Presentation Information
[PPS03-P06]Preliminary Study for 3D Shape Reconstruction Methods Applicable for Torifune Flyby Observation by Hayabusa2
*Yoshitaka Kuroiwa1, Naru Hirata1 (1.University of Aizu)
Keywords:
asteroid,Hayabusa2,lightcurve inversion,rim profiling
A 3D shape model of an asteroid are important deliverables that should be produced in the early stages of asteroid exploration, as they allow us to estimate the surface topography and internal structure of the target body. In 2026, Japan's asteroid explorer Hayabusa 2 will conduct a flyby of the asteroid Torifune. A flyby is a method of observation in which a spacecraft observes a target celestial body while passing by it at high speed, and by its nature, the data that can be obtained is limited. Careful advance preparation is important to reconstruct an accurate shape model from the limited data. As a part of this kind of activities, we studied expected observation conditions at the flyby operation and applicability of existing shape modeling methods to the data to be obtained under those conditions. We consider following shape modeling methods: Shape-from-Motion; SfM, Stereophotoclinometry (SPC), rim profiling (aka Shape-from-Silhouette; SfS), and lightcurve inversion. In this abstract, we describe preliminary results on following items: estimation of the maximum parallax regarding SfM and SPC, trials shape reconstruction with lightcurve inversion and rim profiling.
Among the methods considered, SfM and SPC utilize the principle of stereo vision. Stereo vision reconstructs a 3D shape of the target based on the parallax between a pair of images taken from different positions. The amount of parallax directly affects the success and accuracy of shape reconstruction. Because the spacecraft’s pointing direction could not be changed during the flyby of Torifune, it was impossible to obtain a parallax greater than the camera’s field of view. Furthermore, due to the significant difference in resolution between stereo pairs in flyby observations, the parallax in pixel units within the lower-resolution image is critical. We estimated the achievable parallax in pixel units under actual observation conditions.
Lightcurve inversion is a method used to estimate the shape of a celestial body by utilizing changes in reflected brightness as it rotates. Attempts have already been made to estimate the shape of Torifune using this technique with ground-based observation data. Even during flyby missions, high-precision lightcurve observations can be conducted prior to close-up imaging. Therefore, lightcurve inversion is expected to be applicable even in situations where stereo vision methods are difficult to employ. While several software options for lightcurve inversion exist, we tested two specific tools—ADAM and the algorithm developed by Kaasalainen—using lightcurve data simulated under flyby observation conditions.
Rim profiling is a technique for estimating the shape of an asteroid based on its observed silhouette in images. Flyby observations can only obtain the rim profile seen from a single direction, but this technique is still useful because it can applicable even in situations where stereo vision methods are difficult to employ, and provide more direct constraints on the shape than lightcurve inversion. Because SPC incorporates rim profiling capabilities, we conducted a test to evaluate applicability of the rim profiling to the flyby observations.
Among the methods considered, SfM and SPC utilize the principle of stereo vision. Stereo vision reconstructs a 3D shape of the target based on the parallax between a pair of images taken from different positions. The amount of parallax directly affects the success and accuracy of shape reconstruction. Because the spacecraft’s pointing direction could not be changed during the flyby of Torifune, it was impossible to obtain a parallax greater than the camera’s field of view. Furthermore, due to the significant difference in resolution between stereo pairs in flyby observations, the parallax in pixel units within the lower-resolution image is critical. We estimated the achievable parallax in pixel units under actual observation conditions.
Lightcurve inversion is a method used to estimate the shape of a celestial body by utilizing changes in reflected brightness as it rotates. Attempts have already been made to estimate the shape of Torifune using this technique with ground-based observation data. Even during flyby missions, high-precision lightcurve observations can be conducted prior to close-up imaging. Therefore, lightcurve inversion is expected to be applicable even in situations where stereo vision methods are difficult to employ. While several software options for lightcurve inversion exist, we tested two specific tools—ADAM and the algorithm developed by Kaasalainen—using lightcurve data simulated under flyby observation conditions.
Rim profiling is a technique for estimating the shape of an asteroid based on its observed silhouette in images. Flyby observations can only obtain the rim profile seen from a single direction, but this technique is still useful because it can applicable even in situations where stereo vision methods are difficult to employ, and provide more direct constraints on the shape than lightcurve inversion. Because SPC incorporates rim profiling capabilities, we conducted a test to evaluate applicability of the rim profiling to the flyby observations.