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Application of Satellite Based Remote Sensing for Monitoring and Mapping of India’s Forest and Tree Cover
Dr. J. K. Rawat
Director, Forest Survey of India
Dr. Alok Saxena
Joint Director, Forest Survey of India
Saibal Dasgupta
Joint Director, Forest Survey of India
Introduction
Forests are ecological as well as socio-economic resource. These have to be
managed judiciously not only for environmental protection and other services but also for
various products and industrial raw materials. Considering the crucial role forests play in
the country’s ecological stability and economic development, the current National Forest
Policy (1988) in India aims at maintaining a minimum of 33 percent of country’s
geographical area under forest and tree cover. This requires periodic monitoring of the
forest cover of the country for effective planning and sustainable development. Forest
Survey of India (FSI), an organization under the Ministry of Environment & Forests
(Government of India) has been mandated to monitor and map country’s forest cover on a
biennial basis. Consequently, FSI has been carrying out assessment of forest cover in the
country using satellite based remote sensing data and has been publishing its findings in
the State of Forest Report (SFR) every two years. Its first assessment of forest cover
made in 1987 was published as SFR 1987 and the latest i.e., the eighth one as SFR 2001.
With the improvement in satellite data resolution and adoption of digital image
processing by FSI, it has been possible to assess forest cover patches as small as 1ha.
However, there exists a significant tree cover wealth outside conventional forest areas,
most of which is less than 1 ha in extent. These include small patches of trees in
plantations and woodlands, or scattered trees on farms, homesteads and urban areas, or
trees along linear features such as roads, canals, bunds etc. and constitute significant area.
In a study done in Haryana State by FSI in 1997, it was found that growing stock of trees
outside forest was approximately seven times than that from natural forests. Trees outside
forests (TOF) are therefore considered an alternative but significant source of fuel,
fodder, timber and environmental services to the local people. In 2001 assessment, FSI
assessed tree cover (less than 1ha in extent) in the country using a stratified sampling and
field inventory, and estimated it to be 2.48% of country’s geographical area. Thereafter,
FSI has developed a methodology based on high-resolution satellite data for mapping and
stratification of TOF leading to an improved sampling design for field inventory.
In the present paper, methodologies of forest cover and tree cover assessments as used by the FSI are discussed.
Forest Cover Assessment:
Till recently, FSI was using mostly visual interpretation of satellite data on 1:250,000 scale for assessment of forest cover. However, in its latest assessment i.e., 2001 assessment, it used digital interpretation of satellite data on 1:50,000 scale for mapping and monitoring forest cover. The present methodology uses Digital Image Processing software and involves the following steps:
Acquisition of satellite data: The digital data of IRS-1C and 1D LISS III is acquired from
NRSA in CD.. India is covered in about 340 scenes, of IRS 1C and 1D. One scene covers
an area of about 20000 km2, having an overlap of about 10% with adjoining scenes.
While procuring the data, care is taken to ensure that it is cloud free (with not more than
10% cloud cover) and therefore data pertaining to the period from October-December is
preferred.
Geometric Rectification of raw data: After downloading the data into computer,
rectification is carried out in each image to provide Latitude and Longitude information
into raw satellite scene using raster based geometric corrections. Rectification carried out
in geographic projection is re-projected in shape of polygonal projection and the scene is
geo-coded with using SOI toposheets.
Mosaicing of rectified scenes: Different scenes, which are already rectified, may have to
be merged together to get one combined FCC (False Colour Composite). FCC of sheet is
extracted from mosaiced scene in a chosen area of interest. Image is displayed in three
bands 3, 2, 1. Masking of non-forest areas is done separately to extract forest areas on the
basis of ground knowledge, cover map of previous cycles and on the basis of information
available through SOI toposheets in the area of interest.
Classification of forest cover using NDVI: Interactive method of display is used for
assigning threshold values for each class (open, dense and scrub) on the basis of the
ground knowledge to highlight forest/vegetated areas. Density class of forest cover and
colour is accordingly allocated. Survey of India toposheets is used for delineating
boundaries of each district and classified map of forest cover is generated.
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