Image registration for multi-band images taken by ONC-T onboard Hayabusa2

TL;DR

This paper presents an improved method for multi-band image registration of ONC-T images from Hayabusa2, achieving high accuracy to support spectral mapping of asteroid Ryugu.

Contribution

The paper introduces an enhanced image co-registration technique combining conventional methods with novel improvements tailored for planetary mission data.

Findings

Achieved image registration accuracy of about 0.1 pixels.

Method is effective for spectral mapping applications.

Applicable to multi-band images with slight positional differences.

Abstract

Hayabusa2, a Japanese sample-return mission to a C-type asteroid, arrived at its target 162173 Ryugu in June 2018. The optical navigation cameras (ONC-T, ONC-W1, ONC-W2) successfully obtained numerous images of Ryugu. ONC-T is a telescopic framing camera with a charge-coupled device (CCD), has seven filter bands in ultraviolet, visible and near infrared wavelength ranges, and were used to map the spectral distribution of the Ryugu surface. Since the locations of a target seen in ONC-T images are slightly different among different wavelength images in one multi-band observation sequence due to changes in spacecraft positions and attitudes during the filter-changing sequence, one of the image processing issues is image co-registration among images for different wavelength bands. To quickly complete the image co-registration to meet a limited mission schedule, we combined conventional image co-registration techniques with several improvements based on previous planetary missions. The results of our analysis using actual ONC-T images indicate that image co-registration can reach accuracy on the order of 0.1 pixels, which is sufficient for many spectral mapping applications for Ryugu analyses.