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ENVISAT Calibration Review MIPAS. Presentation: H. Nett ESTEC / EOP-PPP R. Gessner, P. Mosner Astrium GmbH M. Sanchez Gestido ESTEC / EOP-PPS G. Perron ABB BOMEM Inc. M. Birk DLR-IMF Th. v. Clarmann FZ-IMK A. Burgess ESTEC / EOP-PPP B. Carli IFAC – CNR

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ENVISAT Calibration Review

MIPAS

Presentation:

H. Nett ESTEC / EOP-PPP

R. Gessner, P. Mosner Astrium GmbH

M. Sanchez Gestido ESTEC / EOP-PPS

G. Perron ABB BOMEM Inc.

M. Birk DLR-IMF

Th. v. Clarmann FZ-IMK

A. Burgess ESTEC / EOP-PPP

B. Carli IFAC – CNR

A. Dudhia Univ. of Oxford



LOS mispointing analysis

Orbits # 2622 & 2623 (31 Aug)

Scenario:

  • 3…7 passages per IR star

  • determination of star arrival time through cross-correlation with a reference signal

  • co-addition of individual passages to enhance SNR

    Model:

    Del = A0, pitch+A1, pitch * cos(worb*t - Fpitch)

    Daz = A0, roll +A1, roll * cos(worb*t - Froll)

    [worb = 2*p/Torb (Torb = 6036 s)]


LOS mispointing characterisation

Cross-correlation analysis:

  • sampling at 10 ms ( ~ 0.6 mdeg)

  • ‘peak find’ after co-addition

  • parabolic fit

  • search radius: 750 ms (+/- 45 mdeg pitch)

  • weighting: D1 = 1, D2 = 0.1

    In example (RAFGL 4292):

    Tanx = 1612 s

    Dt = -415 ms

    da = 24.9 mdeg

    total # stars: 62 (2 orbits)


LOS analysis: results

Comparison: LOS calibration in orbits 1522 & 1523 (24-AUG-2002)

A0, pitch = 17.9 mdeg A0,roll = 0.6 mdeg

A1,pitch = 10.7 mdeg A1,roll = 1.7 mdeg

vFpitch = 72.1 deg Froll = -103 deg


  • Recent corrections applied:

  • Mission planning:- correction of inconsistencies in timeline & pointing parameters computation in ESOC and IECF/MICAL - inclusion of ESU misalignment characterisation data

  • LOS calibration s/w. New options

    - ‘de-activate’ signals with too low SNR

    - fit 2 unknowns (bias mispointing for pitch&roll) instead of 6 (bias + harmonics for pitch&roll)

  • Commanding: increased analog gains for D1/D2 to max. values (different PAW tables used for measurement mode and LOS)


LOS mispointing - Conclusions

  • acquisition of IR sources in channels D1/D2; >10 bright IR sources visible

  • ratio 0.1 applied in weighting D2/D1 due to high noise in D2

  • converging NLS fit analysis for roll & pitch (rearward geometries only)

  • pitch error: +2 mdeg … +28 mdeg -> tangent height correction: ~ -1.7 km

    => initial acquisition & pointing knowledge (incl. correction) within budgets

    to be done:

    - verify stability of LOS mispointing over long periods (> 1 month)

    - consolidate IR star catalogue (remove sources with too low SNR)


IF14: FOV check using point-source IR target [1/3]

Approach:

  • Sensing of a point-like IR source through scanning of elev. viewing angle

  • use of Measurement mode (moving Int slides); raw data transmission

  • record AC signal when in all 8 detector channels simultaneously while target passes through FOV (requires on-board recording (RW -> SSR2))


IF14: FOV check [2/3]

  • Selected target: Mercury (acquisition in orbit 1808, 5 July 2002)

  • Sensing start time: ~ Tanx + 4573 s


IF14: FOV check [3/3]

Sampling rate in raw mode: v_samp = 76066 samples/s

v_los (el) = 1.35 deg/s (reached after approx. 0.375 s)

v_pitch ~ -60 mdeg/s (approx. velocity of Mercury)

effective velocity of Mercury's trajectory: v_eff ~ 1.29 deg/s

=> ‘angular’ sampling rate: 17e-6 deg/sample

Initiat tangent height: ~ - 60 km

‘travel’ during acceleration phase: ~ 0.253 deg



IF14: FOV check: detectors C1, C2, D1, D2

Raw signal analysis

C1, C2:

POI1/2=-23.8/21.8 mdeg

(D = 45.6 mdeg)

D1, D2:

POI1/2=- 23.4/23.1 mdeg

(D = 46.5 mdeg)

[POI = point of inflection]


IF14: FOV check: detectors A1, A2, B1, B2

Raw signal analysis

A1, A2:

POI1/2=-23.3/21.7 mdeg

(D = 45.2 mdeg)

B1, B2:

POI1/2=- 23.5/21.9 mdeg

(D = 45.4 mdeg)

[POI = point of inflection]



IF14: FOV check - Conclusions

  • IR signal clearly visible in all detector channels (SNR highest in channels D1/D2)

  • Signal rise fully resolved. Therefore, comparison of POI possible

  • POI positions agree within ~1.3 mdeg for all 8 detector channels!

  • No evidence for asymmetries in elevation patterns or for relative misalignment of individual channels

    future work:

    Further analysis of FOV shapes using of ASP response characteristics


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