Infrared Radiometer for Millimetre Astronomy

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IRMA 20 IRMA 20 µm Water Vapour Radiometer µm Water Vapour Radiometer Operations in the TMT Site Testing Operations in the TMT Site Testing Campaign Campaign Richard Querel, David Naylor, Robin Phillips, Richard Querel, David Naylor, Robin Phillips, Regan Dahl, & Brad Gom Regan Dahl, & Brad Gom Astronomical Instrumentation Group, Astronomical Instrumentation Group, University of Lethbridge, University of Lethbridge, Lethbridge, Alberta, Canada Lethbridge, Alberta, Canada Infrared Radiometer for Infrared Radiometer for Millimetre Astronomy Millimetre Astronomy irma

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irma. Infrared Radiometer for Millimetre Astronomy. IRMA 20 µm Water Vapour Radiometer Operations in the TMT Site Testing Campaign Richard Querel, David Naylor, Robin Phillips, Regan Dahl, & Brad Gom Astronomical Instrumentation Group, University of Lethbridge, Lethbridge, Alberta, Canada. - PowerPoint PPT Presentation

Transcript of Infrared Radiometer for Millimetre Astronomy

  • Infrared Radiometer forMillimetre AstronomyIRMA 20m Water Vapour Radiometer Operations in the TMT Site Testing Campaign

    Richard Querel, David Naylor, Robin Phillips,Regan Dahl, & Brad Gom

    Astronomical Instrumentation Group,University of Lethbridge,Lethbridge, Alberta, Canadairma

  • IRMA ConceptMeasure emission from water vapour lines in the 20m atmospheric window

    Band-pass includes only water vapour transitions

    Theoretical atmospheric model supported by FTS measurements from Mauna Kea (Naylor et. al. PASP 96, 167 (1984))PASP vol. 96, Feb. 1984, p. 167-173

  • AdvantagesOperates at 20 m; near the peak of the Planck function for atmospheric temperatures

    Wide bandwidth (~1 m) signal-to-noise

    Photoconductive detectors offer simplicity, high speed, sensitivity and stability

    Zero RF interference{20 m = 15 THz183 GHz = 1.6 mm

  • IRMA I (1997-1999):Water vapor sensitivity noise-limit (1 sec integration): 1.8 mm PWV at 0.5 mm PWV3.0 mm PWV at 1.0 mm PWV

    IRMA II (2000-2001): Water vapor sensitivity noise-limit (1 sec integration):0.26 mm PWV at 0.5 mm PWV0.44 mm PWV at 1.0 mm PWV

  • Current IRMA Design

  • BTRAM Output for Mauna Kea Site500 cm-1 = 20 m ~ Peak of Planck Curve

  • Steps required to convertVoltage PWV (all are possible sources of error)Voltage FluxAssume linear detector responseHot & ambient BB readingsNeed accurate temperature of BBFlux PWVAtmospheric modelSurface T & PInstrument ResponseA (Throughput)

  • Typical Calibration CycleVoltage (V)

  • BB TAmbientBB THotShutter CloseSkySkyShutter Open & BB OffTypical Calibration CycleBB OnVoltage (V)

  • For the TMT Site Testing required resolution of 0.1mm @ 1.0mm PWV, we need to know the effective BB T < 0.5K

  • Effective Temperature of Blackbody?

    Center sensor = 50.6C; Edge sensor = 45.8C

    Emission calculated for each pixel to determine the total flux emitted from the blackbody.

    Determined effective (uniform) surface T = 48.7C(Data from a 7-14m Fluke Ti-20 Thermal Imager)

  • Normal calibration (High T = 305.9 K)

  • Modified calibration (High T = 302.4 K; -3.5K)

  • 5 days of data using the Normal calibration method and the sensor temperatures

  • 5 days of data,with a modified(-3.5K) Unit 1Hot-temperature

  • IRMA Cross-Calibration

    IDL MPFIT of offset and gain between VISIR data and Gaussian-convolved BTRAM dataReduced 2 = ~0.0959

  • BTRAM

  • BTRAM FactsBlueSky Transmittance & Radiance Atmospheric ModelBuilt in IDLAvailable for Windows & LinuxLine-by-line layer-by-layer Radiative TransferAble to simulate:Atmospheres (7 primary gases)Laboratory Gas Cells (37 molecules)Transmission / Emission / OpacityBatch mode to create data-cubes

  • BTRAM FactsDistributed with HITRAN 2004 Database, any spectral database can be used

    Contains 1,734,469 spectral lines for 37 different molecules

    6 built-in FASCODE Atmospheric ProfilesMid-Latitude Summer (& Winter)Subarctic Summer (& Winter)TropicalUS Standard

  • BTRAM FactsSite-specific Atmospheric Profiles includedAntarctic SummerChajnantor WinterMauna Kea

    Customized Atmospheric Profiles can be imported as comma-delimited text (.csv)

    Output spectra can be exported as Grams compatible .spc file, or as a text file.

  • BTRAM vs. FASCODEDifficult to change FASCODE layeringBTRAM used FASCODE atmospheric layer parameters in a comparison to ensure its accuracy

  • Conclusion & Future workCalibration depends on our hot blackbody

    Uniform hotter blackbody is necessary

    Atmospheric parameters / model errors?

    Lunar spectrophotometer useful calib tool?

    What is FASCODE? MilitaryLength, user unfriendly, why do we need ULTRAM?Tell where zooming