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Fig. 1. Land surface temperature (LST) values plotted against a vegetation index (VI), forming a theoretical triangle model.

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Fig. 2. The study area, located in the southeastern United States.

Table 1. Beginning and ending times of data collection by MODIS satellite during each of the eleven 16-day periods considered in this study.
Period Beginning date
(time 00:00:00)
Ending date
(time 23:59:59)
1 22-Mar-2009 6-April-2009
2 7-April-2009 22-April-2009
3 23-April-2009 8-May-2009
4 9-May-2009 24-May-2009
5 25-May-2009 9-June-2009
6 10-June-2009 25-June-2009
7 26-June-2009 11-July-2009
8 12-July-2009 27-July-2009
9 28-July-2009 12-August-2009
10 13-August-2009 28-August-2009
11 29-August-2009 13-September-2009
3

Fig. 3. Locations and names of the in situ moisture measurement stations in the study area.

Table 2. Names of in situ moisture measurement stations, their networks, and geographic coordinates, for the analyzed data.
Station
number
Station name Latitude, Longitude Network Vegetation type a
1 Little River 31°30´N, 83°30´W SCAN Agriculture
2 Pee Dee 34°18´N, 79°44´W SCAN Agriculture, young pine plantation,
old deciduous forest
3 Wakulla 30°18´N, 84°25´W SCAN Middle-aged pine plantation
4 Watkinsville 33°53´N, 83°26´W SCAN Agriculture, developed areas
5 Youmans Farm 32°40´N, 81°12´W SCAN Agriculture, old pine forest
6 Blackville 33°21´N, 81°20´W USCRN Agriculture
7 McClellanville 33°09´N, 79°22´W USCRN Agriculture, deciduous forest
a Vegetation types in the immediate area (100 m) around each measurement point.
Table 3. Statistical summary of the in situ moisture data used for parameterization into moisture units (m3 m–3).
Soil depth Parameter Little River Pee Dee Wakulla Watkinsville Youmans Farm Blackville McClellanville
cm - m3 m–3 m3 m–3 m3 m–3 m3 m–3 m3 m–3 m3 m–3 m3 m–3
5 Minimum 0.037 0.063 0.014 0.111 0.027 0.034 0.022
Maximum 0.338 0.296 0.140 0.405 0.327 0.213 0.110
Mean 0.103 0.189 0.066 0.204 0.123 0.103 0.052
Std. Dev. 0.038 0.055 0.029 0.069 0.058 0.055 0.017
10 Minimum 0.047 0.051 0.029 0.054 0.038 0.047 0.019
Maximum 0.369 0.251 0.144 0.327 0.304 0.171 0.111
Mean 0.102 0.162 0.077 0.121 0.142 0.089 0.063
Std. Dev. 0.035 0.046 0.025 0.052 0.058 0.038 0.022
20 Minimum 0.056 0.048 0.010 0.067 0.030 0.210 0.012
Maximum 0.229 0.209 0.103 0.331 0.288 0.290 0.133
Mean 0.116 0.137 0.060 0.128 0.137 0.240 0.076
Std. Dev. 0.036 0.039 0.022 0.054 0.061 0.025 0.028
Table 4. Parameters for dry and wet edges of the calculated “triangles” for each of the analyzed eleven 16-day periods.
Period TVDI(NDVI) TVDI(EVI)
Wet edge Dry edge Wet edge Dry edge
amin bmin amax bmax amin bmin amax bmax
1 264.0 33.0 315.2 –19.2 279.0 19.1 310.0 –19.0
2 273.0 20.5 318.0 –23.0 283.1 13.8 311.2 –22.5
3 272.8 24.6 338.0 –40.0 284.0 16.3 325.0 –34.0
4 278.0 10.0 337.2 –38.0 282.0 8.0 324.8 –32.0
5 267.0 26.0 340.6 –39.0 280.6 16.0 324.0 –28.0
6 289.8 3.0 330.8 –25.5 291.4 1.9 333.0 –38.0
7 297.0 –7.4 351.2 –49.0 286.2 6.0 340.0 –49.0
8 268.2 22.6 341.2 –40.0 267.4 30.8 326.0 –29.5
9 253.8 42.0 343.0 –42.5 260.0 42.0 323.4 –26.8
10 237.0 59.0 340.0 –41.0 246.0 62.0 320.0 –22.4
11 247.0 44.0 346.0 –47.0 249.1 60.5 313.0 –12.0
Average 268.0 25.2 336.5 –36.7 273.5 25.1 322.8 –28.5
amax, bmax = linear regression parameters for the dry edge
amin, bmin = linear regression parameters for the wet edge
TVDI – Temperature Vegetation Dryness Index
NDVI – Normalized Difference Vegetation Index
EVI – Enhanced Vegetation Index
4

Fig. 4. Triangular relationships developed for the study area through the use of land surface temperature (LST) and Temperature Vegetation Dryness Index (TVDI) based on the Normalized Difference Vegetation Dryness index (NDVI).

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Fig. 5. Scatterplots with regression lines for in situ soil moisture content at three depths a) 5 cm; b) 10 cm; and c) 20 cm predicted from Temperature Vegetation Dryness Index (TVDI) values. P-values for each regression model are also shown. View larger in new window/tab.

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Fig. 6. Map of soil moisture values calculated from the MODIS based on Temperature Vegetation Dryness Index calculated using Normalized Difference Vegetation Index TVDI(NDVI) (left) and Temperature Vegetation Dryness Index calculated using Enhanced Vegetation Dryness Index TVDI(EVI) (right) for three depth measurements during the second study measurement period (April 7–22, 2009): a) 5 cm; b) 10 cm; and c) 20 cm. View larger in new window/tab.