Calibration-Diagnostics

• Spectral• Photometric/Gain• Polarimetric

• Empirical or hardware calibrators• NIRSPC or G• Disk or Corona

Empirical or special hardware

• Spectral– Sun is best source

• Most accurate• Not always available

– Th-Ar and laser sources should be available• From prime focus they make good system+instrument

diagnostics

• Mostly solar reference, but lamp and laser reference from prime focus will be used by NIRSPC/G for setup and diagnostics in all disk and coronal modes

Calibration

• Photometric/Gain– No absolute photometric gain calibration requirement

(throughput requirement )– Flat-field

• Spatial, use prime focus Halogen (1% accuracy)– Solar data for 10^-3 accuracy (KLL algorithm)

• Spectral, use prime focus Halogen, (KLL TBD)

• In general highest accuracy flat-fields result from data algorithms. Prime focus halogen flat-field screen useful for diagnostic and spectral calibration

Calibration

• Polarimetric– Highest accuracy calibration requirement:

10^-4– External calibrator has little chance to achieve

this (note wavelength, field, and time dependence of ATST Mueller matrix) – although empirical techniques haven’t yet met this goal either

– Important cross terms in Mueller are different for disk and coronal observations, empirical calibration schemes will be different

Empirical IR Disk Polarimetry Calibration

• V often dominates raw spectropolarimetry signal• Fully resolved spectropolarimetric IR line profiles

necessary (e.g. from sunspot umbra)• Assumes no pi component in V line profile• Algorithm tested and used to approximately

“few” x 10^-3 accuracy• Sol. Phys. 153, 143 (1994)• Limitations: low scattered light …?

IR disk polarimetry calibration

IR Coronal polarimetry calibration

• Q,U often dominates (by a large factor) raw V polarimetric signature

• Spectropolarimetric line profiles not resolved, weak-field regime only, although disk calibration technique might be used and extrapolated to needed IR wavelengths

SOLARC Lessons

LCVR Polarimeter

Input array of fiber optics bundle

Re-imaging lens

Prime focus inverse occulter/field stop

Secondary mirror

Primary mirror

Fiber Bundle

Collimator

Echelle Grating

Camera Lens

NICMOS3 IR camera

May 6 2004 Observations

Fe X 171Å image of the solar corona at approximately the time of SOLARC/OFIS observation from EIT/SOHO. The rectangle marks the target region of the coronal magnetic field (Stokes V) observation.

Full Stokes vector observations were obtained on April 6, 2004 on active region NOAA 0581 during its west limb transit.

Stokes I, Q, U, & V Observation:• 20arcsec/pixel resolution• 70 minutes integration on V• 15 minutes integration on Q & UStokes Q & U Scan:• RV = 0.25 R • From PAG 250° to 270°• Five 5° steps

IR Coronal Polarimetry

Spectral Profiles and Mueller Crosstalk

Q

U

V

I

FeXIII

)cI()(V'

uq,Bk

)vI(V

)qI(Q

)uI(U

IMQMUMd

dIkV

VIVQVU

B V profile shift: few x 0.1 pixel

Recovered V profile:<0.0001 crosstalk correction

B=4.6G

Measuring Crosstalk

I/10

v

q

u

v,vfit

0.001 :rms Residual

0.006 161.0M

0.004 064.0M

0007.00046.0M

VU

VQ

VI

Results: Coronal Magnetograms

B=4,2,0,-2 G

Conclusions

• Empirical IR disk crosstalk calibration possible at few x 10^-4– Low scattered light critical, umbral

observation

• Empirical IR coronal crosstalk calibration likely at few x 10^-5– Wavelength stability critical