Title:  The Solar Bolometric Imager

Pietro N.  Bernasconi

On September 1 2003, the Solar Bolometric Imager (SBI) successfully observed the
Sun for several hours while suspended from a balloon in the stratosphere above
New Mexico.  The SBI represents a totally new approach in finding the sources of
the solar irradiance variation.  The mission provided the first bolometric
(integrated light) maps of the solar photosphere, that will allow to evaluate
the photometric contribution of magnetic structures more accurately than has
been achievable with spectrally selective imaging over restricted wavebands.
The more accurate removal of the magnetic features contribution will enable us
to determine if solar irradiance variation mechanisms exist other than the
effects of photospheric magnetism.  The SBI detector was an array of 320 x 240
thermal IR elements whose spectral absorptance has been extended and flattened
by a deposited layer of gold-black.  The telescope was a 30-cm Dall-Kirkham with
uncoated primary and secondary pyrex mirrors.  The combination of telescope and
bolometric array provided an image of the Sun with a flat spectral response
between 0.28 and 2.6 microns, over a field of view of 917 x 687 arcsec with a
pixel size of 2.8 arcsec.  The observing platform was the gondola previously
used for the Flare Genesis Experiment (FGE), retrofitted to house and control
the SBI telescope and detector.  During the 9 hours of flight the SBI gathered
several thousand bolometric images that are now being processed to produce the
first maps of the total solar irradiance.  The SBI flight is also providing
important engineering data to validate the space worthiness of the novel
gold-blackened thermal array detectors, and to verify the thermal performance of
the SBI's uncoated optics in a vacuum environment.  In this seminar I will
describe the characteristics of the instrument, its flight performance, and I
will present the first results of the analysis of the bolometric images obtained
during the flight.