5 ms·

Synthetic aperture radar autofocus and calibration

201 points by nbernard 1y ago

ThisIsTheWay 1y ago
Awesome work. SAR imagery is notoriously fickle, and it is amazing to see these results from a DIYer.
dang 1y ago
Related. Others? Homemade polarimetric synthetic aperture radar drone - https://news.ycombinator.com/item?id=43073808 https://news.ycombinator.com/item?id=43073808 - Feb 2025 (60 comments)
- shash 1y ago
  Same guy. His work is pretty amazing actually. Lots of little details he’s worked out and built upon. Someday I’d like to replicate his designs.
ccgreg 1y ago
I had fun reading this -- the radio astronomy technique called VLBI (very long baseline interferometry) has a ton of overlap, but the jargon words are fairly different. There are plenty of differences: our telescopes are mostly on the surface of the Earth and don't move, VLBI isn't a radar so there's no waveform, etc. The EHT black hole telescope is an example of VLBI.
- shash 1y ago
  Very similar. To the extent that when I’ve worked on synthetic aperture I have used ideas from radio astronomy. And there’s a similar field of synthetic aperture ultrasound which is where I did a ton of work a decade ago.
NoiseBert69 1y ago
I'm an embedded engineer for 15 years now and did some really spicy stuff during my career. This hobbyist SAR project made by hforsten absolutely nuts. Wonderful. He mastered mechanics, electronics, software and applied higher math of the highest difficulty grade. Guess we have to call this "The Holy Quadrivium". Back to the tech: Radar stuff is very interesting. Reverse Engineering cheap FMCW radars from China makes these very accessable to hobbyists too. Often you "only" have to care about the VCO for the frequency sweep and then read back the I/Q channels using two sync'ed ADCs. Then you can play around with algorithms to analyze the signals. These 24GHz Car Speed CW (you see next to streets) radars can be used for classifying rain drops for example. They antenna pattern is quite sharp and they have high gain.
fithisux 1y ago
This is an excellent article and great work. We need more articles uncovering the SAR mechanics, even for Satellite Data.
smath 1y ago
Slightly tangential: this is a wonderful and deep project, that requires a lot of personal time. Lately I've been wondering what social/economic/govt conditions allow for this type of deep thinking + tinkering among working people (not academia). My very rough guess is the US of 1950-60s did, and some other countries today do, but not so much the US of today because the cost of living and time pressures are higher. I'd be curious if anyone has a more detailed answer (or a rebuttal of my thesis altogether).
- selimthegrim 1y ago
  Seems like from anecdotal reports on HN Western Australia might be a place where these conditions still obtain.
- YZF 1y ago
  1650-1750 Britain? https://en.wikipedia.org/wiki/John_Harrison https://en.wikipedia.org/wiki/John_Harrison https://en.wikipedia.org/wiki/Isaac_Newton https://en.wikipedia.org/wiki/Isaac_Newton And I'm sure lots more? Or maybe more generally Europe circa 18th century? Probably a lot more creativity/discovery/"personal projects" vs. the US 50s or 60's would be my guess? So we need prosperity and a monarchy?
  - smath 1y ago
    A benevolent monarchy maybe - like some places in the east (maybe).or maybe UBI? Some way to not have to worry about basic health and needs What places have this today? I see an answer suggesting AUS below. ChatGPT says Switzerland
aidenn0 1y ago
I recall a post on HN about a decade ago where someone made an SAR by modifying one of those toy radar-guns into an FM CW Radar and mounting it on his bike. After trying a few different position-estimation algorithms, he got the best results just by maximizing the contrast.
- ThomasPw 1y ago
  RE "....a post on HN about a decade ago ...." I tried to find (search ) this post but could not...
  - deleted 1y ago
    [deleted]
  - defrost 1y ago
    Homemade synthetic aperture radar (2015) - https://news.ycombinator.com/item?id=10387360 https://news.ycombinator.com/item?id=10387360 https://hforsten.com/homemade-synthetic-aperture-radar.html https://hforsten.com/homemade-synthetic-aperture-radar.html https://hackaday.com/2019/08/15/bike-mounted-synthetic-aperture-radar-makes-detailed-images/ https://hackaday.com/2019/08/15/bike-mounted-synthetic-apert...
    - aidenn0 1y ago
      That's the one. I remember it was of a football field. Apparently I was confusing it with a different article where the FMCW radar was made from a modified toy radar gun though, since this radar appears to be made from scratch.
deleted 1y ago
[deleted]
ACCount37 1y ago
This is mad in all the good ways.

201 points by nbernard 1y ago

Awesome work. SAR imagery is notoriously fickle, and it is amazing to see these results from a DIYer.

dang 1y ago

Related. Others? Homemade polarimetric synthetic aperture radar drone - https://news.ycombinator.com/item?id=43073808 https://news.ycombinator.com/item?id=43073808 - Feb 2025 (60 comments)

shash 1y ago
Same guy. His work is pretty amazing actually. Lots of little details he’s worked out and built upon. Someday I’d like to replicate his designs.

ccgreg 1y ago

I had fun reading this -- the radio astronomy technique called VLBI (very long baseline interferometry) has a ton of overlap, but the jargon words are fairly different. There are plenty of differences: our telescopes are mostly on the surface of the Earth and don't move, VLBI isn't a radar so there's no waveform, etc. The EHT black hole telescope is an example of VLBI.

shash 1y ago
Very similar. To the extent that when I’ve worked on synthetic aperture I have used ideas from radio astronomy. And there’s a similar field of synthetic aperture ultrasound which is where I did a ton of work a decade ago.

NoiseBert69 1y ago

I'm an embedded engineer for 15 years now and did some really spicy stuff during my career. This hobbyist SAR project made by hforsten absolutely nuts. Wonderful. He mastered mechanics, electronics, software and applied higher math of the highest difficulty grade. Guess we have to call this "The Holy Quadrivium". Back to the tech: Radar stuff is very interesting. Reverse Engineering cheap FMCW radars from China makes these very accessable to hobbyists too. Often you "only" have to care about the VCO for the frequency sweep and then read back the I/Q channels using two sync'ed ADCs. Then you can play around with algorithms to analyze the signals. These 24GHz Car Speed CW (you see next to streets) radars can be used for classifying rain drops for example. They antenna pattern is quite sharp and they have high gain.

fithisux 1y ago

This is an excellent article and great work. We need more articles uncovering the SAR mechanics, even for Satellite Data.

smath 1y ago

Slightly tangential: this is a wonderful and deep project, that requires a lot of personal time. Lately I've been wondering what social/economic/govt conditions allow for this type of deep thinking + tinkering among working people (not academia). My very rough guess is the US of 1950-60s did, and some other countries today do, but not so much the US of today because the cost of living and time pressures are higher. I'd be curious if anyone has a more detailed answer (or a rebuttal of my thesis altogether).

selimthegrim 1y ago
Seems like from anecdotal reports on HN Western Australia might be a place where these conditions still obtain.
YZF 1y ago
1650-1750 Britain? https://en.wikipedia.org/wiki/John_Harrison https://en.wikipedia.org/wiki/John_Harrison https://en.wikipedia.org/wiki/Isaac_Newton https://en.wikipedia.org/wiki/Isaac_Newton And I'm sure lots more? Or maybe more generally Europe circa 18th century? Probably a lot more creativity/discovery/"personal projects" vs. the US 50s or 60's would be my guess? So we need prosperity and a monarchy?
- smath 1y ago
  A benevolent monarchy maybe - like some places in the east (maybe).or maybe UBI? Some way to not have to worry about basic health and needs What places have this today? I see an answer suggesting AUS below. ChatGPT says Switzerland

aidenn0 1y ago

I recall a post on HN about a decade ago where someone made an SAR by modifying one of those toy radar-guns into an FM CW Radar and mounting it on his bike. After trying a few different position-estimation algorithms, he got the best results just by maximizing the contrast.

ThomasPw 1y ago
RE "....a post on HN about a decade ago ...." I tried to find (search ) this post but could not...
- deleted 1y ago
  [deleted]
- defrost 1y ago
  Homemade synthetic aperture radar (2015) - https://news.ycombinator.com/item?id=10387360 https://news.ycombinator.com/item?id=10387360 https://hforsten.com/homemade-synthetic-aperture-radar.html https://hforsten.com/homemade-synthetic-aperture-radar.html https://hackaday.com/2019/08/15/bike-mounted-synthetic-aperture-radar-makes-detailed-images/ https://hackaday.com/2019/08/15/bike-mounted-synthetic-apert...
  - aidenn0 1y ago
    That's the one. I remember it was of a football field. Apparently I was confusing it with a different article where the FMCW radar was made from a modified toy radar gun though, since this radar appears to be made from scratch.

deleted 1y ago

[deleted]

ACCount37 1y ago

This is mad in all the good ways.