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).

First Results

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.

Full Resolution CalRoc Image

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.


Primary Calibration Images

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.

Ratio Images (CalRoc/SOHO)

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.