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S2. EUV Irradiance & Calibration

S2. EUV Irradiance & Calibration

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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 - PowerPoint PPT Presentation

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Page 1: S2. EUV Irradiance & Calibration

S2. EUV Irradiance & Calibration

Page 2: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 2February 13-17, 2006

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

Page 3: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 3February 13-17, 2006

Agenda

(slightly modified since the announcement was posted)

1. Overview of EVE calibration

2. Overview of AIA-EVE cross-calibration

3. Discussion• cross-calibration with other instruments• problems• priorities• procedures

Wanted: practical ideas and questions, not necessarily solutions (yet…)

Page 4: S2. EUV Irradiance & Calibration

EVE and those other instruments on SDO

Frank Eparvier

LASP / University of Colorado

[email protected]

Page 5: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 5February 13-17, 2006

Reminder: EVE Instrument Overview

ESPMEGS B/P

MEGS A

SAM

EOP

EEB

EVE Resources

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

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

Spacecraft Coordinates

+X

+Y+Z

SDO Spacecraft

AIAHMI

EVE

Page 6: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 6February 13-17, 2006

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- 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

0.1

1

4

7

10

nm

Page 7: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 7February 13-17, 2006

EVE Science Requirements

Parameter Minimum Success Requirements

Comprehensive Success Criteria

Design Goals

Range 6 or more emissions to specify the chromosphere, TR, and corona, plus the He I I 30.4 nm emission

0.1-105 nm 0.1-105 nm

Resolution 0.2 nm for these lines 0.1 nm for 18 or more emissions to specify the chromosphere, TR, and corona, and 5 nm or better elsewhere

0.1 nm

Time Cadence 60 sec < 20 sec 10 sec Accuracy 35% for 5 nm

intervals and daily average

25% for 5 nm intervals and daily average

20% for brighter emissions

Mission Life 3 years 5 years 5 years, long enough to sample low and high solar activity

Page 8: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 8February 13-17, 2006

EVE Data Products

Level Algorithm purpose

Scientifically Useful

Description File Duration

Daily Volume

(MB)

0A Fast validity check

No TLM consistency/quality checking ~1 minute 76000

0B 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

0C Space Weather Yes Quick-look indices, MEGS-A, MEGS-B, SAM, MEGS-P & ESP

1 minute 36

1 Apply calibration

Yes (SAM, ESP, MEGS-P)

Use measurement equations to produce irradiance units

1 hour 1095

2 Re-grid, extract lines

Yes Bin data to fixed wavelength scale, integrate over emission features with background removal

1 hour 1160

3 Daily average Yes Merge all component data into daily averages, bin to 0.1 and 1 nm

24 hours 0.026

Page 9: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 9February 13-17, 2006

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

Page 10: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 10February 13-17, 2006

MEGS A & B Measurement Equations

Where:

E Solar spectral irradiance(x,y) Detector pixel location

S Raw signal from detectort Integration timeG Detector gain

fFFFlatfield correction

fLinLinearity correction

CBkgBackground signal

CSLScattered light signal

fImagePixel contribution weighting to slit image

Good(x,y) “Good” pixels in slit image

ASlitSlit area

Dispersion (bandpass of single detector element)

RcResponsivity at center of FOV

fFOVPointing within FOV correction

fDegradDegradation correction

f1AUNormalization to 1-AU

Wavelength

EOSHigher order correction

C1 x,y St GfFF fLin

C2 x,y C1 CBkg CSL

E1 C2

ASlit RC fFOV fDegrad f1AU

hc

EMeasured E1 EOS

C3 f Image x,y C2 x,y

Good(x,y )

f Image x,y

Good(x,y )

Page 11: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 11February 13-17, 2006

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

EMeasured E1

2 EOS

2 1

2

C1C1

S2

S 2 G

2

G 2 fFF

2

fFF2 fLin

2

fLin2

12

C2 C1

2 CBkg

2 CSL

2 1

2

E1E1

C32

C32 ASlit

2

ASlit2

2

2 RC

2

RC2 fFOV

2

fFOV2

fDegrad2

fDegrad2 f1AU

2

f1AU2

2

2

12

C3

2 fImage x,y C3

fImage x,y Good(x, y )

2

fImage x, y 2

fImage x,y 2 1fImage x,y

fImage x,y Good(x, y )

2

C2 x, y 2

C2 x,y 2

Good(x, y )

Page 12: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 12February 13-17, 2006

EVE Uncertainty Budget and Verification Matrix

SymbolParameter

DescriptionError

BudgetComponent

Level

Instrument

Level

Spacecraft

Level

On-Orbit

Level

S Signal 34% X X X X

t Integration Time 0.02% X

G Gain 1% X X

fFF Flatfield 2% X X X X

fLin Detector Linearity 0.2% X X

CBkg Background 20% X X X X

CSL Scattered Light 20% X X X

fImage Slit Image Weight 2% X X

ASlit Slit Area 8% X

Dispersion 6% X X

RC Responsivity at Center

12% X X

fFOV FOV Correction 10% X X

fDegrad Degradation Correction

18% X

f1AU 1-AU Correction 0.02% X

Wavelength 0.2% X X

EOS Order Sorting 2% X X

EMeasured Irradiance Product

25%

Page 13: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 13February 13-17, 2006

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.

Page 14: S2. EUV Irradiance & Calibration

Cross-calibration:AIA-EVE,

SDO-everybody else

Page 15: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 15February 13-17, 2006

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

Page 16: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 16February 13-17, 2006

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

Page 17: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 17February 13-17, 2006

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

Estimated X-ray radiance at 3 MK as observed by Yohkoh/SXT as function of limb height.

Yohkoh/SXT 8 May 1992

Page 18: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 18February 13-17, 2006

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.

Page 19: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 19February 13-17, 2006

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.

Page 20: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 20February 13-17, 2006

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?

Page 21: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 21February 13-17, 2006

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?)

Page 22: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 22February 13-17, 2006

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?

Page 23: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 23February 13-17, 2006

Backup Slides

Page 24: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 24February 13-17, 2006

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?

Page 25: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 25February 13-17, 2006

Action Items from EVE Science Workshop (Nov, 2005)Action Item

NumberResponsible

PersonAction Item Description Status Due Date

1Woodraska,

EparvierBetter define the MEGS Quick-Look data for SURF and I&T (e.g. consider display procedures for MEGS Level 0B).

open Dec-05

2 TateCan EVE observations be timed to be consistent with TAI time on intervals of 0.0 (like HMI and AIA)?

open Dec-05

3Eparvier, Kohnert

Add spacecraft roll calibration to EVE calibration plan (CMAD). Should use HMI/AIA roll calibration plan that has discrete roll angles (+/- 26°).

open Jan-06

4 Eparvier, JonesInclude wavelength shift effects more completely in irradiance algorithms and error analysis

open Apr-06

5Pesnell and SDO

data teamsSDO project needs to define standard (common) meta-data specifications open Apr-06

6Woodraska,

Woods

Define the SAM higher level data products (beyond the photon events defined for SAM Level 1A). For example, it might include SAM Level 2 that contains solar irradiance in constant energy bins. Also consider SAM images as virtual product that user specifi

open Apr-06

7Woodraska,

WarrenDefine the critical emissions to extract for MEGS Level 2 data products (and also used in EVE Level 3). At least include the 7 EUV emissions measured by AIA.

open Apr-06

8Woodraska,

Viereck, Tobiska

Develop concept for irradiance server (common interface / platform / format). For example, resolve FTP process (push vs pull) for distributing EVE space weather data products.

open Apr-06

9Pesnell, Eparvier, Bush, Schrijver,

Viereck

Define solar event log for SDO mission (e.g., flare intensity and peak time, flare location on solar disk). Consider creating log as near real-time file using SDO's space weather data products.

open Apr-06

10 Eparvier

Plan to have Solar EUV Irradiance Validation Workshop for spring 2007 to discuss EUV measurements from rocket, TIMED-SEE, SOHO-SEM, GOES-EUVS, STEREO. Also include solar EUV irradiance models in this comparison / validation effort (either part of same wo

open Nov-06

11Jones, McMullin,

WoodraskaDevelop more completely the ESP algorithms that depend on solar EUV irradiance spectra (from MEGS)

open Nov-06

12Woodraska,

CrotserDevelop algorithms to compress MEGS images into spectra. Will need example (predicted) images at different FOV angles.

open Nov-06

13 Bryant, EparvierOptimize filter in-flight operations to reduce data gaps and using only single channel in calibration mode at a time

open Nov-06

14McCaffrey, Eparvier

Select some focussed topics in space weather research for EPO activities open Oct-07

15 WarrenDevelop algorithm to determine differential emission measure (DEM) from EVE spectra. Consider routine production of the disk-averaged DEM and for comparison to AIA image DEM results.

open Oct-07

Page 26: S2. EUV Irradiance & Calibration

AIA/HMI Science Team Meeting Eparvier - 26February 13-17, 2006

Comments from EVE Science Workshop (Nov, 2005)Comment Number

Responsible Person

Comment Description

1Schrijver,

Warren, PesnellIdentify the SolarSoft procedures for removing particle "spikes" in CCD images that might be applicable for EVE data processing

2 KohnertConsider taking prototype (rocket) MEGS to SURF first for calibrations to identify any possible instrument or calibration issues

3 SchrijverConsider full-disk intensity data with corrections for flat-field and despiked as part of the science-quality data products for AIA

4 WarrenSpectral modeling of the EVE data at 0.1 nm resolution to obtain higher spectral resolution is important for AIA-EVE calibration / validation for some of the AIA channels

5 WoodraskaResolve if it is important to include ensemble uncertainties for the ESP Level 1 data that includes an average of 4 measurements taken at 0.25 sec cadence

6 WoodraskaEVE data products do not have to have constant array size. That is, gaps in the measurement sequence are acceptable, and flags for gaps are not expected.

7 WoodraksaSAM Level 1A data product should include the photon events in energy units and location in units of CCD pixels.

8 WoodraskaFor EVE Level 3 data, the daily averaged irradiance will be the mean over the day (instead of median).

9Fuller-Rowell,

Smithtro, Sojka, Solomon

Define optimal wavelength bins for near realtime atmospheric modeling. Also include the FUV range.

10 WoodraskaUse pseudo-calibration correction factors for generating the EVE space weather data products and to subtract off dark measurements with constant scalar (unique scalar for each diode). For example, E = (S - K*D) / R

11 Woodraska Have MEGS data in 1-nm intervals for space weather data products.

12 WoodraskaSpace Weather data products to have 1-min cadence (average) for ESP / MEGS-P data and for MEGS A & B data.

13Eparvier, Schrijver

Define plots / movies for EVE space weather data products and overlap with AIA

14 Woodraska Time stamps in Space Weather data product includes date too.15 Woodraska Do not include SAM data in Space Weather data product.16 Tobiska EVE's photoionization rate results are part of SOLAR2000 model already17 Bailey EVE's photoelectron flux results are still needed for LWS I-T studies / mission.

18Schrijver, Warren

Develop algorithms to link magnetic field and active region evolution to irradiance variations