List of Vegetation Water Content Indices

I have been working on Vegetation Water Content (VWC) Indices for quite sometime now. In my readings, I found quite a number of them: WI = Water Index; NDWI = Normalized Difference Water Index; EWT = Equivalent Water Thickness; WT = Water Thickness; MSI = Moisture Stress Index; NDII = Normalized Difference Infrared Index; PWI = Plant Water Index; SRWI = Simple Ratio Water Index; SR = Simple Ratio; NDVI = Normalized Difference Vegetation Index; CSI = Canopy Structure Index; GVMI = Global Vegetation Moisture Index; RDI = Relative Depth Index; LWCI = Leaf Water Content Index.

Below you will find the details of the equations, meanings and applications. I came up with a table on spectral indices that have been derived and used for estimation of vegetation water content (VWC) based on ratio, or simple mathematical formula of reflectance of two or more wavelengths.

If you wanna use the document, please cite this blog and give us a "love" link :-)

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Digital cameras, remote satellites measure vegetation water demand

Horticultural crops account for almost 50% of crop sales in the United States, and these crops are carefully managed to ensure good quality. But more information is needed about the crops' growth and response to seasonal and climatic changes so that management practices such as irrigation can be precisely scheduled. Existing research can be difficult to generalize because of variations in crops, planting densities, and cultural practices.

Determining growth stage, size, and water needs are especially important for horticultural crops because most crops are grown in limited water environments and require irrigation. The measurement of "canopy light interception" is a primary means of determining water and irrigation needs. Fractional canopy cover (CC) is a relatively easily measured property that is a good indicator of light interception. Canopy cover, the percent of the soil surface covered by plant foliage, is an important indicator of stage of growth and crop water use in horticultural crops. Methods of using remote sensors to determine canopy cover in major crops have been studied for years, but the studies have not included most horticultural crops.

Thomas J. Trout, Research Leader at the U.S. Department of Agriculture's Agricultural Research Service, along with colleagues from the NASA Earth Science Division, recently published a study that addresses the relationship of remotely sensed normalized difference vegetation index (NDVI) relative to canopy cover of several major horticultural crops in commercial fields.

The research team measured canopy cover of 11 different annual and perennial horticultural crops in various growth stages on 30 fields in California's San Joaquin Valley with a handheld multispectral digital camera. Canopy cover was compared with NDVI values calculated from Landsat 5 satellite imagery. According to Trout, "The NDVI was highly correlated and linearly related with measured CC across the wide range of crops, canopy structures, and growth stages, and predicted CC with mean absolute error of 0.047 up to effective full cover.

These results indicate that remotely sensed NDVI may be an efficient way to monitor growth stage, and potentially irrigation water demand, of horticultural crops."

The research indicates that NDVI can potentially provide field-specific and regional estimates of CC for horticultural crops with minimal requirement for supporting information. This new information may also be useful to improve estimates of crop growth stage and water use.

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