How an underwater explosion near Perth, Australia was heard at the SOFAR Station in Bermuda.
(The Perth/Bermuda Experiment.)
(The Perth/Bermuda Experiment.)
Photo courtesy of National Archives.
Now that I have your attention, here is an article (which I cannot reproduce here because of copyright restrictions) that gives some (but not all) of the story.
http://gizmodo.com/how-an-underwater-bomb-in-australia-was-heard-around-th-1480208103
That’s what was reported in the media, but what follows is the REAL STORY!!
The real story:
Lamont Geological Observatory, which was a Geophysical Field Station managed by Columbia University in New York (much the same as SOFAR), owned the research vessel ‘Vema’.
See the Vema page here.
In March 1960, when Vema was off the South-western
coast of Australia, she dropped six 200lb bombs into the ocean to see if there was a clear uninterrupted underwater path between there and Bermuda.
The test was not particularly successful –the sound was just audible on the Bermuda hydrophones. To quote Carl Hartdegen "We had to re-run the tape several times and look for it (the explosions) in the mud (background noise)." It was therefore decided that another test should be conducted using larger bombs – 300 lbs each. However, Vema had a schedule to maintain, and asked the Royal Australian Navy if they could undertake the second test, to which they agreed. It took place on March 20th 1960 at a location some 25 nautical miles North-East of the original location, when HMAS Diamantina dropped the three larger bombs. The change in location came about because of the schedule that HMAS Diamantina needed to maintain.
These three 300lb explosions were heard surprisingly well in Bermuda compared with the earlier 200 lb bombs dropped by Vema, and there was much joy
and excitement to be had by all!!
But why was this test conducted in the first place? (And why was it so important to have it repeated shortly thereafter, when the first attempt did not produce the expected results?) Unfortunately, we will probably never know for certain, unless Lamont Geological Observatory have kept some notes in their Vema archives. One reason stated for the test was to determine whether the Sound Channel Axis could be used for very long-distance communication. “Let’s go as far away as we can, set off some bombs, and see if we can hear them in Bermuda!”
Why Perth, Australia?
It transpires that the antipodal points (see Glossary) of the Bermuda hydrophones “Golf’ and “Juliet” are just a few miles off the coast of Western Australia, near Perth.
I am going to surmise that the actual intent of the experiment was to see what sounds would be heard at the Bermuda hydrophones of an explosion originating at or near their antipodal points. In theory, the volume of the sound received in Bermuda should be louder than the sound received elsewhere nearby, because there would be multiple paths from the antipodes all converging on the Bermuda hydrophone. Unfortunately, both of the antipodal points of the SOFAR hydrophones were about 12 miles off the coast of Australia, and had a water depth of only about 150 feet – nowhere near the depth of the Sound Channel Axis, where he sound source needs to be located.
So they settled for the next best thing, and the test was repeated!!
See P B Maps I for some pretty pictures (and an explanation).
But there were a couple of problems.
1) Why were the HMAS Diamantina recordings so radically louder than the Vema recordings?
and
2) Why did the recording of the HMAS Diamantina explosions show a double peak, as if there were 2 explosions very close together?
(The recording of the original Vema explosions was too weak to see if this was also the case.)
Problem 1) Sound from an underwater explosion travels outward in all directions, generally in a straight line until it meets a hard object, like the ocean floor, or (believe it or not) the ocean surface, where it is reflected back in the direction from which it came, losing some of its energy (volume) in the process and eventually dying out. But sound traveling outwards horizontally (or nearly horizontally) will travel vast distances because of a (physically logical) quirk of nature known as the Sound Channel Axis (SCA), until it bumps into something hard, like a seamount, an island, or a continent.
The source location off Australia was chosen because it was almost the exact antipodal point** of the SOFAR hydrophones Golf & Juliet, there appeared to be an uninterrupted Great Circle path to Bermuda, just bypassing the Kerguelen & Crozet Islands, the Southern tip of Africa, and the Eastern tip of Brazil. These were the days before satellite navigation and GPS, and the maps available lacked the accuracy of today, particularly in ocean floor topography.
The pressure detonators used to trigger the explosions were somewhat erratic in accuracy and in their choice of detonation depths. It is possible that the detonators used by HMAS Diamantina caused the explosions to trigger much closer to the Sound Channel Axis (SCA) than the Vema explosions, hence more energy entered the SCA, hence the recordings were louder when heard at Bermuda. Certainly, the increase of 50% in the size of the charge would have helped increase the volume of sound arriving in Bermuda, but by the laws of physics, this alone would not have been enough for the dramatic difference in arrival signals between the 2 tests.
So it seems quite likely that the difference of 25 nautical miles in HMAS Diamantina's location allowed the Diamantina explosions to find a better path through the Kerguelen/Crozet/Africa/Brazil window than the Vema's source location allowed.
Problem 2) At the time, it was suggested that the second arrival appearing on the Diamantina explosions was from a reflection off the continental shelf off Brazil, traveling a somewhat longer path, and hence arriving later. I don't recall whether there was any analysis undertaken to determine if the later arrival (about 35 seconds) was consistent with the approximate added length of the proposed path. Nor do I recall whether any other explanation was put forward at that time.
Below is a series of letters between Carl Hartdegen and the Captain of HMAS Diamantina. Note: There was no Internet or e-mail in those days, and long distance phone calls were incredibly expensive!
http://gizmodo.com/how-an-underwater-bomb-in-australia-was-heard-around-th-1480208103
That’s what was reported in the media, but what follows is the REAL STORY!!
The real story:
Lamont Geological Observatory, which was a Geophysical Field Station managed by Columbia University in New York (much the same as SOFAR), owned the research vessel ‘Vema’.
See the Vema page here.
In March 1960, when Vema was off the South-western
coast of Australia, she dropped six 200lb bombs into the ocean to see if there was a clear uninterrupted underwater path between there and Bermuda.
The test was not particularly successful –the sound was just audible on the Bermuda hydrophones. To quote Carl Hartdegen "We had to re-run the tape several times and look for it (the explosions) in the mud (background noise)." It was therefore decided that another test should be conducted using larger bombs – 300 lbs each. However, Vema had a schedule to maintain, and asked the Royal Australian Navy if they could undertake the second test, to which they agreed. It took place on March 20th 1960 at a location some 25 nautical miles North-East of the original location, when HMAS Diamantina dropped the three larger bombs. The change in location came about because of the schedule that HMAS Diamantina needed to maintain.
These three 300lb explosions were heard surprisingly well in Bermuda compared with the earlier 200 lb bombs dropped by Vema, and there was much joy
and excitement to be had by all!!
But why was this test conducted in the first place? (And why was it so important to have it repeated shortly thereafter, when the first attempt did not produce the expected results?) Unfortunately, we will probably never know for certain, unless Lamont Geological Observatory have kept some notes in their Vema archives. One reason stated for the test was to determine whether the Sound Channel Axis could be used for very long-distance communication. “Let’s go as far away as we can, set off some bombs, and see if we can hear them in Bermuda!”
Why Perth, Australia?
It transpires that the antipodal points (see Glossary) of the Bermuda hydrophones “Golf’ and “Juliet” are just a few miles off the coast of Western Australia, near Perth.
I am going to surmise that the actual intent of the experiment was to see what sounds would be heard at the Bermuda hydrophones of an explosion originating at or near their antipodal points. In theory, the volume of the sound received in Bermuda should be louder than the sound received elsewhere nearby, because there would be multiple paths from the antipodes all converging on the Bermuda hydrophone. Unfortunately, both of the antipodal points of the SOFAR hydrophones were about 12 miles off the coast of Australia, and had a water depth of only about 150 feet – nowhere near the depth of the Sound Channel Axis, where he sound source needs to be located.
So they settled for the next best thing, and the test was repeated!!
See P B Maps I for some pretty pictures (and an explanation).
But there were a couple of problems.
1) Why were the HMAS Diamantina recordings so radically louder than the Vema recordings?
and
2) Why did the recording of the HMAS Diamantina explosions show a double peak, as if there were 2 explosions very close together?
(The recording of the original Vema explosions was too weak to see if this was also the case.)
Problem 1) Sound from an underwater explosion travels outward in all directions, generally in a straight line until it meets a hard object, like the ocean floor, or (believe it or not) the ocean surface, where it is reflected back in the direction from which it came, losing some of its energy (volume) in the process and eventually dying out. But sound traveling outwards horizontally (or nearly horizontally) will travel vast distances because of a (physically logical) quirk of nature known as the Sound Channel Axis (SCA), until it bumps into something hard, like a seamount, an island, or a continent.
The source location off Australia was chosen because it was almost the exact antipodal point** of the SOFAR hydrophones Golf & Juliet, there appeared to be an uninterrupted Great Circle path to Bermuda, just bypassing the Kerguelen & Crozet Islands, the Southern tip of Africa, and the Eastern tip of Brazil. These were the days before satellite navigation and GPS, and the maps available lacked the accuracy of today, particularly in ocean floor topography.
The pressure detonators used to trigger the explosions were somewhat erratic in accuracy and in their choice of detonation depths. It is possible that the detonators used by HMAS Diamantina caused the explosions to trigger much closer to the Sound Channel Axis (SCA) than the Vema explosions, hence more energy entered the SCA, hence the recordings were louder when heard at Bermuda. Certainly, the increase of 50% in the size of the charge would have helped increase the volume of sound arriving in Bermuda, but by the laws of physics, this alone would not have been enough for the dramatic difference in arrival signals between the 2 tests.
So it seems quite likely that the difference of 25 nautical miles in HMAS Diamantina's location allowed the Diamantina explosions to find a better path through the Kerguelen/Crozet/Africa/Brazil window than the Vema's source location allowed.
Problem 2) At the time, it was suggested that the second arrival appearing on the Diamantina explosions was from a reflection off the continental shelf off Brazil, traveling a somewhat longer path, and hence arriving later. I don't recall whether there was any analysis undertaken to determine if the later arrival (about 35 seconds) was consistent with the approximate added length of the proposed path. Nor do I recall whether any other explanation was put forward at that time.
Below is a series of letters between Carl Hartdegen and the Captain of HMAS Diamantina. Note: There was no Internet or e-mail in those days, and long distance phone calls were incredibly expensive!
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Here is a picture of the Diamantina explosions as recorded by the Bermuda hydrophones.
oo00OO00oo Analysis of HMAS Diamantina's course and the location of the explosions. oo00OO00oo
These diagrams were part of the documentation for another project (unrelated to The Perth Bermuda Experiment). I believe they are more “Representational” than “Accurate”. The lower diagram is just a blow-up of the centre of the upper diagram. The origin of these diagrams is unknown at present.
The solid line running in a diagonal zig-zag from lower right to upper left is the (supposed) track of the HMAS Diamantina, with navigation notes added. HMAS Diamantina navigated "the old-fashioned way" using 'celestial fixes', and 'dead reckoning'. There was no radar nor LORAN in this area, and GPS was not even a dream!
The location of the earlier Vema experiment is shown on the diagram with a X immediately above the word “Vema”.
The lower of the two dashed lines shows the great circle path to Bermuda. (I have no idea what the line marked ‘Sphere’ represents.)
WGS84 is the designation of this particular chart.
HMAS Diamantina got a couple of fixes from prominent land markers at 1630 and 1730, and as night fell, headed for the target area. The diagram shows fixes at 2000, and again at 0600 and 0800 the next morning after the detonations, although I speculate as to the accuracy of the positions plotted on this diagram. (All times shown are local.)
The Captain’s Log states that once the target area was reached (located at 33° 13”S, 113° 43”E) at 0300, the ship slowed to 4 knots (about 5 mph), and turned to 235°, on the course heading “To Bermuda”. (The Captain’s Log shows 135°, but it is recorded correctly in the subsequent letter to Carl Hartdegen.) The detonations occurred between 0304 and 0315, after which (as indicated in the Captains Log), the ship headed for their next station located at 32° 00”S, 111° 50”E.
But there is a problem with the ‘bulls-eye’ on the diagram. (I have no idea of the purpose of the bulls-eye, other than that it would appear to show how far the sound of the explosions would travel in 5 seconds and 10 seconds. The mathematics works out to be approximately correct.)
The line showing the ship’s track while on the 235° heading is about 25 miles long, and started at 0300. If the ship slowed to 4 knots (5mph) it would take them 5 hours (until 0800) to traverse the 25 miles, and so the OP fix at 0600 as shown on the diagram makes no sense.
If, on the other hand, the ship turned to the North West immediately after the 3rd explosion at 0315, as stated in the Captain's log, then, in order for them to have traversed the 25 miles (in 15 minutes) the ship would have had to be traveling at 100 miles/hour! Impressive!!
So I am highly suspicious of that 25 mile track heading towards Bermuda shown on the diagrams!
I believe the diagrams were created in an attempt to show both an overall picture of the operation, as well as some of the fine detail of the few minutes around the actual explosions, much like a magnifying glass over one portion of the map. The information displayed is certainly questionable.
HMAS Diamantina had agreed to conduct this experiment because the location was very nearly on the course that they would travel on their upcoming assignment, as the Captain’s log states – “As the position to drop these charges was on the route of the Oceanographic cruise, Vema was informed that their request could be carried out.”
The map below is the best I can do to transcribe the information from the questionable diagrams (above) onto Google Earth. I have added (in red) the course that HMAS Diamantina would have followed to reach the station at 32°S, 113° 50’E had they not agreed to this small diversion. During the latter part of the journey, the distance between the 2 courses (the red line and the green line) is about 2 miles!
Tracks of HMAS Diamantina.
Red line. The track that HMAS Diamantina would have taken if she had not deviated to perform the test.
Green line. The track that the diagrams above describe.
The last fix before darkness was at 1730, and I am assuming (with reasonable grounds) that it determined the ship was located at the point where the green line diverges from the red line. The distance from that point to the 'Morning Star' fix 12.5 hours later (along the red line) is 175 miles.
The first section of the green line (up until when HMAS Diamantina turned towards Bermuda) is 108 miles, and took 9.5 hours to complete. This equates to 11.4 miles per hour.
The third section of the green line (from the end of the test to 'Morning Star' is 66 miles. If we assume that HMAS Diamantina traveled at 11.4 mph (as earlier) then that journey took 5 hours & 45 minutes. SO these 2 sections consumer 12.25 hours, leaving 15 minutes for the middle section - the incredible (and impossible) 100 mph journey!!
Red line. The track that HMAS Diamantina would have taken if she had not deviated to perform the test.
Green line. The track that the diagrams above describe.
The last fix before darkness was at 1730, and I am assuming (with reasonable grounds) that it determined the ship was located at the point where the green line diverges from the red line. The distance from that point to the 'Morning Star' fix 12.5 hours later (along the red line) is 175 miles.
The first section of the green line (up until when HMAS Diamantina turned towards Bermuda) is 108 miles, and took 9.5 hours to complete. This equates to 11.4 miles per hour.
The third section of the green line (from the end of the test to 'Morning Star' is 66 miles. If we assume that HMAS Diamantina traveled at 11.4 mph (as earlier) then that journey took 5 hours & 45 minutes. SO these 2 sections consumer 12.25 hours, leaving 15 minutes for the middle section - the incredible (and impossible) 100 mph journey!!
oo00OO00oo Here is my theory of what exactly happened. oo00OO00oo
The first segment of the journey is slightly shorter - 105 miles, with an average speed of 11.1 mph.
The middle segment of the journey is only 1.1 miles, consumed only 15 minutes at a speed of 4.4mph (or 4 knots as recorded in the Captain's Log).
The final segment of the journey is slightly longer - 70 miles, with an average speed of 12.2 mph.
HMAS Diamantina's most economical speed was between 10 to 12 knots (12 to 14 mph), depending on weather conditions. Her top speed was 20 knots (23 mph). This ties in well with the calculated speeds mentioned above.
The History of HMAS Diamantina.
She was constructed in 1944, and served from 1944 but was decommissioned in 1946. She was recommissioned as a hydrographic survey ship from 1949 to 1980. She is preserved as a museum ship at the drydock at the Queensland Maritime Museum in Brisbane.
The middle segment of the journey is only 1.1 miles, consumed only 15 minutes at a speed of 4.4mph (or 4 knots as recorded in the Captain's Log).
The final segment of the journey is slightly longer - 70 miles, with an average speed of 12.2 mph.
HMAS Diamantina's most economical speed was between 10 to 12 knots (12 to 14 mph), depending on weather conditions. Her top speed was 20 knots (23 mph). This ties in well with the calculated speeds mentioned above.
The History of HMAS Diamantina.
She was constructed in 1944, and served from 1944 but was decommissioned in 1946. She was recommissioned as a hydrographic survey ship from 1949 to 1980. She is preserved as a museum ship at the drydock at the Queensland Maritime Museum in Brisbane.
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There is however an issue with the water depth at the explosion site.
The track of the ship during the time of the explosions (either the green line or the white line depending on what you believe) was diagonally from lower right to upper left. The depth chart at the bottom of the diagram is for the green track. Unfortunately, the depth chart reads from left to right, which is a bit counterintuitive for comparing it with the ship's track above which runs from right to left. The red arrow on the upper part of the map matches with the solid vertical line on the depth chart, which (if you could read the numbers) shows a depth of 8,100ft (1350 fathoms), which is the depth that is recorded in the Captain's Log. This is about 5 miles away from the targeted explosion site at 33° 13'S 113° 43'E at the centre of the white track. The depth of water at the targeted site was 7,550 feet (1260 fathoms). |
The Captain's Log from HMAS Diamantina can be viewed here. The entries of interest are at the bottom of page 1, and the top of Page 2 - points11 through 15 of the document.
The end of the story?
Not quite! More to come next time!
Posted Aug. 2014, Edited and expanded Oct. 2020
Thanks to Bill Andrews' granddaughter for alerting me to the Gizmodo article.
Not quite! More to come next time!
Posted Aug. 2014, Edited and expanded Oct. 2020
Thanks to Bill Andrews' granddaughter for alerting me to the Gizmodo article.