1. Calibration-Diagnostics Spectral Photometric/Gain Polarimetric Empirical or hardware calibrators NIRSPC or G Disk or Corona

2. 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

3. 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

4. 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

5. 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 …?

6. IR disk polarimetry calibration

7. 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

8. 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

9. 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 & U Stokes Q & U Scan: RV = 0.25 R  From PAG 250° to 270° Five 5° steps

10. IR Coronal Polarimetry

11. Spectral Profiles and Mueller Crosstalk Q U V I FeXIII V profile shift: few x 0.1 pixel

12. Recovered V profile: <0.0001 crosstalk correction B=4.6G

13. Measuring Crosstalk I/10 v q u v,vfit

14. Results: Coronal Magnetograms B=4,2,0,-2 G

15. 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