Advanced search  
Pages: 1 [2] 3 4 ... 10   Go Down

Author Topic: Odds of Spotting Survivors from the Air  (Read 124801 times)

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #15 on: November 11, 2011, 10:28:17 AM »

I can't believe you're still trying to defend this trench.

The gentleman is nothing if not entrenched...  ;D

It is not hard to imagine how easily people could have been missed if on the island - that's a lot of land to cover and the techniques and equipment weren't exactly ideal.  The evident confusion as to the scale of vegetation from the air by at least one observer suggests it might have been hard to appreciate how difficult spotting a tiny figure might have been, should one have emerged in the right open spot at the right moment.

The report of 'signs of recent habitation', whatever exactly these 'markers' were, and the apparent absence at that time of just whom that might have been will probably haunt most of us for some time.  It is not at all a given that a lone survivor, or two, would have been spotted without the aid of some more obvious artifact - like a fair-sized cabin-class twin monoplane - being clearly present.  I would like to think it was still visible in the surfline or something, but it's all too possible that the plane was already well-awash in heavy surf or even nearly gone from sight by that date.

LTM -
------------------------
The issue of vegetation does not apply to people standing in the clear, on the beach or on the reef flat, and the cumulative probability of detection in that case is 95% after only two passes. I never said it was a certainty that they would have been spotted only that it was highly probable, a much higher probability than Ric estimated. Like I said, I have posted the POD tables and everyone is invited to do their own calculations and come to their own conclusions. And keep in mind, the agencies that developed the POD tables, the Coast Guard, the Navy, the Army, and the Air Force, don't have a dog in this fight. They developed these tables for the critical purpose of conducting thorough searches to save lives so there is every reason to accept that these are the most accurate estimates of the probability of detection. You want to "imagine" that it would have been very difficult to spot Earhart but the POD tables were not developed by "imagination" they are based on hard data analyzed by serious grown-ups.

It is very easy to spot objects submerged under water from an airplane, ever fly over the Bahamas? Ten foot deep water looks just like dry land from the air. That is the reason airplanes were used to spot even deeply submerged U-Boats in WW2. Unless the plane had floated away or had sunk very deep over the edge of the reef (so deep, in fact, that it could never have been washed back onto the reef flat) it is also likely that the Lambrecht fight would have spotted the Electra even if it was underwater.

gl
« Last Edit: November 11, 2011, 11:46:31 AM by Gary LaPook »
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5907
  • "Do not try. Do or do not. There is no try" Yoda
Re: Odds of Spotting Survivors from the Air
« Reply #16 on: November 11, 2011, 11:05:50 AM »

1. We have both stated our positions regarding the probability that Earhart and Noonan would have been detected by Lambrecht and the other 5 aviators in his search formation if they had been on the island.

Search formation?  Tell me how you know they used any kind of formation in searching the island (without using the words "would have").  There were three airplanes, each with a pilot and an observer.  Lambrecht's observer was Seaman First Class J.L. Marks. He had flown just once before on this cruise, with Lambrecht on the morning flight the day before.  The other observers on the McKean/Gardner/Carondelet Reef flight were Radioman 3rd Class Williamson who rode in the rear cockpit of Fox's airplane, and Lt. C. F. Chillingworth, the ship's Ass't 1st Lt. and Damage Control Officer, who rode behind Bill Short.  More often than not during the Earhart search, the observers seem to have been whoever could cadge a ride - one of the three "AVCADs" (Aviation Cadets) or one of the ship's officers.

Your position is that there was a 80 to 90% chance that they would have been missed by the searchers and my interpretation of the cumulative POD table is that the probability of their being missed was only 10% if they were in the treeline and only a 5% chance if they were standing out in the open, on the beach or on the reef flat. I posted the tables so the reader can do his own calculation and come to his own conclusion, it ain't rocket science.

You just don't get it about this "would have" business.  Now you're putting the words in MY mouth.  What I wrote was:
"According to present- day Civil Air Patrol Probability of Detection (POD) tables, the chance of Colorado’s planes locating the aircraft in the course of a single inspection of each island was on the order of 10 to 20 percent.   In other words, if the Earhart plane was on one of the islands of the Phoenix Group, there is an 80 to 90 percent chance that Colorado’s search missed it."

I made a statement about the probability indicated by the modern day POD tables. You and I disagree about how to interpret those tables.  That's fine, but I did not say there was a 80 to 90% chance that they would have been missed by the searchers.  My "position" is that Lambrecht didn't see anybody. 

In my prior post, for simplification, I assumed the strip of land making up Gardner Island between the lagoon and the sea was half a nautical mile wide (3038 feet), but this was an overstatement.

Wait a minute, you mean you've gone on and on about all this and you're only NOW familiarizing yourself with the actual dimensions and characteristics of the island?  Have you even looked at the DVD?  Let me make it easier for you (and any forum subsribers who are not yet TIGHAR members).
The Aerial Tour of Nikumaroro is now up on YouTube.  Just click the link.

2. Regarding the radios in the planes, even if the planes did not have VHF or HF voice capability but only CW to communicate with the Colorado there was nothing to stop them from sending morse code messages from plane to plane, the radios work both ways.

I don't know that each of the planes was equipped with a radio.  Do you?  I do know that, according to the Colorado deck log, throughout the entire voyage only one of the aircraft, Fox's airplane 4-0-6, carried a radioman.

3. You asked "where did I state that?"

Well, you wrote the following in your November 4th post:

"So if Earhart and Noonan were in the vicinity of Camp Zero (about a quarter of a mile north of the shipwreck and inland under the buka trees for shade) when the planes came over, why weren't they seen?"

That's right, but you claimed,
"You state that at that time Earhart was at "camp Zero" a quarter mile north of the ship and inside the treeline for shade, so very close to the beach."

You keep putting words in my mouth.  Don't you see the difference between "if Earhart and Noonan were in the vicinity of Camp Zero" and "at that time Earhart was at "camp Zero"?

4. Since your statement as to where you think camp zero was located is pure speculation then I have the right to also speculate. I think that if they were on the island that they made their camp on the beach near he NC so as to be near where they expected any searchers would look first and to have the benefit of any little breezes that might come along instead of going through all the tough scaevola brush to be in a windless and oppressively hot location under the trees. They built a shelter out of either vegetation or with materials salvaged from the plane or a combination of both.

We all have the right to speculate. My speculation about where they camped is based upon having spent rather a lot of time on that particular beach and in the buka forest (although not the buka forest on that particular part of the island).  What is your speculation based on?

5. You speculate that Lambrecht (and the other two planes) only did a cursory "circle and zoom" and then flew away but using your own estimate of the time they were over Gardner, 18 to 28 minutes, it is simple math to show that each of the three planes had enough time to make three to five complete circuits of the island, a total of 9 to 15 passes over each spot on the island for the flight of three planes. They were motivated to find Earhart (everyone wants to be a hero) so it is much more likely that they did a very thorough job in conducting this search than your speculation that they were off on a lark.

I think everyone can make up their own mind about what the pilots and other personnel aboard Colorado thought about their mission.  Short's letter is revealing. "This whole business is certainly a royal pain in the neck..."
The headline of the ship's newspaper "The Colorado Lookout" was Plane Search Halts Cruise.

6. Looking just at the Lambrecht search, as interpreted through the use of the modern tables in the National Search and Rescue Manual and the CAP manual which show that there is a very high probability that they would have been spotted if they had been on the island, my conclusion is that it is highly probable that they were NOT on the island at the time the search was made.

As I recall you also concluded that it was highly probable that Noonan could successfully navigate to Howland Island, and that it was impossible for AE and FN to fly down the LOP to Gardner, and that it was nearly certain that the plane, if washed over the reef edge, would float indefinitely.  I'll say this - your way of reaching conclusions is a lot more economical than our way.
« Last Edit: November 11, 2011, 11:08:03 AM by Ric Gillespie »
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #17 on: November 11, 2011, 07:36:31 PM »




------------------------
The issue of vegetation does not apply to people standing in the clear, on the beach or on the reef flat, and the cumulative probability of detection in that case is 95% after only two passes.
gl

----------------------------

It was interesting watching the helicopter tour of the island. I note that from 10:02 to 10:19 it wasn't difficult at all to see the three people in the open wading out to the skiff even though only their heads and shoulders were above the surface of the water. And then again at 11:57 you can still see the three waders on the east side of the lagoon from a position offshore from the western shore of the island, a distance of 3,000 feet, a half NM.

gl
« Last Edit: November 11, 2011, 07:53:19 PM by Gary LaPook »
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5907
  • "Do not try. Do or do not. There is no try" Yoda
Re: Odds of Spotting Survivors from the Air
« Reply #18 on: November 11, 2011, 07:53:38 PM »

it wasn't difficult at all to see the three people in the open wading out to the skiff even though only their heads and shoulders were above the surface of the water.

Thanks for demonstrating how difficult it is to tell what you're looking at from the air at Nikumaroro.  Wading out to the skiff at the Seven Site the water is never over knee deep.
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #19 on: November 11, 2011, 11:01:28 PM »

it wasn't difficult at all to see the three people in the open wading out to the skiff even though only their heads and shoulders were above the surface of the water.

Thanks for demonstrating how difficult it is to tell what you're looking at from the air at Nikumaroro.  Wading out to the skiff at the Seven Site the water is never over knee deep.
---------------------------
O.K. it was still easy to see them.

gl
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #20 on: November 11, 2011, 11:05:32 PM »

Something that struck me after watching the TIGHAR DVD from the helicopter was the lack of birds - or maybe they just didn't show up because of the speed of that lil' guy? I remember the Colorado planes decided to fly at 400 feet because of the risk of collision with clouds of seabirds - which virtually eliminated any chance of seeing anyone on the ground.

LTM,
Monty Fowler,
TIGHAR No. 2189 CER
---------------
Yah, what happened to the birds?

gl
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5907
  • "Do not try. Do or do not. There is no try" Yoda
Re: Odds of Spotting Survivors from the Air
« Reply #21 on: November 12, 2011, 06:27:52 AM »

Yah, what happened to the birds?

They're there, roosting in the trees. We stayed high enough to not stir them up.  The pattern of typical bird activity at Niku is pretty interesting.  There are small birds - fairy terns and noddys - that stay down low.  Not a factor to aircraft.  The big birds are boobys and frigates.  The boobys fly out to sea early in the morning and catch fish by diving into the water.  They come home around 10 or 11 o'clock with their gullets full of fish.  The frigates are waiting for them, circling around, riding the thermals over the buka forest at about 300 feet.  They dive on the boobys, scaring them into puking up their fish which the frigates grab on the fly.  Mid-airs are not uncommon.  I've had to dispatch several boobys found on the ground with broken wings.
Usually by noontime everybody is back to their roost.  The aerial tour was flown early in the afternoon.

Lambrecht wrote:
"As in the case of the subsequent search of the rest of the Phoenix Islands one circle at fifty feet around M’Kean aroused the birds to such an extent that further inspection had to be made from an altitude of at least 400 feet."

Taken literally, he's saying that they made their first pass over all of the islands at 50 feet but then had to climb to at least 400 feet because they had aroused the birds - but I'm not sure that's what he means. 
Logged

Andrew M McKenna

  • Administrator
  • *
  • Posts: 680
  • Here I am during the Maid of Harlech Survey.
Re: Odds of Spotting Survivors from the Air
« Reply #22 on: November 12, 2011, 11:20:29 AM »


----------------------------

It was interesting watching the helicopter tour of the island. I note that from 10:02 to 10:19 it wasn't difficult at all to see the three people in the open wading out to the skiff even though only their heads and shoulders were above the surface of the water. And then again at 11:57 you can still see the three waders on the east side of the lagoon from a position offshore from the western shore of the island, a distance of 3,000 feet, a half NM.

gl

At 10:02 - 19, the helicopter is right on top of them, and if Ric didn't point them out and if the skiff wasn't there, my guess is that many folks would not have realized that those dots were people.


At 11:57, it is pretty easy to see those people because the camera image is highly zoomed in on them.  Much harder to see with the naked eye, in fact before the zoom at 11:55, you can't even pick out the skiff, a 21 ft red object in the lagoon, out in the open.

Which takes me back to the discussion of Search Visibility.  What is the search visibility in this case when we cannot pick out and recognize the skiff from 3000 ft?  Certainly not 4 miles.  This just points out that the search visibility has to be relative to the object you are looking for, not just any object you can see and recognize as you have suggested.  Taken to the extreme, you would not take the distance you can see an object such as the Empire State Building, or the Graf Zeppelin and use that as your search visibility for looking for a person.  It just doesn't make sense, and in the end leads to an unrealistic POD as you yourself have elegantly demonstrated by suggesting that the POD for one pass over heavily forested areas is 30%, and 90% after 8 passes.

Anyone who has seen the aerial tour should think about this.  There are 4 persons visible in the video, and they are fairly easy to find because they are pointed out by the narrator, and in one case they are in a group next to a red boat.  How easy would it have been to pick out those persons, white shirt and all, if they weren't pointed out to you?  And, think about this, there were 11 TIGHARs on Niku that day (3 divers were on the Naia), 4 of whom just happened to be at the edge of the trees that can be seen, but can any of you pick out the other 6 who were back in the trees, even when we know where they are?  And that is from 200 ft off the deck.

Now imagine you are flying 200 ft higher than the helicopter and there are only two persons, maybe just one, down in the trees.  What is the probability of seeing them?  Certainly not 30%.  If the AE was back in the bush when the search planes happened to show up, there would be virtually no way to be spotted in the short time the aircraft were overhead.

Andrew
« Last Edit: November 12, 2011, 11:22:27 AM by Andrew M McKenna »
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #23 on: November 12, 2011, 10:12:12 PM »


----------------------------

It was interesting watching the helicopter tour of the island. I note that from 10:02 to 10:19 it wasn't difficult at all to see the three people in the open wading out to the skiff even though only their heads and shoulders were above the surface of the water. And then again at 11:57 you can still see the three waders on the east side of the lagoon from a position offshore from the western shore of the island, a distance of 3,000 feet, a half NM.

gl



Which takes me back to the discussion of Search Visibility.  What is the search visibility in this case when we cannot pick out and recognize the skiff from 3000 ft?  Certainly not 4 miles.  This just points out that the search visibility has to be relative to the object you are looking for, not just any object you can see and recognize as you have suggested.  Taken to the extreme, you would not take the distance you can see an object such as the Empire State Building, or the Graf Zeppelin and use that as your search visibility for looking for a person.  It just doesn't make sense, and in the end leads to an unrealistic POD as you yourself have elegantly demonstrated by suggesting that the POD for one pass over heavily forested areas is 30%, and 90% after 8 passes.

Andrew

Andrew, I think I can convince you that your understanding of the Probability Of Detection tables is incorrect. You think that "Search Visibility" means the distance that the object you are searching for can be detected. If this were the case then there must be another table in the CAP Manual listing the distances that various objects can be detected with a title such as "Search Visibilities of Various Objects" but there is no such table. Without such a table then each searcher must make his own guess as to the distance that various objects could be spotted to use as the "search visibility"  value for entering the POD table. Obviously this can't be correct because ten different pilots could come up with ten different search visibilities for the same object such as a small aircraft or a person. And something else, surely there must be large objects that can be spotted further away than 4 mi, such as a crashed B-52, so why doesn't the POD table cover these cases and have columns extending to greater distances as you would expect if your idea of search visibility were the correct one.

But this is not the only proof I have that you are mistaken. I am attaching page 150 of CAP manual which contains the definitions of the terms. "Meteorological Visibility" is the distance that large objects such as mountains can be seen while "Search Visibility" is the distance that small objects such as cars can be seen. It states that "search visibility is always less than meteorological visibility" comparing the same types of visibilities with no mention of different types of search objects. Look at the definition of "Scanning Range" which is the distance that a searcher "is expected to have a good chance of spotting the search objective" so scanning range is what you have mistaken for search visibility. To make this even more clear, the definition continues, "Scanning range can be less than but never greater than the search visibility" so these are obviously two different things.


Additional proof is supplied by looking at the attached pages 155 to 158 of the CAP manual that works through an example of how to use the POD tables. The given facts are a Cessna 172 lost in flat terrain and "flight visibility is forecast to be more than 10 miles." Based on this information the example uses the 4 mi search visibility column in the POD table because the flight visibility was equal to or greater than 4 mi. I have marked the appropriate values in the POD table with red. You will argue that the reason that the 4 mi column was used is that a Cessna 172 can be spotted at 4 mi but, if so, where did that information come from? But we can show that this is not the case because a second example is also given, this time searching for a Cessna 182. A Cessna 172 and a Cessna 182 are virtually indistinguishable from the air, they both have 36 foot wingspans and the 172 is 27 feet long and the 182 is 28 1/2 feet long  so they should both be detectable at the same distance, the same scanning range. The facts given include "current visibility in the area is 3 miles." I have marked the values used in this example in blue on the POD tables and it is clear that the "3 mi" column was used and was based on the current visibility being 3 miles. Again note that there was no mention of "search visibility" in the stated facts only "flight visibility" and "current visibility" neither of which have any relationship to the distance at which these two similar planes could be spotted.

The National Search And Rescue Manual covers ocean searches in much more detail than land searches. Tables 4-4 through 4-9 cover searches for 25 different kinds of objects from a person in the water to, 1 to 25 person life rafts, power boats from less than 15 feet up to 90 feet, sailboats from 15 feet up to 90 feet, and ships from 90 feet up to greater than 300 feet. This is the kind of table that is missing from the CAP land search manual. These tables list the distance at which you have an 80% probability of detection based on altitudes from 300 feet up to 3,000 feet, prevailing visibility from 1 NM to 30 NM and also divided by fixed wing and helicopter. For example, there is an 80% probability of spotting a ship longer than 300 feet with visibility of 30 NM and from an altitude of 500 feet at a distance of 20.7 NM. For a 40 foot power boat the distance is 8.25 NM using the same conditions. So we know that these objects are large enough to be spotted at those distances. Using your analysis you would think that if the visibility goes down to 10 NM that you would be able to see the large ship at 10 NM as restricted only by the visibility since it is large enough to be seen at twice that distance and you would expect no change for the 40 foot boat since it is large enough to be visible only at 8.25 NM so it shouldn't be further restricted by a 10 NM visibility. But, in fact, if the visibility goes down to 10 NM the spotting distance goes down to 6.6 NM for the 300 foot ship and 4.05 for the the 40 foot power boat. Lower visibilities make it harder to see objects even though they stay the same size and are closer than the limit of visibility. This is what the search visibility columns accomplish in the CAP manual, accounting for the greater difficulty of spotting an object with lower visibility (less clarity of the atmosphere) and these columns have nothing to do with the size of the object or how far it could be spotted in perfect conditions.

gl
« Last Edit: November 12, 2011, 10:20:30 PM by Gary LaPook »
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5907
  • "Do not try. Do or do not. There is no try" Yoda
Re: Odds of Spotting Survivors from the Air
« Reply #24 on: November 13, 2011, 08:02:03 AM »

Gary forgot to attach the definitions from page 150 of the CAP manual.  Here they are:

Meteorological Visibility - the maximum distance at which large objects, such as a mountain, can be seen.

Scanning Range - the lateral distance from a scanner's search aircraft to an imaginary line on the ground parallel to the search aircraft's ground track. Within the area formed by the ground track and scanning range, the scanner is expected to have a good chance at spotting the search objective. Scanning range can be less than but never greater than the search visibility.

Search Visibility - the distance at which an object on the ground (CAP uses an automobile as a familiar example) can be seen and recognized from a given height above the ground. Search visibility is always less than meteorological visibility. [Note that on the POD chart that the maximum search visibility listed is four nautical miles.]


I interpret this to mean that Search Visibility changes based upon the size of the object. CAP uses an automobile as a familiar example.  At best, you can see a car on the ground from four miles away. That's why the maximum search visibility listed is four nautical miles.  Scanning Range is much more specific and is "the lateral distance from a scanner's search aircraft to an imaginary line on the ground parallel to the search aircraft's ground track."

If anything is proved by all this it's that the CAP POD tables do not contemplate a search for anything smaller than a car.  Most people are smaller than most cars.
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2980
Re: Odds of Spotting Survivors from the Air
« Reply #25 on: November 13, 2011, 08:39:02 AM »

Now imagine you are flying 200 ft higher than the helicopter and there are only two persons, maybe just one, down in the trees. 

In correcting our understanding of the difference between the helicopter and the naval aircraft, don't we also have to imagine a different field of vision for the pilot and observer as compared to that of the heli pilot and observer?

It seems to me that helicopters make excellent observation platforms.  The rotor is above the observers.  A camera operator often can shoot directly down and to the side of the fuselage, giving a much better view than is possible from the cockpit of a biplane. 

In other words, the geometry of the visible area is different.  At the same altitude and airspeed, the biplane occupants must look further forward at a smaller slice of the horizon than the occupants of the helicopter.  The wedge that the biplane observers see is marked by the fuselage of the biplane on one side and the wings on the other.  The folks in the helicopter don't have such large constraints on their field of view.

This is just a guess ...
LTM,

           Marty
           TIGHAR #2359A
 
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5907
  • "Do not try. Do or do not. There is no try" Yoda
Re: Odds of Spotting Survivors from the Air
« Reply #26 on: November 13, 2011, 08:49:53 AM »

In other words, the geometry of the visible area is different.  At the same altitude and airspeed, the biplane occupants must look further forward at a smaller slice of the horizon than the occupants of the helicopter.  The wedge that the biplane observers see is marked by the fuselage of the biplane on one side and the wings on the other.  The folks in the helicopter don't have such large constraints on their field of view.

This is just a guess ...

I have considerable time in both helicopters and open cockpit biplanes.  Marty is right.

This is not a guess......
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #27 on: November 13, 2011, 05:35:12 PM »

Gary forgot to attach the definitions from page 150 of the CAP manual.  Here they are:

Meteorological Visibility - the maximum distance at which large objects, such as a mountain, can be seen.

Scanning Range - the lateral distance from a scanner's search aircraft to an imaginary line on the ground parallel to the search aircraft's ground track. Within the area formed by the ground track and scanning range, the scanner is expected to have a good chance at spotting the search objective. Scanning range can be less than but never greater than the search visibility.

Search Visibility - the distance at which an object on the ground [1](CAP uses an automobile as a familiar example) can be seen and recognized from a given height above the ground. Search visibility is always less than meteorological visibility. [Note that on the POD chart that the maximum search visibility listed is four nautical miles.]


[2]I interpret this to mean that Search Visibility changes based upon the size of the object. CAP uses an automobile as a familiar example.  At best, you can see a car on the ground from four miles away. That's why the maximum search visibility listed is four nautical miles.  Scanning Range is much more specific and is "the lateral distance from a scanner's search aircraft to an imaginary line on the ground parallel to the search aircraft's ground track."

If anything is proved by all this it's that the [3]CAP POD tables do not contemplate a search for anything smaller than a car.  Most people are smaller than most cars.

----------------------

I attached page 150 to my prior post, go back and look.
https://tighar.org/smf/index.php?action=dlattach;topic=508.0;attach=309

1. An automobile is only an "example" of thing that a pilot might look for in order for the search pilot to estimate what the actual visibility in the search area is (search visibility) which is likely to be different than the "meteorological visibility" as measured at the airport. If you can identify a car on the ground it doesn't mean you have 4 mi search visibility only that you know that it is a car. After you identify the car you estimate how far away it is and that distance is the measure of search visibility.

2. Perhaps you missed this part of my post:

"Look at the definition of "Scanning Range" which is the distance that a searcher "is expected to have a good chance of spotting the search objective" so scanning range is what you have mistaken for search visibility. To make this even more clear, the definition continues, "Scanning range can be less than but never greater than the search visibility" so these are obviously two different things."

3. The manual states that persons on the ground are the second most common search subjects so the CAP contemplates searching for persons and uses the POD table to plan the search for people  and to assess the effectiveness of the completed search.

If you are correct that the smallest thing covered by the POD table is the size of a car, since people are the second most common object searched for, where is the correction table that would be necessary to adjust the percentages derived from the POD tables to account for the smaller object of a person. And why don't the tables include greater distances than 4 mi because you can certainly see a crashed B-52 more than 4 mi away?

gl
« Last Edit: November 13, 2011, 07:25:27 PM by Gary LaPook »
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #28 on: November 13, 2011, 11:25:10 PM »


-------------------------------


You can prove this to yourself. Go outside and look down the sidewalk and I'll bet you can see people walking a quarter mile (two city blocks) down the sidewalk. 
gl

--------------------------------------
By chance today I had the opportunity to see how far I can see an object the size of a person. I was driving on the freeway and I noticed up ahead a person on a motorcycle, I could clearly see his body and shoulders. When he passed an exit ramp I looked at my odometer and then again when I passed the exit. Turns out he was .5 miles ahead of me.  I then drove faster so I could close the distance until I could see his helmet clearly. I did the same experiment and I could see his helmet clearly a .3 miles. Although I don't claim that this was representative of the conditions in the bush at Gardner the test conditions were similar to spotting someone in the open on the island. So it is possible to see a human sized object at .5 miles under optimum conditions, and maybe more. You can repeat this experiment for yourselves.

gl

Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Odds of Spotting Survivors from the Air
« Reply #29 on: November 13, 2011, 11:33:56 PM »

Gary forgot to attach the definitions from page 150 of the CAP manual.  Here they are:

Meteorological Visibility - the maximum distance at which large objects, such as a mountain, can be seen.

Scanning Range - the lateral distance from a scanner's search aircraft to an imaginary line on the ground parallel to the search aircraft's ground track. Within the area formed by the ground track and scanning range, the scanner is expected to have a good chance at spotting the search objective. Scanning range can be less than but never greater than the search visibility.

Search Visibility - the distance at which an object on the ground (CAP uses an automobile as a familiar example) can be seen and recognized from a given height above the ground. Search visibility is always less than meteorological visibility. [Note that on the POD chart that the maximum search visibility listed is four nautical miles.]


I interpret this to mean that Search Visibility changes based upon the size of the object. CAP uses an automobile as a familiar example.  At best, you can see a car on the ground from four miles away. That's why the maximum search visibility listed is four nautical miles.  Scanning Range is much more specific and is "the lateral distance from a scanner's search aircraft to an imaginary line on the ground parallel to the search aircraft's ground track."

If anything is proved by all this it's that the CAP POD tables do not contemplate a search for anything smaller than a car.  Most people are smaller than most cars.

Note, the definition of "search visibility" says "the distance at which an object on the ground (CAP uses an automobile as a familiar example) can be seen and recognized from a given height above the ground." It DOES NOT say "the distance at which an object on the ground (CAP uses an automobile as a familiar example) can be seen and recognized from a given distance." So your assertion that the CAP considers 4 mi as the distance that a car sized object can be spotted is disproved by the definition itself.

Andrew pointed me to this reference:

http://www.cap-es.net/NESA%20MAS/Aircrew%20Chapter%209%20-%20Search%20Planning%20and%20Coverage.ppt

and I am attaching the definitions slide from there. You will note in this reference there is no mention of an automobile in the definition of "search visibility" so there is no reason to think that the distance that you can see an automobile is taken as any kind of standard for determining "search visibility."

gl
« Last Edit: November 14, 2011, 12:14:23 AM by Gary LaPook »
Logged
Pages: 1 [2] 3 4 ... 10   Go Up
 

Copyright 2021 by TIGHAR, a non-profit foundation. No portion of the TIGHAR Website may be reproduced by xerographic, photographic, digital or any other means for any purpose. No portion of the TIGHAR Website may be stored in a retrieval system, copied, transmitted or transferred in any form or by any means, whether electronic, mechanical, digital, photographic, magnetic or otherwise, for any purpose without the express, written permission of TIGHAR. All rights reserved.

Contact us at: info@tighar.org • Phone: 610-467-1937 • Membership formwebmaster@tighar.org

Powered by MySQL SMF 2.0.18 | SMF © 2021, Simple Machines Powered by PHP