The spectral resolution of an Earth Observation sensor refers to the number of spectral bands this sensor can capture. Spectral bands are wavelength intervals in the electromagnetic spectrum. Sometimes, spectral bands are also called spectral channels. Spectral resolution is related to a sensor’s ability to distinguish between different Earth’s surface features based on their spectral properties. A high number of spectral bands means high spectral resolution, with many bands meaning an increasingly smaller range of wavelengths covered by a single band. The spectral resolution of an Earth observation sensor can range from a single very broad band for panchromatic black and white images over a few bands in the case of multispectral sensors (e.g. Landsat family, SPOT, Sentinel-2) to 200 or even more channels for capturing hyperspectral images. Multispectral or hyperspectral sensor imagery has a higher degree of discriminating power than a single band sensor. Another definition of the spectral resolution can be given by the spectral sensitivity of a sensor, which can be specified by the definition of the full width, half maximum (FWHM) as being the spectral interval measured at the level at which the response of the instrument reaches one-half of its maximum values. Spectral satellite sensors can only gather radiation which is able to pass the Earth’s atmosphere. The atmosphere contains gases, aerosols, ice crystals and water droplets, which absorb and scatter parts of the radiation passing through the atmosphere. Wavelength ranges which do not allow radiation to pass through on their way to the satellite sensors are called absorption bands and those getting through to the sensor are called atmospheric windows. This means that spectral sensors can only operate in these atmospheric windows and the spectral bands should be placed in the wavelength ranges of the atmospheric windows.
Discuss how different spectral resolution of EO sensors influences their potential for vegetation mapping
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