  Optical imperfections, misalignments, aberrations, and even dust can
significantly limit sensitivity in high-contrast imaging systems such as
coronagraphs. An upstream deformable mirror (DM) in the pupil can be used to
correct or compensate for these flaws, either to enhance Strehl ratio or
suppress residual coronagraphic halo. Measurement of the phase and amplitude of
the starlight halo at the science camera is essential for determining the DM
shape that compensates for any non-common-path (NCP) wavefront errors. Using DM
displacement ripples to create a series of probe and anti-halo speckles in the
focal plane has been proposed for space-based coronagraphs and successfully
demonstrated in the lab. We present the theory and first on-sky demonstration
of a technique to measure the complex halo using the rapidly-changing residual
atmospheric speckles at the 6.5m MMT telescope using the Clio mid-IR camera.
The AO system's wavefront sensor (WFS) measurements are used to estimate the
residual wavefront, allowing us to approximately compute the rapidly-evolving
phase and amplitude of speckle halo. When combined with relatively-short,
synchronized science camera images, the complex speckle estimates can be used
to interferometrically analyze the images, leading to an estimate of the static
diffraction halo with NCP effects included. In an operational system, this
information could be collected continuously and used to iteratively correct
quasi-static NCP errors or suppress imperfect coronagraphic halos.
