1. Defence Science and Technology Organisation (DSTO), 13 Garden St, Eveleigh, NSW 2015, Australia.
2. Corresponding author.
3. Coffey Geotechnics Pty Limited, 8/12 Mars Rd, Lane Cove West, NSW 2066, Australia.
4. Systems Exploration (NSW) Pty Ltd, Box 6001, Dural Delivery Centre, NSW 2158, Australia.