CHAPTER 9 Band Algebra and Vegetation Indices BAND TRANSFORMATIONS A. Dermanis.
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Estimation of Vegetation Indices and Biomass by the Fusion of LiDAR Data and Landsat Images in Mudumalai Forests of the Western Ghats, India Indu Indirabai1*, M.V. Harindranathan Nair1 School of Environmental Studies, Cochin University of Science & Technology, Kochi, Kerala, India.
Jaishankar. R. Nair2
C.V Raman Laboratory of Ecological Informatics, IIITM-Kerala, Technopark Campus, Thiruvananthapuram, Kerala, India.
. Rama Rao Nidamanuri3 Department of Earth & Space Sciences, Indian Institute of Space Science and Technology, Valiamala, Thiruvananthapuram, Kerala, India.
Abstract
Accurate estimation of biomass and vegetation indices of forests play a significant role in monitoring
ecological processes, global distribution of forests as well as the forest ecosystem productivity. Biomass and the vegetation indices in forest are highly correlated and their accurate estimation is required for carbon budget studies. Both passive and active remote sensing systems have immense potential to estimate vegetation parameters with varying accuracies and cost. Major challenge for these technologies is the estimation of vegetation indices along with the structural parameters in a highly complex biodiversity forest ecosystem such as Western Ghats. The objective of the present study is the estimation of vegetation indices and biomass in Mudumalai forest of Western Ghats regions of India by the fusion of space borne LiDAR (ICESat/GLAS) data with the Landsat Imagery (ETM+/8OLI). The structural parameters from the LiDAR data and the spectral parameters from Landsat imagery are integrated based on the pixel based image registration techniques. The vegetation indices extracted in this study are Normalized Difference Vegetation Indices(NDVI), Difference Vegetation Indices (DVI), Enhanced Vegetation Indices(EVI), Green Difference Vegetation Indices (GDVI), Green Ratio Vegetation Indices (GRVI), Leaf Area Index(LAI), Green Normalised Difference Vegetation Indices (GNDVI), Moisture Stress Index(MSI), Normalised Difference Water Index(NDWI), Ratio Vegetation Index(RVI), Soil Adjusted Vegetation Index(SAVI). The results indicate that biomass estimated have strong correlation(r=0.98) with in situ measurements. The approach revealed that the integration method used in the study leads to meaningful extraction of the vegetation indices and biomass. The study represents an important step towards future tasks of biomass and carbon budget estimation of heterogeneous forests in India. The study provides contributory benchmarks for monitoring the forest health conditions, moisture content, chlorophyll content and forest growth rate which also can possibly help to model global carbon cycle, deforestation and forest degradation.
Keywords--- Vegetation Indices; Biomass; Full waveform; ICESat; GLAS; Landsat; LiDAR; Support Vector Machine.
I. INTRODUCTION
Forest ecosystems of Western Ghats
region of India are characterised by large number
of woody and non woody tree species along with
shrubs, moss covers and thick understorey
vegetation. Monitoring the forest health conditions
and measurement of the biophysical parameters is a
challenge in these heterogeneous forests.
Vegetation indices as well as biomass are
the simple and effective forest parameters which
are generally used to indicate canopy density, forest
health, moisture content, chlorophyll content, forest
growth rate. In several studies, biomass and
vegetation indices are strongly correlated [1], [2].
Normalised Difference Vegetation Index (NDVI) is
a common and most widely used index in the case
of global environmental vegetation monitoring and
climate change [3],[4],[5]. The other common
vegetation indices include Difference Vegetation
Indices(DVI)[6],[7], Enhanced Vegetation Indices
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(EVI) [8],[9],Green Difference Vegetation Indices
(GDVI)[10],Green Ratio Vegetation Indices
(GRVI)[11],Green Vegetation Indices(GVI) [12],
[13], Leaf Area Index(LAI) [14], [15], Green
Normalised Difference Vegetation Indices
(GNDVI) [16], [17], Moisture Stress Index (MSI)
[18],[19], Normalised Difference Water
Index(NDWI) [20],[21], Ratio Vegetation
Index(RVI) [22], [23],Soil Adjusted Vegetation
Index(SAVI)[24]. Several studies were done based
on these indices.
Traditional methods for vegetation
parameter estimation are found to be time
consuming, expensive and have limited spatial
coverage. Remote Sensing technologies including
active and passive methods can estimate the
vegetation parameters to a great extent [25],[26].
There are so many remote sensing technologies for
the estimation of vegetation indices by the
appropriate selection or combination of
wavelengths. Multispectral remote sensing
technologies like Landsat series are found to be
useful for estimating biomass and vegetation
indices in several studies [27],[28],[29]. However
the use of optical remote sensing imagery can only
provide horizontal structure of forest but are
limited in the case of estimating vertical structural
details [30],[31]. The evolution of Light Detection and
Ranging (LiDAR) is relatively successful and
promising for the estimation of structural
parameters. The introduction of this technology
provides three dimensional structure of forest
including vertical and horizontal structures. LiDAR
is found to be useful for estimating the canopy
heights, canopy density, vegetation cover etc and in
forest measurements in several case studies
[32],[33],[34],[35]. The extensive literature review
shows that airborne LiDAR have tremendous
applications in the estimation of forest density,
biomass and the vegetation parameters [36], [37],
[38], [39], [40], [41] ,[42]. But it is evident from
these studies that the airborne discrete return
LiDAR have limitations including high cost and
limited spatial coverage.
The introduction of the space borne full
waveform LiDAR, Geoscience Laser altimetry
system onboard Ice Cloud and land Elevation
satellite (ICESat) launched in January 13, 2003,
which can provide full wave form LiDAR data with
global coverage and large footprint having diameter
70m with 172m spacing. GLAS ICESat data have
found applications in measuring the 3D information
of forest in global scale [43], [44], [45], [46], [47],
[48],[49],[50]. Several studies are done to integrate
GLAS data with optical imagery for the extraction
of forest attributes [51],[52]. But it is found from
the literatures that most of these studies are done in
homogeneous forests which are of pine deciduous
types. But the forest ecosystem of Western Ghats is
highly complex and heterogeneous which consists
of large number of woody, non woody tree species
and thick understory cover. The methodology of
integration of LiDAR data with Landsat imagery
has not been yet done in India for the estimation of
vegetation indices and the biomass, which signifies
the novelty of this approach.
The objective of the given study is to
extract the vegetation indices and biomass in
Mudumalai region of Western Ghats of India by the
combination of GLAS ICESat LiDAR data and
Landsat Imagery. The results obtained indicated
strong correlation of 97.58% with the measured
values which shows the relevance of the study. The
methodology applied in this study can be used to
understand the forest health conditions, degradation
as well as forest monitoring, management and
practices.
II. MATERIALS AND METHODS
A. Study Area The location of the study area is depicted
in the Fig 1. The study area is Mudumalai forests
(411 km2) in Tamilnadu, which is one of the
protected forests in the Western Ghats region of
India. Mudumalai forest has an annual rainfall of
range 1700mm and the type of forests is of tropical
moist deciduous, dry deciduous, semi evergreen
and thorn forests. The elevation values ranges from
960m to 1266m for the forest area
Fig 1: Study area Mudumalai Forest (Source: Esri Arcgis Earth)
B. Data Sets Used Space Borne LiDAR Data
Multispectral satellite imagery
Ground validation data
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1. Space Borne LiDAR Data The GLAS data used in the given study was
collected through the ICESat/GLAS NSIDC
website. The waveform data used in the study
contains the land elevation and the elevation
distribution corrected for atmospheric and geodetic
effects. About 15 passes were procured for the
study site. The data collected are pre-processed by
ICESat /GLAS tools for the conversions needed for
the extraction of the data and waveform
visualisation. The data sets were filtered by means
of the available quality flags including i_satCorrflg,
i_gvl_rcv for saturation, presence of cloud and
validity of elevation. The GLAS data distribution
along with the elevation values obtained from the
LiDAR data for Mudumalai region is shown in the
Fig 2.
Fig 2: GLAS data distribution over the study area.
2. Multispectral Satellite Imagery: Landsat products are used for the vegetation
indices extraction in the given study. The Landsat
data were downloaded through USGS earth
explorer (https://earthexplorer.usgs.gov/). The
Landsat imagery were pre-processed to reduce the
atmospheric effects and clouds by atmospheric
calibration techniques. The reflectance values were
computed for the Landsat imagery used in the
study.
C. Methodology The methodology depicting the estimation of
vegetation indices and biomass is shown in the
Fig.3. The GLAS data after extraction were
processed to obtain the structural parameters which
were further used for the fusion with the Landsat
imagery.
Fig 3: Flow chart depicting the methodology.
I. Extraction of Vegetation Indices The calibrated Landsat imagery were
integrated with the GLAS derived elevation models
by appropriate registration techniques which
resulted in an enhanced single image with
additional information. From the GLAS data,
structural parameters in the given area were
estimated from the digital surface models and the
elevation models generated. The following
vegetation indices were extracted from the
integrated data set.
a. Normalized Difference vegetation Indices (NDVI)
Normalized Difference vegetation Indices
(NDVI) is calculated using (1) and the values
ranges from 0 to 1.
NDVI=REDNIR
REDNIR
(1)
The values of NDVI range from 0 to 1 and
have sensitive response for even low vegetation
and calculated through normalisation procedure.
NDVI is related to canopy structure and canopy
photosynthesis but sensitive to effects of soil
brightness, soil colour atmosphere, clouds and leaf
canopy shadow. NDVI is calculated for the
integrated data sets. NDVI is found to be sensitive
to the effects of soil brightness, soil colour
atmosphere etc. NDVI specifies the structure of
canopies in the study area and the rate of
photosynthesis of canopies in the forest.
b. Difference Vegetation Indices (DVI) Difference Vegetation Indices (DVI), also
called Environmental vegetation index is applied to
vegetation ecological monitoring of the study area.
The DVI is calculated using (2).
DVI=NIR –RED (2)
Using both the Landsat images, DVI is obtained.
DVI index accounts for the difference between soil
and vegetation
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c. Enhanced Vegetation Indices (EVI) Enhanced Vegetation Indices (EVI) corrects
the soil and atmospheric effects and is useful in
high leaf area index where NDVI may saturate.
Blue reflectance region is used in the index in order
to correct for soil back ground regions and reducing
atmospheric influences. The EVI for the study site
was calculated as in (3).
EVI=2.51BLUE*7.5RED*6NIR
REDNIR
(3)
d. Green Difference Vegetation Indices (GDVI)
Green difference vegetation indices (GDVI) are calculated for the study area and it is related to
nitrogen content. The GDVI for the given study
was computed using (4).
GDVI = NIR - GREEN (4)
e. Green Ratio Vegetation Indices (GRVI) Green Ratio Vegetation Indices (GRVI) is
simple to interpret and less sensitive to cover
variations with high vegetation cover areas. The
index is very sensitive to photosynthetic rates in
forest canopies. The GRVI for the study area was
calculated using (5).
GRVI=GREEN
NIR
(5)
f. Leaf Area index (LAI) Leaf Area index (LAI) is defined as the total
one sided green leaf per area. It is considered as a
climate variable as well as a very important canopy
characteristics. All vegetation indices have an
interrelationship with LAI. It is used to calculate
the foliage cover and is an indication of vegetation
dynamics, water and carbon cycling. For the given
study, the LAI is calculated as in (6).
LAI=3.618×EVI-0.118 (6)
g. Green Normalised Difference Vegetation Indices (GNDVI)
Green Normalised Difference Vegetation
Indices (GNDVI), is sensitive to chlorophyll
concentration measuring green spectrum from
540m to 570 m. GNDVI is calculated as in (7).
GNDVI=GREENNIR
GREENNIR
(7)
h. Moisture Stress Index (MSI) Moisture Stress Index is found to be very
sensitive to increasing canopy water content and
can be used in canopy stress analysis, productivity
prediction and modelling ecosystem physiology.
The higher values indicate great water stress and
less water content. MSI is calculated using (8).
Moisture Stress Index=NIR
SWIR
(8)
i. Normalised Difference Water Index (NDWI)
Normalised Difference Water Index can
distinguish water and vegetation extracting water
bodies and it is a ratio combining NIR and Green
which can enhance water spectral signals. It has
wide applications in forest canopy stress analysis,
leaf area index studies, fire hazard studies and plant
productivity analysis. The index can be calculated
using (9).
NDWI=SWIRNIR
SWIRNIR
(9)
j. Ratio Vegetation Index (RVI) Ratio Vegetation Index (RVI) is used for green
biomass estimation and monitoring at high density
vegetation cover because it has high correlation
with biomass. RVI index is given by (10).
RVI= RED
NIR
(10)
k. Soil Adjusted Vegetation Index (SAVI) Soil Adjusted Vegetation Index (SAVI)
suppresses the effect of soil pixels and it contain a
canopy background adjustment factor with value
0.5 which is a function of vegetation density and
can be used in areas with relatively sparse
vegetation. SAVI is given by (11).
SAVI=
0.5REDNIR
REDNIR1.5
(11)
II. Estimation of biomass Biomass is estimated for the study area by
making use of the supervised learning non
parametric regression algorithm. Support vector
machine learning algorithm is used in the given
study, which mainly establishes a relationship
between tree biomass and vegetation indices. The
integrated data which is the combination of LiDAR
point cloud and Landsat Imagery is processed by
means of the support vector machine algorithm for
regression and classification. The biomass
estimated for the study area is depicted in the Fig 7.
III. RESULTS AND DISCUSSION
For Mudumalai region, about 11 vegetation
indices are estimated. The mean and standard
deviation of the vegetation indices were also noted.
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The vegetation indices extracted are depicted in the
Fig 4, Fig 5 and Fig 6. Biomass values were
compared with the measured values and the
correlation between biomass and NDVI is also
noted. The NDVI values of the region and the
biomass are also related such that for higher NDVI
values, the biomass is high.
Fig 4: NDVI, DVI, EVI and GDVI for Mudumalai on
integrating LiDAR point cloud with Landsat Image
Fig 5: GRVI, LAI, MSI and NDWI for Mudumalai on integrating LiDAR point cloud with Landsat Imagery
Fig 6: GNDVI, RVI and SAVI for Mudumalai on integrating
LiDAR point cloud with Landsat Imagery
Fig 7: Estimated Biomass of Mudumalai forest by Support
Vector Machine algorithm
Fig 8: Scatter plot showing the variation of estimated biomass
and measured values
The biomass of Mudumalai region
obtained from image estimates varies at a range of
130.5 t/ha to 385.4 t/ha. The estimated biomass and
the measured biomass are compared by means of
the scatter plot and the results indicated a strong
correlation of 97.58%. Fig 8 shows the variation of
estimated verses measured biomass.
The results indicated that the integrated
product of LiDAR GLAS data with Landsat images
can extract the vegetation indices in an effective
manner. Biomass are also computed which can be
an indirect indicator of the carbon content in the
forest area. A significant correlation is seen
between the biomass and the vegetation indices.
The paper presented the potential of the
combination of GLAS data and Landsat images for
the extraction of vegetation indices along with the
structural parameters in a cost effective and
accurate way. Vegetation indices were calculated
based on the spectral parameters thus ensuring the
quality of the results as well as the ability to
identify the forest conditions and the canopy
changes.
IV. CONCLUSION
The major conclusions of the study are the
following. The study estimated the vegetation
indices and the biomass by the integration of space
borne LiDAR and Landsat images in the
Mudumalai forest of Western Ghats. The
vegetation indices estimated are NDVI, DVI, EVI,
GDVI, GRVI, LAI, GNDVI, MSI, NDWI, RVI and
SAVI. Biomass for the study area is also estimated
with 97% accuracy. The study focussed on a cost
effective and accurate estimation of the vegetation
indices along with the structural parameters by the
integration approach. The results have good
correlation with the in situ measurements.
The significance of this study is that
structural parameters can be estimated along with
the vegetation parameters by the integration
technology which is not possible in the case of
other methods. The approach used here is not yet
used in the heterogeneous complex forests of
Western Ghats, which depicts the novelty of this
method. The methodology used in this study can
overcome the limitations of traditional methods as
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well as passive remote sensing technologies. The
vegetation indices calculated here were a good
indicator of the forest canopy cover, moisture
content, vegetation density, biomass and the
vegetation growth. The data fusion of the GLAS
and the Landsat images proved to be a promising
technology for the forest structural and vegetation
parameters in addition to the accurate estimation of
biomass. The vegetation indices extracted showed
accurate and desirable results which can play a
significant role in the national forest monitoring
and the forest management practices.
Acknowledgment
Special thanks to the National Snow and
Ice Data Centre (NSIDC), for the distribution of
ICESat/GLAS product 14 data and providing the
data processing software. Sincere thanks to Kerala
State Council for Science Technology and
Environment (KSCSTE), Thiruvananthapuram,
Kerala, India for funding of the research work.
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