SAR uses active sensing, where the sensor emits a radar beam and measures the response after interacting with the environment. Active sensing means that SAR has a unique variety of acquisition modes compared to optical acquisition modes.
Different modes are used depending on what is required, such as a better azimuth resolution or a longer swath.
SAR collections offer imagery that is captured in four primary acquisition modes: spot, site, strip, and scan.
In the spot mode, the antenna beam is focused on a point for an extended period. The mode provides the highest azimuth resolution out of all modes.
The site mode can be viewed as a sliding variation of the spot mode. It is similar to spot, but instead of illuminating a fixed point on the ground, the angle is slowly varied to slide the illumination point along the ground. The mode provides a longer swath than the spot mode, but lower azimuth resolution.
In the strip mode, the center of the antenna beam is fixed in elevation and moves with the satellite. The result is a single continuous strip. The mode provides a longer swath than the site mode, but lower azimuth resolution.
In the scan mode, the antenna beam moves between sub-swaths to acquire adjacent coverages that are processed into one long and wide scene. Each sub-swath is illuminated by multiple pulses but for a shorter time than in the strip mode, resulting in lower azimuth resolution.
| Collection | Spot | Site | Strip | Scan |
|---|---|---|---|---|
| Capella Space |  | | |  |
| ICEYE | Standard Fine Extended | | | |
| KOMPSAT‑5 | Standard Enhanced Ultra | | Standard Enhanced | Standard Enhanced |
| TerraSAR-X | Standard High resolution High resolution 300 MHz | | | Standard Wide |
| Umbra | | | | |
| Collection | Spot | Site | Strip | Scan |
|---|---|---|---|---|
| Capella Space | | | | |