Resolution is the ability to distinguish objects in a given direction. Unlike optical imagery, SAR imagery can have different resolutions in different directions. Resolution in a given direction can vary based on the chosen acquisition mode, incidence angle, and radar signal bandwidth.
The azimuth resolution refers to the image resolution in the radar platform’s travel direction.
The length of the receiving antenna typically restricts azimuth resolution, but SAR platforms can use their movement to overcome this. The various acquisition modes manipulate how the radar beams are transmitted and received, and this can further improve the azimuth resolution. For example, in the spot SAR acquisition mode, the radar beam is focused on a specific target for longer to improve the azimuth resolution.
The ground range resolution is measured along the ground plane. Detected and geocoded SAR imagery represents information in the ground plane.
It’s independent of the radar platform’s height. It depends on the transmitted signal’s bandwidth and the radar platform’s incidence angle.
Unlike spatial resolution for optical imagery, ground range resolution improves for larger incidence angles as the slant plane becomes more aligned with the ground plane.
The slant range resolution is measured along the slant plane, which lies along the radar platform’s line of sight. Complex SAR imagery represents information in the slant plane.
It’s independent of the radar platform’s height and incidence angle and determined solely by the bandwidth of the transmitted signal.
| Class | Range of values |
|---|---|
| Very high resolution (VHR) | ≤ 50 cm |
| High resolution (HR) | From > 50 cm to ≤ 2 m |
| Medium resolution (MR) | From > 2 m to ≤ 20 m |
| Low resolution (LR) | > 20 m |
| Collection | LR | MR | HR | VHR |
|---|---|---|---|---|
| Capella Space |  | |  | |
| ICEYE | | | | |
| KOMPSAT‑5 | | | | |
| TerraSAR-X | | | | |
| Umbra | | | | |
| Collection | LR | MR | HR | VHR |
|---|---|---|---|---|
| Capella Space | | | | |
How does multi-looking affect SAR resolution?
Multi-looking is a SAR processing technique that reduces noise by averaging multiple independent looks for the same target. It improves image quality by averaging the effects of noise, but it can reduce the effective azimuth and range resolutions.
Complex SAR imagery, especially SLCs, is generally derived from single-look SAR data. Detected and geocoded SAR imagery is generally derived from multi-looked SAR data.