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A Brief Introduction to Ice-Penetrating Radar

lindzey.github.io

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Re: A Brief Introduction to Ice-Penetrating Radar

#11

Post by lindzey »

b_emery wrote: post #8
a2tech wrote: post #2

Thats really pretty amazing. Filtering out the 'echos' would clearly make the data more useful, but I can see how thats almost impossible without very clever engineering

I'm not familiar with SAR, but it seems like they could use more than just 2 antennas to produce a more directional receive array. I work with HF radars (2-30 MHz) and this is basically what we do. There is a lot of clever engineering out there - that one doesn't need to be too clever to apply.

Yes - this idea has definitely taken over my imagination. A different research group (https://www.cresis.ku.edu/) has been working on this, but the processing techniques are still evolving.

Do you have papers describing y'all's processing? I'd love to learn more!

Re: A Brief Introduction to Ice-Penetrating Radar

#12

Post by bluusteel »

Really nice writeup! I wish more graduate students would blog about their research in this way. Could be a great way to educate the public and convey the importance of government research funding.

I wonder how big the reflection coefficient is for the air/ice interface. It seems like it would be huge. So maybe ground based techniques offer better coupling at the cost of not being able to survey as much area?

Re: A Brief Introduction to Ice-Penetrating Radar

#13

Post by lindzey »

bluusteel wrote: post #12

Really nice writeup! I wish more graduate students would blog about their research in this way. Could be a great way to educate the public and convey the importance of government research funding. I wonder how big the reflection coefficient is for the air/ice interface. It seems like it would be huge. So maybe ground based techniques offer better coupling at the cost of not being able to survey as much area?

We record on two channels, "high gain" and "low gain", separated by ~50dB. I showed the high gain products in this post, and the surface absolutely does saturate the detectors. The system was designed so that near-surface returns don't saturate the low gain channel.

We transmit 8kW, and the air/ice surface reflection coefficient is ~0.08 (~-11dB). Flying at ~600m above the surface, spreading loss actually contributes more to signal attenuation (1/(2*h)^2 ~= -62dB).

Our instrument is optimized for seeing through the entire ice sheet, mapping deep layers and the bed. Other (also airborne) instruments operate at higher frequencies, trading higher resolution for less penetration. I'm not super familiar with groups using ground-based ice-penetrating radar, but one big tradeoff is $$$. The airplane is hugely expensive to operate, whereas ground-based just needs a snowmobile.

Re: A Brief Introduction to Ice-Penetrating Radar

#14

Post by hn9780470248775 »

lindzey wrote: post #11
b_emery wrote: post #8

Earlier quoted context omitted.

I'm not familiar with SAR, but it seems like they could use more than just 2 antennas to produce a more directional receive array. I work with HF radars (2-30 MHz) and this is basically what we do. There is a lot of clever engineering out there - that one doesn't need to be too clever to apply.

Yes - this idea has definitely taken over my imagination. A different research group ( https://www.cresis.ku.edu/ ) has been working on this, but the processing techniques are still evolving. Do you have papers describing y'all's processing? I'd love to learn more!

I think "phased array radar" is the relevant search term.

Re: A Brief Introduction to Ice-Penetrating Radar

#15

Post by ambicapter »

a2tech wrote: post #2

Thats really pretty amazing. Filtering out the 'echos' would clearly make the data more useful, but I can see how thats almost impossible without very clever engineering

Can't they do some frequency hopping or encode some sort of timestamp in the radar signal to identify when they sent out the wave they're receiving?

Re: A Brief Introduction to Ice-Penetrating Radar

#16

Post by lindzey »

ambicapter wrote: post #15
a2tech wrote: post #2

Thats really pretty amazing. Filtering out the 'echos' would clearly make the data more useful, but I can see how thats almost impossible without very clever engineering

Can't they do some frequency hopping or encode some sort of timestamp in the radar signal to identify when they sent out the wave they're receiving?

This is a pulsed system - we send out 1us wide chirped signals, then listen for their returns before sending out the next signal. So - we know how far away a return is, but the tricky bit is knowing which direction it came from, since our beam pattern is so wide.

We do use a chirped signal in order to improve vertical resolution - convolving the outgoing pulse with the returned trace gives us the equivalent resolution of a ~80ns pulse, but with more power.

Re: A Brief Introduction to Ice-Penetrating Radar

#17

Post by b_emery »

lindzey wrote: post #11
b_emery wrote: post #8

Earlier quoted context omitted.

I'm not familiar with SAR, but it seems like they could use more than just 2 antennas to produce a more directional receive array. I work with HF radars (2-30 MHz) and this is basically what we do. There is a lot of clever engineering out there - that one doesn't need to be too clever to apply.

Yes - this idea has definitely taken over my imagination. A different research group ( https://www.cresis.ku.edu/ ) has been working on this, but the processing techniques are still evolving. Do you have papers describing y'all's processing? I'd love to learn more!

I do have papers. I recently wrote a paper where we used backscatter from container ships to calibrate our radars. I'll try to email it to you, but here it is:

http://euler.msi.ucsb.edu/papers/2014_emery_apm_from_soo.pdf

It has some of the basic processing techniques.

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