Theory And Technology Research On Astronomical Orientation Based On Lunar Observations

Compared with traditional astronomical methods,the orientation determination one based on lunar observations has the advantages of anti-interference and no error accumulation.Furthermore,this new method can solve the problem of invisible stars in cloudy weather to some degree.Also,realizing moon-based orientation through the camera imaging mode can effectively remove human intervention.Lastly,combined with laptop's instrument control and data processing,the automatic acquisition of heading angle can be achieved.A set of moon phase simulation software is designed in this paper.Two methods are proposed to extract the central position of the moon,that is,the circle fitting method and the ellipse fitting method.According to the imaging characteristics of the moon,we use the indoor full physical simulation dome of starry sky to calibrate the camera's inside azimuth elements.In addition,we use the tilt sensor and horizon image to calibrate the camera's outside azimuth elements respectively in land and sea environment.We use scientific grade CCD and fisheye lens to constitute the fisheye camera.Combined with tilt sensor,astronomical timer and laptop,the moon –based orientation device is made up.Experiments on land and at sea were carried out,and preliminary success was reaped,filling the gaps in research of the related fields.The main work and innovation points of this paper are summarized as follows:(1)The theoretical basis and basic principle of astronomical orientation based on lunar observations are presented in this paper.Furthermore,the error sources of heading angle are analyzed theoretically.The result shows that the accuracy of heading angle is mainly affected by the location accuracy of observation station,the extraction accuracy of moon center,the accuracy of principal point's coordinate and the accuracy of camera's attitude parameters.(2)A set of moon phase simulation software is developed independently,which has two operating modes including dynamic and static ones.In this way,moon phase simulation at any time and anywhere in the world can be realized,thus offering simulation data source of the moon phase to later chapters.(3)The Sobel-Zernike operator is introduced in this paper to achieve sub-pixel edge detection of the moon phase.Two methods(including the circle fitting method and the ellipse fitting method)are put forward to achieve accurate selection of the real lunar edge,which is used to fit the central position of the moon.A semi-physical simulation experiment and an actual one were carried out to test the accuracy these methods.Data from the semi-physical simulation experiment manifest that the external accuracy of the circle fitting method is 0.44 ~ 6.07 arc-seconds and that of the ellipse fitting method is 2.78 ~ 17.20 arc-seconds.It needs to be noted that the results are from moon images roughly located at the centre of field of view.As for the actual moon images,the ellipse fitting method is chosen to process them,by which the internal accuracy better than 7.81 arc-seconds is obtained.(4)The simulated stars which have good imaging quality and whose luminance is controllable in the indoor dome are taken as observation targets in this paper.Making use of these location-aware stars,the camera's inside azimuth elements can be successfully calibrated.A tilt sensor is introduced on land to calibrate the camera's outside azimuth elements.Meanwhile,a method by imaging indoor and outdoor is proposed to determine the attitude parameters of the camera.On the other hand,the horizon image is used at sea to calibrate the camera's outside azimuth elements.Similarly,a horizon fitting algorithm based on altitude angle constraint is proposed to determine the attitude parameters of the camera.(5)Based on a fisheye camera,a tilt sensor,an astronomical timer and a laptop,the astronomical orientation method on land based on lunar observations utilizing super wide field of view is proposed.Also,based on a fisheye camera,an astronomical timer and a laptop,the astronomical orientation method at sea based on lunar observations utilizing super wide field of view is proposed.Actual experiments were carried out respectively on land and at sea.The experiment on land manifests that after 15 minutes' tracking shoots,the internal accuracy could be superior to ?7.5?,and the external accuracy could approximately reach ?20?.The experiment at sea manifests that the average deviation of heading angle between moon-observing method and star-observing method is 71.2?.