John Powell • February 27, 2018 at 6:01 am UTC
Here is an interesting image of an aircraft and a secondary image (halo, ghost whatever) taken near Benalla VIc.
1. What is the secondary image? Is it something the satellite creates? or weather? or just a distorted shadow.
2. I cannot work out the scaling as it appears to be close to the surface.
3. This image location is at least 200Km from the nearest airport Tullamarine and not on a regular flight path.
Any suggestions?Shona Chisholm • February 27, 2018 at 11:21 pm UTC
Most optical satellites like DigitalGlobe’s WorldView satellites have two separate cameras – one for high resolution B&W imagery, and a lower resolution Colour (Multi=spectral) Camera – for efficiency reasons, so the image files are much smaller to download from the satellite. eg. 50cm resolution B&W and 2m Multi. Then the two images are merged to produce a 50cm colour image.
You usually don’t notice the difference between B&W and colour with stationary objects but anything that’s moving quickly like aeroplanes will be slightly offset because of the timing difference between the two images being taken – which is really only split seconds. It means that the plane is definitely moving rather than just sitting in a field somewhere, but I’m not sure where it’s going? I guess a really keen plane spotter who’s good with numbers could calculate the height it’s travelling at based on the length of plane, distance it’s moved etc. etc
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