IRMA 20µm 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 Infrared Radiometer for Millimetre Astronomy irma

WVR Workshop, Wettzell, Germany, October 10, IRMA Concept Measure emission from water vapour lines in the 20μm atmospheric windowMeasure emission from water vapour lines in the 20μm atmospheric window Band-pass includes only water vapour transitionsBand-pass includes only water vapour transitions Theoretical atmospheric model supported by FTS measurements from Mauna Kea (Naylor et. al. PASP 96, 167 (1984))Theoretical atmospheric model supported by FTS measurements from Mauna Kea (Naylor et. al. PASP 96, 167 (1984)) PASP vol. 96, Feb. 1984, p

WVR Workshop, Wettzell, Germany, October 10, Advantages Operates at 20 μm; near the peak of the Planck function for atmospheric temperaturesOperates at 20 μm; near the peak of the Planck function for atmospheric temperatures Wide bandwidth (~1 μm) … ↑ signal-to-noiseWide bandwidth (~1 μm) … ↑ signal-to-noise Photoconductive detectors offer simplicity, high speed, sensitivity and stabilityPhotoconductive detectors offer simplicity, high speed, sensitivity and stability Zero RF interferenceZero RF interference { 20 µm = 15 THz 183 GHz = 1.6 mm

WVR Workshop, Wettzell, Germany, October 10, IRMA I ( ): Water vapor sensitivity noise-limit (1 sec integration):Water vapor sensitivity noise-limit (1 sec integration): 1.8  m PWV at 0.5 mm PWV1.8  m PWV at 0.5 mm PWV 3.0  m PWV at 1.0 mm PWV3.0  m PWV at 1.0 mm PWV IRMA II ( ): Water vapor sensitivity noise-limit (1 sec integration):Water vapor sensitivity noise-limit (1 sec integration): 0.26  m PWV at 0.5 mm PWV0.26  m PWV at 0.5 mm PWV 0.44  m PWV at 1.0 mm PWV0.44  m PWV at 1.0 mm PWV

WVR Workshop, Wettzell, Germany, October 10, Current IRMA Design

WVR Workshop, Wettzell, Germany, October 10,

7

8

9

10

WVR Workshop, Wettzell, Germany, October 10,

WVR Workshop, Wettzell, Germany, October 10, BTRAM Output for Mauna Kea Site 500 cm -1 = 20 μm ~ Peak of Planck Curve

WVR Workshop, Wettzell, Germany, October 10, Steps required to convert Voltage → PWV (all are possible sources of error) Voltage → Flux Assume linear detector responseAssume linear detector response Hot & ambient BB readingsHot & ambient BB readings Need accurate temperature of BBNeed accurate temperature of BB Flux → PWV Atmospheric modelAtmospheric model Surface T & PSurface T & P Instrument ResponseInstrument Response AΩ (Throughput)AΩ (Throughput)

WVR Workshop, Wettzell, Germany, October 10,

WVR Workshop, Wettzell, Germany, October 10, Typical Calibration Cycle Voltage (V)

WVR Workshop, Wettzell, Germany, October 10, BB T Ambient BB T Hot Shutter Close SkySky Shutter Open & BB Off Typical Calibration Cycle BB On Voltage (V)

WVR Workshop, Wettzell, Germany, October 10,

WVR Workshop, Wettzell, Germany, October 10,

WVR Workshop, Wettzell, Germany, October 10, For the TMT Site Testing required resolution of 1.0mm PWV, we need to know the effective BB T < 0.5K

20 Effective Temperature of Blackbody? Center sensor = 50.6°C; Edge sensor = 45.8°CCenter sensor = 50.6°C; Edge sensor = 45.8°C Emission calculated for each pixel to determine the total flux emitted from the blackbody.Emission calculated for each pixel to determine the total flux emitted from the blackbody. Determined effective (uniform) surface T = 48.7°CDetermined effective (uniform) surface T = 48.7°C (Data from a 7-14μm Fluke Ti-20 Thermal Imager)

WVR Workshop, Wettzell, Germany, October 10, Normal calibration (High T = K)

WVR Workshop, Wettzell, Germany, October 10, Modified calibration (High T = K; -3.5K)

WVR Workshop, Wettzell, Germany, October 10, days of data using the “Normal” calibration method and the sensor temperatures

WVR Workshop, Wettzell, Germany, October 10, days of data, with a modified (-3.5K) Unit 1 Hot-temperature

WVR Workshop, Wettzell, Germany, October 10, IRMA Cross-Calibration IDL MPFIT of offset and gain between VISIR data and Gaussian-convolved BTRAM dataIDL MPFIT of offset and gain between VISIR data and Gaussian-convolved BTRAM data Reduced Χ 2Reduced Χ 2 = ~ = ~0.0959

WVR Workshop, Wettzell, Germany, October 10, BTRAM

WVR Workshop, Wettzell, Germany, October 10, BTRAM Facts BlueSky Transmittance & Radiance Atmospheric ModelBlueSky Transmittance & Radiance Atmospheric Model Built in IDLBuilt in IDL Available for Windows & LinuxAvailable for Windows & Linux Line-by-line layer-by-layer Radiative TransferLine-by-line layer-by-layer Radiative Transfer Able to simulate:Able to simulate: –Atmospheres (7 primary gases) –Laboratory Gas Cells (37 molecules) –Transmission / Emission / Opacity –Batch mode to create data-cubes

WVR Workshop, Wettzell, Germany, October 10, BTRAM Facts Distributed with HITRAN 2004 Database, any spectral database can be usedDistributed with HITRAN 2004 Database, any spectral database can be used Contains 1,734,469 spectral lines for 37 different moleculesContains 1,734,469 spectral lines for 37 different molecules 6 built-in FASCODE Atmospheric Profiles6 built-in FASCODE Atmospheric Profiles –Mid-Latitude Summer (& Winter) –Subarctic Summer (& Winter) –Tropical –US Standard

WVR Workshop, Wettzell, Germany, October 10, BTRAM Facts Site-specific Atmospheric Profiles includedSite-specific Atmospheric Profiles included –Antarctic Summer –Chajnantor Winter –Mauna Kea Customized Atmospheric Profiles can be imported as comma-delimited text (.csv)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.Output spectra can be exported as Grams compatible.spc file, or as a text file.

WVR Workshop, Wettzell, Germany, October 10, BTRAM vs. FASCODE Difficult to change FASCODE layeringDifficult to change FASCODE layering BTRAM used FASCODE atmospheric layer parameters in a comparison to ensure its accuracyBTRAM used FASCODE atmospheric layer parameters in a comparison to ensure its accuracy

31

WVR Workshop, Wettzell, Germany, October 10,

WVR Workshop, Wettzell, Germany, October 10, Conclusion & Future work Calibration depends on our hot blackbodyCalibration depends on our hot blackbody Uniform “hotter” blackbody is necessaryUniform “hotter” blackbody is necessary Atmospheric parameters / model errors?Atmospheric parameters / model errors? Lunar spectrophotometer useful calib tool?Lunar spectrophotometer useful calib tool?