SAR and Ensemble, their relationships
- theandybrock
- Nov 5, 2022
- 2 min read
Updated: Nov 6, 2022
One of our team member, Morgan, presented his discovering on what band of electromagnetic wave we could use for Synthetic Aperture Radar(SAR) in our meeting. Upon confirming the exact band we will be using, we discovered little flaw on the NASA's website.
That's right, the wording "penetrate". It delivers the idea, on what extent we can observe a tree, but not entirely correct, don't get my idea? It's okay, take a look at the following first:
From the above figure, we can clearly see the longer the wavelength gets(frequencies goes the other way around), the more we can see through. But according to the formula of calculating an energy of a proton:
Energy is proportional to frequency, that makes the above tree example seems odd since higher energy gives you more power to penetrate objects. Well NASA is NASA, there's only a slight chance that they would make a mistake. It's a result of diffractions, something like this:
The longer the wavelength, the more a wave can bend around a corner (or a aperture). In the tree example, the apertures are created by leaves overlapping each others. And that's why a longer wavelength wave can see through those leaves and to the branches.
Question is, if higher frequency "penetrates" an object more, why don't we utilize X-ray or even Gamma-rays for our SAR antenna? Well of course, first of all, it costs too much power. But most of all, consider how a X-ray machine work. Instead of getting reflections of waves, it's more like a on-way trip:
The reason we can tell the difference of bones and fleshes is due to the different extent of photon's penetration ability on different objects.
The above figure gives an interesting analogy between wavelength and real life objects. Gamma ray has such a small wavelength that it would just pass the atoms composing the detector! As the wavelength gets smaller, we can eventually penetrate and detect smaller things. As we look closer through different wavelengths, from macro to micro,
Ex, From: To:
Biomass Forest=>Tree-Cluster=>Tree=>Tissue=>Cell=>Atom=>String
we'd find similarity between different layers of object introducing the concept of Fractals and Resemblance (As the video below suggested). Different from our conventional knowledge of Fractals, this operates on a multiscale, a spectrum .
This is why X-ray and any high frequency machine works as a one-way trip, it punctures into objects and if we want to consider Reflection, Refraction, Diffraction, the wavelength and structure of the object has to be taken into account. It's basically about oscillation and how the three physics phenomena above works. This also explains why the NASA website mentioned that the example are used specifically on broadleaf trees, because it matters.
And so we could further tell how a formation of an object affects it's characteristics, which elevates this onto a higher aspect --Ensemble. A part of the 5Ex, Equilibrium/Entropy/Encoding/Entanglement.
References:
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