4.1  The absolute sensitivity as a function of wavelength.

The absolute sensitivity ef(l) [counts/photons] as a function of wavelength.

The absolute sensitivity of the NI spectrographs is a combination of:

the reflectivity of the primary mirror, the secondary mirror and the scan mirror;

the efficiencies of the gratings;

and the quantum sensitivity of the VDS detector.

The wavelength dependence of absolute sensitivity is therefore a combination of the wavelength dependence of all these various factors.

4.1.1  Calibration within the Software

The following table shows the progress of the various calibrations implemented within the software:

    Version     Date        Notes

1    16-Sep-1996    Original calibration, based on pre-flight absolute
                    measurements and in-flight line ratios.

2    23-Dec-1998    Modified calibration, based on EGS sounding rocket
                    measurements and reanalysis of the pre-flight data.

3    28-Feb-2000    Modified NIS-1 calibration, based on SERTS and EGS
                    sounding rocket measurements.  NIS-2 curve unchanged.

4    21-May-2002    Modified NIS-2 calibration, based on reanalysis of EGS
                    sounding rocket measurements.  Incorporated
                    second-order NIS-2 curve.  Modified GIS calibration
                    curves.

It is important to note that any raw data run through the current software will use the LATEST calibration values irrespective of the observation date, but instrumental effects (eg MCP burn in) will depend on both the actual observation date, and the time when the latest corrections have been put into the database (hence on when you analyse the data).