LYRA the Lymanalpha Radiometer onboard PROBA2 LYRA Calibration

LYRA the Lyman-alpha Radiometer onboard PROBA-2 LYRA Calibration: Ongoing Efforts and Problems SCSL Meeting Bern 18 -19 April 2007

Contents n n I. Recapitulation II. New Tests III. Flatfields and Off-Pointing IV. Calibration Procedures

I. Recapitulation n Choice of filters and detectors n Simulation with solar spectra n Configuration selected (12 channels) n BESSY campaigns: for each channel… n n n Linearity Stability, drift LEDs, dark current Spectral responsivity, expected signal and purity Homogeneity, flatfield n Recommendation n Head 2 nominal, Head 1 weekly, Head 3 monthly

II. New Tests n Cadence, response time n n n Sinus wave (approx. 20 s) detected in one channel Noise (below 200 ms) analyzed Detailed report TBD n BESSY campaign February 2007 n n Drift, saturation (incl. slit variation, interruption) Additional flatfields for channels 1, 2, (3) Responsivities updated (more reliable for Al-channels) Detailed analysis TBD n Pulsed LED n n Estimate dark currents, LED responses, degradation? Overcome drift effects?

Sample pulses from test with heads 1 and 2. Visual LEDs commanded approx. every 270 ms, data sampled with 20 ms integration time

Averaged pulses, +/- standard deviation, from test with heads 1 and 2. Differences in behavior between MSM (1 -1, 1 -3, 2 -1, 2 -3, 2 -4), AXUV (1 -4), and PIN (1 -2, 2 -2) detectors.

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.

Consequences n Tests during commissioning phase (e. g. dark current, vis. LED, uv. LED, vis+uv. LED, constant and pulsed, with door closed, later with door open) n LED and dark current analysis in frequency units n Telemetry requirements

III. Flatfields and Off-pointing e. g. spatial responsivity channel 1 -3:

Consequences n Unlike imager: only beam, integrated n Simulation of off-pointing effects n n n -25% with 1 degree off-pointing -1% with 5 arcmin off-pointing Negligible with 10 arcsec off-poiting Generalize for possible roll TBD Details TBD n Commissioning phase n n n 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)

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

Selected configurations: filter detector nominal FWHM measured 1 -1 Ly XN 1 -2 Herzberg 1 -3 Aluminium 1 -4 Zr (300 nm) + + MSM 12 PIN 10 MSM 11 AXUV 20 D 121. 5 +/- nm 200 -220 nm 17 -80 nm 1 -20 nm 116 -126 nm 197 -218 nm (1)-2. 4, 17 -35 nm (1)-1. 3, 6 -15 nm 2 -1 Ly XN 2 -2 Herzberg 2 -3 Aluminium 2 -4 Zr (150 nm) + + MSM 21 PIN 11 MSM 15 MSM 19 121. 5 +/- nm 200 -220 nm 17 -80 nm 1 -20 nm 116 -126 nm 199 -219 nm (1)-1. 4, 17 -27 nm (1)-1. 3, 6 -12 nm 3 -1 Ly N+XN 3 -2 Herzberg 3 -3 Aluminium 3 -4 Zr (300 nm) + + AXUV 20 A PIN 12 AXUV 20 B AXUV 20 C 121. 5 +/- nm 200 -220 nm 17 -80 nm 1 -20 nm 116 -126 nm 198 -219 nm (1)-2. 4, 17 -35 nm (1)-1. 3, 6 -15 nm

[LYRA 1 -1 rest signal / n. A] = 0. 015 * [LYRA 1 -2 total signal / n. A] [LYRA 1 -1 pure signal / n. A] = [LYRA 1 -1 total signal / n. A] - [LYRA 1 -1 rest signal / n. A] ["Lyman-alpha" solar signal / (W m-2)] = 0. 0975 * [LYRA 1 -1 pure signal / n. A]

Consequences n Get more spectral samples, enhance S/W n Soft X-ray contamination in (Al-)channels 3 n n n Absolute radiometric calibration vs. information from hi-res time development? Flags in data products? Remarks from Don Mc. Mullin n ASCII, FITS, IDL-restore files? n Commissioning phase n n n Degradation test Cross-calibration with LYRA heads Cross-calibration with other instruments (SWAP? SUMER? ? )