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No, I believe that you are still mis-interpretting the push broom scanners. A greyscale push broom scanner would have a single row of pixels that are lined up p
by tgb 13y ago
No, I believe that you are still mis-interpretting the push broom scanners. A greyscale push broom scanner would have a single row of pixels that are lined up perpendicularly to the direction of travel and whose rays are in the plane perpendicular to the direction of travel. So yes, these rays would span many kilometers, but only in one direction. In order to image a 2D area of the planet the entire satellite would need to traverse down it linearly - which is something that satellites happen to be quite good at given how fast they are moving. This is almost like how a document scanner works - it translates a line of sensors across a document to construct a full 2D image.
For a full color image, three linear sensors are used, each displaced some distance along the direction of motion. So the fact that the rays are spreading out in the perpendicular doesn't change the distance the satellite must travel to image the next part.
For example, your second paragraph doesn't hold. The large separation of rays only occurs in the direction perpendicular to that of travelling. Note how your method would be imaging the same place multiple times on each pass whereas a push broom scanner would capture each one just one.
For your third paragraph, I agree that this could be done but that's simply not how the sensors are aligned and that difference is important. In particular, it's the very difference that I'm trying to point out.
- InclinedPlane 13y agoI'm not quite sure why you aren't getting this. The view of the Earth that each pixel has isn't separated by the same distance as their separation on the sensor. Do you agree with that? The important part is that it's also true for the different color lines as well. That's what I'm trying to explain. The view of each color line may traverse 1mm for every 1mm the satellite moves in orbit, but that has nothing to do with the separation of the lines. The important thing is that the view of, say, the green color line will not be identical to the view of the red color line when they are at the same relative physical position in orbit (e.g. a fraction of a second apart in the orbital motion) because the view of each color line is at a different angle through the optics. And because of that the portion of the Earth that each line is viewing at a given time is separated by a considerable distance, and there is then a considerable time separation between when a given spot on the Earth is imaged by each color line. My other examples are trying to provide hypothetical scenarios to help get you to understand why your preconceived ideas about how push broom scanning works have important gaps, they're not meant to explain how things work in this particular example.