wrote mph by mistake.
Mike
----- Original Message -----
From: <mdb1225@comcast.net>
To: <rebel-builders@dcsol.com>
Sent: Thursday, November 22, 2007 11:46 AM
Subject: Re: [rebel-builders] laser tape measure
----------------------------------------------------------------->The speed of light is 186,000 miles per second..
-------------- Original message --------------
From: "Mike Davis" <mike.davis@dcsol.com>
--------------------------> ListI think there are a number of problems that would need to be addressed.
Even at 70 mph and 10 ft altitude, and that laser traveling at 186,000
mph,
you will still have moved .09322" before the reflection got back to you.
OK, that's only 1/10 of an inch, pretty small movement. But this is
assuming that the laser is aligned perfectly perpendicular to the surface
of
the water, and that the water surface is glassy smooth and reflective.
1. Keeping that laser perpendicular to the water would require a gimbaled
housing with gyro stabilization... not really that hard to do now a days
with the small piezo gyros available, wouldn't be too expensive either,
maybe $300 or $400... but it would be unnecessarily complicated I think.
2. Most of these "lasers" in products like this are actually LEDs in the
near infrared range, which unfortunately is almost entirely absorbed by
water... very little reflection.
3. How big is the receiving element on this device? 1/10" at 10', is 1/5"
at 20', is 1" at 100'. Assuming you can point that laser straight down,
and
the surface is smooth and reflective, you'd likely need a parabolic
reflector at least 4" in diameter to reliably catch the return and bounce
it
into the receiving element. Again, this could be done, but how much
effort,
expense, and complication do you want here.
I think with some research, you could find a home made radalt that is
much
simpler in design, cheaper to make, and more reliable in operation. Most
radalts operate around 4.3 GHz, compared to the 800 MHz to 1.3 GHz range
of
common LED type lasers... so you will not have a problem with your signal
being absorbed/dissipated by the very surface you're trying to measure.
If you're a glutton for punishment, do a search on Hyperspectral imaging
to
get a better understanding of some of the above concerns regarding
infrared.
Mike
----- Original Message -----
From: "David Jackson"
To:
Sent: Thursday, November 22, 2007 10:00 AM
Subject: RE: [rebel-builders] laser tape measure
1. The laser is travelling at the speed of light. You are not going to
leave the reflection behind.
2. Worst case is glassy water that is clear, like some mountain lakes.
The beam might not reflect enough off that water. If you are depending
on
the laser to get you down safely you might end up as a statistic.
3. I would stick with using the proven glassy water techniques taught
with the seaplane rating. They work.
4. There may be legal consequences if the laser is inadvertently shone
into another aircraft.
Dave J
e - again?> >> > Garry> >> > WAL
T
ER KLATT wrote:> >> I did?? But sounds like something I could have used
a
few times...> >>> >> Are you thinking of having that in case of getting
caught with an engine > >> out over glassy water?> >>> >> Walter (must
not
forget to take my AZ pills)> >>> >> ----- Original Message -----> >>
From:
Garry Wright > >> Date: Thursday, November 22,
2007 9:09 am> >> Subject: [rebel-builders] laser tape measure> >> To:
rebel-builders@dcsol.com> >>> >>> Walter Klatt suggested the use of a
laser tape measure as a low> >>> level> >>> (below 100') altitude
device.
You can get these at Home Depot> >>> for about> >>> $99US.> >>>> >>>
Does
anyone know if these tape measures (laser not sonic) will> >>> bounce>
properly off water and indicate altitude above the water?> >>>> >>> Has
anyone done this?> >>>> >>>> >>> Garry> >>> 068R C-FOKM> >>>> >>>> >>>> List archives located at: https://mail.dcs
ol.com/login> >>> username "rebe
l
" password "builder"> >>> Unsubscribe:
rebel-builders-unsubscribe@dcsol.com> >>> List administrator:
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"rebel" password "builder"> >> Unsubscribe:
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