Learn satellite tasking & Earth observation

Satellite tasking is the process of commanding an Earth-observation satellite to collect a new image of a specific area of interest at a specific time, as opposed to buying an existing archive image.

The off-nadir angle (ONA) is the angle between a satellite sensor's line of sight and the straight-down (nadir) direction; a larger ONA lets the satellite image areas to its side but at lower resolution and image quality.

Revisit time is the average time between successive opportunities for a satellite (or constellation) to image a given area of interest at an acceptable look angle.

Swath width is the width of the ground strip a satellite sensor captures in a single pass; wider swaths cover more area per pass but typically at lower resolution.

A sun-synchronous orbit (SSO) is a near-polar low-Earth orbit whose plane precesses to keep a fixed local solar time at each equator crossing, so a satellite images every location under consistent sun illumination.

Optical satellites capture reflected sunlight (so they need daylight and clear skies), while SAR (synthetic aperture radar) satellites actively illuminate the ground with radar and can image day or night and through clouds.

A satellite ground track is the line traced on Earth's surface by the point directly beneath the satellite (the sub-satellite point) as it orbits.

A TLE (Two-Line Element set) is a compact, standardized encoding of a satellite's orbit at a moment in time, and SGP4 is the propagation model that turns a TLE into the satellite's position and velocity at any future time.