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.
At nadir (ONA ≈ 0°) a satellite images the ground directly beneath it at its best resolution. By slewing to a larger off-nadir angle, an agile satellite can image targets hundreds of kilometres to either side of its ground track — dramatically improving how often it can reach a given area (revisit).
The cost is image quality: at higher ONA the ground sample distance grows, the atmospheric path lengthens, and geometric distortion increases. Most tasking requests therefore set a maximum acceptable ONA to bound quality.
When planning an acquisition you specify the ONA range you'll accept. A tight range (e.g. 0–20°) prioritises quality but reduces how many passes qualify; a wide range (e.g. 0–45°) maximises opportunities. For SAR satellites the equivalent concept is the incidence-angle range.
Yes. As the off-nadir angle increases, the ground sample distance grows and the atmospheric slant path lengthens, so effective resolution and image quality decrease, in exchange for wider access and more frequent revisit.
Use the tightest range your quality needs allow. 0–20° favours quality; widening toward 0–45° increases the number of qualifying passes when timeliness matters more than resolution.
Plan a real acquisition over your area on the interactive map, browse the satellite catalog, or read the tasking guides.