AMS Meeting, January 2008J1.3. Eparvier - 1 EXIS: The Next Generation of Solar EUV and X-Ray Sensors for GOES-R + F.G. Eparvier, T.N. Woods, W. McClintock, P.C. Chamberlin, A.R. Jones, & R. Viereck

AMS Meeting, January 2008J1.3. Eparvier - 2 NOAA requires the monitoring of the solar irradiance variability that controls the variability of the terrestrial upper atmosphere (ionosphere and thermosphere). This requirement supports NOAA’s space weather operations and is implemented with two instruments: XRS = X-Ray Sensor –XRS measures the solar soft x-ray irradiance in two bandpasses at nm and nm –On GOES manifest from beginning of program (~1978 on SMS) –all past and present instruments are ionization chambers with Be filters –XRS Purpose: Monitor solar flares that can disrupt communications and degrade navigational accuracy EUVS = Extreme UltraViolet Sensors –Through a combination of measurements and modelling, EUVS determines the solar EUV spectral irradiance in the nm range –first included on GOES in 2006 (GOES-13, in on-orbit storage) as transmission grating spectrographs measuring 5 broad bandpasses –EUVS Purpose: Monitor solar variations that directly affect satellite drag / tracking and ionospheric changes, which impact communication and navigation operations XRS/EUVS Science Overview

AMS Meeting, January 2008J1.3. Eparvier - 3 GOES-R EXIS EXIS = EUV and X-ray Irradiance Sensors –New definition of instrumentation for GOES-R –EXIS concept designs presented here are the result of a two year formulation phase –EXIS consists of EUVS, XRS, and a combined electronics box (EXEB) to control subsystems and do command and data handling interface with spacecraft EUVS XRS EXEB EXIS = EUV and X-ray Irradiance Sensors The Key Components of EXIS: EUVS = Extreme Ultraviolet Sensor XRS = X-Ray Sensor EXEB = EUVS/XRS Electrical Box

AMS Meeting, January 2008J1.3. Eparvier - 4 Primary Goal: continue into the future the nm and nm X-ray irradiance measurements that have been ongoing for over 30 years Secondary Goal: improve the XRS instrumentation and the measurements –signal to noise: current XRS “bottoms out” at solar minimum –dynamic range: capture solar minimum and largest flares –accuracy: better calibration and degradation tracking –lifetime: build an XRS that will last for 5 yr ground storage, 5 yr on-orbit storage, and 10 yr operation X-Ray Sensor (XRS)

AMS Meeting, January 2008J1.3. Eparvier - 5 XRS Design Concept Each XRS channel (A & B) has: –Two photometers: Different sized apertures give different dynamic ranges to capture solar minimum and solar maximum conditions (high and low gains for each channel) Large overlap in both dynamic ranges adds redundancy in measurements –Each photometer is a silicon diode with Be filters (thicknesses scaled to match previous XRS bands) –Low-power, low-noise electrometers XRS also has: –Dark channel for simultaneous background corrections –Improved calibration methodology –Improved measurement to irradiance conversion

AMS Meeting, January 2008J1.3. Eparvier - 6 XRS Measurements & Products Standard Measurements/Products: – nm and nm calibrated irradiances (matching past XRS bandpasses) –Available at 3-sec cadence w/ –Flare start, peak, end times Potential Advanced Products: –XRS ratios Temperature modeling of flares Higher spectral resolution modeling of flares

AMS Meeting, January 2008J1.3. Eparvier - 7 Extreme Ultraviolet Sensor (EUVS) Primary Goal: Determine the EUV irradiance and its variability and to provide a continuing record into the future for the EUV Secondary Goal: Improve the EUVS instrumentation and the measurements –Accuracy: improved calibration methodology and degradation tracking (particular issue in the EUV) –Lifetime: build an EUVS that will last for 5 yr ground storage, 5 yr on-orbit storage, and 10 yr operation –Dynamic range and signal to noise: capture full range of solar EUV variability –FOV sensitivity: build an EUVS that will not be sensitive to, or has well understood, variations across FOV EUV Variability

AMS Meeting, January 2008J1.3. Eparvier - 8 EUVS Design Concept Analyzed several design solutions in Formulation Phase Trade Study (based on technical, programmatic, and cost discriminators) resulted in the current EUVS design concept: Three reflection grating spectrographs to measure different wavelength ranges –Capture emissions from Corona, Transition Region, and Chromosphere –Use these emissions as proxies in a spectral model to reconstruct the full EUV spectral range –“Bootstrapping” calibration technique allows for accurate long-term tracking of degradation Note: Chromospheric measurement is of MgII C/W ratio, which is also a required NOAA measurement

AMS Meeting, January 2008J1.3. Eparvier - 9 EUVS Design Overview EUVS Concept –Three channels that provide accurate proxies for the emissions from the chromosphere (CH), transition region (TR), and corona (COR) Measures 84% of the energy in nm range Measures 27% of the wavelength range (5-127 nm) –Measured proxies are used to model the full EUV range (0-135 nm) CC B A Channel Range (nm)  (nm) Optical DesignProxy On-Orbit Calibration A Spectrograph (grazing incidence)COR Fe XV 28.4 nmTR He II 25.6 nm TR He II 30.4 nm B Spectrograph (normal incidence)TR H I nm TR Si IV/O IV nm CH C III nm CH C II nm C Spectrograph (normal incidence)CH MgII C/W RatioNone (self-calibrating)

AMS Meeting, January 2008J1.3. Eparvier - 10 “Bootstrapping” Degradation Tracking Degradation tracking is built in with this approach –Channel C does not require absolute calibration: Product is a ratio of core to wing of MgII spectral feature NOAA Mg II C/W index has been proven as a reliable chromospheric proxy for 25 years A flatfield lamp will track non-uniform degradation across the diode array –Channel C can track degradation in Channel B: The MgII C/W ratio is an excellent chromospheric proxy which can be used to track relative changes in chromospheric emissions at other wavelengths The Channel B lines: C III nm and C II nm are chromospheric emissions, changes in which can be tracked by MgII C/W A flatfield lamp will track non-uniform degradation across the diode array, thereby tracking absolute changes in the HI Ly-  nm and Si IV / O IV nm, transition region emissions –Channel B can track degradation in Channel A: Ly-  in Channel B is a transition region emission which is an excellent proxy for other transition region emissions Channel A lines He II 30.4 nm and He II 25.6 nm are transition region emissions A flatfield lamp will track non-uniform degradation across the diode array, thereby tracking absolute changes in the coronal emissions in A This “boot-strapping” degradation tracking has been tested with TIMED-SEE data and has been validated by the TIMED-SEE sounding rocket underflights.

AMS Meeting, January 2008J1.3. Eparvier - 11 EUVS Proxy Model Proxy Model in 5-nm intervals using multiple proxies (based on FISM): –Chromosphere: MgII C/W  EUVS-C –Transition Region: H I nm  EUVS-B –Corona: Fe XV 28.4 nm  EUVS-A –X-ray: 0-4 nm  XRS This model is based on TIMED SEE measurements of the solar EUV irradiance from nm –SEE Level 3A (Version 7) data used in 2002 and 2003 –XUV (0-27 nm) results have larger deviations - expect improvements in this range with SDO EVE measurements Model accuracy is combination of the average deviation and TIMED SEE accuracy Average deviation for multiple proxy model is 0.1-8% (mean is 2.7%) Model accuracy is 10-13% (mean is 10.5%) Proxy Model Equation:

AMS Meeting, January 2008J1.3. Eparvier - 12 EUVS Measurements & Products Standard Measurements (at 30-sec cadence): –Emission Line Irradiances: Corona: Fe XV 28.4 nm Transition Region: He II 25.6, He II 30.4, H I 121.6, and Si IV/O IV nm Chromosphere: C III and C II nm –Photospheric Continuum and Chromospheric Mg II h,k lines Standard Products (at 30-sec cadence): –Irradiances: 5-35 nm in 10-nm bins, in 40 nm bins, nm –Mg II C/W Ratio Potential Advanced Products: –Irradiances: nm in 1-nm, 5-nm, or any resolution desired (uncertainty increases with resolution) any specific lines or bands (e.g nm to match SOHO-SEM) –EUV flare indices, ratios, and temperatures –Atmospheric ionization rates

AMS Meeting, January 2008J1.3. Eparvier - 13 EXIS Summary EXIS is designed to meet the solar EUV and X-ray irradiance monitoring needs for the GOES-R program The EXIS data has the potential for new data products for space weather use