#193214 - 01/11/1004:25 AMMore good signal mirror videos - on YouTube
[Re: rafowell]
rafowell
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Registered: 11/29/09
Posts: 261
Loc: Southern California
Originally Posted By: rafowell
Air Force Academy retired survival training director Peter Kummerfeldt lectures/demonstrates signal mirrors for 4:34 of this 5:28 long video clip online:
I've looked through the various survival signal mirror videos on YouTube and put together a "playlist" of those I thought were good, sorted roughly by my ranking.
[ Disclosure: many of these are mine <grin>, though only one of the top seven. ]
#1: Survival Signal Mirror Flashes at 0.7, 11.1, 43 mile range {Mine} #2: Starflash survival signal mirror 2x3" #3: Survival: How to use a Signal Mirror. #4: Ed Viesturs Survival Essentials { Some non-mirror stuff, but demo of Rescue Flash #5: MDB signal Mirror PT1 { Part 1 of a 3-part review of Rescue Flash & 4 others} #6: MDB signal Mirror PT2 #7: MDB signal Mirror PT3 #8: 3"x5" Glass Signal Mirror at 44 miles - digital zoom {mine} #9: 01 { Comparison of 5 signal mirrors - field test } #10: Signal Mirror { comparison: mirror, Altoids tin, aluminum foil} #11: 22 mile flash, 3"x5" glass mirror {mine} #12: 22 mile flash, 2"x3" plastic mirror {Rescue Flash, mine} #13: 3"x5" glass signal mirror at 44 miles - digital zoom {mine} #14: 3"x5" glass signal mirror at 44 miles {mine} #15: Signal Mirror Flashes at 11.1 miles (3"x5" glass mirror) {mine} #16: espejos de señal (signal mirrors) {flashes from multiple sites}
_________________________
A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB)(Ocean Signal PLB)
#207777 - 09/11/1007:15 PMNice new signal mirror video, plus 3 old ones.
[Re: rafowell]
rafowell
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Registered: 11/29/09
Posts: 261
Loc: Southern California
Here's another signal mirror video that was posted recently. Note that the user tried aiming the mirror with and without the "fireball" aiming aid, and found the aiming aid worked much better for them. Interesting to hear the reactions of folks who hadn't seen a signal mirror in action before.
(The Peter Kummerfeldt video at the start of this thread is offline at the moment, but I contacted the reporter and he says he'll get it back online - I'll post again when that happens.)
While I've posted it elsewhere, here's a WWII training video for mirrors aimed by the "double-sided mirror" method, with general discussion of signal mirror range, etc. (Slow start, but there is narrative and video after a minute or so).
Here again (not new) is my video of a 3"x5" glass mirror at 0.7, 11.1 and 43 miles (the last on a _very_clear day).
This last is the 2"x3" American Medical Kits "Rescue Flash" mirror designed by Doug Ritter, at 22 miles. Note that the telephoto video is more sensitive than the naked eye, but you can here me call out the flashes that were visible to my (middle aged) naked eyes.
_________________________
A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB)(Ocean Signal PLB)
#207791 - 09/12/1002:16 AMRe: Nice new signal mirror video, plus 3 old ones.
[Re: sotto]
rafowell
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Registered: 11/29/09
Posts: 261
Loc: Southern California
Originally Posted By: sotto
My understanding is that even a board freshly dipped in water will give a strong sun reflection.
If a board is the best you've got, wetting it down is worth a shot (or any flat material). It is likely to have the advantage of a lot of area to make up for the lower reflectance.
I'd make sure it is the best I had, though. Flat window glass is better, and flat sheet metal better yet. There have been several rescues due to reflected light from ration tins.
The wet board suffers from:
[1] lower reflectivity [2] poor flatness [3] the problem of aiming
In detail:
[1] lower reflectivity
You're basically reflecting off the surface of water, which is less reflective than a mirror, though the disadvantage does drop at shallow angles[A]. A good glass mirror has a reflectivity of better than 85% When signaling directly to the sun (e.g., East at dawn) the glass mirror is 40 times more reflective than water, and plain window glass twice as much. When the sun is directly overhead (noon at the equator) and you are signaling to the horizon (90 deg sun-mirror-target), the glass mirror is still 29 times as reflective as the water, and the window glass 1.8 times as much. When the sun-mirror-target angle is 135 degrees, the mirror is still 7 times as reflective as the board.
[2] poor flatness
What makes a good signal mirror surprisingly bright is that the sun beam reflected off a flat surface is very narrow and concentrated - about 0.54 deg in diameter, or the apparent size of Lincoln's head on a penny held at arms length (or a full moon). If non-flatness doubles the width of that cone, the brightness drops 4x (though it is admittedly easier to hit something). That's why, as an improvised mirror, the window glass is far better than the wet board - the flatness is better as well as the reflectivity.
[3] The problem of aiming
What makes a real signal mirror much better than a plain mirror is the aiming aid. As the maker of this week's video learned, it is far easier to hit your target with a retroreflective aiming aid than with the "vee-finger" approach.
My understanding is that even a board freshly dipped in water will give a strong sun reflection.
If a board is the best you've got, wetting it down is worth a shot (or any flat material). It is likely to have the advantage of a lot of area to make up for the lower reflectance.
I'd make sure it is the best I had, though. Flat window glass is better, and flat sheet metal better yet. There have been several rescues due to reflected light from ration tins.
The wet board suffers from:
[1] lower reflectivity [2] poor flatness [3] the problem of aiming
In detail:
[1] lower reflectivity
You're basically reflecting off the surface of water, which is less reflective than a mirror, though the disadvantage does drop at shallow angles[A]. A good glass mirror has a reflectivity of better than 85% When signaling directly to the sun (e.g., East at dawn) the glass mirror is 40 times more reflective than water, and plain window glass twice as much. When the sun is directly overhead (noon at the equator) and you are signaling to the horizon (90 deg sun-mirror-target), the glass mirror is still 29 times as reflective as the water, and the window glass 1.8 times as much. When the sun-mirror-target angle is 135 degrees, the mirror is still 7 times as reflective as the board.
[2] poor flatness
What makes a good signal mirror surprisingly bright is that the sun beam reflected off a flat surface is very narrow and concentrated - about 0.54 deg in diameter, or the apparent size of Lincoln's head on a penny held at arms length (or a full moon). If non-flatness doubles the width of that cone, the brightness drops 4x (though it is admittedly easier to hit something). That's why, as an improvised mirror, the window glass is far better than the wet board - the flatness is better as well as the reflectivity.
[3] The problem of aiming
What makes a real signal mirror much better than a plain mirror is the aiming aid. As the maker of this week's video learned, it is far easier to hit your target with a retroreflective aiming aid than with the "vee-finger" approach.
OK, I looked at those equations, and it looks like the best signaling mirror then would be a flattened stick silvered on one side rather than a small rectangle (i.e. a ruler or yardstick shape) and held vertically and swept slowly back and forth across the target a la the beam from a Rescue Laser Flare. It would be highly reflective and theoretically throw a beam with a larger angle and with a greater chance of sweeping across the target (or horizon) in the case of "wishful" signalling. As I recall, the Fresnel lenses in the old lighthouses were long narrow prisms rather than relatively short rectangles. One could flatten one side of a hiking staff, for example, and mount a plexiglas mirror on it. I'm gonna try that sometime when I get tired of hanging upside down over the Santa Monica freeway for grins. ;-)
Edit: In the course or thinking about this further, I ran across this compact potentially useful solution:
#212751 - 12/09/1006:41 AMV-finger signal mirror tutorial, comparisons
[Re: rafowell]
rafowell
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Registered: 11/29/09
Posts: 261
Loc: Southern California
Here's a new signal mirror training video on YouTube, and some comparison of results using various methods of aiming signal mirrors.
The new video teaches the "V-finger" method of aiming signal mirrors, a method taught in USAF survival manuals for aiming improvised signal mirrors.
There's a lot of good stuff in this <4 minute video - I think this video was extremely well done. The author has other survival-themed videos I plan to look at.
- The video illustrates the V-finger method from many points of view:
signaler's point of view
profile view of signaler
side view of signaler
receiver view of signaler
- It also adds
tips on making the flash look artificial and deliberate
safety tips
some physics
mention of signaling with moonlight
notes that many of your flashes will miss using V-finger
While knowing how to use an improvised reflector as a signal mirror is important, I stress that you will put many more flashes on your target if you use a mirror with a retroreflective aiming aid (e.g. the Doug Ritter designed Rescue Flash, the Ultimate Survival StarFlash used by the USAF and USCG, Coghlan's glass "Survival Signal mirror", Coglan's floating "Sight-Grid Signal Mirror" etc.).
Does a good aimer make a big difference?
You bet!
In the video above, the signaler gets about 22 solid flashes/minute using V-finger. In the video below, a newbie gets over 60 flashes/minute with a mesh retroreflective aimer.
In the flashing sequence of the first video (2:40-3:03) I see 8 solid flashes* in 22 seconds (about 22 flashes/minute), at short range, and if I look closely, I see 13 faint flickers as well, so at least 58 flashes/minute are going out, but most are missing, as his voiceover notes.
In contrast, in the video below, my friend's flashes hit me nearly continuously, using a mirror with a mesh retroreflector aimer. This is all the more impressive when you know this is my friend's first session with this mirror (which I loaned him), and I'm seeing these nearly continuous flashes with my naked eye at a range of 22 miles. (My counting in the narration is to try to see how many seconds of essentially continuous illumination he could manage.)
( Full screen version at YouTube ) This is a solid clue that hitting the target using V-finger aiming isn't as easy as you'd like - but why is it hard?
The first video also illustrates some of the problems you face with V-finger aiming.
First, the signal mirror beam is very narrow. At 3:47 into the first video, you can see the mirror spot on the stop sign. See how small that spot is - a fraction of the apparent width of a finger, and an even smaller fraction of the space between the V-finger. At my arm length, the spot is the apparent size of Lincoln's head on a penny, as seen on the right photo at this link.
Since the mirror lights both fingers in the V-finger, the naive may think that any target they see between the V-finger will be hit. As you can see from the spot on the stop sign - not even close.
Your flash will be on target with the V-finger technique if: (a) Your target is exactly (remember Lincoln's head) centered between your V-fingers. (b) Your mirror flash is exactly centered on your V-fingers ( with a small mirror, the V-finger spread is slightly wider than the flash, so you can see the edges of the light rectangle on your fingers and use that to center the mirror flash on your fingers). (c) Your eye is exactly centered on the physical mirror ( I would mark the center of the bottom edge of the mirror, hold the mirror right over my eye, and look under it, right below the center of the mirror.)
Even if you get two of these three exactly right, if the third is wrong by the apparent width of Lincoln's head, then your target won't get the full flash. You've got to get all three right. ( At short range, you get a bit of a break - they may see the (much) fainter diffuse glint that occurs around the main flash.)
Fine, you say, but for those in trouble who don't have a signal mirror on them, what are they to do other than V-finger?
My first suggestion would be - make your own aimer on the spot - if you have a mirror, it isn't hard to make an aimer that will really give you a step up.
=== Field-expedient signal mirror aimer - aiming hole ===
The first "step up" in mirror aimers is to put a ~ 1/8" sighting hole in the reflector - you can scrape off the silvering on the back of a glass mirror to make a sighting hole, drill a hole in a metal/plastic mirror, or, if you've procrastinated until you are in trouble, auger a hole in a CD/DVD with your knife point.
Now, you can look through that hole at the target, line up your finger tip with the target, catch the "shadow spot" cast by the hole on your finger, and carefully transfer the shadow spot back and forth from the fingertip to the target.
In the next video, my friend is using this method for the first time, at 22 mile range, using the "Silent Universal Signals Mirror" a thin lightweight 2"x3" stainless steel
This segment is twice as long as the 22 second flashing segment in the first video, and you can hear me counting out 22 hits - about 11 hits for every 8 with V-finger. However, that's at 22 mile range (though with 8x binoculars). Looking carefully at the video (full screen, HD), even at 22 miles I see more than 20 flashes in each of the first and second segment, so at a more realistic range of 5 miles or so (where the flashes will be over 19 times brighter) the receiver will be seeing many more flashes than I did here.
rafowell ... thanks for posting some very interesting data on the visibility of mirror flashes. My takeaway is that I can count on about 20-25 miles for a mirror flash, but i might get lucky with much greater distances if the observer is in the same direction as the sun.
Incidentally, I have some independent confirmation from the Coast Guard. I asked one of their helo pilots what type of rescue signal they recommend. He told me that mirror flashes were by far the most effective signal on sunny days, and could be seen over 20 miles.
Your data have persuaded me that there is some value in having a larger mirror, such as a 3 inch x 5 inch device.
#240228 - 01/29/1209:27 AMSignal Mirror Tests at 22 mile range
[Re: rafowell]
rafowell
Enthusiast
Registered: 11/29/09
Posts: 261
Loc: Southern California
We tested a dozen signal mirrors over a 22-mile range today.
We'd used this range before, but not tested a 2"x3" glass mirror, so we made sure to test one this time.
My tester found the Coghlan's 2"x3" glass mirror and the Rescue Flash easiest to use.
To get a feel for the number of flashes, I recommend these be played back in full screen (use the icon at the bottom right of the frame at YouTube) and 720HD quality (use the "gear" icon at the bottom of the frame).
Note that the camera sees many more flashes than I call out with my naked eye (it is an 18x telephoto - comparable sensitivity to my eye with 7x50 binoculars).
Arranged in descending brightness (not all mirrors posted to YouTube)
One geeky technical note - to provide a target visible at 22 miles to sight to, I used a British World War II heliograph with 5" diameter mirror: http://www.youtube.com/watch?v=paEyVKJNIYs
_________________________
A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB)(Ocean Signal PLB)
#240370 - 02/01/1204:26 AMRe: Signal Mirror Tests at 22 mile range
[Re: rafowell]
Aussie
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Registered: 11/12/10
Posts: 205
Loc: Australia
Rafowell, those are some awesome tests. They are very informative.
I must admit I was not expecting much flash from 22mi, but as you say, the camera captures more that you can “see”. It does seem that a SAR would have to be paying attention to spot that flash
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