Do the operators flying single pilot NVG carry out landings to unrecced LS or do they fly HLS to HLS and just use the goggles for terrain clearance and lookout?
They do both. Some countries and organisations apply differing limitations, but most adhere to the international standard in some form: For operations below 500 ft, or to/from unpreparred HLS then two crew are required to be using, current, and qualified on NVG (one of them the PIC). At our operation we use a pilot and crewman mix. The crewman does the same ground school and has a three hour flight training course. All crew are limited to landing in an area no smaller than 40m X 40m until they gain sufficient experience (at least 50 hours).
If they are carrying out landings to unrecced sites do they use white light (nightsun or equivalent) to recce for wires and is the crewman on NVG as well?
White light use is mandatory at our organisation and a pilot steerable white light is minimum equipment for Australian NVG ops. We absolutely use white light - regardless of illumination or cultural lighting. It is a fundamentally different proposition than our old military ops.
For a visibility estimate do you work on the observed Met vis or do you try and judge 5000m (or 3000m) visually on goggles?
This is done so differently in different countries. In Australia, you have to be able to comply with NVFR - that means observed met has to be 5000m plus. When conducting NVG flight, you have to be able to see the unlit terrain 5000m ahead (i.e. judged by pilot using NVG). This is because viz doesnt equal ground illum and why we captured both aspects (wx and illum) with one limit. It is not uncommon in the Northern Territory for example to have unlimited viz but be so dark as to not meet the 5000m on NVG. In that instance we simply fly at 1000 - 1500 ft and descend only upon arrival at the scene or HLS.
If you encounter a large shower (CB for example) and the vis comes below 5000m, is a climb to LSALT the best option? I only ask this because according to your rules I wouldn't have been able to complete a hospital transfer the other night - although we were at 500' agl, the vis came down regularly to 1000 - 1500m and with large showers and forecast CB activity, an instrument abort to safety alt wasn't an option.
In Australia we have three options for encountering low viz: turn back to regain, climb to LSALT or land and wait. I cannot comment on your operation as I believe that you know your area best. In the scenario you painted, NVG flight would not be permitted in Australia. You may use wx reduced to no less than scattered cloud below 1000 ft 2nm either side of the acft path if you are fully IFR capable.
The only way we could have considered your situation is to declare a mercy flight. This is a good system as it requires a detailed risk analysis of the situation prior to conducting it, and it seeks to reduce the emotional responses that traditionally leads to many such flights (and pprune arguements later!!).
The light levels graph may not take into account cultural lighting but it still gives you a good idea of what the real light levels are going to be when you get away from the built up areas - for us working over the sea and in fairly rural areas of the UK it is a much better guide than visibility.
As above, NVG ground viz is not met viz. NVG ground viz is determined by so many variables that it is not possible to predict the actual illumination based on the chart - hence discarding it as a go/no go. Variables include (but are not limited to) relative humidity, prescence and thickness and hieght of cloud, smoke areas, dust and other obscurants, haze layers and polution, rain, moon angle moon size, moon orbit phase, waxing or waning moon, presence of cultural lighting, etc, etc, etc.
By requiring that the pilot can see 5000m into unlit terrain, we capture all those variables in one hit.