The X-Ray Sensor (XRS) has been making observations of the solar soft X-ray irradiance for over thirty years onboard National Oceanic and Atmospheric Administration's (NOAA) Geostationary Operational Environmental Satellites (GOES). The XRS provides critical information about the solar activity for space weather operations, and the standard X-ray classification of the solar flares is based on its measurements. The GOES-R series of XRSs, with the first in the
series to launch in 2014, has a completely new instrument design. The XRS spectral bands remain the same as before by providing the solar X-ray irradiance in the 0.05-0.4 nm and 0.1-0.8 nm bands. The changes include using Si photodiodes instead of ionization cells to improve performance, using multiple channels to allow wider dynamic range, providing quadrant photodiodes for real-time flare location measurements, and providing accurate radiometric calibrations using
the National Institute of Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility (SURF) in Gaithersburg, Maryland.
The Solar Dynamics Observatory (SDO) Extreme ultraviolet Spectro-Photometer (ESP), as a part of the Extreme
ultraviolet Variability Experiment (EVE) suite of instruments, was calibrated at the National Institute
of Standards and Technology (NIST) on the Synchrotron Ultraviolet Radiation Facility (SURF) Beam Line 2
in February 2007. Precise ESP alignment to the SURF beam was achieved through successive scans in X, Y,
Pitch and Yaw, using a comparison of the four channels of the ESP quad photodiode as a measure of alignment.
The observed alignment between the ESP and the other instruments in the EVE package was found to be in
very good agreement with that measured at the Laboratory for Atmospheric and Space Physics (LASP) at the
University of Colorado during ESP/EVE integration. The radiometric calibration of the ESP photometers in
the spectral range around 4.4 nm (central zeroth order), and the four first order channels centered at about
18.9, 25.4, 29.8, and 36.1 nm was performed with SURF synchrotron radiation. The co-alignment of the SURF
beam and the ESP optical axis for each energy and injected current was determined based on quad diode (QD)
photometer responses (photodiode count-rate data). This determined beam position was later used to obtain
exact energy-wavelength-flux profiles for each of the calibration energies and to calculate the quantum efficiency
of the ESP channels. The results of this calibration (quantum efficiencies) are compared to the previous ESP
NIST calibration results at SURF Beam Line 9 and to SOHO/SEM efficiencies.
The NASA Solar Dynamics Observatory (SDO), scheduled for launch in early 2009, incorporates a suite of instruments
including the EUV Variability Experiment (EVE). Two channels of EVE, the Multiple EUV Grating Spectrograph
(MEGS) A and B channels use concave reflection gratings to image solar spectra onto CCDs to measure the solar
extreme ultraviolet (EUV) irradiance from 5 to 105 nm. MEGS provides these spectra at 0.1nm spectral resolution every
10 seconds with an absolute accuracy of better than 25% over the SDO 5-year mission. The calibration of the MEGS
channels in order to convert the instrument counts in to physical units of W/m2/nm was performed at the National
Institute for Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility III (SURF III) located in
Gaithersburg, Maryland. Although the final post-environmental calibrations have yet to be performed, preliminary
results from the pre-environmental calibrations show very good agreement with the theoretical optical design given by
Crotser et al. Further analysis is still needed in regards to the higher order contributions to determine the final first
order QT for all channels, but two techniques are currently being analyzed and show promising results.
The NASA Solar Dynamics Observatory (SDO), scheduled for launch in 2009, incorporates a suite of instruments
including the EUV Variability Experiment (EVE). The Multiple EUV Grating Spectrograph (MEGS) channels use
concave reflection gratings to image solar spectra onto CCDs that are operated at -100°C. MEGS provides 0.1nm
spectral resolution between 5-105nm every 10 seconds with an absolute accuracy of better than 25% over the SDO 5-
year mission. Characterizations and selection testing of the CCDs and the thin foil filters for SDO EVE have been
performed with both in-band and visible illumination. CCD selection was based on results from testing in LASP facility
Calibration and Test Equipment (CTE3) as well as results from at testingMIT. All CCDs meet the requirements for
electronics gain, flat field, Quantum Efficiency (QE), dark current, reverse clock, CTE, bad pixels and the -120°C
survival test. The thin foil filters selection was based on tests performed at LASP facilities and NIST. All filters provide
>106 attenuation of visible light with the proper EUV transmission needed for order sorting capabilities and are free of
critical pinholes.
The rocket Extreme Ultraviolet Grating Spectrograph (EGS) instrument is flown onboard a sounding rocket as an underflight calibration for the Solar Extreme Ultraviolet Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The first calibration flight took place from the White Sands Missile Range in New Mexico on February 8, 2002. Both preflight and postflight calibrations are performed in the extreme ultraviolet (EUV) range from 26.5 to 117.2 nm and the far ultraviolet (FUV) range from 120 to 196 nm to determine an accurate quantum throughput (QT) for the EGS instrument. These calibrations are performed using Beam Line 2 at the National Institute of Standards and Technology Synchrotron Ultraviolet Radiation Facility III. This QT determination has an uncertainty of about 10% for the EUV region and around 4.2% for the FUV region. Once the QT for the instrument is found from the calibrations, it is applied to the solar spectrum obtained during the flight in order to get the absolute spectral irradiance with an uncertainty of approximately 12%. The rocket EGS is planned for an annual calibration flight to track the long-term changes of SEE EGS.
The rocket Extreme ultraviolet Grating Spectrograph (EGS) instrument is flown onboard a sounding rocket as an underflight calibration for the Solar Extreme ultraviolet Experiment, or SEE, onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. The first calibration flight took place from the White Sands Missile Range in New Mexico on February 8, 2002. Both pre-flight and post-flight calibrations are performed in the extreme ultraviolet (EUV) range from 26.5 nm to 117.2 nm and the far ultraviolet (FUV) range from 120 nm to 196 nm in order to determine an accurate quantum throughput (QT) for the EGS instrument. These calibrations are performed using Beam Line 2 (BL2) at the National Institute of Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility III (SURF-III). This QT determination has an uncertainty of about 6% for the EUV region and around 3.5% for the FUV region. Once the QT for the instrument is found from the calibrations, it is applied to the solar spectrum obtained during the flight in order to get the absolute spectral irradiance with an uncertainty of approximately 10%. This rocket spectrum is then applied to the SEE EGS to obtain absolute irradiance values for the satellite instrument and to calibrate it for changes, such as degradation, that have occurred since its own pre-flight calibrations. This calibration transfer is done by scaling the SEE EGS solar spectrum at the time of the rocket flight to the rocket spectrum to get the same irradiance values, which produces a scaling factor that can be applied to other SEE EGS measurements. The rocket EGS is planned for an annual calibration flight to track the long-term changes of SEE EGS.
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