Restoring high-speed motion blur in spacecraft imagery: Enhanced views of Mars' moon Phobos

Motion-induced blur resulting from the high relative ground velocity between spacecraft and planetary bodies significantly deteriorates image quality, complicating detailed analyses of planetary surface features. Notable examples include Mars Express SRC images of Phobos, Viking Orbiter 2 VIS images of Deimos, and Rosetta OSIRIS images of comet 67P/Churyumov–Gerasimenko. To mitigate this issue, we implemented an image restoration method based on modeling the motion-induced point-spread function (PSF) and employing Wiener deconvolution to reverse the blur effects.

Our method was applied specifically to Super Resolution Channel (SRC) images acquired by the Mars Express High-Resolution Stereo Camera (HRSC) [1], which achieved unprecedented resolutions (<1.0 m/pixel) of the Phobos surface during orbit 5851 (23 July 2008) and orbit 8974 (9 January 2011) [2]. Despite their superior ground-sampling distance, these images had previously not been extensively utilized due to significant noise artifacts ("pepper" pixels) and severe motion blur [3], hindering geological interpretations and high-precision photogrammetric product generation (e.g., Ernst et al., 2023 [4]).

Our processing pipeline begins with Level 3 SRC images in PDS format. Noise artifacts are conventionally reduced using a boxcar filter implemented through the powerful USGS ISIS "noisefilter" function. Metadata (StartTime, StopTime, ImageTime, exposure, pixel size, focal length, CCD center coordinates) are extracted from ISIS cubes using the USGS Ale software. Given the very short exposure times (approximately 14 ms for orbit 5851 images and 16 ms for orbit 8974 images), the target's apparent motion on the focal plane during exposure can be accurately approximated as linear, differentiating this case from longer-duration sinusoidal jitter motions. We generated a linear PSF by computing spacecraft boresight intersections with the Phobos surface from SPK, CK, and DSK kernels (Ernst et al. 2023 Phobos shape model v02 NoOffset, ~9 m precision) via SpiceyPy [5]'s subpnt function. Wiener deconvolution was subsequently applied, utilizing an empirically determined optimal signal-to-noise ratio (SNR) of 16 dB, aligning closely with previous findings for SRC images (Oberst et al., 2006).

We successfully restored SRC images from orbit 5851 (h5851_0002_src3 to h5851_0004_src3; Figure 1) and orbit 8974 (h8974_0002_src3 to h8974_0008_src3; Figure 2), significantly reducing blur and enhancing geological feature visibility. Our pipeline establishes a robust and objective framework for future restoration and analysis of motion-blurred planetary imagery.

References

1. Neukum, G.; Jaumann, R. HRSC: The High Resolution Stereo Camera of Mars Express. In Mars Express: The Scientific Payload; ESA: 2004; Volume SP-1240, pp. 17-35.
2. Witasse, O.; Duxbury, T.; Chicarro, A.; Altobelli, N.; Andert, T.; Aronica, A.; Barabash, S.; Bertaux, J.L.; Bibring, J.P.; Cardesin-Moinelo, A.; et al. Mars Express investigations of Phobos and Deimos. Planetary and Space Science 2014, 102, 18-34, doi:10.1016/j.pss.2013.08.002.
3. Oberst, J.; Schwarz, G.; Behnke, T.; Hoffmann, H.; Matz, K.D.; Flohrer, J.; Hirsch, H.; Roatsch, T.; Scholten, F.; Hauber, E.; et al. The imaging performance of the SRC on Mars Express. Planetary and Space Science 2008, 56, 473-491, doi:10.1016/j.pss.2007.09.009.
4. Ernst, C.M.; Daly, R.T.; Gaskell, R.W.; Barnouin, O.S.; Nair, H.; Hyatt, B.A.; Al Asad, M.M.; Hoch, K.K.W. High-resolution shape models of Phobos and Deimos from stereophotoclinometry. Earth, Planets and Space 2023, 75, 103, doi:10.1186/s40623-023-01814-7.
5. Annex, A.M.; Pearson, B.; Seignovert, B.; Carcich, B.T.; Eichhorn, H.; Mapel, J.A.; Von Forstner, J.L.F.; McAuliffe, J.; Del Rio, J.D.; Berry, K.L. SpiceyPy: a Pythonic Wrapper for the SPICE Toolkit. Journal of Open Source Software 2020, 5, 2050, doi:10.21105/joss.02050.

Figures

Figure 1 SRC images of orbit 5851 before (top) and after (bottom) restoration

Figure 2 SRC images of orbit 8974 before (top) and after (bottom) restoration