Comment by sjburt
18 hours ago
The diffraction limit (under 1.22 h* lambda/d) of a 1m optic at 250km in visible light is about 17cm. How can you achieve 10cm resolution?
18 hours ago
The diffraction limit (under 1.22 h* lambda/d) of a 1m optic at 250km in visible light is about 17cm. How can you achieve 10cm resolution?
Clarity is designed for a GSD (ground sample distance) of 10 cm. Generally the industry uses resolution<>GSD interchangeably. Agree it's not the true definition of resolution. But I'd argue the diffraction limit is an incomplete metric as well, like how spatial sampling is balanced with other MTF contributors (e.g. jitter/smear). For complete metrics, we like 1) NIIRS or 2) % contrast for a given object size on the ground (i.e. system MTF translated to ground units, not image-space units).
The main performance goal for us was NIIRS 7, and we decomposed GSD/MTF/SNR contributors optimized for affordability when we architected the system
How do you manage along-track smear? At those altitudes you're pushing close to 8km/s. Traditionally you'd either need to keep the satellite rotating through the collect or somehow keep the integration time in the single digit microseconds.
TDI (time delay integration)
A little more detail that we didn't get into in the post. The 3-CMG control mode we first uploaded was v1. We had plans to improve the agility with later versions. In v1, we didn't have quite enough rate to match earth's, even with max TDI. We called it Banana Scanning. Kind of like slipping over the earth.
Net - the CMG imagery we captured had a few pixels of along-track smear in it. Which would have been removed in post-processing if we had made it through focus cal.
1 reply →