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Most planes broadcast their position via ADS-B while they are in the air. On land those are picked up by ground stations. For a long time we had bad coverage of

Most planes broadcast their position via ADS-B while they are in the air. On land those are picked up by ground stations. For a long time we had bad coverage of planes at sea, but in part in response to Malaysia Airlines Flight 370 the Iridium satellite network now also picks those signals up, giving us global coverage. The satellite coverage is limited to the frequencies used by airliners and business jets, but those are the ones we are most concerned with finding if they go down.

defrost 2y ago
As a point of curiousity, air geophysical survey craft (planes, helicopters) don't broadcast their position via ADS-B .. except perhaps at the start and end of a survey grid or at the turn point of a survey line. If they "disapear" it's no great mystery as to where they might be .. they have thoroughly planned to within a metre flight paths and are on contract to drape specific areas. However, they are loaded with instrumentaton: magnetic sensors, radiometric sensors, EM sensors for EM surveys, multiple GPS receivers and calibrate to neutral for data collection runs (like zero'ing a scale with a empty tub on when cooking to just measure the tub contents and not the tub). There's an aversion to unshielded equipment, extranuous broadcasts, and pilots wearing glow underwater divers watches with radium dials.
- jjwiseman 2y ago
  I feel like I've seen lots of geophysical survey aircraft using ADS-B for their entire flights. Do you have a reference?
  - defrost 2y ago
    Sure, we kept it off during aquisition on all 14 airframes for hundreds of millions of line kilometres gathered across multiple countries; Mali, Fiji, PNG, Central and Northern Australia, the DRCs, various 'stans, India | Pakistan and elsewhere. Perhaps others had different practices or flew different instruments such as optical photogrammetry. If you're seeing gridding at 80m ground clearence perhaps it's crop spraying or perhaps your software is infilling lines from turnpoint position blipping with nothing for the next 50km. EDIT: I note you submitted this article and have an interest in aerial surveillance programs, I'm simply recounting the practices of one rather busy Australian geophysics company thta was subsumed into Fugro some time past. We considered aircraft and crew safety and had a 20+ year no crash no lives lost record and regularly considered aircraft position signals .. that said we avoided "polluting" the spectrum with broadcasts when aquiring signal and largely relied on off grid checkins (even just three radio blips) ever few completed lines. I dare say some operators contracted for non EM work (say, radiometric survey) might broadcast during aquisition lines but I find it hard to believe that a good operator would broadcast during EM runs.
    - jjwiseman 2y ago
      I was thinking of airborne electromagnetic (AEM) surveys (e.g., https://www.ramboll.com/projects/water/aem-mapping-california-s-groundwater https://www.ramboll.com/projects/water/aem-mapping-californi...) when I wrote that, but after checking my notes, I found that I had misremembered: I actually hadn't been able to find any ADS-B tracks that were clearly survey flights!
      - defrost 2y ago
        That tracks .. geophys surveys, whether active (sending out signal to ground and listening to the return) or passive (bat airs across the spectrums), are predicated on having as 'neutral' a recording post as possible .. blatting out radio spectrum data that would have to be removed from the record in post just isn't "the way". Aeromag and radiometrics tend to be low level and tight; 80m ground clearance, 200m line spacing (unless for regional levelling of multiple small infill surveys). Photogrammatic sureys are higher with much wider spacing, the frames are large and there's really only need for a 50m or less overlap to get a good broad area mosaic. I'm guessing you have routines to analyse and classify flight activity by path characteristics and coarsely bucket activity?

defrost 2y ago

As a point of curiousity, air geophysical survey craft (planes, helicopters) don't broadcast their position via ADS-B .. except perhaps at the start and end of a survey grid or at the turn point of a survey line. If they "disapear" it's no great mystery as to where they might be .. they have thoroughly planned to within a metre flight paths and are on contract to drape specific areas. However, they are loaded with instrumentaton: magnetic sensors, radiometric sensors, EM sensors for EM surveys, multiple GPS receivers and calibrate to neutral for data collection runs (like zero'ing a scale with a empty tub on when cooking to just measure the tub contents and not the tub). There's an aversion to unshielded equipment, extranuous broadcasts, and pilots wearing glow underwater divers watches with radium dials.

jjwiseman 2y ago
I feel like I've seen lots of geophysical survey aircraft using ADS-B for their entire flights. Do you have a reference?
- defrost 2y ago
  Sure, we kept it off during aquisition on all 14 airframes for hundreds of millions of line kilometres gathered across multiple countries; Mali, Fiji, PNG, Central and Northern Australia, the DRCs, various 'stans, India | Pakistan and elsewhere. Perhaps others had different practices or flew different instruments such as optical photogrammetry. If you're seeing gridding at 80m ground clearence perhaps it's crop spraying or perhaps your software is infilling lines from turnpoint position blipping with nothing for the next 50km. EDIT: I note you submitted this article and have an interest in aerial surveillance programs, I'm simply recounting the practices of one rather busy Australian geophysics company thta was subsumed into Fugro some time past. We considered aircraft and crew safety and had a 20+ year no crash no lives lost record and regularly considered aircraft position signals .. that said we avoided "polluting" the spectrum with broadcasts when aquiring signal and largely relied on off grid checkins (even just three radio blips) ever few completed lines. I dare say some operators contracted for non EM work (say, radiometric survey) might broadcast during aquisition lines but I find it hard to believe that a good operator would broadcast during EM runs.
  - jjwiseman 2y ago
    I was thinking of airborne electromagnetic (AEM) surveys (e.g., https://www.ramboll.com/projects/water/aem-mapping-california-s-groundwater https://www.ramboll.com/projects/water/aem-mapping-californi...) when I wrote that, but after checking my notes, I found that I had misremembered: I actually hadn't been able to find any ADS-B tracks that were clearly survey flights!
    - defrost 2y ago
      That tracks .. geophys surveys, whether active (sending out signal to ground and listening to the return) or passive (bat airs across the spectrums), are predicated on having as 'neutral' a recording post as possible .. blatting out radio spectrum data that would have to be removed from the record in post just isn't "the way". Aeromag and radiometrics tend to be low level and tight; 80m ground clearance, 200m line spacing (unless for regional levelling of multiple small infill surveys). Photogrammatic sureys are higher with much wider spacing, the frames are large and there's really only need for a 50m or less overlap to get a good broad area mosaic. I'm guessing you have routines to analyse and classify flight activity by path characteristics and coarsely bucket activity?