Welcome to the EIT CALROC World Wide Web server.
Welcome to the home page for the NRL Extreme-ultraviolet
Imaging Telescope Calibration Rocket (EIT CalRoc). The EIT CalRoc program
is a cooperative effort invloving contributions from all the groups of
the
EIT
Consortium. The EIT CalRoc flight was successfully
conducted 16 October 1997, from White Sands Missile Range, New Mexico (WSMR).
The first application of the CalRoc images was published in the proceedings
of the SPIE:
"In-Orbit performance
of the EIT instrument on-boad SOHO and intercalibration with the EIT CalRoc"
1998, Defise, J.M., Moses, D., Clette, F., SPIE 3442.15.
The relative pixel-to-pixel calibration obtained from the comparison
of the the EIT SOHO and the EIT CalRoc provides a useful flat-field and
important information on the degradation mechanism. The absolute
calibration was compromised by the delay between calibration of the EIT CalRoc
at the IAS synchrotron light facility and launch of the CalRoc.
The last image taken during the EIT CalRoc flight can be viewed by clicking
on the thumbnail image below. This is a 1024x1024 image in the 171 Angstrom
bandpass. The image has been scaled for presentation in a GIF format.
The primary
calibration images are now available. These are a series of 512x512
images taken in each waveband around the apogee of the fight. The reduced
spatial resolution images require shorter exposure and readout times than
full resolution images. Thus, 512x512 images can be obtained in all wavelengths
during the time of minimum absorption of the residual atmosphere.
Preliminary images of the ratio
of the EIT CalRoc data to the EIT SOHO data are now available. Although
this analysis requires much more work, the preliminary results are very
interesting. In this first approach, the images have been normalized at
their edges. The most obvious difference is that the detector response
in the region covered by the solar disk has degraded to about 50% of the
response at the edge of the field of view. There is increased degradation
at the limb, corresponding to the increased EUV dose in this region. There
is also increased degradation in the active region bands for the same reason.
Although it is difficult to scale the GIF images to also show the pattern
in the degradation caused by the shadow of the filter support grid for
the focal plane filter, this pattern can be seen in the Fe IX,X and Fe
XII ratio images. Sharp, small scale structures in these ratio images are
artifacts of the time difference between the SOHO and CalRoc images. This
problem is the worst for the He II ratio image (in which a SOHO data dropout
causes further problems).
CalRoc Corrections Applied to the SOHO EIT Data
From the above ratios, a general flatfield correction can be derived for
the SOHO EIT images. Such a correction can then be applied to data from
the time immediately before and after the CalRoc flight. The validity of
this correction will slowly decline with increasing time from the CalRoc
flight because of the changing level of degradation with time. Proceedures
for tracking the relative degradation are under development. A very preliminary
example of the general CalRoc correction can be seen in the CalRoc
corrected 18 October 1997 Fe IX,X SOHO EIT image. This should be compared
with the uncorrected
Fe IX,X SOHO EIT image from the SOHO Summary Database. The most obvious
improvements are the removal of spurious darkening at the limb and the
removal of the residual burned-in grid pattern from the focal plane filter
support grid. These improvements represent a major advance for observational
programs invloving features extending from the disk to beyond the limb
(e.g. EUV plumes and jets).
This welcome page is still under development.
