孫榮煜

(中國(guó)科學(xué)院紫金山天文臺(tái)南京210008)

空間碎片光學(xué)觀測(cè)中若干問(wèn)題研究

孫榮煜?

(中國(guó)科學(xué)院紫金山天文臺(tái)南京210008)

地基光學(xué)觀測(cè)是探測(cè)空間碎片的重要手段.本文從目標(biāo)搜索方案的制定、目標(biāo)質(zhì)心提取、目標(biāo)精密定位以及目標(biāo)關(guān)聯(lián)4方面入手,研究提升設(shè)備探測(cè)能力、提高目標(biāo)觀測(cè)精度的方法.

首先,為了滿足對(duì)GEO(Geosynchronous Orbit,地球同步軌道)空間碎片探測(cè)的要求,克服長(zhǎng)時(shí)間曝光CCD像元飽和溢出的問(wèn)題,使用多幀連續(xù)曝光圖像疊加的方法,增加圖像的寬容度,同時(shí)保證系統(tǒng)的探測(cè)能力.實(shí)驗(yàn)表明,疊加10幀連續(xù)圖像,有效消除了像元飽和的情況,提升目標(biāo)信噪比約3.2倍,提升探測(cè)能力約2.5 mag,使用底片常數(shù)的均值計(jì)算目標(biāo)位置,精度符合要求.使用星像幾何形態(tài)檢測(cè)與線性關(guān)聯(lián)的方法,處理了IADC(Inter-Agency Space Debris Coordination Committee)AI23.4的光學(xué)聯(lián)測(cè)數(shù)據(jù),關(guān)聯(lián)139個(gè)目標(biāo)弧段,其中116個(gè)弧段對(duì)應(yīng)星表中99個(gè)目標(biāo),并得到這些目標(biāo)的實(shí)測(cè)星等、初軌半長(zhǎng)徑、軌道升交點(diǎn)經(jīng)度、軌道傾角分布.

其次,提出了一種基于先驗(yàn)信息的探測(cè)方法.該方法通過(guò)先驗(yàn)信息,在圖像中碎片星像的鄰域設(shè)置波門,計(jì)算波門內(nèi)的局部背景閾值,輔以相關(guān)的判據(jù)檢測(cè)目標(biāo),隨后使用矩方法及線性平移計(jì)算碎片質(zhì)心在整幅圖像中的位置.實(shí)驗(yàn)表明:該方法復(fù)雜度低,計(jì)算精度優(yōu)于0.5 pixel,計(jì)算時(shí)間短于0.5 s,可以高效地探測(cè)空間碎片.為了解決空間碎片光學(xué)觀測(cè)圖像中的拖尾與星像重疊問(wèn)題,使用數(shù)學(xué)形態(tài)學(xué)算子處理了星像.結(jié)果表明,該方法較好地去除了圖像中的拖尾、分離了圖像中的恒星星像與目標(biāo)星像,提高了目標(biāo)的檢測(cè)效率與定位精度.

再次,基于數(shù)學(xué)形態(tài)學(xué)算子,結(jié)合全局閾值分割圖像、矩方法計(jì)算星像質(zhì)心,實(shí)現(xiàn)了一套星像信息提取算法.大量實(shí)測(cè)數(shù)據(jù)的實(shí)驗(yàn)結(jié)果表明,該方法對(duì)于1 K×1 K圖像處理時(shí)間約為0.2 s,處理低軌與高軌目標(biāo)的精度分別為適合于空間碎片觀測(cè)數(shù)據(jù)的實(shí)時(shí)處理.為了減小圖像退化對(duì)處理精度的影響,使用數(shù)學(xué)形態(tài)學(xué)算子,沿圖像多個(gè)方向卷積,最后疊加所有處理過(guò)的圖像得到最終結(jié)果.實(shí)驗(yàn)表明,該方法提高了圖像中目標(biāo)與恒星的信噪比及定位精度.

最后,由于GEO空間目標(biāo)視運(yùn)動(dòng)速度較慢,給目標(biāo)快速自動(dòng)關(guān)聯(lián)帶來(lái)難度.基于Lucas-Kanade算法,在星像鄰域開窗,統(tǒng)計(jì)星像的移動(dòng)速度,給定閾值判別,實(shí)現(xiàn)了相鄰幀短曝光圖像間GEO目標(biāo)的自動(dòng)關(guān)聯(lián).實(shí)驗(yàn)表明:該算法穩(wěn)健可靠,星像位移計(jì)算精度為10?3,計(jì)算時(shí)間快于0.1 s.

Space debris has been recognized as a serious danger for operational spacecraft and manned space fl ights.Discussions are made in the methods of high order position precision and high detecting efficiency for space debris,including the design of surveying strategy,theextraction of object centroid,the precise measurement of object positions,the correlation and catalogue technique.

To meet the needs of detecting space objects in the GEO(Geosynchronous Orbit),and prevent the saturation of CCD pixels with a long exposure time,a method of stacking a series of short exposure time images is presented.The results demonstrate that the saturation of pixels is eliminated e ff ectively,and the SNR(Signal Noise Ratio)is increased by about 3.2 times,the detection ability is improved by about 2.5 magnitude when 10 seriate images are stacked,and the accuracy is reliable to satisfy the requirement by using the mean plate parameters for the astronomical orientation.A method combined with the geometrical morphology identi fi cation and linear correlation is adopted for the data calibration of IADC (Inter-Agency Space Debris Coordination Committee)AI23.4.After calibration,139 tracklets are acquired,in which 116 tracklets are correlated with the catalogue.The distributions of magnitude,semi-major axis,inclination,and longitude of ascending node are obtained as well.

A new method for detecting space debris in images is presented.The algorithm sets the gate around the image of objects,then several criterions are introduced for the object detection,at last the object position in the frame is obtained by the barycenter method and a simple linear transformation.The tests demonstrate that this technique is convenient for application,and the objects in image can be detected with a high centroid precision.In the observations of space objects,the shutter of camera is often removed,and the smear noise is ineluctable.Based on the di ff erences of the geometry between the stars and the smear noise,two operators of the mathematic morphology are presented to resolve this problem. Tests carried out indicate that the smear noise can be removed e ff ectively,and the detection rates of the objects and stars are improved distinctly.Due to the relative movement between space debris and background stars,the blending of objects and stars is ineluctable.In view of the geometric di ff erences between the stars and the objects,a technique for separating the blended objects based on the mathematical morphology is presented.It’s sufficiently fl exible to be applied,and the blended images can be separated e ff ectively with a high degree of centroid precision.

Here we present an automatic technique which optimally detects and measures the sources from the images of optical space debris observations.Tests demonstrate that the technique performs well from the point of view of the fast and accurate detection.An automatic image reconstruction method is also presented,the variable structural elements along multiple directions are adopted for the image convolution,and then all the corresponding convolved images are stacked.With this method,the position accuracies of background stars are improved distinctly.

A technique based on the Lucas-Kanade algorithm is presented to detect the GEO objects between two short exposure time frames automatically.The experiments demonstrate that this method works e ff ectively and robustly,the displacement precision of object images is about 10?3,and the computing time is less than 0.1 s.

Research on Optical Observation for Space Debris

SUN Rong-yu
(Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing 210008)

10.15940/j.cnki.0001-5245.2015.01.010

?2013-07-07獲得博士學(xué)位,導(dǎo)師:紫金山天文臺(tái)趙長(zhǎng)印研究員;rysun@pmo.ac.cn