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Post details Post   (Contract pics)
Mountain Rescue Te.. by simon3   (Show all posts)
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found the explanat.. by jackill   (Show all posts)
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simon3
2011-08-16 13:17:29
"Laser Beam" from simon3 Contract pics
Picture: Laser Beam (Contract pics)

Lasers in the mist
On the top of Stumpa Dúloigh jackill did his usual thing of assessing where the highest point actually is. MountainViewers have tended to use the Abney Level as a way of assessing this. In this case the highest point appears to be some metres from the junction of two fences. jackill was assessing the distance from this junction to the highest point where I was with the camera. He has a handy little laser rangefinder gadget for this which showed the fence junction to be 21m from the highest point.

The laser light shows up nicely, being scattered by the misty air. Shows up that is except when it was getting near to the camera - something that begs explanation. As anyone knows who takes photos in the Irish mountains, mistiness is a huge issue. In this case the mistiness is Mie scattering caused by water droplets. These are rather large compared to the scattering caused by small particles that causes blue skies (Rayleigh scattering). Mie scattering also has another important quality. Most of the scattered light goes forward close to the original line of travel. So when viewing the droplets in the beam from a distance you see them because you and they are nearly in line. However, nearer, the angle is different and you can't see the beam.

It's all beautifully explained here:
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html

And the relevance? Well knowing about the two types of mist and what, if anything, you can do about them is really useful for upland photographers. For example, because of forward Mie scatter the sun or the moon tend to get a whitish halo around them when there are large particles in the air. The same doesn't happen for Rayleigh scattering - you don't see a blue halo around the sun. This laser beam is a great example of the physics.
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RECENT CONTRIBUTIONS 1 2 3 .. 21 Next page >>
Summit Summary
Binn Charrach: NE finger from the Twelve Bens offers a way in.
Collaborative entry Last edit by: simon3, scapania, wicklore 4 hours ago.
Knockpasheemore (Binn Charrach) is a small summit at the end of a 2km ridge heading NE from the lower scree slopes of Benbaun, and makes a worthwhile climb either in its own right, or as a diversi...

  
Summit Summary
Bencorrbeg: Shapely outlier, serious scrambling.
Collaborative entry Last edit by: simon3, Onzy 6 hours ago.
Bencorbeg dominates views from the mouth of the Gleninagh Valley. Although only 577m, the full extent of this height is seen when the mountain is viewed from north or east, as the mountain plunges...

  
Summit Comment
Oileán an Chlaí: Island in Bertraghboy Bay
simon3 3 days ago.
Oghly Island is around 250m from the driveable Inishnee island.

Track
Beast of Bencorrbeg tackled from the south.
simon3 3 days ago.
As many others have said Bencorrbeg is a serious scrambling challenge. This track was an attempt to reach it from the ... walk, Len: 14.0km, Climb: 669m, Area: Bencorrbeg, Twelve Bens (Ireland) Benco

  
Summit Comment
Lettershinna Hill: Grass top, distant heights.
simon3 3 days ago.
As paddyhillsbagger found, the Bens form a backdrop to the top of Lettershinna. This picture was taken during a generally mist covered period one May day.

  
Track
The Heights of Malta
madfrankie 3 days ago.
When you're considering hiking trips abroad, Malta is not likely to be high on anyone's list. It's small and the human f walk, Len: 8.4km, Climb: 40m, Area: Malta, Dingli ()

Summit Comment
Inis Leacan: Island south of Roundstone.
simon3 3 days ago.
Inishlacken is a small island south of Roundstone. Here it is viewed from Inishnee.

  
Track
Wicklow: Glenmalure to Glendalough
Onzy 3 days ago.
Glenmalure to Glendalough viw Wicklow Way & the Spinc... walk, Len: 11.3km, Climb: 540m, Area: Dublin/Wicklow (Ireland)

  
Summit Summary
Benglenisky: Southern Bens easiest way up.
Collaborative entry Last edit by: simon3 3 days ago.
Driving towards Clifden along the N59, go 2km past the Benlettery Hostel and take the minor road on the right. I.5km along this, at point L750 499, there is a large space for parking on the right,...

Track
Waterfalls Galore
march-fixer 4 days ago.
There are two major waterfalls in Jamaica. Dunn's River Falls and Reach Falls. Reach Falls is by far the most beautiful walk, Len: 6.2km, Climb: 109m, Area: Jamaica, Portland ()

  
Summit Comment
Binn Bhriocáin: Rocky top from afar.
simon3 3 days ago.
The rocky top of Letterbreckaun viewed from Bencorrbeg in the Twelve Bens which is 4.5km away.

  
Forum: General
Lough Curra - 14/05/2019 - 05:17
GSheehy 4 days ago.
There was white horses and they were comin' at me at a pace nowAnd there was a blue sirocco blowin' cold into my faceThe sun was risin' on the other side of the ridges.....And it was almost like T...


RECENT CONTRIBUTIONS 1 2 3 .. 21 Next page >>