Home > Geospatial Application Papers > Environment > Conservation & Monitoring
Abstract


Lidar Remote Sensing for forest Ecosystem studies in India

MD Behera
Visiting Scientist, NERC-ESSC, The University of Reading, UK.


Abstract
Lidar technology has evolved in the last four decades to become a prominent remote sensing tool for forest ecosystem studies. For both economic and environmental reasons, it is critical to measure and understand the spatial organisation of forest ecosystems. It offers a great potential for conservation and management of India’s invaluable forest wealth. Typical remote sensing images allow analysing various attributes of forests, but are limited in their ability to represent spatial patterns only in two-dimensional space. The advantage of using lidar remote sensing for forestry applications is that it provides data on three dimensional forest structures characterising vegetation heights, vertical distribution of canopy materials, crown volume, sub canopy topography, biomass, vertical foliage diversity & multiple layers, height to live crown, large tree density, leaf area index, physiographic or life form diversity etc., through direct and indirect retrievals. Thus, Lidar technology offers an emerging challenge to the management of India’s forests, the panorama of which ranges from evergreen tropical rain forests in the Andaman and Nicobar Islands, the western Ghats and the north-eastern states, to dry alpine scrub high in the Himalaya to the north. The technology could be utilised to address various aspects of forest ecosystem management, not possible previously with the data available from aerial photographs, optical and radar satellites or even by ground measurements. If cautiously planned, Lidar can form the most scientific and accurate means of forest management in the country, viz., the three dimensional data set can be used to redefine the only existing ‘forest types’ classification1 that classifies Indian forests in to 16-major and 22- minor forest types based on structure, physiognomy and floristic properties of vegetation.

Lidar is an accurate, fast and versatile measurement technique, which can complement or partly replace other geo-data acquisition technologies and open up new exciting areas of application. The prediction of forest parameters is either direct or indirect. For direct measurement, a characteristic such as height is estimated by first minus last return of the raw data alone or by applying a linear transformation to the raw data. Indirect estimates are most often based on first estimating a fundamental parameter such as height that is then fed into a predictive model for biomass and volume. Laser technique may prove most useful to detect changes in the aboveground carbon stores of tropics, where the most rapid and significant climate and vegetation changes are expected over the next decades. Such measurements will improve our understanding of the effects of these factors on land degradation and the hydrological and biological systems. The combination of Lidar data and satellite remote sensing data could also be very useful for describing biodiversity and monitoring changes in biodiversity. There is a large potential for savings, if laser data and image data could be collected simultaneously and stand delineation and characteristics usable for stratification could be derived from existing auxiliary data and automated methods.

Lidar is a precise tool for measuring topography, vegetation height and cover as well as complex attributes of canopy structure and function. It may be useful in detecting habitat features associated with particular species, including those of rare and endangered. Different indices of structural complexity could be useful to identify areas of probable high biodiversity, thus providing inputs to GAP analysis programmes. By identifying various classes of forest structures and canopy gaps, associated with varying fire behaviour, it may help in fire prevention. In future, it would boost the study of canopy science and physical attributes of vegetation canopy structure. The presence of specific organisms and the richness of wildlife communities can be highly dependent on the three-dimensional spatial pattern of vegetation, especially in systems where biomass accumulation is significant. Individual animal and bird species are invariably associated with specific three-dimensional features in forests. Other functional aspects such as forest productivity may be related to forest canopy structure, which is measured precisely from Lidar data.

It is amply clear that Lidar technique has become a very prominent tool to collect accurate high-resolution three-dimensional data. In addition, the typical characteristics of Lidar data have opened up the possibility of using them for many other applications, which were not thought of earlier. Notwithstanding the increasing use of this technology world over, it has not yet been available in India. However, this technology has the potential of conserving the precious national forest resources and providing better understanding of management, which are difficult to comprehend otherwise, due to the limitations imposed by conventional and other data collection techniques. Forest management strategy in India should be based on very reliable, Lidar-derived database on forest structure and their productive potential.

India is one of the important centres of biodiversity, having contributed 167 species of plants whose origin and diversity is in this country. Due to indiscriminate felling of trees, the forest area has been drastically shrinking. Lidar-derived information can be used for selective tree felling and other forestry management issues in the country. Lidar has the potential to contribute for the achievement of the objectives of ‘national forest policy’ that aims at (i) ensuring environmental stability and ecological balance including atmospheric equilibrium, which are vital for the sustenance of all life forms, human, animal and plant, (ii) deriving direct economic benefit (iii) setting up a national goal to have a minimum of one third of the total area of the country under forest or tree cover etc. In the hills and in mountainous regions, Lidar technology can help maintaining two third of the area under such cover in order to prevent erosion and land degradation and to ensure the stability of the fragile ecosystem. The Forest Survey of India (FSI), which presently uses satellite remote sensing data to achieve its present objectives, can improve qualitatively by the use of Lidar technology. The accuracy of density level forest stratification would be benefited from the use of Lidar-based 3-dimensional dataset. Supplemented with IRS satellite dataset, FSI can well improve its ‘forest cover monitoring – mandate’ at a cycle of two years, thus providing information in policy making and planning for existing deforestation and increasing green cover of the country.

This article aims at providing the recent trends in Lidar applications to forestry and discusses the prospects of this technology in Indian context. The term Lidar and laser has been defined along with the basic principles and advantages of Lidar remote sensing. Various research issues have been analysed in terms of studies done, using helicopter/air borne; small/large footprint and discrete/continuously pulsed laser sensors across the globe. The objective of this article shall be achieved, if various researchers/planners from different government and non-governmental organisations would take initiatives and start preparing ground work for utilising the marvels of this technology, and if various teaching/training organizations involved in remote sensing applications to forestry, would include details of the Lidar technology in to the course curriculum to generate trained manpower, for the greater benefit of the nation and its mankind.