Crop development analytics rely heavily on vegetation indices. Remote sensing technology allows applying them, providing precise data and long-distance control. Normalized Difference Water Index (NDWI) accurately measures moisture content in vegetation cover and soil, making it a reliable indicator of plant water stress. This index utilizes information from the Near-Infrared (NIR) and Short Wave Infrared (SWIR) channels to estimate leaf water content at the canopy level.
Combining the SWIR and NIR bands gives a chance to enhance the precision of assessing vegetation water content, enabling more effective monitoring in arid regions. The SWIR reflectance captures changes in vegetation water content and spongy mesophyll structure, while the NIR reflectance is influenced by leaf structure and dry matter content. Integrating these two bands can minimize leaf structure and dry matter content variations.
The application options of the given technology are quite extensive. They include agriculture irrigation monitoring and forest fire risk assessment. This is especially important in the context of climate change, as many industries need to adapt to erratic weather patterns and erratic climate patterns. In addition, the comprehensive information obtained using satellite technology allows you to closely monitor events and changes, making decisions to protect the environment and prevent or minimize damage.
How to Calculate NDWI
The given index was created to identify open water areas and measure their murkiness by reducing the impact of soil and vegetation cover reflectance. It is achieved by utilizing both near-infrared and green visible bands.
To calculate NDWI, the near-infrared (NIR) and short-wave infrared (SWIR) ranges reflectances are used. The formula looks like this:
NDWI = (Green – NIR)/(Green + NIR)
NIR has a wavelength range of 0.841-0.876 nm, while SWIR ranges from 1.628-1.652 nm.
NIR reflectance measures plant foliage's dry matter content and leaves' internal structure, while SWIR reflectance indicates changes in plant water content and mesophyll structure. The application of the NIR and SWIR bands combination makes it possible to measure the exact water content of plants, as the water in the internal structure of the leaf affects the spectral reflectance in SWIR.
How It Works
NDWI measures the water content of vegetation and ranges from -1 to +1. Low values indicate the vegetation is under water stress; higher values indicate adequate moisture levels.
Values of this index can be visualized in graphs and maps showing the spatial distribution of water stress on vegetation and its change over time. When creating such maps, several colors are usually used, each corresponding to a specific range of values. Although there is no general, standardized color palette, most software applications use one similar to the NDWI palette.
Determining the moisture content of plants and soil has many applications. For example, values of this index can be helpful in fire risk assessment. The index also helps locate and delineate water bodies on a map by tracking changes in their transparency. Water reflects very little light outside the visible spectrum in the infrared range, and NDWI uses this characteristic to monitor water turbidity.
NDWI & NDVI
Using vegetation indices with satellite imagery saves money, covers more territory, and provides faster data analytics in a preferred format. It also enables constant monitoring regardless of weather conditions, reducing the need for expensive UAV observations.
The NDWI is a more precise way of measuring plant humidity than the NDVI. It uses a water absorption band closely related to moisture, unlike the NDVI, which uses chlorophyll's light-absorbing properties. During droughts, a plant's condition is heavily influenced by water stress, making the NDWI more reliable than the NDVI based on chlorophyll.
Both of these indices are extremely valuable for agriculture. The companies create tools which enable the calculation of NDVI and NDWI index values. EOS Data Analytics, a reliable provider of satellite imagery analytics, developed an online platform for precision agriculture EOSDA Crop Monitoring. It is an all-in-one solution that helps farmers to make data-based decisions for effective farming management.
NDVI calculation is available on the platform, while NDWI is available on request. Access to this valuable data enables farmers to get up-to-date and reliable information on crop health and helps to improve planning and management. The NDWI index is a helpful tool for detecting flooded agricultural lands, identifying flooded sites of fields, detecting irrigated farmland, and identifying wetlands.
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