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To be clear: you're saying that each of the the sensor lines are at slightly different angles and that this is due to sharing (at least for some of them) the sa

by tgb 13y ago

To be clear: you're saying that each of the the sensor lines are at slightly different angles and that this is due to sharing (at least for some of them) the same lens? If so, that shared lens would be exactly the part of this that I was missing. Honestly, it doesn't look like there's a shared lens between the red and the other two, as you point out, but I guess it could be sharing a lens with the "unused lines" marked in the diagram that puts it at a distinct angle. As a test of my understanding - would I be correct in saying that when the article says "The red and infrared rows are paired on one CCD array, while the green and blue sensors are on a second array, which is why the red plane often seems much further ahead than the green and blue planes." it's going a little too far: there's no reason that the red line would have to be inherently at a greater angle than the other three? I used to interpret this line as just meaning "the green and blue are closer together than the red is, so the red image will be further apart" but that should be insignificant. I'm curious - does anyone know how they calibrate this kind of equipment or are the tolerances good enough that they don't really need to? Do they take passes over known objects to calibrate or do some algorithmic test for how well the three colors match up (in a non-moving example).

mannykannot 13y ago
To the first question: yes, and after a bit more thought, I realize that this assembly must be designed to use a single lens, as the sensor arrays are close together, which would make it difficult to have any other optical arrangement. The pictured assembly would form the back of the camera, where the rectangular CCD array (or film) goes in a conventional camera. The picture shows that the red sensor is further from the green one than the blue is, simply because it is on a separate sub-assembly. If the infra-red image showed on the pictures, it would be as far from the red one as the green one is from the blue. Given the order of the arrays on the camera, the IR image of the plane would be ahead of the red image, meaning that the IR is the last of the four images taken. Incidentally, the pictures show the aircraft are experiencing considerable wind drift, especially in the case of the top-left picture, where you can see the contrail. This indicates strong winds, and probably also a relatively low airspeed for the aircraft. The orientation of the waves suggests a head- or tail-wind, but to get that drift, it must be different at the airplane's altitude (which probably is not high if it is searching.)

by tgb 13y ago

mannykannot 13y ago

To the first question: yes, and after a bit more thought, I realize that this assembly must be designed to use a single lens, as the sensor arrays are close together, which would make it difficult to have any other optical arrangement. The pictured assembly would form the back of the camera, where the rectangular CCD array (or film) goes in a conventional camera. The picture shows that the red sensor is further from the green one than the blue is, simply because it is on a separate sub-assembly. If the infra-red image showed on the pictures, it would be as far from the red one as the green one is from the blue. Given the order of the arrays on the camera, the IR image of the plane would be ahead of the red image, meaning that the IR is the last of the four images taken. Incidentally, the pictures show the aircraft are experiencing considerable wind drift, especially in the case of the top-left picture, where you can see the contrail. This indicates strong winds, and probably also a relatively low airspeed for the aircraft. The orientation of the waves suggests a head- or tail-wind, but to get that drift, it must be different at the airplane's altitude (which probably is not high if it is searching.)