How does radar reveal the shapes of near-Earth asteroids?

Radar reveals the shapes of near-Earth asteroids by analyzing radio signals reflected from their surfaces. By employing high-power radar transmitters, astronomers can bounce signals off these bodies and measure the precise time delay and the spectrum of the returned echoes.12

These measurements allow researchers to image surface features with high resolution and deduce critical physical characteristics, such as rotation rates and dimensions. For example, radar observations have been instrumental in distinguishing between different physical models of asteroids; in the case of the asteroid Geographos, radar imaging successfully ruled out a binary model, revealing it to be a single, highly elongated object. Similarly, radar data has identified other asteroids, such as Castalia, as appearing to be two bodies in contact. By providing direct imaging capabilities, radar overcomes the limitations of relying solely on light-curve analysis, which can be difficult to interpret when distinguishing between irregular shapes and spotted surfaces.123