Presentation #309.05 in the session Physical Characteristics of Cometary Nuclei.
We use photometric model to examine the details of the illumination and observing geometry of the comet surface that shows subtle differences of the physical properties with the image obtained by the Rosetta OSIRIS Narrow Angle Camera (NAC) [1,2].The photometric properties  are related to surface composition, texture, porosity, roughness, and grain size; can help us understand the local alteration processes. We investigate these photometric properties of various locations on the surface of 67P’s nucleus at various perihelion distances. We generated a sufficient photometric dataset for this study. But the continuously changing nature of 67P surface is causing bulk registration problems. Our study shows that for many of the images a single shape model (SHAP7 ) is not sufficient for consistent control. The surface changes vary significantly and would require numerous shape models of varying resolution. We examined the control data quality for each datasets. We found that the most common reason that causes problems in the control is either surface change or that the image data resolution is far from the shape model resolution. The irregular shape of 67P made it hard for project and mapping the surface in a regular lat lon projection system. We will report our detailed photometric analysis for a few different geomorphological sites.
Acknowledgments: The work is supported by NASA under Grants 80NSSC19K0421 and 80NSSC20K1152 and partially by the SSERVI16 Cooperative Agreement (#NNH16ZDA001N), SSERVI-TREX.
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 Preusker, F., Scholten, F., Matz, K.D., Roatsch, T., Hviid, S.F., Mottola, S., Knollenberg, J., Kührt, E., Pajola, M., Oklay, N. and Vincent, J.B., 2017. The global meter-level shape model of comet 67P/Churyumov-Gerasimenko. Astronomy & Astrophysics, 607, p.L1.