We already do something vaguely similar with MLAT, measuring the time delay from transponder signals at different receiver sites. MLAT data can be used for eit

We already do something vaguely similar with MLAT, measuring the time delay from transponder signals at different receiver sites. MLAT data can be used for either unofficial situational awareness in non-radar facilities (to display non-ADS-B aircraft), and in some limited cases can be fed directly into official radar displays when running in sensor fusion mode.