Development of the Satellite
Remote Sensing activities in Sri Lanka M.P. Salgado Deputy Surveyor General, Sri Lanka Bandulatha Adikari - C.R.S. Abstract Use of Aerial photographs for interpretation and mapping was practiced in Sri Lanka, from about 1960. The compilation of the Base maps on 1/50000 scale, using photogram metric techniques, commenced around 1977. During this time, the Scientists and the Planners in Sri Lanka considered the introduction of satellite remote sensing to its mapping activities, to supplement the acquisition of the urgently needed Land resources data required for the development programmes. Outcome of these efforts was the establishment of the Swiss-Sri Lanka collaborative remote sensing project for the period 1980-1988, with the emphasis for the production of the 1/100000 scale, District land use maps of Sri Lanka. The experiences gained through this project activities are mainly in the application of analogue techniques for the interpretation and mapping. We are also concerned with the constraints experienced, imposed due to the delays in the procurement of satellite imagery, cloud cover, limitations in the analogue techniques for the interpretation of satellite imagery in the context of the Sri Lankan condition etc. Our aspirations for the gradual transition to digital remote sensing in the face of the escalation of the costs due to the commercialization of the production of satellite imagery, the development of the indigenous expertise to meet this challenge, are presumably common concerns, of the developing nations of the Asian Region, and calls for closer regional collaborations, while seeking improved technical cooperation form the developed and industrial countries of the world. Introduction Aerial Remote Sensing was introduced to Sri Lanka in 1956, and during the period 1956-1960, the entire Island was photographed on the scale of 1/40,000. This aerial photographic coverage was the basis for the systematic updating of the existing national map series on 1 mile to 1 inch scale, photogrammetry for topographic mapping, and photo interpretation for land use maps. Over the years the updating process of the National map series has fallen into arrears, resulting in a general deficit of upto date basic special planning information. However general surveys and the photogrammetic capabilities of the survey dept. have been steadily improved over the years. In 1980 a new aircraft was made available to the dept. instead of updating the existing national map series, a new topographic map series was considered on 1/50000 scale, to be completed over 5 years period. This was also the period where large development projects were planned. Alternate strategies had to be considered for the urgently needed land use data required for this purpose. With the introduction of the earth resources satellite in the seventies, the Swiss Government was requested to assist in the introduction of satellite remote sensing techniques to assist in the introduction of satellite remote sensing techniques, that would help the country in its search for urgently needed basic land use data and mapping. This resulted in the establishment of the centre for remote sensing within the survey department in collaboration with the Swiss govt. the major component of work under this project was in the production of 1/100000, district land use maps by the use of analogue techniques in the interpretation of bulk MSS & RBV imagery and aerial photographs, supported by extensive ground truthing utilizing a multi-stage approach. Thorough the Swiss-Sri Lanka remote sensing project, certain progress has also been achieved in the domain of digital image processing. General information about Sri Lanka Sri Lanka is an Island situated approximately 60 to 100 North in latitude and 700 to 820 E in Longitude in the Indian Ocean. Total land area amounts to about 65,500 sw kilometers, with a population of about 17 million. Sri Lanka is an agricultural country with rice being its staple food. The other major agricultural products are Tea, rubber and coconuts. Topographically the country is divided into three zones, the lowlands situated between 0-300 meters amount to about 78% of the land, the intermediate zone between 300-900 meters amount to 20% of the land and the central highlands over 900 meters amounts to the balance 2% of the land. The highest mountain in Sri Lanka, Pedurutalagala is about 2525 meters. On the basis of rainfall the Island is divided into two major ecological systems the wet zone and the dry zone. The dry zone is very arid and it receives only very little rain. Hence in this region rain water has to be stored for agriculture. For this reason in this zone one witnesses a large number of tanks and irrigation systems built by our ancient kings to store and distribute the water. Air Photography The country is fully covered on the 1:40,000scale of photography during the period 1956-60. since the Survey department possessed a new air craft in 1980, (Cessana Eagh 421C) the entire Island had been re-photographed on the scaled o 1:50000, 1:20000 and 1:10000. These photography is utilized for photo-interpretation and for photogramatic mapping. There is also much user demand for these photography. Topographical maps of Sri Lanka The very first series of topographical maps of Sri Lanka on the scale of one inch to the mile (1:63,360) was produced during the period 1897-1925. These are 72 maps on this scale covering the Island. Over the years, the updating process of the one inch Topographicl map series has fallen into arrears. Also the need to adopt a metric scale, demanded the shift to produce a new implementation of the Agricultural Base Mapping Project (ABMP) for the production of the 1:50,000 scale Maps, with better data content and contour interval to cover the entire Island. Though originally intended to complete the production of this map series in 5 years for 1980-85, due to constraints, this shall be completed only in this year. In this new series of topographical maps, the preparation of the manuscript was by photogrammetry. From the beginning the Survey Dept. has developed its photogrammetric capabilities for mapping, today the Air Survey Branch is a well equipped organisation within the survey dept. with its own survey air craft, on RC 20 Aerial camera, a photo laboratory, several precision photogrammetric plotters and a group of trained photogrammetric operators and other technical staff. Land use mapping in Sri Lanka 1956-60 First aerial photo cover during 1956-60 was used for the preparation of this series of land use maps. With the one inch topo maps as a base, the photographs were reduced and mosaiced together. Agricultural landuse and forest types were derived by photo interpretations; and intensive field verifications. The above completed type boundaries were transferred to the respective mosaics. The resultant efforts was s series f 72 maps covering Sri Lanka published in 1958 with complete classification of the agricultural land use and forest types included in the map legend. The Sri Lanka -Swiss project for Land Use Mapping With the launching of the Earth Resource satellites in the Seventies, the Sri Lanka Government, requested to assist in the introduction and the use of satellite remote sensing technology for the acquisition, mapping and monitoring of the urgently needed basic spatial resource data. The Swiss government attached this responsibility to the Remote Sensing Section of the Department of Geography, University of Zurich to develop the technology for the use of satellite remote sensing imagery for the resource data acquisition in Sri Lanka. The emphasis for the beginning was for the use of the available resources, and the development of the application of medium level technology for the data acquisition. From our point of the sustainability of the project, it was considered very important :- The establishment of a central agency, the centre for remote sensing (CRS) for co-ordinating and carrying out all planned mapping activities and use assistance programmes. Training of local counterparts and CRS staff. To build up closer links with the respective agencies interested in adopting remote sensing techniques in their work. The implementation phase of the project commenced in 1980. District land-use mapping in Sri Lanka The important activity of the CRS was the production of the land use maps on a district basis, on the scale of 1:10,0000. The so called multi-stage approach, to use satellite imagery, aerial photos, already available maps and other data sources, were used integrally in the production of this map series. Local expertise in the fields of agriculture and forestry together with co-ordination from the district level organisation was sought. The available aerial photographs were interpreted at the CRS, and were thoroughly checked in the fields. Computer enhanced landsat MSS colour composites were produced from digital tapes, using and optronics system in Switzerland. These were corrected for the Transverse Mecater Projection, adopted for the national mapping. Landsat imagery was then enlarged to 1:100000 scale. Transparent overlays giving the geometric details of the one inch sheets were reduced to the same scale and were overlaid on the corresponding satellite images. Each photographic model interpretation was then reduced with corrections and placed as a mosaic on the satellite images which served as the thematic and the geometric base. Problem areas were further checked and corrected. Data completion, cartography, computation and annotation proceeded the final printing of the district land use maps, complete with the legend of different land - use types. Each land use category cover was assembled on a separate peel-coat open window mask and is thus available for any future use. The district land use mapping programme under the Swiss Sri Lanka project, comprising of 22 district land use maps was originally planned to the completed in five years for 1980-85. However due to various constraints this work was delayed and shall be completed by the end of the year. Monitoring of land use changes - Masking techniques For monitoring changes in the land by using satellite imagery, a masking techniques was developed. Masks were prepared in such a way that all areas except the land-use category to be monitoring are covered. These masks are then overlayed on to a new satellite image of the identical areas, thus covering the other land use types except the one type that is monitored. Simple techniques are used for the super imposition of the mask on to the satellite imagery. Using the predetermined spectral signatures of the land use category under consideration changes can be easily detected. Monitoring Seasons Rice Crops Rice is the staple of food of Sri Lanka and forecasting the rice yields seasonally is very important for agricultural planning. DRS carried out a research project for monitoring the rice crops in the major rice growing areas of Sri Lanka. Available base maps delineating the paddy growing areas of Sri Lanka were assembled. These were updated using aerial photographs, thus forming the Bench marks for the rice crop monitoring exercise. With this data, masks were prepared for the padyland, enabling the separation of paddy fields from other corps, settlement and scrub lands which normally surround the paddy fields. Some of these different types of land use may appear in the same red colour on the colour composites, thus making difficulties in the direct use of satellite imagery for the identification of paddy. By placing the paddy masks on the satellite imagery, taken 2-6 weeks prior to harvesting, can be used for the identification of the paddy growing areas during a season. Monitoring Forest Cover Changes Forest cover map of entire Sri Lanka on the scale of 1/500000 using only satellite imagery was prepared in 1981. This was improved by the information availed from 1/100000 district land use mapping programme, spot data, and a new forest map including different categories of forest types was prepared and shall be printed towards the letter part of 1990. Masking techniques were used for the assessment of the deforestation in the Trincomalee district during the 6 years period 1973 to 1979. This survey revealed that the southern part of this period due to encroachments and official deforestration for sugar-cane cultivation. This amounts to a 2.5% annual decrease according to the extent involved. Training programme of Swiss Sri Lanka Project Permanent staff of the CRS were trained on the job through out, beginning from 1981. This included the training in photo-interpretation, planning images, cartographic work etc additionally there was the lecture programmes on organisational, technical and theoretical aspects spanned over a period of about 2 years. The training was supported by handouts, visual aids, examples of remote sensing data. The training programmes were conducted by the Swiss experts and local counterparts. Various user organisations are also closely collaborating with the CRS. Two training courses each about 2 weeks duration were given to these officers as an introduction to remote sensing and they proceeded to get on the job training for period of 3-6 months. The officers, from the forest department, tea research institute, urban development authority, department census and statistics, national aquatic resources agency and various other organisations participated in the user training programmes. A reader on remote sensing has been compiled consisting the major introductory information to the subject, which serves as a basis for training courses. These programmes were repeated over the years for the permanent staff and for the user organisations.
In 1983 a concentrated introductory course in computer techniques. Programming and use, was introduced to the CRS staff. This was followed up in 1984 by having lectures on electronic data analysis and digital image processing and specific introduction to the CRS microcomputer system. On requests made by various districts organsiations, beginning from 1984 CRS conducted a series of seminars in different districts of Sri Lanka, to explain the use of land use maps for the district administrations. Mapping activities of the survey dept. and CRS use assistant programmes of the CRS were explained and fields visits were organised to demonstrate the application of maps, Aerial photographs, satellite imagery etc which could be used by the district administrations in their work. From the inception of the CRS, analogue techniques were adopted for the land use mapping in Sri Lanka. However since of late, most of the remote sensing technicians have under gone the basic training of digital processing at the AIT (Bangkok) last year a Swiss expert conducted some lectures and conducted workshop on the use of the image processing software ERDAS, to a selected group of technicians and officers of the survey department. Few of the senior staff of the survey department have also undergone more comprehensive training in digital image professing at international institutions. For digital image processing, the CRS have a earth resources data analysis system (ERDAS). With these facility we are able to use CCTs direct for image processing. The Swiss-Sri Lanka remote sensing project, which is funded by the government of Switzerland and Sri Lanka. Whereby Sri Lanka has obtained equipment and the services of Swiss experts during the period of 1980-90. Co-operation with Thailand and India for obtaining Land-sat imagery, Toulovse France for spot imagery co-operation with the united state national oceanic and atmospheric administration obtaining the Met sat data and early warning of impending disasters. Co-operation with the Asia institute of technology (Bangkok) and other international Agencies in training of staff.
Regional co-operation in Asia and the Pacific is achieved through the UNDP Regional remote sensing programme, executed by the ESCAP. This programme co-ordinated training facilities, the sharing in information, pilot projects on remote sensing activities. ACRS conducted by the Asia Association on remote sensing enables the scientists in the Asia region for sharing of technical advanced in their work. Land use change is a common effect of human activity, and the development activities of the government. Dynamism of the change varies for place to place. Thus the updating of the land use maps have to be continuous, cyclic or periodic depending the locality under consideration. To check the feasibility of the use of M.SS and TM imagery for updating of land use maps, investigations were carried out in 2 test areas in the Badulla district. The method chosen was based on the masking techniques and was applied to 9 land use categories. Areas appearing exceptionally bright and dark on the new satellite imagery were considered to be the potential changes, were masked. During the field visits the interpretations were verified and statistically verified. Similar tests were planned to be carried out in the Anuradhapura District including MSS, TM and spot imagery. New aerial photography to calibrate the different data sources were also planned. Due to unforeseen problems, this test were confined to the use of MSS and TM imagery. In both these tests, comparison of the real change with the potential changes indicated by satellite imagery revealed a corresponding accuracy of about 60% for flat area. But for hilly frequent cloud shadows were found to interfere heavily with the potential land use changes indicated in the imagery. Hence subjected to intensive field checking, this method could be applied for updating, thematic mapping inflate areas. Later tests carried with spot imagery for the updating of topographical maps and production of new series of 1/50,000 land use maps proved to be very promising with about 75% correspondence in the verification of the interpretations. Conclusion Through the Sri Lanka, Swiss project, CRS has developed medium level technologies in the mapping and the monitoring of its Land-use data base. Tests with the use of TM and spot imagery for updating of the land use data base, provides feasible, but time consuming results. Further development of the digital processing and mapping capabilities of the CRS, together with the training of the indigenous staff in the operational and maintenance of such systems is recommended. In this direction as well a for the acquisition of timely and cloud free satellite imagery, regional and international co-operation are south. With the commercialization of the resource data satellite systems, costs of spatial imagery are bound to escalate beyond the reach of developing countries like Sri Lanka. If we are to stand alone in our endeavours for the continuation of development in the use of satellite imagery for mapping and monitoring and timely updating of the resource data-base, it will be of paramount importance to seek further regional and international co-operation. References
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