[HN Gopher] Synthetic aperture radar autofocus and calibration
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       Synthetic aperture radar autofocus and calibration
        
       Author : nbernard
       Score  : 183 points
       Date   : 2025-10-08 05:11 UTC (3 days ago)
        
 (HTM) web link (hforsten.com)
 (TXT) w3m dump (hforsten.com)
        
       | ThisIsTheWay wrote:
       | Awesome work. SAR imagery is notoriously fickle, and it is
       | amazing to see these results from a DIYer.
        
       | dang wrote:
       | Related. Others?
       | 
       |  _Homemade polarimetric synthetic aperture radar drone_ -
       | https://news.ycombinator.com/item?id=43073808 - Feb 2025 (60
       | comments)
        
         | shash wrote:
         | 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 wrote:
       | 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 wrote:
         | 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 wrote:
       | 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 wrote:
       | This is an excellent article and great work.
       | 
       | We need more articles uncovering the SAR mechanics, even for
       | Satellite Data.
        
       | smath wrote:
       | 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 wrote:
         | Seems like from anecdotal reports on HN Western Australia might
         | be a place where these conditions still obtain.
        
         | YZF wrote:
         | 1650-1750 Britain?
         | 
         | https://en.wikipedia.org/wiki/John_Harrison
         | 
         | 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 wrote:
           | 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 wrote:
       | 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.
        
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       (page generated 2025-10-11 23:01 UTC)