阅读说明：本技术 一种近地小天体可观测极限视星等的估算方法 (Estimation method for observable extreme satellites and the like of small celestial bodies near the earth ) 是由 张益恭 王建成 苏婕 于 2020-06-30 设计创作，主要内容包括：本申请公开了一种近地小天体可观测极限视星等的估算方法,包括以下步骤：观测夜拍摄一幅包含背景恒星的CCD图像,曝光时间为T<Sub>R</Sub>；通过星图匹配建立所拍摄CCD图像与星表对应区域映射关系,之后选取一颗恒星目标,通过星表可知该恒星视星等为M<Sub>R</Sub>；由所拍摄CCD图像计算得该恒星目标的光通量Intensity<Sub>R</Sub>,典型未饱和恒星像半高全宽值为FWHM<Sub>R</Sub>,星像目标区域半径为r；按照近地小天体可观测极限视星等M<Sub>O</Sub>与近地小天体运动速度V<Sub>O</Sub>、等效曝光时间T<Sub>O</Sub>关系的表达式计算得到M<Sub>O</Sub>、V<Sub>O</Sub>和T<Sub>O</Sub>的关系模型,将目标的运动速度V<Sub>O</Sub>、确定的等效曝光时间T<Sub>O</Sub>代入计算得到的关系模型内,得到该条件下估算的近地小天体的可观测极限视星等。(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 T R (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 catalogue R (ii) a Calculating the luminous flux Intensity of the sidereal target from the captured CCD image R Typical unsaturated sidereal image full width at half maximum value is FWHM R The radius of the star image target area is r; m of extreme stars observable according to small celestial bodies near the earth O Speed V of motion of small celestial body near the ground O Equivalent exposure time T O Calculating the expression of the relation to obtain M O 、V O And T O The motion speed V of the object O Determined equivalent exposure time T O And 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.)

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 T_R；

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 catalogue_R；

Calculating the luminous flux Intensity of the sidereal target from the captured CCD image_RTypical unsaturated sidereal image full width at half maximum value is FWHM_RThe radius of the star image target area is r;

setting minimum signal-to-noise ratio threshold SNR required by star image target detection_LCorresponding to the lowest luminous flux of the detectable star imageIn the formula Std_BgdCalculating 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 earth_OSpeed V of motion of small celestial body near the ground_OEquivalent exposure time T_OThe expression of the relationship:

calculating to obtain M_O、V_OAnd T_OIn the relation model of (1), wherein V_RFor small celestial bodies near the ground during the exposure time T_RThe fastest moving speed of the inner observable limit;

the moving speed V of the small celestial body close to the ground of the target_ODetermined equivalent exposure time T_OAnd 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.

When V is_O≤V_RThe small celestial body near the ground moves slowly, and long exposure is directly carried out according to the mode of observing fixed stars;

when V is_O>V_RThe 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 images_OThe observation effect of (1).

2. The method of estimating small celestial near-earth observable extreme stars, etc. of claim 1, wherein SNR is_LTaking 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 × FWHM_R≤r≤2×FWHM_R。

4. The method of claim 1, wherein the fastest moving speed V is_RIs calculated by the formula

K is a pixel scale of a telescope used for observation; and in the single CCD exposure time T_RThe moving distance of the small celestial body is equal to FWHM_R。

5. The geodetic cube of claim 4The estimation method of the celestial observable limit satellites is characterized in that the number of the preset number of images is calculated by the following steps: exposure time of a single imageThe minimum number of images taken isLight flux of moving target of single image with integer And the condition integrity needs to be satisfied_s>Noise_readWherein Noise_readIs the readout noise when the camera exposure time is T.

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 T_R；

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 catalogue_R；

Calculating the luminous flux Intensity of the sidereal target from the captured CCD image_RTypical unsaturated sidereal image full width at half maximum value is FWHM_RThe radius of the star image target area is r;

setting minimum signal-to-noise ratio threshold SNR required by star image target detection_LCorresponding to the lowest luminous flux of the detectable star imageIn the formula Std_BgdCalculating 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 earth_OSpeed V of motion of small celestial body near the ground_OEquivalent exposure time T_OThe expression of the relationship:

calculating to obtain M_O、V_OAnd T_OIn the relation model of (1), wherein V_RFor small celestial bodies near the ground during the exposure time T_RThe fastest moving speed of the inner observable limit;

the moving speed V of the small celestial body close to the ground of the target_ODetermined equivalent exposure time T_OAnd 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, SNR_LTaking 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 × FWHM_R≤r≤2×FWHM_R.

Optionally, the fastest moving speed V of the observable limit of the small celestial body near the ground_RIs calculated by the formula

K is a pixel scale of a telescope used for observation; and in the single CCD exposure time T_RThe moving distance of the small celestial body is equal to FWHM_R。

Optionally, the number of the preset number of images is calculated by: exposure time of a single imageThe minimum number of images taken isLight flux of moving target of single image with integerAnd the condition integrity needs to be satisfied_s>Noise_readWherein Noise_readIs 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 T_R；

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 catalogue_R；

Calculating the luminous flux INtensity of the sidereal target from the captured CCD image_RTypical unsaturated sidereal image full width at half maximum value is FWHM_RThe radius of the star image target area is r;

setting minimum signal-to-noise ratio threshold SNR required by star image target detection_LCorresponding to the lowest luminous flux of the detectable star imageIn the formula Std_BgdCalculating 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 earth_OSpeed V of motion of small celestial body near the ground_OEquivalent exposure time T_OThe expression of the relationship:

calculating to obtain M_O、V_OAnd T_OIn the relation model of (1), wherein V_RFor small celestial bodies near the ground during the exposure time T_RThe fastest moving speed of the inner observable limit;

the moving speed V of the small celestial body close to the ground of the target_ODetermined equivalent exposure time T_OAnd 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. V_oCan be inquired through a small celestial body calendar.

When V is_O≤V_RThe 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 T_O；

When V is_O>V_RThe 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 images_OThe 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 is_AFor viewing the stars, etc., of object A, M_BTo observe the stars, etc., of object B_ALuminous flux of object A, Intensity_BThe 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, Std_BgdThe method comprises the steps of calculating the number of pixels of an area for calculating the star image background standard deviation, wherein N is the star image luminous flux, the background calculation area is shown in figure 1, the calculation of the star image background is carried out on the outer circle of an effective area of the star image, namely, the area is larger than the circle with the radius R and smaller than the circle with the radius R (a user-defined value), further, in order to reduce errors, P is set, R is smaller than P and smaller than R, the background calculation area is carried out in the range of P and R, in the further step, P is larger than R5 pixels, R is larger than P8 pixels, the calculation area of the star image luminous flux is shown in figure 2, the calculation area of the star image luminous flux is selected according to the effective radius R of the star image, and then N is × R is selected as the². 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 SNR_LThen the minimum luminous flux corresponding to the detectable star image is Intensity_L。

In a single CCD exposure time T_RIn, the celestial body movement distance is equal to the typical FWHM_RWhen the moving speed of the celestial body corresponding to the extreme sight star is V_R。

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 body_OEquivalent exposure time T_OThe expression of the relationship is:

thereby enabling the establishment of M_O、V_OAnd T_OThe relationship model of (1).

When V is_O≤V_RThe 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 T_O。

When V is_O>V_RThe moving speed of the moving object is high, and the equivalent exposure time is T through superposition of a plurality of images_OThe observation effect of (1). At this time, the exposure time of a single imageThe minimum number of images to be captured isLuminous flux of single image moving targetAnd the condition integrity needs to be satisfied_s>oise_readWherein Noise_readIs the readout noise when the camera exposure time is T. As will be understood by those skilled in the art, in astronomy, T_OAnd 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.