1 / 26

S2. EUV Irradiance & Calibration

S2. EUV Irradiance & Calibration. EUV Observations. Most of the new missions that make the next 5 years of solar observations look so exciting carry EUV/SXR instruments Solar-B EIS, XRT STEREO SECCHI EUVI GOES SXI, XRS Two of the three SDO instruments are strongly focused on the EUV

darryl
Download Presentation

S2. EUV Irradiance & Calibration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. S2. EUV Irradiance & Calibration

  2. EUV Observations • Most of the new missions that make the next 5 years of solar observations look so exciting carry EUV/SXR instruments • 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: • EVE calibration is important for understanding the effects of irradiance variability on the atmosphere • AIA calibration is important for understanding the 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 AIA/HMI Science Team Meeting

  3. Agenda (slightly modified since the announcement was posted) • Overview of EVE calibration • Overview of AIA-EVE cross-calibration • Discussion • cross-calibration with other instruments • problems • priorities • procedures • Wanted: practical ideas and questions, not necessarily solutions (yet…) AIA/HMI Science Team Meeting

  4. EVE and those other instruments on SDO Frank Eparvier LASP / University of Colorado eparvier@lasp.colorado.edu

  5. EEB +X EOP +Z +Y Spacecraft Coordinates SAM ESP MEGS B/P MEGS A Reminder: EVE Instrument Overview • Key Components • EVE Optical Package (EOP) • MEGS • MEGS A + SAM • MEGS B + P • ESP • EVE Electrical Box (EEB) • Processor & Memory • Interfaces (1553 & HSB) • Power / Heaters / Control • CCD power converters • ESP power converters EVE AIA HMI SDO Spacecraft AIA/HMI Science Team Meeting

  6. Dl 0.1 1 4 7 10 nm How does EVE measure the EUV? • Multiple EUV Grating Spectrograph (MEGS) • At 0.1 nm resolution • MEGS-A: 5-37 nm • MEGS-B: 35-105 nm • At 1 nm resolution • MEGS-SAM: 0-7 nm • At 10 nm resolution • 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 • 17.5, 25.6, 30.4, 36 nm • At 7 nm resolution • 0-7 nm (zeroth order) • In-flight calibrations from ESP and MEGS-P on daily basis and also annual calibration rocket flights AIA/HMI Science Team Meeting

  7. EVE Science Requirements AIA/HMI Science Team Meeting

  8. EVE Data Products AIA/HMI Science Team Meeting

  9. Calibration is a Lifetime Commitment The Calibration Essentials: • Understand the Measurement Equation: • Know all the parameters that go into the measurement to irradiance conversion and assess how to best quantify each • Do a thorough error analysis and uncertainty budget • Calibrate pre-flight: • Use a standard radiometric EUV source • Primary standards, such as NIST SURF-III source, are preferred (note: SURF beam flux known to <1% for EUV ranges) • Track in-flight: • Any instrument changes that will affect results • E.g. detector flat fields, gain changes, temperature effects, background signals, … • Re-Calibrate in-flight: • As close after launch as possible (changes since pre-flight calib.) • On a regular basis thereafter in order to track absolute changes • E.g. redundant channels, on-board sources, rocket underflights, proxy models • Validate: • With measurements made with other instrumentation • Comparisons with models AIA/HMI Science Team Meeting

  10. MEGS A & B Measurement Equations Where: AIA/HMI Science Team Meeting

  11. MEGS-A & B Error Analysis • 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): • For bright solar emission features the primary contributors to accuracy are the uncertainties in RC (the responsivity of the instrument) and the fDegrad (degradation correction) • For dim solar emissions, other uncertainties dominate, such as the precision of the measurement and the various corrections to the signal AIA/HMI Science Team Meeting

  12. EVE Uncertainty Budget and Verification Matrix AIA/HMI Science Team Meeting

  13. EVE In-Flight Calibration Activities • Continuous Internal Cross-Calibrations: • Overlapping Channels within EVE • Daily: • Filter wheel movements (dark, alternate filters) • Flat field lamps for MEGS CCDs (LEDs) • Quarterly Maneuvers: • Cruciform Scans: ±150 arcmin in 3 arcmin steps • Gives gross FOV changes and locates edges of FOV for relative boresight calibrations to SAM and AIA guide telescope • FOV Maps: ±10 arcmin in 5 arcmin steps (5x5 map) • 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: • Fly prototype instruments on sounding rocket periodically. • Calibrate rocket instruments at NIST before and after flight to transfer best calibration to EVE. AIA/HMI Science Team Meeting

  14. Cross-calibration:AIA-EVE,SDO-everybody else

  15. Overview: AIA/EVE cross-calibration • Spectral response η(λ) (effective area) of AIA channels determined by component-level calibration measurements • Mirrors (primary determination of bandpass) • Filters • CCDs • System-level effects • Estimated BOL relative calibration accuracy for AIA is 15% • 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: • 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 AIA/HMI Science Team Meeting

  16. Refining the Cross-calibration • First-order calibration should be easy to implement, but a few questions remain: • What cadence? (yearly? monthly? daily? 10 seconds?) • How do we interpret the resulting scale factors? • 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 cross-calibration: • Field of view • Spectral resolution • Bandpass uncertainty AIA/HMI Science Team Meeting

  17. Yohkoh/SXT 8 May 1992 Estimated X-ray radiance at 3 MK as observed by Yohkoh/SXT as function of limb height. Field of View • AIA field of view is 41 arc-minutes (to edge of CCD) / 46 arc-minutes (vignetting circle) • 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 • Higher fraction for lower-temperature lines • Depends on size and location of particular structures AIA/HMI Science Team Meeting

  18. Spectral Resolution • Spectral resolution of ~ 1 Å results in calibration errors • 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 1-25% compared to using the blue spectrum. AIA/HMI Science Team Meeting

  19. Bandpass Uncertainty • 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. AIA/HMI Science Team Meeting

  20. Questions (1 of 3) For AIA-EVE cross-calibration: • How often should we perform "first-order" calibration? • What data products are necessary for this cross-calibration? • What sort of operational coordination is necessary? Coordination with rocket underflights? • How do we interpret the resulting scaling factors? • 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? • What improvements in spectral modeling can be made to enhance calibration accuracy? • Can AIA-EVE cross-calibration be used to constrain Fe abundance? • What role can DEM extraction from AIA play in cross-calibration, and extending the spectral range of EVE? AIA/HMI Science Team Meeting

  21. Questions (2 of 3) For EIS-AIA-EVE inter-calibration: • How does EIS-AIA cross-calibration feed back into AIA-EVE cross-calibration? • Is it possible to get full-disk spectra with EIS? • If not, how do we cross-calibrate with EVE? • If so, how can we coordinate this cross-calibration? • Will it be possible to cross-calirbate EIS with the LASP rocket this year? For XRT-EVE cross-calibration: • Can the EVE SAM and ESP be used to cross-calibrate with XRT? • Would this be useful? • What sort of coordination is necessary? How often should this be done? etc. Can XRT and AIA be cross-calibrated? How? (Using DEM extraction?) AIA/HMI Science Team Meeting

  22. Questions (3 of 3) Are TRACE and EIT going to be observing during SDO? • If so, how do we cross-calibrate with AIA? • If not, how do we establish continuity between the AIA dataset and the EIT/TRACE datasets? • How important is this cross-calibration? For AIA, how important is it to have accurate: • Absolute calibration? • Relative calibration (channel-to-channel)? • Bandpass shape calibration? AIA/HMI Science Team Meeting

  23. Backup Slides AIA/HMI Science Team Meeting

  24. EVE and AIA Inter-Calibrations • EVE spectra can be convolved with AIA bandpasses and compared with integrated images to transfer an absolute irradiance calibration from EVE to AIA. • What’s needed for this transfer? • 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: • 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? AIA/HMI Science Team Meeting

  25. Action Items from EVE Science Workshop (Nov, 2005) AIA/HMI Science Team Meeting

  26. Comments from EVE Science Workshop (Nov, 2005) AIA/HMI Science Team Meeting

More Related