MASTER THESIS Impact hazard assessment from the automatic detection of meteoric and reentry fireballs recorded by the SPMN network Eloy Peña Asensio SUPERVISED BY Josep Maria Trigo Rodríguez TUTOR Miquel Sureda Anfres Universitat Politècnica de Catalunya Master in Aerospace Science & Technology February 2020 Title of the master thesis BY Eloy Peña Asensio DIPLOMA THESIS FOR DEGREE Master in Aerospace Science and Technology AT Universitat Politècnica de Catalunya SUPERVISED BY: Josep Maria Trigo Rodríguez Institut de Ciències de l'Espai (IEEC-CSIC) TUTOR: Miquel Sureda Anfres Departamento de Física - ESEIAAT ABSTRACT The disruption of asteroids and comets can produce meteoroids that end up impacting the Earth’s atmo- sphere, creating shock waves or even excavating craters so they generate hazardous scenarios. In this thesis different software tools have been developed with the aim of automating the detection and analysis of fire- balls from multiple station video recordings. Given the automatic video processing, it opens the possibility of providing early warnings associated with shock waves and massive meteorite arrival to the ground. As an example of reduction procedure two meteoric events have been analyzed, obtaining their real atmo- spheric trajectories, characterizing their flight and computing their respective heliocentric orbits. A method to estimate meteorite-dropping likelihood has also been implemented. In one of the study cases, NASA satel- lite data has been used to reconstruct the fireball trajectory and compute its mass and luminosity. Finally, the implications for impact hazard assessment associated to meter-sized meteoroids are dis- cussed and assess in view of recent evidence. Barcelona, February 2020 i CONTENTS List of Figures v List of Tables vii 1 Introduction 1 1.1 Meteoric Phenomena.......................................1 1.2 Impact Hazard..........................................3 1.3 SPMN Network..........................................4 1.4 Thesis Goals...........................................5 2 Methodology and Frameworks7 2.1 Software.............................................7 2.2 Databases and Libraries......................................7 2.2.1 SAO............................................8 2.2.2 Astropy and PyEphem...................................8 2.2.3 Orbit Calculator Software.................................8 3 Automatic Detection and Analysis of Meteors9 3.1 Computer Vision Techniques...................................9 3.1.1 Moving Object Tracking.................................. 10 3.1.2 False Positive Avoidance.................................. 13 3.1.3 Star Identification..................................... 14 3.2 Photometry: Magnitude Estimation................................ 17 3.2.1 Extinction Correction................................... 17 3.2.2 Atmospheric Refraction Correction............................ 17 3.2.3 Aberration of Light Correction............................... 18 3.2.4 Aperture Photometry................................... 19 3.2.5 Photometric Mass..................................... 20 3.3 Reconstruction of the Atmospheric Trajectory.......................... 21 3.3.1 Standard and Equatorial Coordinates........................... 21 3.3.2 Extended Method..................................... 23 3.3.3 Extension for Fish-eye and Wide-Field Lens........................ 24 3.3.4 Simplex Method...................................... 26 3.3.5 Stereoscopic Intersection................................. 28 3.3.6 Measured Points Projection on the Averaged Trajectory.................. 29 3.3.7 Characterization of the Atmospheric Flight........................ 31 3.3.8 Radiant Computation: Zenith Attraction and Diurnal Aberration............. 35 3.4 Calculation of Errors in Radiant Determination.......................... 36 4 Study Cases 39 4.1 Taurid Fireball: SPMN251019B.................................. 39 4.2 Sporadic Superbolide: SPMN160819............................... 45 5 Discussion: Implication for Impact Hazard 53 6 Conclusions and Future work 57 Bibliography 59 iii LISTOF FIGURES 1.1 Illustration of meteoroids, meteors, fireballs, superbolides, meteorites and micrometeorites. Adapted from [Rendtel, 1993]........................................2 1.2 Schematic figure shows the intersection of images taken from two stations resulting in the me- teor’s trajectory. Adapted from [Roggemans, 1987]............................5 3.1 Image processing block diagram of each frame of the recorded video................. 10 3.2 Frames from a real video of SPMN300319B fireball, an intermediate step in the processing and the final result. Depicted temporarily from left to right, and from top to bottom in processing. It is shown a first frame without a meteor, a detection of the meteor, a false positives due to glare, a rejected frame when explosion, a detection of the meteor being larger and the detection of the meteor trail................................................... 12 3.3 Basic scheme of operation of a Kalman filter................................ 13 3.4 Simple example of classification using DBSCAN clustering algorithm. Red dots are classified as core, since yellow dots are attainable only by A they are core too and blue N point is considered noise....................................................... 14 3.5 Clustering algorithm and statistical calculations for discard false positives and automatically select the points corresponding to the trajectory in a real case (SPMN300319B fireball 2.1). From left to right: All detected points, clusters found and noise, and selected cluster........... 14 3.6 Block diagram of the star plate coordinates finder algorithm...................... 15 3.7 Sequence of the process of obtaining the coordinates of the stars in the photo. Depicted tem- porarily from left to right. Sequence of the process of obtaining the coordinates of the stars in the photo. It shows the first frame of the video, the overlapping of all valid frames without detec- tion, the application of the ORB algorithm after a logarithmic correction, the classification with the clustering algorithm and the final result. The second application of the cluster algorithm to merge the points very close to the stars has been omitted in this figure................ 16 3.8 Illustration of the refraction produced by the atmosphere on an observed star. Adapted from [Tatum, 2019].................................................. 18 3.9 Schematic drawing on the aberration of the light produced by the speed of Earth’s translation with respect to that of the light. The apex A, the north polar P and a random star X are shown.. 19 3.10 Conceptual scheme showing misalignment between the standard axes (», ´) and the plate axes (x, y). Adapted from [Roggemans, 1987].................................. 22 3.11 Illustration of stereographic projections. On the left, a star Q and its projection Q0 are repre- sented. Q0 is on the tangent plane to the sphere at the optical center point C, which is the standard coordinate system. On the right, the North Celestial Pole P, its projection P 0 and the spherical triangle that define CPQ are also represented. Adapted from [Tatum, 2019]....... 22 3.12 The basis of the extended method is to consider the equations of the movements between the coordinate axes in the plane. Adapted from [Tatum, 2019]....................... 24 3.13 Conceptual correction of barrel distortion produced by a wide-field lens............... 25 3.14 Application example of the Simplex method. The initial triangle is represented in blue, with P the largest error and M the smallest one. R is the substitution point for reflection, E for expan- sion and C for contraction. The calculated plate centre is depicted in purple............ 27 3.15 Block diagram of the Simplex method. Adapted from [Steyaert, 1990] and [Trigo-Rodriguez et al., 2005]................................................... 27 3.16 Graphical representation of the real meteor trajectory calculation by intersecting the planes and obtaining the radiant by projecting backwards until the collision with the celestial sphere. It is shown the vertical projection as well.................................... 28 3.17 Schematic diagram for radiant error computation. On the left, the two largest possible devia- tions for each apparent trajectory are shown, which delimits the margin of error of the calcu- lated radiant. On the right, the four possibilities of deviation assuming the worst case....... 37 v vi LISTOF FIGURES 4.1 SPMN251019B apparent trajectory recorded and reduced from Eivissa (a), Folgueroles (b) and Montseny (c). Reference stars and constellation are pointed out.................... 41 4.2 SPMN251019B apparent radiant based on the records from Eivissa (orange), Folgueroles (red) and Montseny (green) plotted into the celestial sphere with propagation errors. Ecliptic, equa- torial plane and the nearby constellations of the Northern hemisphere are show.......... 42 4.3 SPMN251019B atmospheric trajectory based on the records from Eivissa (orange), Folgueroles (red) and Montseny (green). Vertical projection (white) and observation range are shown..... 43 4.4 Plot of observational data with velocity normalized to entry velocity and height normalized to the atmospheric scale height for the SPMN251019B event........................ 44 4.5 The bounding line for a 50 g meteorite is shown in black for the case where there is no spin (¹ 0) and in gray where spin allows uniform ablation over the entire surface (¹ 2/3)...... 45 Æ Æ 4.6 SPMN160819