Observed data products and Mappings of Thermal Infrared Imager onboard . T. Arai1 ([email protected]), H. Demura2, T. Kouyama3, H. Senshu4, Y. Ogawa2, T. Fukuhara5, T. Okada6, S. Tanaka6, T. Matsunaga1 1 National Institute for Environmental Studies (NIES), 2 The University of Aizu, 3 National Institute of Advanced Industrial Science and Technology 4 Chiba Institute of Technology, 5 Rikkyo University, 6 Japan Aerospace Exploration Agency (JAXA) JAXA Abstract TIR is an infrared thermal imager onboard the Hayabusa2 spacecraft, which will perform thermal imaging of C-type asteroid through in situ observations during the rendezvous phase from 2018 to 2019. The main purpose of TIR is to determine the thermal properties of the asteroid surface and to reveal the asteroid evolutional history such as physical properties of the originally coalesced bodies, orbital changes due to the Yarkovsky effects, and the thermal evolution. In this study, data products of TIR in concerned with global mapping using the Earth observation data and geometric correction using the observation data during the Hayabusa2 Earth swingby are introduced. The observed data products are already available at the JAXA’s website: http://darts.isas.jaxa.jp/planet/project/hayabusa2/ Introduction TIR onboard Hayabusa2 The thermal infrared imager (TIR) is a thermal infrared camera onboard the Hayabusa2 spacecraft, which performs thermography of the asteroid 162173 Ryugu (formerly 1999 JU3). It will estimate the Uncooled micro-bolometer array thermophysical properties of the asteroid surface materials through in-situ observations in 2018 and 2019 328 x 248 pixel resolution (Okada et al., 2016). TIR takes images of 328 x 248 pixels, and the spatial resolution is 0.051°/ pixel with 16.7 x 12.7 degrees FOV the field of view (FOV) of 16.7°x 12.7°. The band-pass filter of TIR limits the detection range of the (~10 m＠10 km) thermal radiation emitted from targets to wavelengths of 8 to 12 μm. In this study, data products of the 8-12 μm band-pass filter Earth and Moon observation, and geometric correction during the Hayabusa2 Earth swingby are introduced. Data Products TIR nominally observes at the altitude of 20 km from the asteroid (home position of the Hayabusa2 spacecraft). TIR will take global temperature images at sunlit areas during one asteroid day (~60 images / of about 7.6 hours (Muller et al., 2011)) and make the thermal property maps of the global asteroid surface. .. The observed data will be automatically converted from raw digital images to temperature images using a UNIX-based computer at ISAS/JAXA and the University of Aizu by using the calibration BD “HEAT” (Endo et al., 2017). Raw data and part of Level-1 data are currently available on JAXA's website (DARTS), including the Earth and the Moon images taken with TIR on Dec. 2015. Here, the outlines of Level-1 ~ Level-5 products are described:

Level-1. Temperature and radiance: Level-2. Intermediate data: Level-3a. Thermal inertia and Level-3b. Detail map Level-4. 4D Cube: Level-5. Thermal Simulator: The brightness temperature and The observed pixel coordinates Thermal emissivity map: More detail analytic thermal Absolute temperature data The surface temperature radiance images converted from raw connect to the planetocentric Global maps of the thermal models for multiple facets of converted from brightness simulator for the asteroid digital number images. The analysis coordinates, generated by the inertia Γ and the thermal the asteroid shape model is temperatures. Their Ryugu. It is corrected for the tool "HEAT" searches best-fit SPICE kernels. The file format is emissivity ε are derived from a fitted to observed data, radiometric and geometric temperature dependency of calibrated data at near temperature text tables (px, py, brightness one-dimensional non-steady- including surface roughness, corrections are completed. the surface physical properties of the sensor in the observation from temperature, distance, state heat transfer model for multiplying scattered and The data provides absolute by using the results of the the pre-launch experiment DB longitude, latitude, solar phase local areas. The heat model is reabsorbed radiations, which surface temperatures by laboratory experiments because of reduction of sensor angle, solar incidence angle, fitted to observed temperature have been developed at Chiba correction of the net thermal (Sakatani et al., 2012). In background (Endo et al., 2017). solar emission angle). profiles by a least-squares Institute of Technology and emissivities at local areas of particular, surface particle size method with parameters Γ and ε. ISAS/JAXA (Takita et al., 2017). the asteroid. and porosity will be simulated. Geometric Correction After the Earth swingby of the Hayabusa2 spacecraft, TIR observed the Moon on Dec. 5 to Dec. 22, 2015. The geometric correction was performed by adjusting the detected pixels of the moon to the anticipated Moon position in J2000 coordinate system for 16 points by a least-squares fitting. The data was used for the alignment corrections, such as a rotation forward, and an inclination of the boresight forward, and the Flame Kernel of SPICE kernel (FK) was updated. The resulting positional accuracy is less than 100 km The positioning difference at from 340000~350000 km observation for the Earth center position determined with the The Earth center the center of the Earth surface Earth limb position. This result indicates that the positioning accuracy of the asteroid position is searched by a is less than 100 km from the observation will be achieved in ~6 m @ 20 km altitude. However, image corner is circle fitting with observed distance of 340000 ~ distorted about 1 or 2 pixels. Therefore, detail image distortion will be corrected in the determining the limb 350000 km (~ 300 km / pixel). position of the Earth. asteroid observation phase by the observation of particular objects on the surface. Geometric correction by the Moon observation. Summaries The observed data products of the TIR are ready at the JAXA’s website (DARTS). The thermal inertia and thermal emissivity map of the asteroid Ryugu‘s surface will be provided (Level-3a) in the asteroid rendezvous phase. The higher degree products will be generated by model calculations with multiplying scattered absorption, radiation, which is derived by least-squares fittings for each polygon facet of the asteroid shape model (Level-3b). The positioning accuracy of the global maps is currently ~6 m at the 20 km home position (spatial resolution of the TIR is about 20 m / pixel @ 20 km). When the surface material samplings are TIR + Coast line by IDL TIR + SELENE LALT grid performed, the TIR will take close-up images at low altitudes of about 5 m (5 mm resolution / pixel). These close-up images will be used for improving the positioning accuracy of TIR.