Polychromatic imaging method

A polychromatic imaging method in the spectral band of 360 nm to 950 nm used for observation, comprising the following steps:

• carrying an image-sensing optical system on board an aircraft or spacecraft, said image-sensing optical system comprising a telescope and being adapted to form views, in at least one focal plane, respectively based on radiation within several spectral sub-bands each contained within the observation spectral band;
• placing at least one array of photodetectors in said at least one focal plane, in order to capture an intermediate image of each view formed by the image-sensing optical system at a resolution associated with said intermediate image;
• respectively capturing the intermediate images of a same scene for each spectral sub-band;
• and
• merging the intermediate images respectively captured for the spectral sub-bands, in order to form a final polychromatic image,
• the telescope of the image-sensing optical system determining a pupil which is common to the spectral sub-bands, and a dimension of said common pupil setting a spatial cutoff frequency which is different for each spectral sub-band,
• the spectral sub-bands comprising a first spectral sub-band and at least one other spectral sub-band extending towards long wavelengths, with said other spectral sub-band extending towards the long wavelengths having at least one wavelength greater than an upper limit of said first spectral sub-band, the pupil of the telescope being sized such that the spatial cutoff frequency for the first spectral sub-band is greater than a Nyquist frequency of the intermediate image captured for said first spectral sub-band,
• the method being characterized by the pupil of the telescope additionally being sized so that the spatial cutoff frequency, for said other spectral sub-band extending towards the long wavelengths, is less than the Nyquist frequency of the intermediate image captured for said first spectral sub-band.