LYRA Calibration DRB Meeting ESTEC 15 June 2007 LYRA the Lyman-alpha Radiometer onboard PROBA-2

Contents 1. Radiometric Model 2. Calibration Software 3. Flatfields 4. Off-Pointing 5. LEDs, Dark Currents 6. Integration Time 7. Stability Conclusions

1. Radiometric Model: Calibration Procedure Telemetry from spacecraft: LUMPS unpacking, decompression =>[cnt] exposure time =>[Hz] fixed Instrumental effects: variable Voltage-Frequency-Converter (VFC) =>[V] resistance =>[A] off-pointing, degradation, drift, dark current, dead time (+/- %) =>[A] Conversion to (solar) physical units: absolute radiometric calibration =>[Wm-2]

1. Radiometric Model: Selected Configurations

1. Radiometric Model: Measured Responsivity

1. Radiometric Model: Simulation of Sample Spectra

[LYRA 1-1 rest signal / nA] = * [LYRA 1-2 total signal / nA] [LYRA 1-1 pure signal / nA] = [LYRA 1-1 total signal / nA] - [LYRA 1-1 rest signal / nA] ["Lyman-alpha" solar signal / (W m-2)] = * [LYRA 1-1 pure signal / nA] 2. Calibration Software: Example Lyman-alpha Channel 1-1

[LYRA 1-4 pure signal / nA] = [LYRA 1-4 total signal / nA] ["Zirconium" solar signal / (W m-2)] = interp[LYRA 1-4 pure signal / nA] 2. Calibration Software: Example Zirconium Channel 1-4

3. Flatfields: Orientation

3. Flatfields: Solar Beam on Detector Plane

4. Off-Pointing: Simulation e.g. spatial responsivity channel 1-3:

4. Off-Pointing: Consequences Simulation of off-pointing effects -25% with 1 degree off-pointing -1% with 5 arcmin off-pointing (jitter?) Negligible with 10 or 20 arcsec off-pointing Generalize for possible roll TBD Details TBD Commissioning phase Confirm simulation results with off-pointing tests Establish nominal pointing together with SWAP Determine functional relationship between off-pointing and necessary deduction for calibration (fixed table)

from test with heads 1 and 2. Visual LEDs commanded approx. every 270 ms, data sampled with 20 ms integration time 5. LEDs, Dark Currents: Sample Pulses

Averaged pulses, and fits of their decay phase, from test with heads 1 and 2 MSM and AXUV detectors can all be fitted well; time constants are similar. PIN detectors cannot be fitted this way. Final averages or fitted plateau values can be used to estimate dark current or LED response, resp. 5. LEDs, Dark Currents: Estimates

6. Integration Time: Fluctuations Long integration times (> 0.2 s): (Ir)regular fluctuations, 0.05% - 0.1% around trend

6. Integration Time: Random Noise Short integration time (0.01 s): Gaussian fit, st.dev. (4.75) / signal (1675) = 0.28% e.g. channel 3-3: / = 0.15%

6. Integration Time: Dead Time Correction dead time: microseconds max. correction (at 0.01 s integration time): 0.1%

7. Stability: Drift in (MSM-) Channel 1-3

Conclusions Calibration concept, software: basically ready Updates: latest test results, new sample spectra, details Cross-calibration during commissioning phase, degradation?