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An Overview of the “ Triangle Method ” for Estimating Surface Evapotranspiration and Soil Moisture from Satellite Imagery

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ABSTRACT

An overview of the ‘triangle’ method for estimating soil surface wetness and evapotranspiration fraction from satellite imagery is presented here. The method is insensitive to initial atmospheric and surface conditions, net radiation and atmospheric correction, yet can yield accuracies comparable to other methods. We describe the method first from the standpoint of the how the triangle is observed as obtained from aircraft and satellite image data and then show how the triangle can be created from a land surface model. By superimposing the model triangle over the observed one, pixel values from the image are determined for all points within the triangle. We further show how the stretched (or ‘universal’) triangle can be used to interpret pixel configurations within the triangle, showing how the temporal trajectories of points uniquely describe patterns of land use change. Finally, we conclude the paper with a brief assessment of the method's limitations.

No MeSH data available.


Related in: MedlinePlus

Isopleths of moisture availability (Mo) overlaying the pixel envelope shown in Figure 2, as determined from the SVAT model. The ordinate values are plotted as NDVI (left side) and fractional vegetation cover (Fr; right side) and the abscissa is the radiant temperature. The thin curvy line below the Mo labels denotes the bottom part of the pixel envelope in Figure 2.
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f4-sensors-07-01612: Isopleths of moisture availability (Mo) overlaying the pixel envelope shown in Figure 2, as determined from the SVAT model. The ordinate values are plotted as NDVI (left side) and fractional vegetation cover (Fr; right side) and the abscissa is the radiant temperature. The thin curvy line below the Mo labels denotes the bottom part of the pixel envelope in Figure 2.

Mentions: Figure 4 shows the modeled moisture availability isopleths superimposed on the pixel distribution in Figure 2, Mo = 0 and 1.0, respectively, corresponding to the warm and cold edges. Stretching implies that the derived values for Mo and EF are relatively insensitive to the choice of initial conditions, as the isopleths within the triangle will not change their configuration drastically with any reasonable choice of those conditions. Thus, Mo=0 and Mo=1 will always border the pixel envelope and Mo=0.5 will always appear somewhere in the middle of the triangle. The same is true for the relative stability of EF isopleths within the triangle.


An Overview of the “ Triangle Method ” for Estimating Surface Evapotranspiration and Soil Moisture from Satellite Imagery
Isopleths of moisture availability (Mo) overlaying the pixel envelope shown in Figure 2, as determined from the SVAT model. The ordinate values are plotted as NDVI (left side) and fractional vegetation cover (Fr; right side) and the abscissa is the radiant temperature. The thin curvy line below the Mo labels denotes the bottom part of the pixel envelope in Figure 2.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3814871&req=5

f4-sensors-07-01612: Isopleths of moisture availability (Mo) overlaying the pixel envelope shown in Figure 2, as determined from the SVAT model. The ordinate values are plotted as NDVI (left side) and fractional vegetation cover (Fr; right side) and the abscissa is the radiant temperature. The thin curvy line below the Mo labels denotes the bottom part of the pixel envelope in Figure 2.
Mentions: Figure 4 shows the modeled moisture availability isopleths superimposed on the pixel distribution in Figure 2, Mo = 0 and 1.0, respectively, corresponding to the warm and cold edges. Stretching implies that the derived values for Mo and EF are relatively insensitive to the choice of initial conditions, as the isopleths within the triangle will not change their configuration drastically with any reasonable choice of those conditions. Thus, Mo=0 and Mo=1 will always border the pixel envelope and Mo=0.5 will always appear somewhere in the middle of the triangle. The same is true for the relative stability of EF isopleths within the triangle.

View Article: PubMed Central

ABSTRACT

An overview of the ‘triangle’ method for estimating soil surface wetness and evapotranspiration fraction from satellite imagery is presented here. The method is insensitive to initial atmospheric and surface conditions, net radiation and atmospheric correction, yet can yield accuracies comparable to other methods. We describe the method first from the standpoint of the how the triangle is observed as obtained from aircraft and satellite image data and then show how the triangle can be created from a land surface model. By superimposing the model triangle over the observed one, pixel values from the image are determined for all points within the triangle. We further show how the stretched (or ‘universal’) triangle can be used to interpret pixel configurations within the triangle, showing how the temporal trajectories of points uniquely describe patterns of land use change. Finally, we conclude the paper with a brief assessment of the method's limitations.

No MeSH data available.


Related in: MedlinePlus