Being new to WA I have only just discovered that the DoT holds LiDAR generated bathymetry for coastal waters (the image was in a proposal request from DoT to my company to undertake a geophysical survey of the coastal reserve immediately north of the Two Rocks Marina).  Light detection and ranging (LiDAR) mapping is an accepted method of generating precise and directly georeferenced spatial information about the shape and surface characteristics of the Earth.  For anyone interested a LiDAR 101 explanation can be found at: http://www.csc.noaa.gov/digitalcoast/_/pdf/lidar101.pdf.

LiDAR data is expensive to obtain because it must be captured from the air by specialised equipment.  A number of government agencies and private companies undertake LiDAR surveys for specific purposes and will commission the collection of LiDAR data.  The data may then be purchased by others and is generally about $100 per square kilometre (assuming that it is available for your area of interest).  Once purchased, it may be imported into a range of different mapping applications and manipulated and presented for specific purposes.  Working with LiDAR data requires specialist knowledge and computer software.

Without having a specific knowledge of the DoT LiDAR data set, I would say that it would have been captured to provide a better understanding of the offshore features of the coastline.  This would be important to DoT as it regulates shipping and the like and knowledge of the sea floor would be important for a number of purposes (for example, currents in particular places are highly dependant on the shape of the sea floor).  The bathymetry would have been generated by using the different colour spectrum in the captured data and calibrating this with known water depth to produce a graded image that reflects sea floor features.  As always, there is an error bound that is associated with the data and this is not stated on the image (general land based LiDAR errors are about 150mm) but I would expect it to exceed land based LiDAR errors.  Nevertheless, the image is a very accurate representation of the ocean floor over the area presented.

So, you can not just "log on" to a site and get easy access to LiDAR data in the format you desire.  I know what most people would like for fishing purposes is a LiDAR generated image of the Perth Metro coast on a spacially referenced base that can be interpreted through a simple computer application such as Microsoft Paint (if you move the cursor over the image, coordinates are presented that reflect actual eastings and northings).  I have a few contacts in DoT and will make some enquiries about the availability of its data and the format it is in.  I may then be able to make a map that has the desired properties and make that available to Fishwrecked members.  It is probably a "hard ask" but I will give it a crack.  Barring that, I should be able to get an image of the Perth coast such as the one presented and make that available where location positions can be generally determined from the scales on the x and y axis of the image.

The technology available nowdays is quite remarkable really.