[P-PS04] Recent advances in the science of Venus

[PPS04-P06] An alternative method to recover the true contrast of Venus' night-side cloud features in Akatsuki/IR2 images

*Takehiko Satoh^1,3, Takao M. Sato² (1.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 2.Hokkaido Information University, 3.The Graduate University for Advanced Studies, SOKENDAI)

Keywords:Observation of Venus' night-side, Infrared sensor, Point-spread function, Restoration

The 2-um camera IR2 onboard Akatsuki utilizes a 1M pixels PtSi CSD/CCD sensor manufactured by Mitsubishi Electoric, Co. Ltd. The infrared-sensitive pixels are located on the bottom of a 400-um thick Si substrate. The pixels convert incoming infrared radiation to electrons via the photo-electric effect, thus the conversion efficiency is not very high (of the order of a few to several percents). The unused light continues beinf multiplly reflected between the two surfaces of the Si Substrate, causing a very elongated point-spread function (PSF) of IR2. This significantly degrades the contrast of Venus' night-side cloud features due to the contamination by the light spreading from the intense day crescent. Satoh et al. (2021) developed a method to improve the quality of night-side data by combining 2.26-, 2.32-, and 1.735-um images. They named the method "Restoration by Simple Subtraction" or RSS in short. An alternative method is possible for the data acquired after the superior conjunction of Venus (June 2016) because a 2.02-um imaging was inserted to characterize the light spreading from the dayside. We will report the initial performance of this new method "Restoration by Subtraction of 2.02-um image" or RS202. The quality of this method is evaluated against the sharp cloud discontinuity feature which apparently requires the best possible contrast restoration to study the cloud structure.