How satellites see
Earth-observation sensors measure energy reflected or emitted by the planet. Different wavelengths reveal different physical properties.
Optical imagers are intuitive but depend on daylight and clear skies. Synthetic-aperture radar actively illuminates the surface and can operate at night or through clouds. Hyperspectral sensors separate light into many narrow bands to identify material signatures.
Resolution is not one number. Spatial, spectral, temporal, and radiometric resolution trade against one another—and against cost and data volume.
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