Agriculture is illustrated by a combination of satellite bands SWIR1, NIR, Blue with fixed stretch applied on apparent reflectance. This band combination is useful for the monitoring of crops, which appear as a vibrant green. Bare earth appears as a magenta color, and non-crop vegetation seems as more subdued shades of green.
The bands’ combination operates in the best spectral region to differentiate vegetation conditions and varieties. Because water is a strong IR absorber, the bands’ combination delineates water bodies and distinguishes between moist and dry soils. In this band combination grasslands and croplands shows brighter tone (higher reflectance) than the forest. It also separates bare croplands form croplands. Since standing crops has a brighter tone in a close IR region, they appear with a brighter hue, and because of moisture content in the bare croplands, they have darker tone appearance. In the bands’ combination, urban areas, highways and barren lands are not highlighted where they appear as a dark tone.
How IR interacts with the vegetation is essential for interpretation and processing of a remote sensing data of agricultural using the band combination. A plant leaf usually has a low reflectance in a visible spectral region due to the strong absorption by chlorophylls, a high reflectance in the NIV on account of internal leaf scattering and zero absorption, and a comparatively low reflectance in infrared going beyond 1.3 μ due to the strong absorption by the water. The plant canopy reflectance is similar but is changed by the incident solar radiation non-uniformity, leaf areas, plant structures, background reflectivity and shadows. Satellites sensors obtain an integrated view of these effects, where each crop type tends to have a specific signature which allows its discrimination. When physiological stresses and disease affect reflectance properties of the leaves directly, the pronounced initial variations often occur in a visible spectral region rather than in the infrared due to the chlorophyll sensitivity to the physiological disturbances. The primary basis for the stress conditions detection in plant community or a crop by the satellite sensors is not an alteration in characteristics reflectance of individual leaves, but the reduction the total leaf area that is exposed to those sensors. The reduction might come from the direct leaves loss, orientation change, or the overall plant growth suppression. In cases like this, the infrared reflectance looks like it decreased more than visible reflectance due to the infrared enhancement reduction because of the increase in background exposure and fewer multiple leaf layers.
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