I was reading through the inquisitive posts below, by Dave and they got me thinking:
Whould it be prudent to run levels on the Moon or some other smaller orb; or should some other method be used to establish a vertical datum on something with a smaller diameter than Earth?
TIA
Dougie
If You Ran Levels On The Moon
It would be very critical that equal backsight and foresights were maintained due to the much small radius of the survey surface.
But why does it matter, since there is no fluid to flow on the surface?
Only pipe flow would be reasonable and pipe loses due to friction would far exceed any gravitational affects.
Which brings up a question, who is going to issue professional licenses to surveyors and engineers on the Moon?
Paul in PA
If You Ran Levels On The Moon
> But why does it matter, since there is no fluid to flow on the surface?
>
Ah contraire mon ami!
How about Titan or Europa or Io or Enceladus?
Titan has lakes of liquids all over. Most likely methane or ethane being it's about 200 below zero there. Being of much smaller gravity, rain drops are the size of golf balls and fall much slower. Then you have the "tiger stripes" of Enceladus constantly spewing out snowfall in the south polar region.
Nevermind their "geoids" change shapes as they orbit their gas giant host. So much for any vertical datum maintaining any consistency. 🙂
If You Ran Levels On The Moon
I'm going to guess that even an invar tape wouldn't mitigate the temperature differences you're going to experience, i could be wrong but, if your backsight has the rod in full sunlight, and your backsight is completely shaded...the error could be compounding.o.O
I don't know why ....
you couldn't run levels on the moon. The moon has gravity - granted about 1/6 of earth - and a fairly stable surface, so you should be able to run conventional levels. Bubbles and pendulums might be a little slow to settle, but everything should work.
Now I have no idea what the geoid would be like, but that doesn't keep me from leveling.
> I would fully expect that within a few years of surveyors on the moon there would be a nice little garden of rebar pounded in around that flag planted in 1969 and endless threads about the bogus theory of proportioning of the LLSS grid...
I don't know why, but that made me laugh.
Now I wonder who will mark Alan Sheppard's famous golf ball strike from the 70 or 71 mission. Apollo 14 I think. Would the PGA folks recognize it since he hit with one hand on the club? 6 or 7 iron I believe and it would surely be a distance record. Who would rule on the ball should he "garden" it. "I'll just have to get one of pesky rebars out of the way". 😀
How appropriate given my avatar.
Hello Dr. Chandra. I'm ready for my first lesson.
If You Ran Levels On The Moon
> But why does it matter......
Surely the only reason we collect vertical data is not because we want to know where the water will flow.
The true shape of the geoid is most critical for navigation. The better the model; the better it is to navigate.
Dougie
As I recall from the Apollo days ...
When we were doing the phototriangulation for the Apollo Lunar Landing Charts at Army Map Service, the vertical datum used was the apparent low of the landing site. Contours were then developed photogrammetrically with reference to that datum low. It was all relative with each landing site uncorrelated to any others. Orientation to "level" was based on stellar attitude cameras to the theoretical center of mass of the Moon.
