Thread by @steffanwatkins

🇺🇸 People stop me on the street all the time and ask me, Stef, how can you tell where in the United States there are too few #ADSBexchange receivers to geolocate aircraft that aren't broadcasting their precise location data using multilateration (#MLAT)?
Great question!

Here's what you do:
filter by altitude, between 10,000-40,000 ft, that restricts the results to aircraft which are flying high enough that we should home four or more receivers are in line of sight, a requirement for #MLAT.

Then filter so you only see the Mode-S-transponder-transmitting aircraft

Or just use this link,
inaccurate.adsbexchange.com/?filterAltMin=…

Let's take USAF KC-135 61-0311 as an example

We can tell more or less where they are, somewhere around the loop they're doing over Washington and Montana, but over on the left under Signal you see they have 1 receiver that's got them in line-of-sight (LOS), and #MLAT requires 4.

If you wanted to pick up the rough location of that aircraft you'd need to deploy another 3 receivers to locations beneath/nearby their flight path so you *might* get 4+ receivers to collect their Mode-S transmissions simultaneously and estimate their location in the sky.

Wherever you see a Mode-S plane icon, there's a need for another ground based receiver, to try and use multilateration to derive their real location, Mode-S locations on the map are only accurate to *hundreds* of km.

(NB: multilaterate = 4 data points, triangulate = 3 points)

There are 140+ other aircraft worldwide in the same boat right now. If you live near any of these plane icons, consider deploying an #ADSBexchange receiver to collect the transmissions from the planes above your house.
inaccurate.adsbexchange.com/?filterAltMin=…

How to set up an SDR receiver to collect ADS-B / Mode-S transponder data and feed the data to #ADSBexchange.

adsbexchange.com/how-to-feed/