Underflight calibration of SOHO/CDS and Hinode/EIS with EUNIS-07
Tongjiang Wang, Roger J. Thomas, Jeffrey W. Brosius, Peter R. Young,, Douglas M. Rabin, Joseph M. Davila, Giulio Del Zanna

TL;DR
This paper presents updated radiometric calibrations for SOHO/CDS and Hinode/EIS using EUNIS-07 sounding rocket data, improving the accuracy of solar EUV measurements and confirming instrument responsivities.
Contribution
It introduces a direct calibration transfer method from EUNIS-07 to EIS and updates the CDS calibration, demonstrating improved accuracy and consistency with laboratory measurements.
Findings
CDS responsivity is too low by a factor of 1.5 using standard calibration.
EIS responsivity decreased by about 1.2 after one year of operation.
EUNIS-07 calibration confirms EIS responsivity and laboratory response shape.
Abstract
Flights of Goddard Space Flight Center's Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) sounding rocket in 2006 and 2007 provided updated radiometric calibrations for SOHO/CDS and Hinode/EIS. EUNIS carried two independent imaging spectrographs covering wavebands of 300-370 A in first order and 170-205 A in second order. After each flight, end-to-end radiometric calibrations of the rocket payload were carried out in the same facility used for pre-launch calibrations of CDS and EIS. During the 2007 flight, EUNIS, SOHO CDS and Hinode EIS observed the same solar locations, allowing the EUNIS calibrations to be directly applied to both CDS and EIS. The measured CDS NIS 1 line intensities calibrated with the standard (version 4) responsivities with the standard long-term corrections are found to be too low by a factor of 1.5 due to the decrease in responsivity. The EIS calibration…
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