16 June 2005 Measuring Phase Variations at the SMA Using the IRMA Water Vapour Monitor Robin Phillips James DiFrancesco Tyler Bourke David Naylor

16 June 2005 IRMA I & II IRMA II: Test measurements: Dec 2000 – Mar 2001 Water vapor resolution (1 sec integration): –0.26  m pwv at 0.5 mm pwv –0.44  m pwv at 1.0 mm pwv IRMA I: Development: 1997 – 1999 Test measurements: Dec 1999 Water vapor resolution (1 sec integration): –1.8  m at 0.5 mm pwv –3.0  m at 1.0 mm pwv Developed in Lethbridge (student project) Tested on JCMT Situated outside membrane Mainly used in skydip mode

16 June 2005 IRMA I & II

16 June 2005 IRMA I Results Data collected in December, 1999 Water vapor resolution (1 sec integration time): –1.8  m at 0.5 mm pwv –3.0  m at 1.0 mm pwv Stared with 183 GHz WVM –High degree of correlation with 183 GHz measurements

16 June 2005 IRMA Advantages Operates at 20 μm; near the peak of the Planck function for atmospheric temperatures Wide bandwidth => better signal-to-noise Photoconductive detectors offer simplicity, high speed, sensitivity and stability Small size and mass, low maintenance Low complexity => high reliability, low cost Zero RF interference 20 µm = 15 THz 183 GHz = 1.6 mm

16 June 2005 IRMA III Features Compact design to maximise possible mounting options Cryogen-free Stirling-cycle refrigerator Minimisation of moving parts for mechanical longevity Sealed modular construction to resist harsh environmental conditions Ethernet-based onboard computer to simplify communications Fully remote operation Performance target: –10 m beam width at 1 km –Resolution better than 1 µm PWV in 1 s –Minimum 10 Hz sample rate

16 June 2005

Hawaii tests ~3 weeks initial testing outside JCMT Moved to SMA Operated for 4 months

16 June 2005

Current and future work Contracted by Gemini to upgrade system and operate loaner for 3-6 months. TMT project has purchased 3 units for site testing in Chile, Mexico (and maybe Hawaii). Las Campanas observatories have purchased one unit (with a loaner until we can build one). Collaboration with AASTINO project to site test Dome C.

16 June 2005

Data reduction steps Detector signal goes to ADC which provides onboard Rabbit micro with ‘counts’ representing voltage. Voltage needs converting to spectral power using periodic black body measurements –Conversion varies with: Cooler base temperature Internal box temperature Sepectral power needs converting to pwv using radiative transfer model of atmosphere. –Requires atmospheric profile –Varies with ambient temperature and pressure

16 June 2005 Voltage during calibration sequence

16 June 2005 Black body temperature during calibration

16 June 2005

SMA data: Peak-to-peak ~200deg phase shifts (obs freq 230GHz) IRMA data: 0.1mm pwv => 0.6mm path => 155deg phase shifts

16 June 2005

SMA data: Peak-to-peak ~200deg phase shifts (obs freq 230GHz) IRMA data: 0.1mm pwv => 0.6mm path => 155deg phase shifts