Coordinated 1996 HST and IRTF Imaging of Neptune and Triton. I. Observations, Navigation, and Differential Deconvolution

On 13-14 August 1996, we carried out the first coordinated contemporaneous imaging of Neptune, using the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 and the NASA Infrared Telescope Facility (IRTF) NSFCAM InSb camera to obtain high spatial resolution absolutely calibrated imagery at wavelengths from 0.2 to 2.5 μm. We used nine HST orbits to provide unique dynamical coverage of a single rotation of Neptune. During three orbits we obtained virtually simultaneous groundbased images. These data provide an extended range of wavelengths that sample the Rayleigh scattering regime, both strong and weak methane bands, and strong near-infrared hydrogen collision-induced opacity bands, from which strong constraints can be obtained on the properties of Neptune's cloud features. We developed very precise navigation techniques, which were required to achieve colocation of the observations from these different observatories. Technique advances include compensating for limb profile distortions by bright cloud features in HST images and dealing with a nearly invisible limb in the near-IR groundbased images. We achieved RMS center-finding accuracy of 0.003''-0.006'' (0.05-0.1 pixels) for HST navigations. To obtain the subpixel navigation accuracy of the groundbased images, we determined NSFCAM pixel scale versus wavelength and as a function of location on the detector, establishing a distortion correction equation for NSFCAM imaging. This permitted use of a navigation method based on offsetting from Triton, with which we achieved IRTF center-finding accuracy of 0.02'' (0.1 pixel) RMS, and 0.2-0.3 pixels absolute. We developed a novel differential deconvolution method for significantly reducing deconvolution artifacts within the planetary disk and improving convergence properties for planetary cloud features, resulting in by far the most detailed groundbased images of Neptune yet obtained without speckle imaging or adaptive optics.