Resolved Observations of Geostationary Satellites from the 6.5 m MMT

Date: September 2015

Authors: Hart, M., Rast, R., Jefferies, S., Hope, D.

Abstract: We report observations of a number of geostationary spacecraft recorded in the J, H, and Ks bands (centered around 1.2 µm, 1.6 µm, and 2.2 µm) at the 6.5 m MMT telescope in January 2015. With adaptive optics, the satellites were resolved at close to the diffraction limit in each of the wavebands. True color images may be recovered from the multiple wavebands, while the large aperture allows accurate photometric calibration with excellent time resolution of even small, faint objects in these distant orbits. Of note are our observations of solar panels, which can only be satisfactorily imaged in bands longer than their cut-off wavelengths. Since the cut-off is generally in the neighborhood of 1.5 – 2 µm, the panels will only be well resolved by telescopes larger than 4 m. In one case observed at the MMT, solar panels were seen to span approximately 24 m, twice the extent described in published data

Fast Tomographic Reconstruction of Atmospheric Turbulence from Micro-lens Imagery

Date: September 2014

Authors: Nagy, J., Hart, M., Jefferies, S., Hope, D.

Abstract: We consider using data acquired from a micro-lens array through which multiple images of the full field-of-view of an astronomical target are formed to attempt to reconstruct the 3-D wave front for the observations. This opens the door for both a beacon-less wave front sensor and imaging of fields-of view substantially larger than the isoplanatic angle. The reconstruction problem can be modeled as a large-scale linear inverse problem, but standard algorithms used for 3-D computed tomography (CT) reconstruction cannot be applied because measured data are only taken from limited angular range, leaving entire regions of the frequency space un-sampled. However, we show that there is substantial structure in the mathematical model that can be exploited to obtain a robust algorithm that is amenable to efficient implementations.

High-Resolution Imaging through Strong Atmospheric Turblence Over Wide Fields of View

Date: September 2013

Authors: Jefferies, S., Hope, D., Hart, M., Nagy, J.

Abstract: We use numerical simulations to study the prospective performance of a dual channel imaging system for observing space-based targets through strong atmospheric turbulence: one channel of the system employs aperture diversity and the other an imaging Shack-Hartmann wave-front sensor. The raw images acquired by this setup are processed using a blind restoration algorithm that captures the inherent temporal correlations in the observed phases. This approach, which strengthens the synergy between the image acquisition and post-processing steps, shows strong potential for providing high-resolution imagery at high levels of atmospheric turbulence. The approach may also allow for the separation of the phase perturbations from different layers of the atmosphere and offers promise for accurate restoration of images with fields of view substantially larger than the isoplanatic angle.

Multi-frame Myopic Deconvolution for Imaging in Daylight and Strong Turblence Conditions

Date: September 2011

Authors: Jefferies, S., Hart, M., Hope, D., Hege, E. K., Briguglio, R., Pinna, E., Puglisi, A., Quiros, F., Xompero, M.

Abstract: We describe results from new computational techniques to extend the reach of large ground-based optical telescopes, enabling high resolution imaging of space objects under daylight conditions. Current state-of-the-art systems, even those employing adaptive optics, dramatically underperform in such conditions because of strong turbulence generated by diurnal solar heating of the atmosphere, characterized by a ratio of telescope diameter to Fried parameter as high as 70. Our approach extends previous advances in multi-frame blind deconvolution (MFBD) by exploiting measurements from a wavefront sensor recorded simultaneously with high-cadence image data. We describe early results with the new algorithm which may be used with seeing-limited image data or as an adjunct to partial compensation with adaptive optics to restore imaging to the diffraction limit even under the extreme observing conditions found in daylight.

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