Factors affecting crop spectral signatures
Plants have a particular way to reflect the electromagnetic radiation. This unique characteristic is known as the vegetation’s spectral signature. Reflectance of vegetation is very low in the blue and red regions of the electromagnetic spectrum, slightly higher in the green region and high in the near infra-red.
The normal growth process of a plant can be disrupted when it goes through a stress period. When in stress, the plant is not functioning properly because of one or more causes. When a plant is stressed, it usually expresses certain visible symptoms, but also some that are not visible to the human eye. Stress symptoms may appear in all of the plants of the field or in some portions of the field, depending on the cause.
Stress is caused by a number of external factors such as:
- Water shortage (drought)
- Nutrient deficiency
- High concentration of damaging chemicals (toxicity)
- Extreme acidity or salinity in the soil
- Fungal, bacterial or viral infection
- Attack from insects or other organisms, above or below the ground
- Extreme temperatures (heat or frost)
- Root suffocation or lack of space for the roots to develop (e.g. saturation of clay soil with water or soil compaction)
- Lack of sunlight
- Structural damage by weather conditions (wind, snow, ice)
- Competition with other plants for light, nutrients, water or space
Vegetation Spectral Signature
Vegetation covers a large portion of the Earth’s land surface. It’s role on the regulation of the global temperature, absorption of CO2 and other important functions, make it a land cover type of great significance and interest. Remote sensing can take advantage of the particular manner that vegetation reflects the incident electromagnetic energy and obtain information about the vegetation.