A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Flinders' Survey of Australia.
From: Lee Martin
Date: 2008 Mar 14, 12:51 +1000
From: Lee Martin
Date: 2008 Mar 14, 12:51 +1000
----- Original Message ----- From:
To: Sent: Thursday, March 13, 2008 9:25 AM Subject: [NavList 4658] Re: Flinders' Survey of Australia. > > Peter, you wrote: > "This is something that I have heard/read again and again although that, > of > course, does not make it true. It certainly sounds unlikely, particularly > to anyone from long-established and well-mapped places. My understanding > is > that this applies particularly to parts of the north west (the 'top end' > of > the state of Western Australia) coast that have always been and remain > particularly isolated and barely inhabited. As well, the coast is a > complicated one with many off-shore islands and reefs, plus the tidal > range > is comparatively great. So all in all a good place to avoid." > > Yes, I can imagine. It would not surprise me at all if Flinders' positions > were still the best available, let's say, fifty years ago. But I would bet > they've been superceded. Similarly, there were some positions measured by > Cook in the South Pacific that were the best available until some time in > the middle of the 20th century. I can imagine one possible exception: > soundings. There's no real replacement for direct depth soundings, and > it's > very possible that there are some from the 18th/early 19th centuries still > present on Australian charts today. > > And: > "Did I mention the crocodiles? " > > LOL. No. But I bet they're friendly and cute. > > -FER I have a collection of electronic charts covering the whole of Australian waters, digitized in 2006 and 2007. I have done a quick sample of these charts covering more remote areas of Australia, and all are based on Royal Australian Navy hydrographic surveys of the 1990s. I also have a collection of paper charts covering the east coast of Australia through to the north-west of Western Australia. These charts have various publication dates ranging from the 1980s to the present day. Again, I took a sample of these charts covering remote areas and found that all are based on Royal Australian Navy hydrographic surveys, dating from the 1960s through to the 1990s. In my reply (NavList 4586) to George's original request (NavList 4573) for information on this topic, I made mention of Wreck Reef in the Coral Sea where Flinders was shipwrecked. Charts of that remote speck, and nearby remote reefs, are all based on Australian hydrographic surveys. My knowledge of the history of hydrographic surveys of Australian waters is sketchy. However, I believe the British Admiralty began its surveys of Australian waters from about the mid 1800s, continuing into the early 1900s, by which time I think it had fairly comprehensive coverage. The Australian authorities made a major effort to update and expand those surveys during the war, in the context of imminent Japanese invasion of Australia. The next major survey effort was in the 1960s, undertaken by the Royal Australian Navy. I suspect the Navy achieved complete coverage of Australian waters at that time. A similar effort was taking place on the Australian landmass at that time, and the 1960s saw the first consistent coverage of the entire Australian landmass, in terms of mapping. I think the next major hydrographic survey effort took place during the 1990s into the 2000s, using modern techniques to update the 1960s surveys. I think Flinders work would have progressively fallen into disuse starting from the mid-1800s. Also, the accuracy of Flinders work should not be overrated. For example, Flinders had Wreck Reef at 22� 11" South, 155� 3" East, whereas the chart has it at 22� 11" South, 155� 28" East. Flinders acknowledged that his longitude was rough: the clocks had been knocked about during the shipwreck and his estimate of longitude was based on ships distance run since the last estimate of longitude. In my retracing of Flinders steps I have found that almost all of his locations are out, sometimes by a small amount, sometimes a large. In saying that, I still think Flinders survey stands as a wonderful piece of work at the time. His survey was undertaken on the fly, in a leaky ship which was literally disintegrating underneath his feet, with the cyclone season bearing down upon him, and with his support vessel having to depart very early in the survey. Flinders did not have the luxury of time, of landing on every point of significance and fixing its position as accurately as possible: rather, he followed the then accepted procedure of landing on the coast every so often, every 40 to 80 miles say, trying to fix the position of those land falls as accurately as possible, and filling in the bits in between with triangulation based upon ships distance run. Frank wondered whether perhaps Flinders soundings might have survived in use. My first comment on that is that an isolated sounding by itself, without accurate reference to tide, is not of much use to a chart maker. In the absence of tide information, the sounding can only serve to provide an indication of depth. My second comment concerns current methods for determining depth. The Royal Australian Navy uses laser airborne technology known as LADS. The entire Australian coastline has been covered using this technology, and the Royal Australian Navy is extending coverage to the edge of the continental shelf. Some performance indicators of this technology are: accuracy of depth better than 300 mm, spatial accuracy better than 15 metres (that is, standard GPS accuracy), and survey coverage of 54 square kilometers per hour of aircraft operation. Reference http://www.hydro.gov.au/aboutus/lads/lads.htm . Greater accuracy for shipping channels and important waterways is obtained using survey ships. A friend of mine works on a Queensland survey vessel, and he tells me that accuracy is better than 25 mm for both depth and spatial location. This sort of accuracy is obtained using laser and GPS technology, with post processing of the GPS data. Clearly this sort of surveying is only possible where post processing is available. Lee Martin PS enquiring minds might wonder why accuracy of 20 mm is required. As an example, bulk carriers of the order of 200 to 220,000 tonnes are permitted to leave Gladstone, Queensland, with a minimum depth clearance in the shipping channel of 900 mm (I think from recollection of the regulations that 900mm is the standard minimum clearance). Ships can apply to the harbor master to leave with a clearance of less than that, and ships have left with a clearance of 350 mm. Needless to say, this requires some pretty fine management all round. The shipping channels are regularily surveyed, inspected visually, and graded to remove any undulations that may form on the seabed. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavListemail@example.com -~----------~----~----~----~------~----~------~--~---