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GRID CALIBRATION OVERVIEW
GOAL:
 | Knowledge to ~1% of grid pair transmission, modulation amplitude and phase, |
as a function of energy and source offset,
expressed in a manner that can be efficiently applied to the data.
MOTIVATION:
| Artifact-free light-curves |
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| High dynamic range imaging |
| Unbiased and artifact-free spectroscopy |
METHOD:
- Obtain optical, x-ray, mass and thickness calibration data on individual grids
- Define a tractable grid model consistent with calibration data
- Calculate single grid transmission, spatial modulation and phase (E, angle)
- Combine single grid results to get grid pair transmission, modulation amplitude and phase.
(Sub-collimator response table)
- Integrate and interpolate sub-collimator response table as necessary for individual flares.
(Grid response matrix)
- Use in-flight self-calibration to refine grid models as needed.
PRIMARY OBSERVATIONAL DATA
| OPTICAL MEASUREMENTS OF GRID SURFACE |
 | Average pitch |
| Average rms deviation |
| Slat width distribution (+unknown constant) |
| Average slit orientation |
| Position of slits (phase) |
| X-RAY |
| Peak transmission for Cd109, Co57, Cs137 (23, 122, 662 kev) |
| FWHM of single grid transmission at 23 and 122 kev |
| 1-degree transmission at 122 and 662 kev |
| MISCELLANEOUS |
| Mass of stacked grid (Tecomet) |
| Grid thickness at rims (Tecomet) |
| Dimensions and mass of typical spare blades (VBC) |
| No direct measurements of slit widths of individual layers (Tecomet) |
| No direct measurement of surface density of unetched Tecomet grid layers |
| No direct measurements of average profile of stacked slit edges |
| No direct measurements of tilt distribution for VBC blades |
| Optical data fully analyzed |
| Used as basis for grid alignment |
| Alignment independently confirmed by gridlet test |
| Determination of grid model parameters is in progress |
| VBC grid data self-consistent to 1 – 2% |
| Tecomet grid parameters consistent to ~5% |
| Software to convert grid parameters to sub-collimator response table is working |
| Some additional features are being added |
| Software to apply grid calibration data for imaging and spectroscopy is in SSW. |
GOAL
| Use internal redundancy to fine-tune grid parameters. |
FEATURES
| Approach: Adjust grid parameters until corrected count rate ratios are independent of (low) energy and flare location |
| High energy response is not sensitive to details of grid model. |
| Uses count rates, rather than modulation (much more sensitive) |
| Recalculated sub-collimator response table should be stable and common to all flares |
| Not a user-task. |
| Procedures to be verified before launch using simulated data. |
EXAMPLES OF TECHNIQUE
| Grid phase determined by elimination of ‘wobble’ in single sub-collimator image |
| Tilt is corrected by elimination of 4-second periodicity in corrected light curves |
| Slit/thickness ratio is determined by elimination of 2-second periodicity in corrected count rates. |
| Effective slit width is determined by comparing peak Tecomet and VBC grid count rate ratios |
