By any measure, Friday will prove a critical day in the search for Prabhdeep Srawn.
If the missing bushwalker has survived 11 nights in the remote wilderness of the Kosciuszko National Park, bolstered efforts to find body heat using forward imaging infrared scanners could prove critical.
If the 25-year-old Canadian Armed Forces reservist has perished in snow and sub-zero temperatures, the inevitable decision to move from rescue to recovery could take place today.
Any experienced bushwalker knows that the closer together contour lines on a map are, the thicker and more difficult the terrain.
Rescuers believe Mr Srawn may have set out to walk from Charlottes Pass Village to walk to Mount Kosciuszko, walking the popular trail by a reverse route and getting lost near the 2142m Carruthers Peak.
Straying from the track or getting lost in the knee-high snow which fell on the day he set out would see Mr Srawn quickly end up in the thick contours between the nearby Mt Sentinel and Lady Northcote’s Canyon.
The area around the nearby Geehi River is where missing walkers have been found in the past.
One experienced bushwalker told Fairfax Media parts of the area are so rugged, a search party could pass 5 metres from another person without knowing they were there.
Thursday’s search efforts focused around the canyon, with a second day of reports that a male voice – possibly calling “help” – had been heard.
Part of the aerial search closed in on creek beds and waterways near the Guthega Dam.
Reports of voices and a sustained on-the-ground presence of between 20 and 30 SES, police and National Parks and Wildlife officers gave hope to the Srawn family who monitored the activity via phones and police radio in Jindabyne.
Speaking for her parents and dozens of friends and family campaigning on social media, Mr Srawn’s sister Mandeep said the family had talked to the media for the first time in the hope the Australian Defence Force would become involved in the search.
“He is very independent and is the strongest person I know,” a resolute Mandeep said.
“The army would be the best people to know what he would be thinking or doing in the situation, if he is acting logically and was able to keep himself warm.”
With her ashen-faced parents sitting silently nearby, Ms Srawn said she believed her brother could have harnessed survival skills to sustain himself.
Supporters in Canada, the United States and Australia continue to share information and updates on the search on Facebook and Twitter, lobbying media outlets including The New York Times and The Guardian to cover the disappearance, and messaging senior Canberra politicians to send in ADF troops.
Peter Hosking of the Kosciuszko Huts Association said the voices heard in the search area could have been noise from wild dogs or echos and that Mr Srawn’s chances of survival would be enhanced by taking shelter below the snow line.
“There are two clear days ahead [on Friday and Saturday] and then two days of mixed conditions so the sooner we get more people in there, the better,” Mr Hosking said.