27 Sr
= Solar irradiance EVI
= Enhanced Vegetation Index from MODIS e
max
= Constant Light Utilization Efficiency Term T
= Optimal temperature for plant production W
= Monthly water deficit The e
max
term is set uniformly at 0.39 g C MJ-1 PAR, a value that derives from calibration of predicted annual NPP to previous field estimates Potter et al.,
1993. T is computed with reference to derivation of optimal temperatures T
opt
for plant production. W is estimated from monthly water deficits, based on a
comparison of moisture supply precipitation and stored soil water to potential evapotranspiration PET. T and W value based on the estimation data from
climatic data. The equitation for estimation monthly NPP values is :
NPP = EVI e
max
FPAR TW …………………….………………… 15
NPP = Net primary production gC m
-2
year
-1
e
max
= Constant Light Utilization Efficiency Term EVI
= Enhanced Vegetation Index from MODIS FPAR = Fraction Photosynthetically Active Radiation from MODIS
T = Optimal temperature for plant production
W = Monthly water deficit
3.4.5. Ground Truth
Ground truth refers to information that is collected on location. In remote sensing, this is especially important in order to relate image data to real
features and materials on the ground. The collection of ground-truth data enables calibration of remote-sensing data, and aids in the interpretation and analysis of
what is being sensed. More specifically, ground truth may refer to a process in which a pixel on a satellite image is compared to what is there in reality at the
present time in order to verify the contents of the pixel on the image.
28 Ground truth is usually done on site, performing surface observations and
measurements of various properties of the features of the ground resolution cells that are being studied on the remotely sensed digital image. It also involves taking
geographic coordinates of the ground resolution cell with GPS technology and comparing those with the coordinates of the pixel being studied provided by the
remote sensing software to understand and analyze the location errors and how it may affect a particular study. In this study, ground truth conducted in two
province of Sumatra Aceh and South Sumatra Province. The information that is collected “on location” ground truth information derived from secondary data
from other agency or institution. The general flow-chart of research study as show in Figure 3.2.
Figure 3.2 Flowchart of the research estimation of NPP
Vector data
MODIS Data
Mosaicking
Geometric Correction
Estimation of EVI and FPAR
Spatial Distribution of
NPP Climate data
Ground Truth Map Display of Spatial
