Which method is used in along-track scanning?

In along-track scanning, a linear array is employed to collect data directly along the satellite's path. This method allows the sensor to gather information in the direction of the satellite's movement, effectively capturing images of the ground or other features as it travels. The linear array consists of multiple detectors aligned in a straight line, which can efficiently record data over a wide area while the satellite continues its orbit. This technique is particularly useful for applications that require continuous monitoring of the surface, such as environmental studies, agricultural assessments, and urban planning.

The other methods mentioned involve different scanning techniques or technologies that are not specific to along-track scanning. For instance, the rotating mirror technique is characteristic of cross-track scanning, where data is collected across a swath rather than along the path of the satellite. The synthesized aperture technique, typically used in radar systems, enhances imaging resolution over broader areas rather than focusing solely along the flight path. Gravitational detection is not applicable for data collection in the context of along-track scanning and pertains to a different principle used in determining celestial objects or properties of the Earth's gravitational field.