreme stars, etc. of claim 1, wherein SNR isLTaking the value of 3.
3. The method for estimating small celestial observable near-earth extreme stars, etc. of claim 1, wherein the calculation formula for calculating the number of pixels N in the area for calculating the luminous flux of a fixed star image is:
N＝π×r2
wherein r has a value in the range of 1.25 XFWHMR≤r≤2×FWHMR。
4. The method of claim 1, wherein the fastest moving speed V isRIs calculated by the formula
K is a pixel scale of a telescope used for observation; and in the single CCD exposure time TRThe moving distance of the small celestial body is equal to FWHMR。
5. An estimation method of near-earth small celestial observable limit satellites and the like according to claim 4, wherein the number of the preset number of images is calculated by: exposure time of a single image
The minimum number of images taken is
Light flux of moving target of single image with integer
And the condition integrity needs to be satisfiedS＞NoisereadWherein NoisereadIs the readout noise when the camera exposure time is T.
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