AF 447 Search to resume
How AUVs work
For those interested in the technical challenges faced by these underwater birds, here's an interesting site, with some videos of what goes on on the ship and underwater.
Plane Shaped Rocks | Search for Amelia
Plane Shaped Rocks | Search for Amelia
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Grizzled,
I learned some years ago of a case involving a pretty large freighter at sea, which litteraly exploded at the surface of a smaller pond than the Altlantic, the Mediterranean sea, where such event should be clearer, once registered by sismographers. All sismic datas around the date and location of the explosion were carefully screened. But nothing would tell any difference betwenn that explosion - or impact, in case of an a/c crash - and usual sismic activity. It got lost in the "background noise", so to say.
I learned some years ago of a case involving a pretty large freighter at sea, which litteraly exploded at the surface of a smaller pond than the Altlantic, the Mediterranean sea, where such event should be clearer, once registered by sismographers. All sismic datas around the date and location of the explosion were carefully screened. But nothing would tell any difference betwenn that explosion - or impact, in case of an a/c crash - and usual sismic activity. It got lost in the "background noise", so to say.
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grizzled
Way back in the mid 60s when I was a student at the University of Michigan I worked for one of their geophysical research labs, a seismology department. One experiment was field work recording blasts that took place off Delaware in the ocean using small surface seismometers in various places around the Northeast and Midwest as far east as Western Indiana. The blasts were something like 100# charges dropped into the ocean. They were visibly detectable in raw data into Northern Michigan from well sited instruments.
At the time of the experiments conditions were ideal. The ocean was as calm as it ever gets off Delaware. And there were no storms in between. That is one data point.
The second experiment I aided with was a precursor to something I kibitzed professionally 5 years later - using seismometers for intrusion detection with the intention of implementing it in Vietnam. Footsteps were very plain and very hard to disguise with shuffling and such. DC3s were uncannily obvious in the seismometer tape recordings WAY before the voice track could discern the plane's propellers. And there was a way to mask footsteps. Heavy winds made it difficult, and a DC3 going overhead also made it difficult.
That's a second data point.
If Swiss Air 111 hit the water within about 125 miles of Nova Scotia then the coupling for the event into the ground would be pretty good. (The Delaware tests were in comparatively shallow water.) The coupling for AF447 would be bad, it would have to hit with enough energy that it left a signature easily distinguishable from storm events, and you'd have had to have sensors closer to the event than the nearest real shoreline. Or such is my guess from limited but quite pertinent experience.
Hydrophones might have had a better chance. And with vagaries of sound transmission in the ocean I am not convinced they'd do a whole lot better at locating the crash. They might be able to detect the crash event, though.
Your idea was a good one had the water been substantially shallower and the crash been closer to land. As it is I'd consider it a bad bet. But at this juncture a bad bet may be better than none at all, such as after they've gone through mm43's magic triangle.
{^_^}
So, if no seismic event was recorded within the appropriate time frames for AF447, can one conclude that:
1 The aircraft did not impact the water with sufficient force to leave such a signature (which would tend to eliminate a scenario of an "uncontrolled plunge")? Or,
2 There may not be sufficiently sensitive seismic information available for that area? (I have no idea the practical science / instrumentation behind this, but I do know the USGS, for instance, receives / records even very small seismic events from all over the globe.)
I am assuming that no such event was recorded because, if it were, the impact location would be known.
1 The aircraft did not impact the water with sufficient force to leave such a signature (which would tend to eliminate a scenario of an "uncontrolled plunge")? Or,
2 There may not be sufficiently sensitive seismic information available for that area? (I have no idea the practical science / instrumentation behind this, but I do know the USGS, for instance, receives / records even very small seismic events from all over the globe.)
I am assuming that no such event was recorded because, if it were, the impact location would be known.
At the time of the experiments conditions were ideal. The ocean was as calm as it ever gets off Delaware. And there were no storms in between. That is one data point.
The second experiment I aided with was a precursor to something I kibitzed professionally 5 years later - using seismometers for intrusion detection with the intention of implementing it in Vietnam. Footsteps were very plain and very hard to disguise with shuffling and such. DC3s were uncannily obvious in the seismometer tape recordings WAY before the voice track could discern the plane's propellers. And there was a way to mask footsteps. Heavy winds made it difficult, and a DC3 going overhead also made it difficult.
That's a second data point.
If Swiss Air 111 hit the water within about 125 miles of Nova Scotia then the coupling for the event into the ground would be pretty good. (The Delaware tests were in comparatively shallow water.) The coupling for AF447 would be bad, it would have to hit with enough energy that it left a signature easily distinguishable from storm events, and you'd have had to have sensors closer to the event than the nearest real shoreline. Or such is my guess from limited but quite pertinent experience.
Hydrophones might have had a better chance. And with vagaries of sound transmission in the ocean I am not convinced they'd do a whole lot better at locating the crash. They might be able to detect the crash event, though.
Your idea was a good one had the water been substantially shallower and the crash been closer to land. As it is I'd consider it a bad bet. But at this juncture a bad bet may be better than none at all, such as after they've gone through mm43's magic triangle.
{^_^}
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"Seabed Worker" & "Anne Candies" - 28 April positions
The "Seabed Worker" at 28/1411z was berthed at Port Suape [8°23'47"S 34°57'32"W].
The "Anne Candies" at 28/0338z was at 4°32'22"S 3°02'14"W, 199°T/8.5KT,
and should berth at either Suape or Recife tommorow.
-----------------
Hydrophone detection of explosions in the sea, is the normal practice when undertaking offshore oil exploration. The seismic survey vessel tows a long streamer (up to 1.5NM in length) fitted with in the range of 100 hydrophone detectors. The same vessel also tows about 100 meters from its stern, an array of air guns.
The sensitivity of this system is such that geophysical structures over 5,000m below the the seabed can be detected. Higher resolutions can be had when two vessels work in tandem, and the differential signal is also recorded.
So in short, the sound travels well in the water, penetrates terra firma and echoes back through the same path. All very well and good for what it is designed to do.
Seismometers on the other-hand are designed to detect the vibrations caused by terra firma shifting. The energy generated even by a small tectonic plate shift is normally far greater than a non nuclear explosion on the sea surface, and a force 1 Richter quake would probably be detected a few hundred miles from its source. So, in the case of AF447, if the Atlantic had been ringed by sensitive hydrophones and the best noise cancelling techniques were used, I suspect that with the distances involved the chances of triangulating an aircraft crash by this means would be remote.
I live 25km from an active though currently dormant volcano which has a number of seismometers embedded on its slopes, as detection of activity is difficult from any great distance.
mm43
The "Anne Candies" at 28/0338z was at 4°32'22"S 3°02'14"W, 199°T/8.5KT,
and should berth at either Suape or Recife tommorow.
-----------------
Hydrophone detection of explosions in the sea, is the normal practice when undertaking offshore oil exploration. The seismic survey vessel tows a long streamer (up to 1.5NM in length) fitted with in the range of 100 hydrophone detectors. The same vessel also tows about 100 meters from its stern, an array of air guns.
The sensitivity of this system is such that geophysical structures over 5,000m below the the seabed can be detected. Higher resolutions can be had when two vessels work in tandem, and the differential signal is also recorded.
So in short, the sound travels well in the water, penetrates terra firma and echoes back through the same path. All very well and good for what it is designed to do.
Seismometers on the other-hand are designed to detect the vibrations caused by terra firma shifting. The energy generated even by a small tectonic plate shift is normally far greater than a non nuclear explosion on the sea surface, and a force 1 Richter quake would probably be detected a few hundred miles from its source. So, in the case of AF447, if the Atlantic had been ringed by sensitive hydrophones and the best noise cancelling techniques were used, I suspect that with the distances involved the chances of triangulating an aircraft crash by this means would be remote.
I live 25km from an active though currently dormant volcano which has a number of seismometers embedded on its slopes, as detection of activity is difficult from any great distance.
mm43
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Seismic arrays
Large arrays of very sensitive sesmometers are operated by several countries around the world to verify that no "illegal" nuclear tests are made by anybody. I have tried to get their sensitivity and directional resolution, but failed. Here in Sweden they are operated by the military research institute (FOI). I know that the explosion of the Kursk was detected very much above noise. Does anybody know if similar very sensitive arrays exist in Brazil or Dakar?
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"Seabed Worker" & "Anne Candies" - 29 April positions
At 29/1948z both vessels were berthed at Recife, starboard side to, with the "Anne Candies" astern of the "Seabed Worker".
I suspect the "Seabed Worker" will depart for the search area shortly.
Thanks to broadreach once again for the data.
mm43
I suspect the "Seabed Worker" will depart for the search area shortly.
Thanks to broadreach once again for the data.
mm43
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mm43, there is one significant difference between the towed array setup you describe and a plane crashing on the surface. That's the thermal layers that reflect sound. Once you get below them it's all fine. But anything above the layers is reflected and ducted all over the place, fairly efficiently, with a lot of dispersion and multiple path issues.
(I should have mentioned that in my prior note. I was trying to keep it short.)
{^_-}
(I should have mentioned that in my prior note. I was trying to keep it short.)
{^_-}
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JD-EE, That's where the significance of the air percussion guns come into play. The ELF (low audio spectrum) pulse is used because of its ability to penetrate the inversion layers as well as deep into the terra firma beneath the seabed. Lower frequency means "better" in this type of seismic operation, and the resolution is improved by the difference signal from a tandem operation.
For those not familiar with the ULB pinger issue, it is the subsurface inversion layers that have been fingered for the non detection of the AF447 pinger, and hence the BEA recommendation that the frequency be lowered from 37.5kHz to a nominal 9kHz.
But back to seismic detection of aircraft crashes. It should be remembered that the WTC Twin Towers aircraft impacts were recorded, i.e. the buildings moved, but no meaningful amplitudes were measured over 200 miles miles away. Likewise, it is debatable that the UA93 impact at Shanksville, PA, was actually recorded due to the 3 minutes difference between DFDR/ATC and seismometer times. Perhaps the difference could mean that the vertical percussion wave generated travelled some distance into the earth before being reflected, as signal amplitudes just above the background noise were recorded and triangulation pointed to the crash site.
mm43
- from Woods Hole Oceanographic Institution ....
The air guns are relatively deep penetration sources, operating at 100Hz to about 1200 Hz, to identify subsurface geologic layers and define the subsurface structure. In studies that require less resolution but substantial penetration, the air gun is usually preferable as compared to a water gun, because it is far more efficient at producing low frequency energy.
The air guns are relatively deep penetration sources, operating at 100Hz to about 1200 Hz, to identify subsurface geologic layers and define the subsurface structure. In studies that require less resolution but substantial penetration, the air gun is usually preferable as compared to a water gun, because it is far more efficient at producing low frequency energy.
But back to seismic detection of aircraft crashes. It should be remembered that the WTC Twin Towers aircraft impacts were recorded, i.e. the buildings moved, but no meaningful amplitudes were measured over 200 miles miles away. Likewise, it is debatable that the UA93 impact at Shanksville, PA, was actually recorded due to the 3 minutes difference between DFDR/ATC and seismometer times. Perhaps the difference could mean that the vertical percussion wave generated travelled some distance into the earth before being reflected, as signal amplitudes just above the background noise were recorded and triangulation pointed to the crash site.
mm43
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Hi,
Le Figaro - France : Les pilotes mal formés au «décrochage» des avions
I remember that Airbus telling the training for stall recovery was not necessary for their aircrafts ...
Someone can confirm or infirm this ?
More from the french newspapers ....
http://www.slate.fr/story/20633/air-...7-victimes-vol
Le Figaro - France : Les pilotes mal formés au «décrochage» des avions
INFO LE FIGARO - Several accidents have revealed that the procedures to recover an airplane that could lead to crash landed.
Dazed in the cockpits. Reportedly, a major work is underway to develop safety procedures for crews of all companies in the world. Airbus, Boeing, Bombardier, Embraer, Air France as all companies ... Everybody is associated with what is now a major issue in aviation safety. Airbus announced this great project mid-March to its airline customers. Several recent accidents have revealed that the procedures "Stall" implemented in the event of stalling an airplane are not appropriate, and in some cases, they prevent the crew out of this dangerous situation, and sometimes dramatic. There is talk of dropping out of the plane, but it is actually the wing stalls.
In conventional flight conditions, the air streams flow around the wing and conform to the shape. However, at too high incidence (the angle of the wing with the air), not reattach airflow over the airfoil. The lift of the aircraft decreases. He falls or continues its path because of its inertia and can only crash. In contrast, high speed, airflow can reach the speed of sound. This creates a shock wave that can cause loss of control of the aircraft.
Dropout can occur at low speed, it is called "low stall speed," or high speed, it is called "high speed stall.
Today in all cockpits, the procedure in case of stalling to full throttle to minimize loss of altitude. "This procedure has been pushed by mistake by U.S. authorities," said one familiar with the matter. In a few weeks, the new procedure will recommend only a control stick to reduce the incidence, that is to say things slightly, nosed the plane. This change of method should be common to Airbus and Boeing. "The whole aviation industry has gone astray for more than a decade," says one close to the matter.
From Air France, the drivers are embarrassed to armholes because they do not test flight and can not have a final stance on the issue. They can only rely on the advice of manufacturers. "Air France Airbus maintains its commitment to change this procedure on all aircraft in the world fleet," said Stephen Lichtenberger, CEO of Flight Safety at Air France. The analysis of recent events suggest, in fact, that this change is necessary. " The company says it lights will implement the new procedure as soon as possible, "as soon as we have been addressed by manufacturers having been validated by the certification authorities, namely the European Agency for Safety (EASA).
Flight test
The other major issue is that of training. For today, not a flight simulator can not recreate the settings related to a stall and thus cause the drivers to cope. "We can train pilots to recover from a situation close to the stall, said an instructor of Air France, but not to recover from a stall." "Procedures have been made for people who have never lived on heavy airplane stall, said Claude Lelaie, head of security at Airbus. Only test pilots who know the stall. According to our information, Airbus will offer its customers boarding their flight instructors on board to offer test drive in situ. However, it is unrealistic to imagine all the drivers in the world to flight testing to practice stall recovery.
Dazed in the cockpits. Reportedly, a major work is underway to develop safety procedures for crews of all companies in the world. Airbus, Boeing, Bombardier, Embraer, Air France as all companies ... Everybody is associated with what is now a major issue in aviation safety. Airbus announced this great project mid-March to its airline customers. Several recent accidents have revealed that the procedures "Stall" implemented in the event of stalling an airplane are not appropriate, and in some cases, they prevent the crew out of this dangerous situation, and sometimes dramatic. There is talk of dropping out of the plane, but it is actually the wing stalls.
In conventional flight conditions, the air streams flow around the wing and conform to the shape. However, at too high incidence (the angle of the wing with the air), not reattach airflow over the airfoil. The lift of the aircraft decreases. He falls or continues its path because of its inertia and can only crash. In contrast, high speed, airflow can reach the speed of sound. This creates a shock wave that can cause loss of control of the aircraft.
Dropout can occur at low speed, it is called "low stall speed," or high speed, it is called "high speed stall.
Today in all cockpits, the procedure in case of stalling to full throttle to minimize loss of altitude. "This procedure has been pushed by mistake by U.S. authorities," said one familiar with the matter. In a few weeks, the new procedure will recommend only a control stick to reduce the incidence, that is to say things slightly, nosed the plane. This change of method should be common to Airbus and Boeing. "The whole aviation industry has gone astray for more than a decade," says one close to the matter.
From Air France, the drivers are embarrassed to armholes because they do not test flight and can not have a final stance on the issue. They can only rely on the advice of manufacturers. "Air France Airbus maintains its commitment to change this procedure on all aircraft in the world fleet," said Stephen Lichtenberger, CEO of Flight Safety at Air France. The analysis of recent events suggest, in fact, that this change is necessary. " The company says it lights will implement the new procedure as soon as possible, "as soon as we have been addressed by manufacturers having been validated by the certification authorities, namely the European Agency for Safety (EASA).
Flight test
The other major issue is that of training. For today, not a flight simulator can not recreate the settings related to a stall and thus cause the drivers to cope. "We can train pilots to recover from a situation close to the stall, said an instructor of Air France, but not to recover from a stall." "Procedures have been made for people who have never lived on heavy airplane stall, said Claude Lelaie, head of security at Airbus. Only test pilots who know the stall. According to our information, Airbus will offer its customers boarding their flight instructors on board to offer test drive in situ. However, it is unrealistic to imagine all the drivers in the world to flight testing to practice stall recovery.
Someone can confirm or infirm this ?
More from the french newspapers ....
http://www.slate.fr/story/20633/air-...7-victimes-vol
Air France recently offered tickets to the families of victims of the crash of Flight AF447 Paris-Rio by offering to join Paris on exactly the same flight as the one who died tragically last year, reports the website of Der Spiegel.
Families living in Brazil did not really need this unfortunate coincidence: the flight was offered to attend a ceremony at the Pere Lachaise Cemetery where a memorial in honor of the 228 people who died on June 1, 2009 must be opened. More than 120 victims' relatives planned to travel to Paris on this occasion. But many have not hidden their misunderstanding after learning of the flight schedule and mark-up is keeping them take: flight AF445, starting Sunday night in Rio de Janeiro aboard a Airbus.
"This is exactly the same flight as one that took away our loved ones," said Maarten van Sluys, the president of an association of families of victims at the site of German newspaper. "I do not know what were the intentions of Air France, but it's bad taste and no respect for our very fragile emotional state," he added.
Airbus used for the flight, whose name was changed from AF447 to AF445, would be far from completed, which upset a little van Sluys: "They just need to fill a plane and have decided to to our group of 100 people. "
The victims' association has requested that Air France offers flights to another group, one of the two Boeings that connect Brazil and France every day to avoid having to relive the last moments of their loved ones, that an Air France pilot was described in the columns in Slate. "We would feel much better," said Van Sluys.
Wednesday, April 28, the Office of Investigations and Analysis (BEA) announced that the research of black boxes and the wreckage of flight AF 447, who have still not been found eleven months after the tragedy, would continue . The issue of compensation also remains a thorny issue, a lawyer representing families of victims said Tuesday, April 27 insurers that Air France offered an amicable compensation differ depending on the nationality of the victims: 2.98 million euros per person in the United States, 560,000 euros to 186,000 euros in Brazil and Europe.
Families living in Brazil did not really need this unfortunate coincidence: the flight was offered to attend a ceremony at the Pere Lachaise Cemetery where a memorial in honor of the 228 people who died on June 1, 2009 must be opened. More than 120 victims' relatives planned to travel to Paris on this occasion. But many have not hidden their misunderstanding after learning of the flight schedule and mark-up is keeping them take: flight AF445, starting Sunday night in Rio de Janeiro aboard a Airbus.
"This is exactly the same flight as one that took away our loved ones," said Maarten van Sluys, the president of an association of families of victims at the site of German newspaper. "I do not know what were the intentions of Air France, but it's bad taste and no respect for our very fragile emotional state," he added.
Airbus used for the flight, whose name was changed from AF447 to AF445, would be far from completed, which upset a little van Sluys: "They just need to fill a plane and have decided to to our group of 100 people. "
The victims' association has requested that Air France offers flights to another group, one of the two Boeings that connect Brazil and France every day to avoid having to relive the last moments of their loved ones, that an Air France pilot was described in the columns in Slate. "We would feel much better," said Van Sluys.
Wednesday, April 28, the Office of Investigations and Analysis (BEA) announced that the research of black boxes and the wreckage of flight AF 447, who have still not been found eleven months after the tragedy, would continue . The issue of compensation also remains a thorny issue, a lawyer representing families of victims said Tuesday, April 27 insurers that Air France offered an amicable compensation differ depending on the nationality of the victims: 2.98 million euros per person in the United States, 560,000 euros to 186,000 euros in Brazil and Europe.
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"Seabed Worker" & "Anne Candies" - 30 April positions
"Seabed Worker" cleared the Recife breakwater bound for the Search Zone at 30/1430z (1130 Brazilian Standard Time). ETA Search Zone 03/0230z.
"Anne Candies" remains berthed at Recife.
Update: "Anne Candies" departed Recife around 30/1500z.
mm43
"Anne Candies" remains berthed at Recife.
Update: "Anne Candies" departed Recife around 30/1500z.
mm43
Last edited by mm43; 30th Apr 2010 at 19:01.
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What is the frequency/resolution of the swathe/sidescan system of those AUVs which are deployed by Seabed Worker?
If a CVR/FDR has been flung clear of major wreckage, as sometimes happens in very severe impacts with a water surface, would the sonar have the resolution for such a contact to stand out like a dog's wotsits at the height above seabed at which the vehicles are 'flying'?
Have they deployed a representative sized/reflectivity testpiece to the seabed to verify what such an item would actually look like in the depth, location and conditions of the searchsite with the kit that is doing the 'looking'?
If a CVR/FDR has been flung clear of major wreckage, as sometimes happens in very severe impacts with a water surface, would the sonar have the resolution for such a contact to stand out like a dog's wotsits at the height above seabed at which the vehicles are 'flying'?
Have they deployed a representative sized/reflectivity testpiece to the seabed to verify what such an item would actually look like in the depth, location and conditions of the searchsite with the kit that is doing the 'looking'?
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Low Flier;
The answers to most of your questions can be found in the Search for Amelia website of the Waitt Institute for Discovery. Go through the site carefully, and you will find everything you are looking for.
mm43
The answers to most of your questions can be found in the Search for Amelia website of the Waitt Institute for Discovery. Go through the site carefully, and you will find everything you are looking for.
mm43
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I'm aware of the failed attempt by an enthusiastic amateur to find Amelia Earhart's wreckage. I'm also aware that the referenced website(s) merely say that the AUV can be fitted with either a single or dual frequency sidescan sonar.
My question is: what frequency is being used in the AF447 search?
I could make an educated guess that the two frequencies are something like 120kHZ and 500kHZ. Therein lies a significant problem. The lower frequency probably lacks the resolution to 'see' a smooth sided object as small as a CVR/DFDR. The higher frequency probably lacks the range to insonify a significant swathe at a reasonable flying height for the AUV over such craggy terrain as the present search site(s).
That's why I ask whether they have deployed a similar sized box onto the seabed to demonstrate what it would look like if insonified by the equipment being used.
Sure, there will be a debris field, but in such a depth it is likely to be quite diffuse and probably enormous. An object as small as a recorder box really needs a methodology verifier.
My question is: what frequency is being used in the AF447 search?
I could make an educated guess that the two frequencies are something like 120kHZ and 500kHZ. Therein lies a significant problem. The lower frequency probably lacks the resolution to 'see' a smooth sided object as small as a CVR/DFDR. The higher frequency probably lacks the range to insonify a significant swathe at a reasonable flying height for the AUV over such craggy terrain as the present search site(s).
That's why I ask whether they have deployed a similar sized box onto the seabed to demonstrate what it would look like if insonified by the equipment being used.
Sure, there will be a debris field, but in such a depth it is likely to be quite diffuse and probably enormous. An object as small as a recorder box really needs a methodology verifier.
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Low Flier, I believe the REMUS 6000 AUV fitted side-scan package consists of either:-
1. RESON Seabat 7125 Multi-Beam (200/400 kHz), or
2. Electronic Still Camera & Strobe, or
3. EdgeTech Dual Frequency (110/420 kHz) Side Scan Sonar and Sub-Bottom Profiler
In this case I suspect that the Seabat 7125 is being used, and is operating in the low resolution search mode at 200kHz. The location of a bottom debris field, no matter how dispersed, will enable a systematic backtrack to where the DFDR/CVR will be if torn from their mounts at impact. The location of larger items on the bottom will probably give other clues, like the heading on impact. The engines for example will be nearly straight down, but other items may have variable glide slopes.
The AUV will normally be programed to fly (it can not hover) at a predetermined height above the terrain at a speed commensurate with battery economy, e.g. 3 knots.
Woods Hole Oceanographic Institution have some example imaging of a 14 foot boat with an outboard motor attached, which was located in 3,500 meters. The side-scan images are at 900kHz, and there is overlaid photographic imaging taken with the onboard strobe camera.
The search team have a TRITON deepsea ROV available to them to do any close-up examination and recovery.
Some of the more specific information you are requesting is not in the public domain, and time will probably reveal what was or wasn't done.
mm43
1. RESON Seabat 7125 Multi-Beam (200/400 kHz), or
2. Electronic Still Camera & Strobe, or
3. EdgeTech Dual Frequency (110/420 kHz) Side Scan Sonar and Sub-Bottom Profiler
In this case I suspect that the Seabat 7125 is being used, and is operating in the low resolution search mode at 200kHz. The location of a bottom debris field, no matter how dispersed, will enable a systematic backtrack to where the DFDR/CVR will be if torn from their mounts at impact. The location of larger items on the bottom will probably give other clues, like the heading on impact. The engines for example will be nearly straight down, but other items may have variable glide slopes.
The AUV will normally be programed to fly (it can not hover) at a predetermined height above the terrain at a speed commensurate with battery economy, e.g. 3 knots.
Woods Hole Oceanographic Institution have some example imaging of a 14 foot boat with an outboard motor attached, which was located in 3,500 meters. The side-scan images are at 900kHz, and there is overlaid photographic imaging taken with the onboard strobe camera.
The search team have a TRITON deepsea ROV available to them to do any close-up examination and recovery.
Some of the more specific information you are requesting is not in the public domain, and time will probably reveal what was or wasn't done.
mm43
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Low Flier, what makes you think they are looking for the box? They first have to develop a notion of where to look with high resolution or even optics. They look for larger pieces of the aircraft, such as the engines, first. Then they start looking for the little stuff within an established debris field.
In round numbers the speed of sound in water is 1500 m/s. 120kHz gives a resolution of about 1500/120000/2 (half wavelength) or about 6 millimeters. Anything smaller than that will be hard to resolve. Something 10 times larger should be within the realm of detection without really fancy processing if it's outside the range of sizes of uninteresting objects in the area.
Off hand I'm curious where you got the sonar resolution data you cited. I presume sonar is different from radar, where I do have some engineering know-how. I also do note that the radar problem is seldom trying to detect an object sitting on another object or the ground. I'm willing to learn.
{^_^}
In round numbers the speed of sound in water is 1500 m/s. 120kHz gives a resolution of about 1500/120000/2 (half wavelength) or about 6 millimeters. Anything smaller than that will be hard to resolve. Something 10 times larger should be within the realm of detection without really fancy processing if it's outside the range of sizes of uninteresting objects in the area.
Off hand I'm curious where you got the sonar resolution data you cited. I presume sonar is different from radar, where I do have some engineering know-how. I also do note that the radar problem is seldom trying to detect an object sitting on another object or the ground. I'm willing to learn.
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Low Flier, what makes you think they are looking for the box?
120kHz gives a resolution of about 1500/120000/2 (half wavelength) or about 6 millimeters.
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Sounds like crossed wires....
Yes the boxes is what it's about but to find them it pays to localize the wreck first
This is an almost uniquely great thread, I hope it stays that way.
Yes the boxes is what it's about but to find them it pays to localize the wreck first
This is an almost uniquely great thread, I hope it stays that way.
resolution
Angular resolution will be more like wavelength/effective receiver length. If its synthetic aperture then resolution will be much better than wavelength. Assuming the object reflects sound well enough the key thing will be to keep seabed clutter out of the resolution cell.
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Low Flier, I'm certainly willing to accept your expertise. The half wavelength would be the smallest detectable object. Resolving it to tell what it is would, of course, require a much larger object. I simply mumbled that the box is indeed much larger than the minimum sized object that will cause a reflection.
Is your experience operational or engineering design? If it's the latter I'd love to talk dirty (er engineering) with you.
Do you have experience with chirp techniques? Do they help improve resolution? They certainly do for radar.
And thanks for your information. I do like to learn.
Thanks
{^_^}
Is your experience operational or engineering design? If it's the latter I'd love to talk dirty (er engineering) with you.
Do you have experience with chirp techniques? Do they help improve resolution? They certainly do for radar.
And thanks for your information. I do like to learn.
Thanks
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Update: "Seabed Worker" & "Anne Candies" - 2 May 2010 positions
"Seabed Worker" at 02/14:44z was at 0°26'38"N 32°0'10"W, track 016°T/11.7KT, and heading for the search area.
"Anne Candies" at 02/1255z was 2°14'29S 39°20'56'W, track 304°T/11.1KT, and heading towards the Gulf of Mexico.
Thanks to broadreach for the data.
mm43
"Anne Candies" at 02/1255z was 2°14'29S 39°20'56'W, track 304°T/11.1KT, and heading towards the Gulf of Mexico.
Thanks to broadreach for the data.
mm43
