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Pre-launch calibration plan Requirements and plans for in-orbit calibration

Pre-launch calibration plan Requirements and plans for in-orbit calibration. Frank Helmich/ David Teyssier on behalf of the HIFI calibration group. Calibration Group. HIFI Calibration is a group effort involving many people.

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Pre-launch calibration plan Requirements and plans for in-orbit calibration

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  1. Pre-launch calibration planRequirements and plans for in-orbit calibration Frank Helmich/ David Teyssier on behalf of the HIFI calibration group

  2. Calibration Group • HIFI Calibration is a group effort involving many people. • For this presentation Volker Ossenkopf, David Teyssier, Anthony Marston, Carsten Kramer, Marinus Jochemsen, Tully Peacock, Pieter Dieleman, Willem Jellema, Raphael Moreno provided the main results Calibration requirements and plans

  3. Overview • Calibration frame work • Intensity • Beam • Frequency • Error Budget • Most important contributions • Internal to HIFI • Pointing • Physical models of primary calibrators • Compliance with AIV/ILT • PV plan • Discrepancies Calibration requirements and plans

  4. Calibration Frame Work - Intensity • Intensity requirement: Accuracy 10%, Goal 3% • HIFI has large IF -> Need for separate calibration of the 2 side-bands • Standing waves are expected to occur in the paths between LO, mixer and sky • -> Complete new frame work: • Load calibration • OFF calibration • Source Calibration • HIFI is special compared with ground-based telescopes because the atmosphere is lacking -> We will be able to use a 3-point calibration • Cold load, hot load, blank sky Calibration requirements and plans

  5. Framework: Intensity calibration • Allows for determination of bandpass, receiver noise and forward efficiency (lxTtel) simultaneously • Higher accuracy than standard two-point calibration • Analysis of the spectral ripple in the blank sky measurement (OFF) allows to fit standing waves using a model • Separate calibration terms for both side-bands where coefficients do not necessarily agree Calibration requirements and plans

  6. Intensity calibration • Calibration coefficients • On-ground: Side-band ratio (Gssb)and coupling coefficients to the thermal loads (c and h) • Load calibration = hot-cold measurement provides the bandpass (rec) and the receiver temperature (Trec) • Measurement on the blank sky (OFF) provides the forward efficiency (l) and information on the superimposed standing waves in both side bands (wssb and wisb) • Standing waves can modify the contribution from: • The astronomical source • The telescope • The receiver Calibration requirements and plans

  7. Intensity calibration • Source calibration • Depending on AOT different schemes will be used • These are all based on hot/cold for basic intensity scale and use reference schemes for stable measurements (and/or flat base-lines) • The driving force behind the applied schemes are: • Stability • Optimal use of observing time • See intensity calibration document and all documents on observing modes Calibration requirements and plans

  8. Intensity calibration • Measure internal calibrator radiometric properties • Measure internal calibrator coupling • Side-band ratio (see frequency properties) • Standing wave properties Calibration requirements and plans

  9. Intensity calibration – current knowledge • HBB Coupling (left 600 GHz H; right 570 GHz V) • Coupling almost 100%, but with ripple Calibration requirements and plans

  10. Intensity Calibration – Current knowledge • CBB Coupling (left 600 GHz H; right 570 GHz V) Calibration requirements and plans

  11. Frame Work – Beam Calibration • Beam calibration is needed for: • Determining the focal plane – pointing • Determining the main beam & aperture efficiency – needed for absolute calibration • Measuring the beam profile (PSF) – to calculate, in more detail, the coupling to astronomical sources 900 GHz calculation with blocking by hexapod and secondary Calibration requirements and plans

  12. Focal plane • All mixer-beams (except band 6 high) are measured • Their position on M2 will be checked • In-flight the beams will be measured with respect to Herschel’s bore-sight as a function of chopper position (note that the load positions also have to be determined as a function of chopper position) • Accurate determination follows from dedicated calibration observations • Checks will have to be made when chopper electronics will age Calibration requirements and plans

  13. Aperture and Main Beam Efficiency • These are the parameter which ties knowledge of calibrated astrophysical objects to the intensity scale provided by the hot and cold load • It cannot be measured on the ground since it involves the whole telescope • Simple calculations show: Calibration requirements and plans

  14. Simple calculations Predictions from framework documentcurrently based on simple approach Calibration requirements and plans

  15. Quasi-optical modelling (NUIM) • In conjunction with SRON NUIM are undertaking a comprehensive Quasi-optical Analysis of HIFI, as part of an agreed work package description. • This involves a complete optical analysis of all optical paths within HIFI. • Sky Path • LO Path • Calibration Source Optics • These calculations are very important for assessing beam quality (in HIFI and to out-side) and understanding standing waves Calibration requirements and plans

  16. QO or Physical Optics Calculation • Far field beam patterns have been obtained in “all” bands at two or more frequencies by two methods: • Physical optics beam propagation from the horns/lens antennas through the complete optical system to the sky. • From the illumination of the telescope secondary mirror rim plane, phase flattening and FFT. • The pattern from method 2 can be checked against the pattern from method 1. • Physical optics is not used to get the telescope aperture field directly because of computation size – use method 2, mask the beam pattern and scale to the telescope size. • Results will be presented for channels 1H and 4H only. Calibration requirements and plans

  17. Results from NUI (480 GHz) • The contour plot shows the illumination of the telescope secondary mirror with an edge taper varying between 8.5 dB and 10.5 dB. • The colour plot shows the intensity distribution in the plane of the telescope rim masked for the primary mirror with obscuration. Calibration requirements and plans

  18. Far-field pattern (480 GHz) • Plot of the PO and FFT far field beam patterns showing good agreement gives confidence in use of FFT method. Calibration requirements and plans

  19. PO Calculation results 480 GHz • Pointing: 5.2 arcsec. from geometric design. • Pointing offset V/H: 5.6 arcsec. (!) • HPBW: 42.5 arcsec. • Main beam efficiency: 78.9% • Maximum side lobes: -20dB below peak. • These results are in good agreement with the expected values. Comment: • strut scattering has not yet been included in the model. • An attempt was made but the computation size was too great, even at this lowest end of the HIFI frequency range. • Can modify the mask and treat strut scattering by the FFT. • PO calculations include lab measurements made after the diplexers only for bands 1 and 2. Poor data quality for data taken above the focal plane. Calibration requirements and plans

  20. Calculation results (1122 GHz) • Pointing: 2.3 arcsec. from geometric design. • Pointing offset V/H: 4.0 arcsec. (Factor=4.8!!) • HPBW: 19.0 arcsec. • Main beam efficiency: 76.5% • Maximum side lobes: -21dB below peak. • These results are in good agreement with the expected values. Comment: • strut scattering has not yet been included in the model. • At these frequencies it is reasonable to expect very close agreement with the geometric design predictions. Calibration requirements and plans

  21. Comparison PO and framework calculations Edge Taper (on M2): PO Simple(Plan) 480 GHz: 8.5-10.5 11dB 1122 GHz:11.0-11.5 11dB HPBW: PO Simple 480 GHz: 42.5'' 47.1'' 1122 GHz:19.0'' 20.2'' Potential Problems: - edge tapers deviate from 11dB - illumination not axial symmetric - pointings V/H deviate somewhat Plans: - struts yet missing in PO Calculation(masking) - PO calculation for all bands at the frequencies listed in the framework (on the way) - Documentation Main Beam Efficiencies: PO Simple (1D,rms=0) 480 GHz: 78.9% 76% 1122 GHz:76.5% 76% Calibration requirements and plans

  22. Beam calibration – current knowledge • Band 5 H Power plot (left) and phase plot (right) • Not including further pictures because they all look alike, band 5H, 5V and 4H, 4V Calibration requirements and plans

  23. Calibration Frame Work • Frequency Properties • Frequency calibration measurements address both the calibration of the RF frequency itself and of the frequency resolution (also called here line profile) provided by the instrument. • Effective instrument spectral response = combination of several spectral element responses along the detection chain. • The HIFI instrument consists of the Focal Plane subsystem (FPU), the Local Oscillator subsystem (LO), the Wide Band Spectrometer (WBS), the High Resolution Spectrometer (HRS) and the Instrument Control Unit (ICU). • Each of the subsystems add to the final instrumental line profile Calibration requirements and plans

  24. Frequency properties • Determine if line is in the right place • Through WBS-comb, HRS coupling to master oscillator, “known” lines • Is the spectral resolution as expected? • Fluctuation bandwidth, FWHM of instrumental line response -> on ground and with ref. spectra • Most data will come from stability measurements • Platforming determination • From stability measurements • Spectral purity • Spurious signals – in-flight and on-ground • Spurious responses – ONLY on-ground • Side-band ratio • Gas cell on-ground and check in-flight through small spectral survey Calibration requirements and plans

  25. Frequency Properties - Current knowledge • DM/QM ILT 2005 for HRS and WBS with and without a pumped mixer, but no continuous measurements were performed with the QM-LO: • Bandwidth fluctuation measurement: • Spectroscopic stability considerably worse than specified for WBS: the WBS shows a reduced stability due to thermally instable environment. • The HRS approximately fulfills the stability spec, but relatively strong platforming effects and its fluctuation bandwidth is wider than expected. HRS tests in wide band mode. • BUT the number of tests performed with the QM-LO is insufficient to draw definite conclusions. Calibration requirements and plans

  26. Frequency Properties – Current knowledge • Overall spectroscopic stability time over the 4 GHz IF bandwidth is reduced to about 30s => problem for PSW obs. modes. • WBS stability very sensitive to the temperature • thermal stability within the satellite? • better isolation of the WBS • HRS platforming and spurious • Sideband ratio measurement: DM, and 466-492 GHz only. Calibration requirements and plans

  27. Frequency Properties – Current knowledge • Spurious signals/responses QM tests Source off Source on Calibration requirements and plans

  28. Frequency Properties - Current knowledge • Sideband ratio measurement (2004) over the mixer band: DM, and 466-492 GHz only. • Gain around 1 • FTS scan mixers Calibration requirements and plans

  29. Frequency Properties – Current knowledge Side-band ratio Calibration requirements and plans

  30. Frequency Properties –spectral scan Calibration requirements and plans

  31. Error Budget • Use a general scheme for calibration • Derive exact equations for observing scheme • Estimate errors and apply these to the general scheme Calibration requirements and plans

  32. Error Budget • Goals of the Error Budget • To indicate the total error for HIFI. • To identify which calibration parameters need highest accuracy. • Help clarify tests for ILT and PV phases. • To provide recipe for determining health of HIFI • Original error budget estimates were made at 500GHz and 1.9THz. The error budget is frequency dependant. • The error estimate is made based on observations for calibration purposes on Uranus. Calibration requirements and plans

  33. Error budget @ 500 GHz Calibration requirements and plans

  34. Error Budget at 1900 GHz Calibration requirements and plans

  35. Error Budget contributions • HIFI internal • Side-band ratio • Hot load coupling • Cold load coupling • Hot load temperature • Cold load temperature • All these will be measured: 1-3 ONLY on-ground, temperatures (4 & 5) also in-orbit Calibration requirements and plans

  36. Error Budget contributions • Pointing – goal value is needed ! – likely possible? • Especially APE comes into play, for maps SRPE also matters Calibration requirements and plans

  37. Error Budget contributions • Physical models of the prime calibrators • Models needed for Uranus, Mars, and the 5 brightest asteroids (Mueller) • Models created in Herschel context Calibration requirements and plans

  38. Compliance with AIV/ILT • Side-band ratio – ILT Spectral tests nr. 5 • Hot and cold load coupling – FP S/S & ILT Radiometry tests • Hot and cold load temperatures – standard measurement • This assumes HIFI to be a black box and doesn’t treat disturbing effects • ILT has a series of tests characterizing these effects • Also checks are made for compliance with instrument specification Calibration requirements and plans

  39. Compliance with AIV/ILT • Beam pattern measurements • IF chain characterization • Spectral tests • Spurious signals • Spurious response • Frequency response function • Continuum linearity • Line linearity • Gas cell • Standing waves • Diplexer performance • Stability • IF system • HIFI Calibration requirements and plans

  40. PV plan • PV plan consists of 4 sections, closely following calibration frame work and ILT • Internal parameters – FT and ILT IF; radiometry, stability • Characterization of beams and pointing – ILT beam and measurements of primary calibrators • Spectral properties – ILT spectral tests • Limits of the instrument – ILT (stability) • AOT verification • Current estimates are very inaccurate (AOT implementation lagging behind) • Assuming: • Well calibrated loads • Pointing good • Assuming spurious responses/signals measured in ILT (Signals 11 days ILT; Responses 24 days) • AOT verification is fast Calibration requirements and plans

  41. Compliances & Discrepancies • Coupling to loads – value?/ripples solution to be found • Side-band ratio will be measured – Complete range? and with sufficient accuracy? • Cold and hot load temperatures - OK • Pointing - likely OK(?) • Models of primary calibrators – assumed to be OK, but on the edge • Planned tests of Frequency response function - OK • Planned tests of (internal) Spurious signals – MISSING/marginally ok • Planned test of (ext. Generated) Spurious responses – marginally OK/MISSING • Planned tests of Stability & linearity - OK Calibration requirements and plans

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