Relative velocity algorithms in tomographs.

[Stubby]

You know how you develop a visual image of people, based on their posts? For some reason, my image of you has changed:lol:

 

 

You been stalking me !

[daltontrees]

I think this will not help the headache, but I believe the system works by recording the time taken for a wave to go round an area of decay rather than through it. The extra time taken for the detour indicates the shortest path through normal wood.

 

So say you wanted to fly a small plane from York to Liverpool, and the direct route would go straght over Leeds. But once you get in the air you see storm over Leeds so you immediately aim for the edge of the storm to go round it, taking you over Sheffield and once round it you adjust your course to go straight from there to Liverpool. If your plane always flies at the same speed, you could work out afterwards how long the journey took compared to the direct journey expected time. And it would then be possible to work out the width of the storm.

 

And say someone in the same kind of plane sets off at the same time as you but goes straight through the storm, and gets slowed down by the poor conditions and even though taking a more direct route than you, arrives after you. This tells you something about the conditions that is proportional to the conditions.

 

A third plane of the same kind goes from York to Darlington and encounters no bad weather and makes no detour. This tells you the normal airspeed for the type of plane.

 

This method would work whether you were in a Cessna or a Tornado. As with wood, it is relative time that matters, not absolute time. But you have to know your normal airspeed. There, I bet that makes no sense whatsoever.

Edited October 26, 2014 by daltontrees

[daltontrees]

My new avatar should be

[Stubby]

My new avatar should be

 

Think that's our local hair salon ....

[Gary Prentice]

Jules, a good anology but different from my understanding.

 

Sonic, ultrasonic or acoustic tomography of trees uses sound waves to measure relative differences in wood density, via mathematical algorithms, to produce a colour coded image or representation of the density of the horizontal cross section measured. The sound wave passes through different materials at different velocities according to their density;

 

v=√ E/? Where V=Velocity of stress wave, E=Modulus of elasticity & ? =Density

 

The real problem starts in the presence of cracks and voids, attempting to interprett whether the path of travel is slow or has been diverted and therefore is longer.

 

The baseline travel time for softwoods is approximately1000 µs/m (300µs/ft) and 670µs/m (200µs/ft) for hardwoods. The picus doesn't attempt to use these figures, but uses the highest velocity between sensors as the 'norm' for sound wood to correlate all the other results too

 

The Arborsonic has several thousand tree species recorded, each with its own stored normal velocity -of normal wood/density and the Arbotom appears to use just three standard data inputs, Conifer, ring and diffuse porous.

[Gary Prentice]

And while we're on the subject of density, has anyone got a article or link as to why/how temperature alters the density of wood? Not in woods growth patterns of early/late wood, but seasonally.

 

The questions about resistograph readings in winter - compared to summer.

[daltontrees]

Jules, a good anology but different from my understanding.

 

Sonic, ultrasonic or acoustic tomography of trees uses sound waves to measure relative differences in wood density, via mathematical algorithms, to produce a colour coded image or representation of the density of the horizontal cross section measured...

 

Yes but my analogy wold involve 20 airports in Britain and 19 planes leaving from each one and trying to fly directly to each of the other airports. That is a total of 361 flights, which is quite a lot of data.

 

The mechanisms of sonic tomography measure only time differences between send and receive. The computer does the rest. It doesn't meausre sensity or modulus of elasticity, it infers it as a relative value form the timings of each transit. And each signal received by a transducer won't just be a straight blip, it wil be a fuzz of smaller blips representing a whole range of time values. Obviously the path that goes most directly through the densest wood will give the first blip. But the smaller blips after that will be used by the software to give a picture of the alternative routes that has been taken by the input.

 

I'll be the algorithms aren't too mysterious, what I think is impressive is the amount of data that has to be processed.

 

Cracks sem to be a nightmare for the system. Radial cracks leave no direct route for the input to get to the transducers opposite. A whole different set of algorithms are probably used for this.

[Gary Prentice]

You're right, I was getting tied up on the diversions

[daltontrees]

You're right, I was getting tied up on the diversions

 

I suppose the analogy should include a squadron of planes leaving for each airport from each airport and as soon as a squadron hits bad weather one flies straight through to see how bad it is while the rest break off left and right to see how far round it is.

 

I think I've taken that as far as I can, so I will stop before it gets ridiculous.

[Gary Prentice]

I suppose the analogy should include a squadron of planes leaving for each airport from each airport and as soon as a squadron hits bad weather one flies straight through to see how bad it is while the rest break off left and right to see how far round it is.

 

I think I've taken that as far as I can, so I will stop before it gets ridiculous.

 

Far too late:lol: