Doppler Radar Accuracy Conclusion

Relativity principle is not just for big objects

We often come across relativistic motion dealing with x-rays and gamma rays and accelerated particles now used in medical treatment and disease diagnostics, and of course in creating new particles by head-on collision of particles. All these are done in a small laboratory. Much interesting one is the coordinate system like center of mass coordinate system. In relativistic measurement, you can be an observer sitting in a chair, but you have to assume at you are at the center of mass of the two interacting particles, and your position is changing as both particles are in motion. How silly it looks, for a person not moving at all. So, every thing is just relative in relativistic world. Idea of vacuum is also funny. Vacuum means zero interaction with anything else. Unfortunately electric field can reach infinite distance so it can reach any vacuum and can affect anything that is influenced by its field. Any thing and every thing is affecting everything else or there is a net of forces that binds all and is felt at all points and only differs in its magnitude.

Shyam

I fully agree – there are a lot more small things (particles) moving at relativistic speeds than there are big things.

That said, Doppler radars are probably not used to measure the velocity of particles, or are they?

Yes you do measure Doppler shift of particles, atoms, photons as you do for starts for data on expanding universe or estimating the birth of the universe from big-bang theory.

In fact recoil energy in atomic interaction is Doppler shift and energy is directly frequency (E-hf) under Planks Theory. You can also use it as E = mC^2 if you like where m is rest mass of the photon and other particles.

Raman was first to show that energy of the incident wave can increase in some material when it comes out. Here Doppler energy is added from Phonons to Photons and you get more than what you input.

You also get more in Quantum Dots but that is not a real Doppler effect. It is multi-photon interaction in a hollow well of missing atoms called Quantum Dot, which has a behavior of a large Ghost atom. Gap gets filled by electron cloud and forms energy levels like atom has, but there is no real atom there.

Shyam

Shyam, OK, I understand that Doppler shift can be used to measure instantaneous velocities of particles and galaxies, but only if they emit something that you can measure. Radar measurements mean that you send a signal and measure a reflection. Surely, that's not possible with particles. If it is, can you give some reference(s) to support this view?

Hi

What you see in a mirror is actually multiple interaction of Photons to orbital electrons within matter. First light falls on you face or on electrons that are in the atoms of your body surface. They let this energy bounce back or what we call scattering by electrons. It is not as simple as you see a ball bouncing from Ground. Photons can't come back like that. They first deposit energy and then they emit it out with some delay. Funny thing is that there need not be a head on collision. Just nearby passing photon is captured the way we can catch baseball at arms away. We call this cross section or area which takes part in interaction.

Now if photon has only small energy then it bounces back. If it has x-ray level energy then it kicks the electron out and if it has some more, then it kicks the electron and can have some remaining energy to come back with reduced energy. For photons of energy 1.2MeV and above, the Photon becomes two particles and is no more a Photon thereafter.

This is somewhat simplified for you so a nuclear physicist reading it may get offended. They have greater knowledge than this simple idea. Physics is more short of imagination now.

Now we call particle and photons a wave, that extends from -infinity to +infinity in time. Or Photon is everywhere. Both Photon and electron can enter through two holes at a time as if they were half and half and then again be one. They can tunnel through much larger hills of energy gap the way rats can cross the hill. They can show ghost presence where they were before. They can be anywhere in the matter and their energy levels spread like eagles wings all through matter.

This makes interaction with Photons much easier even though there is a lot of gap between atoms in the matter, which is almost hollow.

Did you ever think of how reflection of refraction actually takes place in the matter and what is responsible for it? why only polished surfaces reflect like mirror?

Shyam

Hi Shyam:

OK, but how does this connect to Doppler radar? Any references?

Maybe it's just miscommunication. When a radar signal bounces off some surface of a moving aircraft, what is the Doppler shift indicating - the aircraft's velocity or the (random?) movement of some electron in the skin of the aircraft?

Just the surface electron density plays a role.

Some materials can scatter the incoming rays and you get part of the scattered wavefront at the receiver. You either work on time domain or frequency domain. For large changes you have time domain and for small changes you have phase shift resulting into interfence patterns or f+f1 and f-f1 components measured in frequency domain called Doppler shift.

Now that velocity of the EM wave does not change so you never get Doppler shit in velocity for EM waves. It is good only for sound waves and ultrasound.

What you get is loss of evergy in EM wave or in simple terms, color change, ie blue turning green or red.

Radars actually work on time domain or time of return wave arrival. Any change in return time is the velocity component.

You know that Ultrasonic imaging of baby for pregnent mothers. That is Doppler radar. It can also be used for monitoring heart motion.

EM Radars are a bit different.

Shyam

Shyam, Your explanation, though qualitative and seemingly offtopic in connection with doppler shift, is pretty good. I'd only argue about your point below:

You wrote "This makes interaction with Photons much easier even though there is a lot of gap between atoms in the matter, which is almost hollow." I wouldn't say that matter is hollow. The regions inbetween atoms are filled with electric and magnetic fields. These fields have inherent momentum, energy, etc. and fill the void between the nuclei.

Right.

Measurement part per billion is very difficult and hence sum and difference in frequency to EM at that level is equally difficult. How do we get greater stability in frequency like atomic clocks is not easy? It is very good if we have only kHz source and look for few Hz changes.

Surface wave Radars work at very low frequencies of medium wave and use large antenna array to get good reflected signal and with good Doppler frequency shift. They make good radars for remote sensing.

Have you seen the aircraft radio landing system? It has two frequencies making long cone of radio wave on the air strip and center portion overlaps a bit to guide the landing aircraft. They can land in utter darkness by tracking the overlapping zone. This advantage is greater at low frequencies. Airstrip can be several km long. Generally 150MHz to 171MHz is used.

Surface waves can bend across the curvature of earth and have easy reach.

Shyam

This is a good reference

http://www.mcwar.org/articles/radar/RadarTutorial. pdf

Shyam

Dear Jorrie

If photon energy used is closer to some resonant absoption bands of the material then doppler shift can be measured very accurately. Please look into hole burning technology where sub nm accuracy sharp band are used and one gets wonderful energy manipulation mechanism in special materials used for information storage using hole burning. This requires low temperature device and little has been achieved at room temperature.

This technology of hole burning uses large array of energy levels in place of spaced discrete energy levels. These levels are either filled or depleted using specific energy exposure. This technology was developed for 1000GByte CDROM storage device. You can use genetic material and other sensitive materials for such purposes. I am no longer involved with this research. However, if you look for information on net for hole burning technology then can locate people working in the area.

What you require is better than 0.1nm wavelength resolution and finally it will reach the limit of Heisenberg uncertainty of measurement.