EUNIS Underflight Calibrations of CDS, EIT, TRACE, EIS, and EUVI
The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a sounding rocket instrument that obtains imaged high-resolution solar spectra. It has now had two successful flights, on 2006 April 12 and 2007 November 16, providing data to support underflight calibrations for a number of orbiting solar experiments on both occasions. A regular part of each campaign is the end-to-end radiometric calibration of the rocket payload carried out at RAL in the UK, using the same facility that provided pre-flight CDS and EIS calibrations. The measurements, traceable to primary radiometric standards, can establish the absolute EUNIS response within a relative uncertainty of 10% over its full longwave bandpass of 300-370A. During each EUNIS flight, coordinated observations are made of overlapping solar locations by all participating space experiments, and identified by subsequent image co-registrations, allowing the EUNIS calibrations to be applied to these other instruments as well. The calibration transfer is straightforward for wavelengths within the EUNIS LW bandpass, and is extended to other wavelengths by means of a series of 'insensitive' line-ratios, with one line of each pair in the calibrated band and the other in the transfer band. In this way, the EUNIS-06 flight is able to update the radiometric calibrations of CDS NISl (plus 2nd order NIS2 near 2x304A), all four channels of EIT, and the three EUV channels of TRACE. The EUNIS-07 flight will further update those missions, as well as both channels of Hinode/EIT and all four channels of STEREO/SECCHI/EUVI. Future EUNIS flights have been proposed that will continue this underflight calibration service. EUNIS is supported by the NASA Heliophysics Division through its Low Cost Access to Space Program in Solar and Heliospheric Physics.