SPECULAR POINT-LIKE QUICK REFERENCE (SPQR)
Research Area: Imaging Technology
Expedition(s): 10 and 11
Principle Investigator(s): ● F. Graziani, University of Rome La Sapienza, Rome, Italy
RESEARCH OBJECTIVES
The objective of the Specular Point-
like Quick Reference (SPQR)
experiment is to evaluate the
possibility of improving the resolution
of ground-based telescopic imaging of
manned spacecraft in orbit. The
concept is to reduce image distortions
due to atmospheric turbulence by
evaluating the Point Spread Function
(PSF) of a point-like light reference.
This is provided by a laser beam
emitted by the ground station and
reflected back to the telescope by a
Cube Corner Reflector (CCR) mounted
on an International Space Station (ISS)
window.
RESULTS
The experiment was successfully performed from March to May 2005. A beam splitter installed
on the 25-inch telescope allowed the incoming light to be divided, filtered, and simultaneously
imaged with 2 10-bit high frame rate digital cameras. The first camera used a broad-band filter
centered at 532 nm and provided an image of the spacecraft, which was distorted by atmospheric
turbulence. The second camera used a notch filter at 532 nm and simultaneously provided a point
spread function for processing of the broadband, visible light image. The broadband image was
the one to be processed in order to achieve the best possible quality image of the spacecraft,
while the narrow band picture was the one need to get the point spread function (PSF) from the
laser beam reflection. The actual PSF had to be compared with the theoretical one (the one we
would have if no atmosphere disturbances were present). Therefore the distortion affecting the
picture could be assessed, hence the deconvolution needed to process the rough image. The
figure above shows the result of deconvolution for an ISS pass that occurred on May 3, 2005. On
the left, an atmospherically distorted image of the ISS is shown under optimal atmospheric
conditions (very stable and clear) and nighttime imaging conditions. On the right is an image that
has been obtained by superimposing several frames and deconvolving them with a PSF. It is
important to note that no matter the perfect tracking and the excellent atmospheric conditions,
the image quality without processing with the PSF would be poor. The SPQR experiment proved
for the first time that a powerful laser could be fired towards the ISS without problems for the
astronauts or the attitude control sensors of the ISS. Furthermore, the use of the PSF and image
Partially improved image of the International Space Station obtained
using a bright feature as a point reference. ESA image.