[Laser] Re: street light EME

[F1AVYopto at aol.com]

>Here are some  thoughts i had on reflections from the moon. 
>The background solar noise  from earthshine is maximum at
>new moon and minimum at full moon. As seen  from the moon,
>the phase of the earth is opposite that of the moon.  So
>that at full moon almost no sunlight is being reflected
>from  earth onto the moon - other than what is refracted
>onto it during an  eclipse. So it makes sense that the best
>times to try this are when the  earth shine noise is the
>least, somewhere between first quarter and last  quarter
>phase. As the moon passes first quarter, less and less  dark
>area is available and also the more off-center your  aim.
>Reflections are coming from increasingly steep angles
>nearing  the edge with the increased losses. I would expect
>the strongest  reflections to be from near the center of the
>moon. I would also expect  the lowest of all noise to be
>during a total lunar eclipse, when there is  no earth-shine
>and no direct sunlight near the FOV. But the earth  refracts
>a sizable amount of light onto the moon during eclipses  -
>being brighter the dirtier the earth's atmosphere. So
>anyway,  it's a trade off between several things when trying
>to find the best time  to try this. 

>Imagine if the moon were a perfect sphere with a  mirrored
>surface. When looking at it from earth, you would see  a
>reversed image of the earth maybe only 1/20 of a degree
>wide (a  rough guess). To see this effect take a look in
>your passenger side rear  view mirror - "objects are closer
>than they appear". The FOV required to  capture all of this
>area would be quite a bit smaller than the moon  itself
>appears in the sky. Most of the reflected energy from  earth
>would be in a small area close to the center of the  moon's
>face, perhaps only 1/10 of the moon's diameter or about  3
>minutes of arc wide. The moon is not a perfect  spherical
>mirror-ball of course and the streetlight radiation  and
>other light coming from the earth illuminates the  entire
>moon's face. So, the entire moon's surface (the usable  dark
>surface anyway) reflects the light back to some degree.  

>* as a side note: At radio frequencies the moon appears
>much  smoother than at optical wavelengths, and this
>"sphere" effect may be  more pronounced. But generally at
>radio frequencies, the beam widths are  larger than the moon
>and it may be hard to even notice this effect at all  with
>small-ish antennas. Some experienced moonbounce people  can
>probably shed some light on that.

>Another thing about  reflections from the moon (at optical
>wavelengths) is that the lunar  surface has a slight
>retro-reflective property due to it being an  "odd"
>non-lambertian reflector. It can be seen in  astronaut's
>photographs from the lunar surface, where the camera  is
>pointed 180 degrees away from the sun. So the moon, as a
>whole,  reflects earth's light back towards earth
>significantly better than you  would expect from a surface
>of a given albedo. It is not as cut and dry  as you  might
>think.

>http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm

>Either  way, it sounds like another reason to include as
>much of the usable  surface as possible in the detector FOV
>in order to capture the maximum  energy. A wider FOV lets in
>more noise though of course.

>If  it's possible to detect this modulated light at all,
>then i can't help  but wonder if one small modulated
>searchlight, well focused and turned  toward the moon, could
>outshine a few cities worth of stray light leaking  upward
>from their outdoor lighting, most of which is pointing  down
>at the ground. 

The moon is a poor albedo lambertian  reflector viewed on a 0,5° angle from 
the Earth.
A lambertian reflector  has a reflective efficiency coefficient versus the 
cosinus of the  incidence angle.
The best area for the aiming could be  the Tycho ejectas sector that gives 
about a 0,2 albedo on a rather big angle (1  / 20° ?) and stays near the 
Earth-Moon axis.
For Europe the best S/N is  certainly during the last quarter phase in winter.
In December the aiming  from the France can be done in the morning, just 
before the daylight and  when the moon is at zenith above the USA. 
During a moon eclipse the main  problem is the photo detector extra shot 
noise.
The light background from the  moon is red/orange and stays very strong even 
with the dielectric filter centred  to the sodium spectrum.
In this condition our 24 cm mirror with its 50 cm  focal length gives to much 
light on the 1 mm² photodiode.
The receiver is  near its saturation  limit.
http://pageperso.aol.fr/F1AVYopto/opto/03-03-2007PC2.jpg
The light  variation film during the 3 march 2007 moon eclipse can be loaded 
at  :
http://foto.star-shine.ch/data/thumbnails/37/2007-03-03%20-%20Lunar%20Eclipse%
20622x500.gif
As  you will notice the background fluctuates strongly with the time but is 
always  very present.
About the street lights to the sky, I think the earth is also a  lambertian 
radiator with globally a half sphere radiation angle.
In France  the total power use for the streets and the roads lamps is well 
over 200  Megawatts !
If the light that goes to the sky is only 1 % of all this power  it is 2 
Megawatts that goes to the sky !
For the USA the total value is  probably very over !
With theses parameters this light detection seems rather  easy to succeed.
Climatic situation over the USA East cost and the moon  configuration seems 
for us the critical parameters.
Another remark about the  100/120 Hz or 300/360Hz choice :
Because the three phase’s network, with a  well equilibrated lamps 
repartition, the 120 Hz component should not be  detectable...
The 360 Hz modulation should be the strongest signal even if  its modulation 
amplitude is only near 1/3 of the amplitude to the one of a  single 
lamp.(Overlapping effect)
However in all directions in the sky, even  over a far and big city, the 
100/120 component stays the strongest detected  signal..?  
73  F1AVY