Future plans

The first results of the IWVM are encouraging, the system is intrinsically stable and fast (chop 200Hz) and nothing that we have seen to date would speak against the infrared technique as being a very promising approach to phase correction of submm astronomical interferometry. Future plans include:

• procure optimised infrared filter
• upgrade to higher resolution data acquisition system (16 bit)
• now that we know the gains, chop frequency and phase of the lock-in amplifier we plan to integrate all the electronics (including chopper drive circuitry) into one module. This will greatly simplify the connections between the various components and further reduce external noise
• redesign IWVM for remote operation over the Net. We intend to construct a web based interface to the IWVM that would allow us to operate the system remotely, download data in real-time and retrieve data from an onboard archive
• with remote operation capability we are planning a 3-month campaign at the JCMT to perform sky-dips every night within $\pm$ 30 mins of the nightly radiosonde launch at 0200 HST. This will allow us to build a statistically significant database to calibrate the IWVM's in terms of mm pwv and revise, if necessary, our model atmosphere. The plan is to operate the IWVM's remotely from Lethbridge requiring minimal assistance from the JCMT staff (eg a TO fills 2 small dewars with LN2 and reboots the computer if necessary.)
• finally, build a clone of the first unit so that we can test the systems on a millimetre interferometer

Note: i) the sensitivity of the IWVM can be increased by using a larger input mirror (eg doubling the diameter to 250mm, which is still practical, increases the sensitivity by a factor of 4). ii) should the cryogenic limit of 77K be dropped, Si:As detectors would allow measurements of water vapour at the 1nm level.