S 2 EUV Irradiance Calibration EUV Observations n
S 2. EUV Irradiance & Calibration
EUV Observations n Most of the new missions that make the next 5 years of solar observations look so exciting carry EUV/SXR instruments q q q n n Solar-B EIS, XRT STEREO SECCHI EUVI GOES SXI, XRS Two of the three SDO instruments are strongly focused on the EUV Calibration of these EUV instruments is essential for a number of reasons: q q q EVE calibration is important for understanding the effects of irradiance variability on the atmosphere AIA calibration is important for understanding thermal structure of the corona Even scientific investigations that don’t explicitly rely on calibrated EUV observations will benefit from cross-calibration of EUV instruments February 13 -17, 2006 AIA/HMI Science Team Meeting 2
Agenda (slightly modified since the announcement was posted) Overview of EVE calibration Overview of AIA-EVE cross-calibration Discussion 1. 2. 3. • • n cross-calibration with other instruments problems priorities procedures Wanted: practical ideas and questions, not necessarily solutions (yet…) February 13 -17, 2006 AIA/HMI Science Team Meeting 3
EVE and those other instruments on SDO Frank Eparvier LASP / University of Colorado eparvier@lasp. colorado. edu
Reminder: EVE Instrument Overview n EEB EOP Key Components q EVE Optical Package (EOP) n MEGS q q MEGS A + SAM MEGS B + P ESP EVE Electrical Box (EEB) n q n n n EVE AIA SAM ESP MEGS B/P HMI +X +Y Spacecraft Coordinates SDO Spacecraft n EVE Resources +Z February 13 -17, 2006 MEGS A n Processor & Memory Interfaces (1553 & HSB) Power / Heaters / Control CCD power converters ESP power converters Power (orbit average) 43. 9 Watts Mass 54. 2 kg Data Rate 2 kbps (engineering) 7 Mbps (science) Dimensions (L x W x H) 99 cm x 61 cm x 36 cm AIA/HMI Science Team Meeting 5
How does EVE measure the EUV? n Multiple EUV Grating Spectrograph (MEGS) q q n At 0. 1 nm resolution n MEGS-A: 5 -37 nm n MEGS-B: 35 -105 nm At 1 nm resolution n MEGS-SAM: 0 -7 nm At 10 nm resolution n MEGS-Photometers: @ 122 nm Ly-a Proxy for other H I emissions at 80 -102 nm and He I emissions at 45 -58 nm EUV Spectrophotometer (ESP) At 4 nm resolution n 17. 5, 25. 6, 30. 4, 36 nm q At 7 nm resolution n 0 -7 nm (zeroth order) In-flight calibrations from ESP and MEGS-P on daily basis and also annual calibration rocket flights q n February 13 -17, 2006 Dl 0. 1 1 4 7 10 nm AIA/HMI Science Team Meeting 6
EVE Science Requirements February 13 -17, 2006 AIA/HMI Science Team Meeting 7
EVE Data Products Level Algorithm purpose Scientifically Useful Description File Duration Daily Volume (MB) 0 A Fast validity check No TLM consistency/quality checking ~1 minute 76000 0 B Assemble images, detailed data verification No Data checks for CRC and pixel parity, parse data packets, merge image data, separate by science channel and filter wheel position ~1 minute 76000 0 C Space Weather Yes Quick-look indices, MEGS-A, MEGS-B, SAM, MEGS-P & ESP 1 minute 36 Use measurement equations to produce irradiance units 1 hour 1095 1 hour 1160 24 hours 0. 026 1 Apply calibration 2 Re-grid, extract lines Yes Bin data to fixed wavelength scale, integrate over emission features with background removal 3 Daily average Yes Merge all component data into daily averages, bin to 0. 1 and 1 nm February 13 -17, 2006 Yes (SAM, ESP, MEGS-P) AIA/HMI Science Team Meeting 8
Calibration is a Lifetime Commitment The Calibration Essentials: n n n Understand the Measurement Equation: q Know all the parameters that go into the measurement to irradiance conversion and assess how to best quantify each q Do a thorough error analysis and uncertainty budget Calibrate pre-flight: q Use a standard radiometric EUV source q Primary standards, such as NIST SURF-III source, are preferred (note: SURF beam flux known to <1% for EUV ranges) Track in-flight: q Any instrument changes that will affect results q E. g. detector flat fields, gain changes, temperature effects, background signals, … Re-Calibrate in-flight: q As close after launch as possible (changes since pre-flight calib. ) q On a regular basis thereafter in order to track absolute changes q E. g. redundant channels, on-board sources, rocket underflights, proxy models Validate: q With measurements made with other instrumentation q Comparisons with models February 13 -17, 2006 AIA/HMI Science Team Meeting 9
MEGS A & B Measurement Equations Where: E Solar spectral irradiance (x, y) S t G f. FF f. Lin CBkg CSL Detector pixel location Raw signal from detector Integration time Detector gain Flatfield correction Linearity correction Background signal Scattered light signal f. Image Pixel contribution weighting to slit image Good(x, y) ASlit area Dispersion (bandpass of single detector element) Responsivity at center of FOV Pointing within FOV correction Degradation correction Normalization to 1 -AU Rc f. FOV f. Degrad f 1 AU EOS February 13 -17, 2006 “Good” pixels in slit image AIA/HMI Science Team Meeting Wavelength Higher order correction 10
MEGS-A & B Error Analysis n The uncertainties of the various correction factors must be propagated through to determine the accuracy of the measured irradiance (note: denotes uncertainty in the units of the variable): n For bright solar emission features the primary contributors to accuracy are the uncertainties in RC (the responsivity of the instrument) and the f. Degrad (degradation correction) n For dim solar emissions, other uncertainties dominate, such as the precision of the measurement and the various corrections to the signal February 13 -17, 2006 AIA/HMI Science Team Meeting 11
EVE Uncertainty Budget and Verification Matrix Symbol Parameter Description Error Budget Component Level Instrument Level Spacecraft Level On-Orbit Level 34% X X 0. 02% X X X S Signal t Integration Time G Gain 1% X X f. FF Flatfield 2% X X f. Lin Detector Linearity 0. 2% X X CBkg Background 20% X X CSL Scattered Light 20% X X X f. Image Slit Image Weight 2% X X ASlit Area 8% Dispersion 6% X X RC Responsivity at Center 12% X X f. FOV Correction 10% X X Degradation Correction 18% X 1 -AU Correction 0. 02% X Wavelength 0. 2% X X Order Sorting 2% X X Irradiance Product 25% f. Degrad f 1 AU EOS EMeasured February 13 -17, 2006 X AIA/HMI Science Team Meeting 12
EVE In-Flight Calibration Activities n Continuous Internal Cross-Calibrations: q n Daily: q q n Overlapping Channels within EVE Filter wheel movements (dark, alternate filters) Flat field lamps for MEGS CCDs (LEDs) Quarterly Maneuvers: q Cruciform Scans: ± 150 arcmin in 3 arcmin steps n q FOV Maps: ± 10 arcmin in 5 arcmin steps (5 x 5 map) n q n Gives gross FOV changes and locates edges of FOV for relative boresight calibrations to SAM and AIA guide telescope Gives finer FOV changes over nominal FOV pointing area (with margin) Also get bonus mapping when AIA and HMI require maneuvers (though their mappings are different and not optimized for EVE needs). Annual Rocket Underflights: q q Fly prototype instruments on sounding rocket periodically. Calibrate rocket instruments at NIST before and after flight to transfer best calibration to EVE. February 13 -17, 2006 AIA/HMI Science Team Meeting 13
Cross-calibration: AIA-EVE, SDO-everybody else
Overview: AIA/EVE cross-calibration n Spectral response η(λ) (effective area) of AIA channels determined by component-level calibration measurements q q n Estimated BOL relative calibration accuracy for AIA is 15% q q q n Mirrors (primary determination of bandpass) Filters CCDs System-level effects Absolute calibration is more difficult Calibration will change due to contamination, degradation, etc. Therefore, cross-calibration with EVE is highly desireable First-order cross-calibration procedure: q q Use EVE MEGS-A measurements of full-disk solar spectral irradiance to predict a full-disk count rate in each AIA channel Compare EVE-predicted count rate with AIA’s measured full-disk count rate, and produce a scaling factor for each channel February 13 -17, 2006 AIA/HMI Science Team Meeting 15
Refining the Cross-calibration n First-order calibration should be easy to implement, but a few questions remain: q q What cadence? (yearly? monthly? daily? 10 seconds? ) How do we interpret the resulting scale factors? n n Contamination? Something else? or is it just an empirical correction, and we don’t worry about it? There are some potential pitfalls to the first-order AIA-EVE crosscalibration: q q q Field of view Spectral resolution Bandpass uncertainty February 13 -17, 2006 AIA/HMI Science Team Meeting 16
Field of View n AIA field of view is 41 arcminutes (to edge of CCD) / 46 arc-minutes (vignetting circle) q n Yohkoh/SXT 8 May 1992 1. 3 -2. 0 pressure scale heights (at T = 3. 0 MK) Based on Yohkoh observations, we estimate that AIA will observe ~ 96 % of the total coronal radiance q q Higher fraction for lowertemperature lines Depends on size and location of particular structures Estimated X-ray radiance at 3 MK as observed by Yohkoh/SXT as function of limb height. February 13 -17, 2006 AIA/HMI Science Team Meeting 17
Spectral Resolution n Spectral resolution of ~ 1 Å results in calibration errors q q n Less than 1% for longer-wavelength (broad) channels Up to 25% for 171 and 94 Å Can be corrected by modeling higher-resolution spectrum Simulated full-disk spectrum (10% AR, 90% QS) shown in blue. Blurred with 1 Å FWHM gaussian and binned at 6 pixels/Å in black. Response of AIA 194 channel shown in red. Folding the black spectrum through the red instrument response results in errors of 125% compared to using the blue spectrum. February 13 -17, 2006 AIA/HMI Science Team Meeting 18
Bandpass Uncertainty n n First-order cross-calibration only allows us to correct the overall scale of the AIA response functions Uncertainties in the bandpass shape are more important; can we use EVE to correct those? Measurements of the MSSTA multilayers. This is not data from an AIA telescope, but the illustration of bandpass variations over the mirror surface is relevant. See the poster by R. Soufli et al. February 13 -17, 2006 AIA/HMI Science Team Meeting 19
Questions (1 of 3) For AIA-EVE cross-calibration: n How often should we perform "first-order" calibration? n What data products are necessary for this cross-calibration? n What sort of operational coordination is necessary? Coordination with rocket underflights? n How do we interpret the resulting scaling factors? q q q n n contamination? something else? not at all? How do we deal with the field-of-view discrepancy? How do we use EVE to correct the bandpass shape of the AIA? To what extent will cross-calibrations rely on spectral modeling? n What improvements in spectral modeling can be made to enhance calibration accuracy? n Can AIA-EVE cross-calibration be used to constrain Fe abundance? n What role can DEM extraction from AIA play in cross-calibration, and extending the spectral range of EVE? February 13 -17, 2006 AIA/HMI Science Team Meeting 20
Questions (2 of 3) For EIS-AIA-EVE inter-calibration: n How does EIS-AIA cross-calibration feed back into AIA-EVE crosscalibration? n Is it possible to get full-disk spectra with EIS? n If not, how do we cross-calibrate with EVE? n If so, how can we coordinate this cross-calibration? n Will it be possible to cross-calirbate EIS with the LASP rocket this year? For XRT-EVE cross-calibration: n Can the EVE SAM and ESP be used to cross-calibrate with XRT? n Would this be useful? n What sort of coordination is necessary? How often should this be done? etc. Can XRT and AIA be cross-calibrated? How? (Using DEM extraction? ) February 13 -17, 2006 AIA/HMI Science Team Meeting 21
Questions (3 of 3) Are TRACE and EIT going to be observing during SDO? n If so, how do we cross-calibrate with AIA? n If not, how do we establish continuity between the AIA dataset and the EIT/TRACE datasets? n How important is this cross-calibration? For AIA, how important is it to have accurate: n n n Absolute calibration? Relative calibration (channel-to-channel)? Bandpass shape calibration? February 13 -17, 2006 AIA/HMI Science Team Meeting 22
Backup Slides February 13 -17, 2006 AIA/HMI Science Team Meeting 23
EVE and AIA Inter-Calibrations n EVE spectra can be convolved with AIA bandpasses and compared with integrated images to transfer an absolute irradiance calibration from EVE to AIA. q What’s needed for this transfer? n n n q q q AIA bandpasses (!) AIA image conversion to irradiance EVE irradiances Can EVE be used to track changing AIA bandpasses? Probably, but how the bleep do we do that? Logistical Questions: n n Do AIA and EVE integrations need to be coincident? Do special data products need to be made for inter-calibrations? How frequently should comparisons be done? Are there special calibration activities on-orbit that should be planned? In conjunction with rocket underflights? February 13 -17, 2006 AIA/HMI Science Team Meeting 24
Action Items from EVE Science Workshop (Nov, 2005) February 13 -17, 2006 AIA/HMI Science Team Meeting 25
Comments from EVE Science Workshop (Nov, 2005) February 13 -17, 2006 AIA/HMI Science Team Meeting 26
- Slides: 26