Enhancing Ground-Based Neptune Observations Using Modified CLEAN Deconvolution

Modified CLEAN is a deconvolution technique derived from the classic CLEAN algorithm, adapted for application to extended planetary targets. We have previously demonstrated its effectiveness in enhancing the spatial resolution of recent (2018) ground-based observations of Neptune, revealing additional atmospheric structure beyond that accessible with standard processing techniques.

We are now extending this work to legacy near-infrared integral-field spectroscopy data obtained in 2009 and 2011 with the Near-infrared Integral Field Spectrograph (NIFS). The older datasets are more challenging to work with as they have stronger artefacts from the optical system and calibration procedures in both the science and standard star measurements.

As with all deconvolution methods, modified CLEAN performs optimally in low-noise conditions, where calibration data are smooth and have a high signal-to-noise ratio. This required a series of preprocessing steps. Principal component analysis was applied to both science and calibration observations to suppress noise and remove instrumental systematics. Telescope pointing information, not explicitly recorded for the original NIFS science observations, was reconstructed from ancillary data. Disk fitting and de-rotation were used to align and combine all observations within individual observing blocks. Finally, residual atmospheric refraction present in the standard NIFS pipeline products was identified and corrected.

These processing steps improve the performance of the modified CLEAN algorithm on the legacy NIFS datasets, giving improved spatial resolution and more reliable interpretation of Neptune’s atmospheric structure. This work demonstrates the continued scientific value of archival ground-based observations when combined with modern data analysis and deconvolution techniques.