What is this plane doing flying back and forth near Sydney at night? As I write this, a mystery plane is going back and forth over south Sydney, Australia:



The plane took of at Bankstown, flies straight from West to East and back, with a distance between paths of about 600m. It maintains a steady height of ca. 4100ft at a speed 120kts. 

It is a Cessna 404, but flightradar24 provides no call sign or any other ID.

I noticed the plane ca. 00:30 on 10 May 2018, as it was at its 8th "lap", and took the above screen shot. It may have gone on for a while, perhaps for an hour or more.

As it's night, no markings on the plane are visible. It has the usual white flashers on the wing tips and the top of the rudder, and the red and green marker lights. The plane is quiet loud (prop), but that's most likely only because it's night and there's no other sound sources in my suburb.

Does anyone have an idea what that plane could be, and what the purpose of such flights could be? Obviously, they (whoever they may be) waited until after the curfew of Kingsford Smith (23:00) to not get in the way of commercial traffic.

Might be similar to this question, but I have no way of knowing whether it is the same. Italy and Australia are different countries. E.g., to my knowledge, Europe doesn't permit Police planes or helicopters above urban areas without reason. Australia does.
With a path like that its most likely surveying something. There are a handful of 404's registered in Australia for areal survey, you can find them on this list.