Multispectral Imaging Indices Explained
At its core multispectral imaging involves acquiring multiple images of the same area of the ground at different wavelengths of light. These images can be combined to create various spectral indices that provide important information about the surface features and properties. The various indices provide valuable information for a wide range of applications, including agriculture, forestry, water resource management, and environmental monitoring.
Here are some commonly used multispectral indices and their applications:
Normalized Difference Vegetation Index (NDVI):
NDVI is a widely used index that measures the amount of live green vegetation in an area. It is calculated by subtracting the reflectance of near-infrared (NIR) radiation from the reflectance of red visible light and dividing the result by their sum. NDVI values range from -1 to +1, with higher values indicating more healthy vegetation.
Green Normalized Difference Vegetation Index (GNDVI):
GNDVI is similar to NDVI but is more sensitive to green vegetation, and is less affected by soil brightness or background reflectance. It is calculated by subtracting the reflectance of green visible light from the reflectance of NIR radiation and dividing the result by their sum.
Enhanced Vegetation Index (EVI):
EVI is a modified version of NDVI that provides a better measure of vegetation in areas with dense canopies or where the soil is visible. It is calculated by combining the reflectance of blue, red, and NIR wavelengths.
Normalized Difference Red Edge (NDRE):
NDRE is an index that measures the difference between the reflectance of red-edge light and NIR radiation, which is particularly sensitive to vegetation stress and biomass. It is used in precision agriculture for crop health monitoring and yield prediction.
Leaf Chlorophyll Index (LCI):
LCI is an index that measures the amount of chlorophyll in leaves, which is an indicator of plant health and photosynthetic activity. It is calculated by combining the reflectance of red and NIR wavelengths.
Modified Chlorophyll Absorption in Reflectance Index (MCARI):
MCARI is another index that measures chlorophyll content in leaves, but it is less affected by changes in leaf structure or background reflectance. It is calculated by combining the reflectance of blue, green, and red wavelengths.
Soil-Plant Nitrogen Index (SPNI) or Structure Insensitive Pigment Index (SIPI3):
SPNI or SIPI3 is an index that measures the amount of nitrogen in plants, which is an important nutrient for growth and productivity. It is calculated by combining the reflectance of red and NIR wavelengths, and is commonly used in precision agriculture for nitrogen management.
Soil Adjusted Vegetation Index (SAVI):
SAVI is similar to NDVI but is adjusted to account for the presence of bare soil in the area. This index is calculated by dividing the difference between the reflectance of NIR and red light by their sum, plus a soil brightness adjustment factor.
Normalized Difference Water Index (NDWI):
NDWI is an index that measures the presence of water in an area. It is calculated by subtracting the reflectance of short-wave infrared (SWIR) radiation from the reflectance of green visible light and dividing the result by their sum. NDWI values range from -1 to +1, with higher values indicating more water.
Normalized Burn Ratio (NBR):
NBR is an index that measures the severity of fire damage to vegetation. It is calculated by subtracting the reflectance of NIR radiation from the reflectance of SWIR radiation and dividing the result by their sum.
Urban Area Index (UAI):
UAI is an index that measures the amount of impervious surfaces in an urban area, such as roads, buildings, and pavements. It is calculated by combining the reflectance of green, red, and NIR wavelengths.
