Am 25.03.2013 06:38, schrieb Mahadeesh:

> Just simple level reflectivity map calculation of the object is only im looking
> for.. Manually creating a program for Electromagnetic imaging like say Ray
> tracing Algorithm , Physical optics method etc is very tedious task...
>
> Thats why I'm planning to use POV ray for reflectivity map calculation of the
> scene or object. From that generated reflectivity map, I was hoping to use it
> for SAR raw echo simulation....
>
> Is my approach feasible one ? Thank you.

I must confess that what you're saying is mostly dutch to me, and I'm 
probably not the only one here; you may need to think of us as stupid 
laymen when it comes to radar science, who need each and every technical 
term explained.

What, to begin with, is a "reflectivity map" as you understand it?

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clipka <ano### [at] anonymousorg> wrote:
> Am 25.03.2013 06:38, schrieb Mahadeesh:
>
> > Just simple level reflectivity map calculation of the object is only im looking
> > for.. Manually creating a program for Electromagnetic imaging like say Ray
> > tracing Algorithm , Physical optics method etc is very tedious task...
> >
> > Thats why I'm planning to use POV ray for reflectivity map calculation of the
> > scene or object. From that generated reflectivity map, I was hoping to use it
> > for SAR raw echo simulation....
> >
> > Is my approach feasible one ? Thank you.
>
> I must confess that what you're saying is mostly dutch to me, and I'm
> probably not the only one here; you may need to think of us as stupid
> laymen when it comes to radar science, who need each and every technical
> term explained.
>
> What, to begin with, is a "reflectivity map" as you understand it?

Hi,

Sorry for the inconvenience caused... I will definitely post the complete
details soon..
Thanks a lot.

Regards,
M

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Christian Froeschlin <chr### [at] chrfrde> wrote:
> You probably need to specify in more detail what you mean by
> reflectivity pattern.
>
> Also, you should be aware that povray can only give you estimates
> on the intensity of reflected light based on simple geometric models,
> in particular not taking into account effects like interference. This
> may limit the usefulness for simulating longer wavelengths.


Hello,

I mean here by reflectivity map is that the target scattering ability i.e.
Electromagnetic scattering of the object. Photographic images that contain only

both the amplitude and the phase information of the scattered EM field from the
scene. But it is very adruous to exactly  simulate scattering of EM field for
each object in the scene.

Hence Im thinking of using POV for giving the values of reflected light
intensity of any scene which is equivalent to reflectivity property of each
object of the scene( may be an approximation I can say).  Presently,Im not
interested in interference effects which will potentially complicate the problem
of SAR image formation.

This an sample SAR image :
https://www.google.co.in/search?q=SAR+image&hl=en&client=ubuntu&hs=bEM&channel=fs&tbm=isch&tbo=u&source=univ&sa=X&ei=Us
xaUZHQMcSIrQebm4GgDA&ved=0CDAQsAQ&biw=1067&bih=713#hl=en&client=ubuntu&hs=cZ1&channel=fs&tbm=isch&sa=1&q=synethetic+ape
rture+radar+image+&oq=synethetic+aperture+radar+image+&gs_l=img.3...14733.26980.4.27340.34.31.3.0.0.0.154.2713.29j2.31.
0...0.0...1c.1.8.img.j2PiLVDb-G4&bav=on.2,or.r_qf.&bvm=bv.44697112,d.bmk&fp=9cd1c99b78ac4f1a&biw=1067&bih=713&imgrc=kuh
ug3D1KiKnvM%3A%3BhL2JrnPfbrQReM%3Bhttp%253A%252F%252Fwww.sandia.gov%252FRADAR%252Fimages%252Fcapitol.jpg%3Bhttp%253A%25
2F%252Fwww.sandia.gov%252FRADAR%252Fimageryku.html%3B1200%3B800

You can note in the image that there are bright spots which is outcome of the
material property and surface. For example, the metal objects will reflect more
when compared with others. Similarily any sharp edges in the building will
produce more bounce effect which makes the spot brighter.

Also note the showdows in the SAR image. These are very much useful in many
remote sensing applications.Finally my intention is to form an SAR image as
shown in the example. Hence complete image generation depends on the
Reflectivity property of the objects in the scene.

Please revert back to me for any sort of question regarding the work.

Regards,
M

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Alain <kua### [at] videotronca> wrote:

> > I'm doing Simulation of Synthetic Aperture Radar( SAR )Mode/(Microwave Imaging).
> >
> > I came to through POV in one of the IEEE research paper and I thought it would
> > be useful for me. There is one segment in my project is scene object
> > reflectivity pattern calculation say the object can be building or car or tree
> > etc...
> >
> > How to calculate the reflectivity pattern using any of the Electromagnetic
> > Imaging Algorithm like Ray Tracing Method / Physical Optics(PO) Method. I
> > suppose that POV can help me on that. It would be very helpful, if i get any
> > sort of suggestion from this group. At least let me know if my understanding is
> > correct or not ?
> >
> > Thanks
> >
> >
>
> You can not simulate any interference pattern from several sources or
> reflective objects. The best you can get is thin film irisation. A very
> narow slit can't show anything but a sharp pattern. Those are crutial
> for any SAR.
>
> For the visible spectrum, you can add some reflection in the finish of
> your objects. Metals have prety uniform reflectivity, but other
> materials normaly have variable reflection.


Hello,

Thanks for replying to my mail. I would like to tell you that, presently im not
looking at interference pattern.

Im planning to generate reflectivity map of any object in the scene. As you
said, it depends on the material property. So we cant simulate each and every
object on the scene to get exact reflectivity property. Hence we have to come to
an approximate method for reflectivity pattern of the Object. Can POV help me on
that ?

Can you please tell me how to add the reflectivity property of the object at its
finish as you mentioned earlier in the scene ? Because adding these values can
improve the final SAR image generation.Also is it possible extract those
reflectivity values from any RGB image ?

I have given sample SAR image for you reference.

https://www.google.co.in/search?q=SAR+image&hl=en&client=ubuntu&hs=bEM&channel=fs&tbm=isch&tbo=u&source=univ&sa=X&ei=Us
xaUZHQMcSIrQebm4GgDA&ved=0CDAQsAQ&biw=1067&bih=713#hl=en&client=ubuntu&hs=cZ1&channel=fs&tbm=isch&sa=1&q=synethetic+ape
rture+radar+image+&oq=synethetic+aperture+radar+image+&gs_l=img.3...14733.26980.4.27340.34.31.3.0.0.0.154.2713.29j2.31.
0...0.0...1c.1.8.img.j2PiLVDb-G4&bav=on.2,or.r_qf.&bvm=bv.44697112,d.bmk&fp=9cd1c99b78ac4f1a&biw=1067&bih=713&imgrc=kuh
ug3D1KiKnvM%3A%3BhL2JrnPfbrQReM%3Bhttp%253A%252F%252Fwww.sandia.gov%252FRADAR%252Fimages%252Fcapitol.jpg%3Bhttp%253A%25
2F%252Fwww.sandia.gov%252FRADAR%252Fimageryku.html%3B1200%3B800

Please let me know if you need more details for my side. Thanks once again.

Regards,
M

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Christian Froeschlin <chr### [at] chrfrde> wrote:
> Mahadeesh wrote:
>
> > I mean reflectivity pattern here as BACK SCATTERING effect of the objects in the
> > scene. Like calculation of single, double and triple bounce effect from the
> > ray.. When all these effects are summed together we get, back scattering effect
> > of the object.I need reflectivity map of any 3D modeled object. I may not
> > require to consider the effects of interference. Just a simple creation of
> > reflectivity map of any object/ scene. Thank you.
>
> It sounds like what you want to achieve could be approximated by
> a light source (possibly a spot light if you have a confined beam),
> diffuse textures for the back scattering, and radiosity for the
> bounces. With the caveat that the light model for diffuse reflection
> probably does not accurately reflect microwave backscattering.
>
> I'm still not quite sure what the end result should be. A normal
> render (camera image) would give you an image of the scene indicating
> how much light is reflected into the direction of the camera for each
> point of the object. If the camera and the light source are in the
> same location that is probably an approximation of an "echo".
>
> If you are more interested in the effect of the  object on the
> surrounding you can put a sphere around the object and see how this is
> illuminated through radiosity. If you want some total measure of light
> scattered from each position of the object regardless of direction,
> things are likely to get tricky although the mesh camera might help.


Hello,

You are exactly right. What you have mentioned in the paragragh one is what im
looking for.

SAR image comes under microwave imaging technology. The SAR image simulation for
an scene is my final output. The input here has to be an image from which i have
to extract the backscattering values for each position in the image/for an
object. Finally using this back scattering values in the any of the pre-existing
SAR algorithm to form SAR equivalent image.

I agree that we cant simulate microwave backscattering effect, but instead of
that an light model is considered here. Can you throw some light on the line
"diffuse texture for the back scattering" as mentioned in your post ? Similarily
on the "radiosity for the bounces" ?

It would be very much useful if POV ray can calculate these values for me ? So
that i can extract those values and use it in my algorithm.

Sample SAR image for your reference.

https://www.google.co.in/search?q=SAR+image&hl=en&client=ubuntu&hs=bEM&channel=fs&tbm=isch&tbo=u&source=univ&sa=X&ei=Us
xaUZHQMcSIrQebm4GgDA&ved=0CDAQsAQ&biw=1067&bih=713#hl=en&client=ubuntu&hs=cZ1&channel=fs&tbm=isch&sa=1&q=synethetic+ape
rture+radar+image+&oq=synethetic+aperture+radar+image+&gs_l=img.3...14733.26980.4.27340.34.31.3.0.0.0.154.2713.29j2.31.
0...0.0...1c.1.8.img.j2PiLVDb-G4&bav=on.2,or.r_qf.&bvm=bv.44697112,d.bmk&fp=9cd1c99b78ac4f1a&biw=1067&bih=713&imgrc=kuh
ug3D1KiKnvM%3A%3BhL2JrnPfbrQReM%3Bhttp%253A%252F%252Fwww.sandia.gov%252FRADAR%252Fimages%252Fcapitol.jpg%3Bhttp%253A%25
2F%252Fwww.sandia.gov%252FRADAR%252Fimageryku.html%3B1200%3B800


PLease let me know if you need more details. Awaiting for your response.

Regards,
M

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:
> Am 25.03.2013 06:38, schrieb Mahadeesh:
>
> > Just simple level reflectivity map calculation of the object is only im looking
> > for.. Manually creating a program for Electromagnetic imaging like say Ray
> > tracing Algorithm , Physical optics method etc is very tedious task...
> >
> > Thats why I'm planning to use POV ray for reflectivity map calculation of the
> > scene or object. From that generated reflectivity map, I was hoping to use it
> > for SAR raw echo simulation....
> >
> > Is my approach feasible one ? Thank you.
>
> I must confess that what you're saying is mostly dutch to me, and I'm
> probably not the only one here; you may need to think of us as stupid
> laymen when it comes to radar science, who need each and every technical
> term explained.
>
> What, to begin with, is a "reflectivity map" as you understand it?


Hello,

Thanks a lot for replying to my question. I would be very much happy to explain
what I know.

As you asked, Reflectivity map means the objects reflectivity property. An
object in real world has the capacity to reflect the light falling on it. Not
only light but any Electromagnetic waves falling on it. So here , Synethetic
aperture Radar (SAR)  mode is an special mode in Radar which uses microwaves as
source and uses it for creating the image. As an photographic image uses light
intensity to form an image, in SAR mode uses object reflectivity to form an
image.

The Radar sends microwaves towards the object, which potentially reflects the
microwaves based on the reflectivity property of the object. Using the energy
contained in the reflected signal (which was based on object reflectivity), SAR
image is formed.

Hence the reflectivity map is the main parameter in the complete  simulation. So
Im looking for generating reflectivity map of any object / scene. Also want to
know if there is any analogous concept in POV which can help me ?

An SAR image for your reference at this link :

https://www.google.co.in/search?q=SAR+image&hl=en&client=ubuntu&hs=bEM&channel=fs&tbm=isch&tbo=u&source=univ&sa=X&ei=Us
xaUZHQMcSIrQebm4GgDA&ved=0CDAQsAQ&biw=1067&bih=713#hl=en&client=ubuntu&hs=cZ1&channel=fs&tbm=isch&sa=1&q=synethetic+ape
rture+radar+image+&oq=synethetic+aperture+radar+image+&gs_l=img.3...14733.26980.4.27340.34.31.3.0.0.0.154.2713.29j2.31.
0...0.0...1c.1.8.img.j2PiLVDb-G4&bav=on.2,or.r_qf.&bvm=bv.44697112,d.bmk&fp=9cd1c99b78ac4f1a&biw=1067&bih=713&imgrc=kuh
ug3D1KiKnvM%3A%3BhL2JrnPfbrQReM%3Bhttp%253A%252F%252Fwww.sandia.gov%252FRADAR%252Fimages%252Fcapitol.jpg%3Bhttp%253A%25
2F%252Fwww.sandia.gov%252FRADAR%252Fimageryku.html%3B1200%3B800

Please have a look. You can note in the image that there are bright spots which
is outcome of the material property and surface. For example, the metal objects
will reflect more when compared with others. Similarily any sharp edges in the
building will produce more bounce effect which makes the spot brighter.

Regards,
M

Post a reply to this message

Mahadeesh wrote:

> I agree that we cant simulate microwave backscattering effect, but instead of
> that an light model is considered here. Can you throw some light on the line
> "diffuse texture for the back scattering" as mentioned in your post ? Similarily
> on the "radiosity for the bounces" ?

it would probably be helpful if you play a bit with povray just to see
how light, objects and textures are defined to render images. The manual
covers this very well.

Basically a texture defines how the surface of an object interacts
with light. For example, a white object will reflect all light and a
black object reflects no light. The amount also depends on the angle
between surface and incident light, with diffuse lighting it it
proportional to cosinus of angle.

Classic raytracing only considers light source and object, but
the radiosity feature of povray can also calculate how the diffuse
reflection from one object can illuminate a second object. Again,
have a look at the manual and sample scenes to learn more.

Note that you will not get phase information from povray (and no
other meaningful results related to wavelength). Colors in povray
are only simulated as RGB and not real spectral response.

Post a reply to this message

Am 03.04.2013 01:07, schrieb Christian Froeschlin:
> Mahadeesh wrote:
>
>> I agree that we cant simulate microwave backscattering effect, but
>> instead of
>> that an light model is considered here. Can you throw some light on
>> the line
>> "diffuse texture for the back scattering" as mentioned in your post ?
>> Similarily
>> on the "radiosity for the bounces" ?
>
> it would probably be helpful if you play a bit with povray just to see
> how light, objects and textures are defined to render images. The manual
> covers this very well.
>
> Basically a texture defines how the surface of an object interacts
> with light. For example, a white object will reflect all light and a
> black object reflects no light. The amount also depends on the angle
> between surface and incident light, with diffuse lighting it it
> proportional to cosinus of angle.

Speaking of light, To simulate SAR imaging you'll probably want to use a 
single light source placed at the camera location.

Post a reply to this message

Christian Froeschlin <chr### [at] chrfrde> wrote:
> Mahadeesh wrote:
>
> > I agree that we cant simulate microwave backscattering effect, but instead of
> > that an light model is considered here. Can you throw some light on the line
> > "diffuse texture for the back scattering" as mentioned in your post ? Similarily
> > on the "radiosity for the bounces" ?
>
> it would probably be helpful if you play a bit with povray just to see
> how light, objects and textures are defined to render images. The manual
> covers this very well.
>
> Basically a texture defines how the surface of an object interacts
> with light. For example, a white object will reflect all light and a
> black object reflects no light. The amount also depends on the angle
> between surface and incident light, with diffuse lighting it it
> proportional to cosinus of angle.
>
> Classic raytracing only considers light source and object, but
> the radiosity feature of povray can also calculate how the diffuse
> reflection from one object can illuminate a second object. Again,
> have a look at the manual and sample scenes to learn more.
>
> Note that you will not get phase information from povray (and no
> other meaningful results related to wavelength). Colors in povray
> are only simulated as RGB and not real spectral response.

Hello,

I will definitely start with the concepts which you mentioned. Thank you.

Regards,
M

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:
> Am 03.04.2013 01:07, schrieb Christian Froeschlin:
> > Mahadeesh wrote:
> >
> >> I agree that we cant simulate microwave backscattering effect, but
> >> instead of
> >> that an light model is considered here. Can you throw some light on
> >> the line
> >> "diffuse texture for the back scattering" as mentioned in your post ?
> >> Similarily
> >> on the "radiosity for the bounces" ?
> >
> > it would probably be helpful if you play a bit with povray just to see
> > how light, objects and textures are defined to render images. The manual
> > covers this very well.
> >
> > Basically a texture defines how the surface of an object interacts
> > with light. For example, a white object will reflect all light and a
> > black object reflects no light. The amount also depends on the angle
> > between surface and incident light, with diffuse lighting it it
> > proportional to cosinus of angle.
>
> Speaking of light, To simulate SAR imaging you'll probably want to use a
> single light source placed at the camera location.

hello,

Yes. You are right.
Actually I'm looking to create the reflectivity pattern of any object/scene
using POV and use that in SAR image generation. Any suggestion for "how to
create reflectivity pattern of any object" ? Thank you.

Regards,
M

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