Signal Mirror flash seen from the air

This (excellent) eight-minute National Park Service safety video for Big Bend Park in Texas includes a 3 second segment showing the flashes of a signal mirror as seen from an aircraft.

It is an unusually good example of how much more visible a signal mirror flash makes you - taken at a decent range, viewable up to HD 1080P quality.

The flash is nearly four minutes in, so here's a link that starts you set to HD 720p video 5 seconds before the flashes:

• 5 seconds before the mirror flash

For the full effect, you can immediately pause the video, set quality to 1080p using the "gear" icon at the bottom left margin, and go to full screen with the bottom leftmost icon before proceeding.

For the full video on YouTube (and I do recommend it), go here: Full Video on YouTube (more options for video size, etc.) or click below:

I took in the entire video. I agree it is an excellent, rational discussion of real outdoor hazards. The cost/benefit ratio of a signal mirror is undeniable. I understand there are instances of mirror flashes alerting aircraft out of sight or hearing - the flashers were simply sweeping the horizon at regular intervals. Can you corroborate?

Great find as usual. Thanks Rafowell!

I enjoyed the full video.

Its nice to know how effective a simple signal mirror can be.

I've always wondered about the effectiveness of typical signaling devices at NIGHT. Does a fairly bright flashlight even have a chance of being seen in a remote area (with essentially no other man-made light sources)? Doug had reviewed hand-held laser devices - I wonder how likely it is that one of those will be seen by an aircraft that is up "looking".

I don't have any experience with contemporary flashlights, but I have seen ACR 4F Firefly strobes routinely work effectively with helicopters on night operations. I don't know the lumen rating of the Firefly, but I suspect that some of the higher powered lights of today are equivalent.

Another good reason to EDC a decent flashlight. Any light may help - I had to dig for this one, which I remembered reading when it occurred in 2008.

"And a 17-year-old girl who was lost in a remote area of New Zealand, at night, in August of 2008 was found when the crew of a rescue helicopter used night-vision goggles to spot the backlight on the girl's cell phone."

Yahoo News Item - Cellphone Light Guides Rescue Helicopter

I couldn't track down the original article but I believe it was verified.

last post ... she was spotted by the backlight of a cell phone ... that is one lucky Kiwi!
HAHAHAHA!!!!!

But back to the signal mirror topic ...
A few years ago I was talking to a CA coast guard pilot (helicopter) and asking him what method for emergency signalling was best ... flares, bright color markings, signal mirrors etc. His reply was that on a day with good weather (direct sunlight) the signal mirror was by far the most effective way of attracting help from aircraft - it could easily been seen from over 20 miles away.

Pete2

I can verify this one:

FNP Story - Cell Phone Used In Rescue

Pete

A small mirror has an extremely high benefit/weight ratio. Just for a fun comparison to a flashlight, I wonder how many lumens a reflection of the sun from one of those small mirrors would be. I know a flashlight would be at night, etc.

I don't remember a reported example of that actually happening (though my memory could be the fault).

Certainly, since at least August 1943, the instructions printed on the back of US (and other) military mirrors have recommended sweeping the horizon in the hopes of this.

Sample instruction language:

• US military issued glass MIL-M-18371 mirrors (1950s to current day)
  
  "EVEN THOUGH NO AIRCRAFT OF SHIPS ARE IN SIGHT, CONTINUE SWEEPING THE HORIZON FOR MIRROR FLASHES MAY BE SEEN FOR MANY MILES, EVEN IN HAZY WEATHER."
• 
  French SOS-643 Military mirror (like American B-1 from 1945) Feb. 1954
  
  "Even though, no aircraft of ships are in sight continue sweepink [sic] the horizon. Mirror flashes may be seen 10 miles, away even in hazy weather."
• 
  BuAer Spec 23M5 (AER) ca. 1950
  
  EVEN THOUGH NO AIRCRAFT OF SHIPS ARE IN SIGHT, CONTINUE SWEEPING THE HORIZON. MIRROR FLASHES MAY BE SEEN FOR MANY MILES, EVEN IN HAZY WEATHER.
• 
  NAVY VERSION OF ESM/I : 11/1943:
  ESM/2
  B-I Red retroreflective aimer mirror, 1945:
  
  "PRACTICE SWEEPING HORIZON WITH AIMED BEAM EVEN IF NO RESCUER IS IN SIGHT, AS MIRROR HAS A RANGE UP TO TEN MILES."
• 
  GENERAL ELECTRIC ESM/I Double-sided mirror (cross-shaped aperture):
  PROTOTYPE: 8/1943: ( ALSO ARMY VERSION, SPEC 40654) 11/1943
  
  "WHEN RESCUE CRAFT ARE NOT VISIBLE, PRACTICE SWEEPING CROSS SHAPED SPOT ALONG THE HORIZON. FLASH MAY BE SEEN 10 MILES"
  
  

Per a Navy manual, a 3x5" glass mirror on a bright sunny day is 8 million candlepower. The actual number is going to be a function of the sun elevation, atmospheric clarity, mirror reflectance, and the sun to target angle included at the mirror.

My calculation:

Aiming at the horizon, assuming a mirror reflectance of 0.85, and the sun directly overhead (beam 45 deg off mirror surface normal), using a standard solar flux atmosphere model[1], I arrived at 4.4 million candela (the modern unit for candlepower) for a mirror surface of 6 square inches (a bit more than the net area of a 2"x3" mirror). That is in rough agreement with the Navy manual, after accounting for the different mirror size. However, the candlepower is so impressive because the beam is so small, not because of the power involved.

A candela is a lumen/steradian, and using 0.5358 deg for the sun diameter (median diameter over the year), all that power is going into a beam subtending only 1/14,560 of a steradian. So, to get lumens, I multiply candelas by 1/14,560, getting 300 lumens.

So, at high noon, beaming to the horizon (in any direction) we are talking 300 lumens - high, but not impressive per se. The reason it is so bright is that all those lumens are being crammed into 1/14,560 of a steradian beam, hence the 4.4 million candlepower.

[1] http://stjarnhimlen.se/comp/radfaq.html#10

Yeah, makes my Surefire & JETBeam lights seem kinda wimpy! I always have my Ritter PSP with mirror on me when I'm out hiking or camping. It's good to know a mirror is such a powerful signalling device.

video won't play, states it is private

So it does, and I can't find a viewable version anywhere. Odd. I put in an email to the Big Bend park staff asking them if there's anywhere we can view it.

The full eight-minute National Park Service safety video for Big Bend Park in Texas:

"This Video Could Save Your Life" by Reine Wonite,

is now back online, and can be viewed and/or downloaded here.

Since the signal mirror flash is 5 minutes into the video, I've extracted it and posted it on YouTube here:
Aerial Signal Flash Footage at YouTube
where you can view it at different sizes and resolutions, forward the link, etc.

I've also embedded a lo-res version here -
it pales compared to the 1080P full-screen version you can see on YouTube, but is very convenient:



I like it because it is (by far) the crispest aerial footage of a signal mirror flash that I've seen.