Zdenek “Denny” Kalensky, Dr. Kian Fadaie and Les Whitney
Canda Centre for Remote Sensing (CCRS)
Geomatics Canada, Earth Sciences Sector, Natural Resources Canada
588 Booth Street, Ottawa, Onario, Canada KIA 0Y7
Canada Centre for Remote Sensing (CCRS) has a long tradition of cooperation with Asian developing countries in strengthening their national remote sensing capacities. This cooperation has included contribution to formulation of the UN-ESCAP Remote Sensing Program for Asia and the Pacific; organization of study programs in Canada for visiting scientists from Asian countries, as well as training courses and workshops in the region; provision of technical assistance for development of national remotes sensing centers and , in particular, for development of capacities for operational application of RADARSAT data. The latter assistance has been implemented under the GlobeSAR program with participation of the following five Asian countries: China, direct RADARSAT data acquisition capacities in the region.
This good cooperation with Asian countries continues and is being further expanded. Its particular feature is close involvement of Canadian remote sensing private sector, comparing some 180 companies at present (1996). This assures not only continuity of strengthening of links among the Canadian and Asian remote sensing companies.
Over the past twenty years, the Canada Centre for Remote Sensing (CCRS) has been involved in a large number of remote sensing technology transfer activities in Asia. Their overall aim has counties. CCRS activities in Asia have included provision of advisory services on institutional remote sensing infrastructures, in particular on establishment of national remote sensing centers, ground receiving stations and data processing facilities; organization of workshops and training courses; arrangement of study tours to Canada; participation in formulation of regional and national remote sensing projects; as tweet as joint implementation of pilot projects.
Such direct assistant to individual Asian countries has been complemented by a long-standing cooperation between CCRS and UN-ESCAP Space Technology Applications Section. In particular, CCRS scientists have frequently participated in the activities of ESCAP Regional Remote Sensing Programme. CCRS participation in UN regional remote sensing inputs to the Global Map project, initiated and led by the National Geographical Institute of Japan, should also be noted.
Use of satellite remote sensing inmost developing countries of Asia has now passed the promotional stage and is entering the operational phase. Asian countries have succeeded with
Development of effective remote sensing infrastructures at the regional and, in a number of countries, at the national levels. This has been reflected in growing operational use of satellite remote sensing in Asia for mitigation of natural disasters, monitoring of land cover, inventory of inland water bodies, mapping of forest and monitoring deforestation, sustainable management of coastal zones, etc.
While present remote sensing technology is already contributing significantly to more effective management of natural resources and environmental protection, recent new developments and those expected in the near future, will further enhance the role of satellite remote sensing as a primary source of geospatial information describing types, states and changes of vegetation, surface water bodies and land degradation. Such information, when reliable, delivered in timely manner and available in user-friendly format, is essential for successful implementation of sustainable development strategies.
One of the most important recent sensing technological development has been the deployment of earth observation (EO) satellites with microwave remote sensing payloads. Several countries have launched EO satellites with synthetic aperture radar (SAR) imaging system in the framework of their experimental programs for civilian applications of microwave remote sensing. Canada has become the first country to design such a satellite, RADARSAT 1, for operational worldwide use and to operate it on a commercial basis.
EO satellites with microwave remote sensing systems are of particular interest to countries with tropical humid climate because their image data recording capability is not affected by clouds nor by rain. For example, the procurement of image data recorded by EO satellites with optical sensor system over extensive areas of south and Southeast Asia has been hampered by their dependence on cloud free conditions. It sometimes took years to obtain good quality images (e.g. in many parts of Indonesia, such as Kalimantan and Sulawesi). Obviously, such delays are unacceptable for many application, in particular for mitigation of natural disasters.
Recognizing RADARSAT’s importance as a new, dependable source of remote sensing data not only for Canada but for all countries, the Canadian Space Agency (CSA), jointly with CCRS and in cooperation with private industry represented by RADARSAT international Inc. (RSI), initiated two international RADARSAT technology transfer programs designed to speed up effective applications of RADARSAT data worldwide: GlobeSAR, and the Applications Development and Research Opportunity (ADRO). Both programs are briefly described in his paper.
2. Radarsat Program
The RADARSAT program consists of three EO satellites with SAR remote sensing payloads. RADARSAT 1 was launched November 4, 1995, RADARSAT 2 is scheduled for launch by the year 2000, and RADARSAT 3 by the year 2005, While RADARSATs 1&2 have partially identical design (Tables 1 &2; Fig. 1), the remote sensing payload of RADARSAT 3 will reflect new technological developments available for operational application at the time of its detail design. A dual-frequency and dual-polarization SAR system, as well as a combination of SAR and multispectral optical remote sensing system are some of the options being considered for the RADARSAT 3 payload.
Figure 1 RADARSAT – 1 SAR Beam Modes
Table 1. RADARSAT -1 Orbit And SAR System Specification
|Design timeframe||5 years|
|Orbit geometry||circular, sun-synchronous|
|Orbit altitude||793km – 821km|
|Orbit period||100.7 minutes|
|Orbit repeat cycle||24 days|
|Orbit repeat cycle||14|
|SAR frequency||5.3 GHz (C-band)|
|SAR wavelength||5.6 cm|
|SAR polarization||horizontal in both directions (HH)|
|SAR antenna||steerable, right looking|
|SAR recording time capacity||28 minutes per each orbit|
|SAR on-board data recording||2 tape recorders (each with 10mintues capacity)|
Table 2. RADARSAT -1 SAR Data products Characteristics
|SAR Beam Mode||Nominal Ground Resolution (m)||Approximate SAR Scene Coverage (Km)||Number of Beam Positions/Incidence Angles||SAR Products Output Scale|
|Fine||10||50 x 50||5 / 37° – 48°||1:50,000|
|Standard||30||100 x 100||7 / 20° – 49°||1:100,000|
|Wide||30||150 x 150||3 / 20° – 45°||1:100,000|
|ScanSAR-N||50||300 x 300||2 / 20° – 50°||1:200,000|
|ScanSAR-W||100||500 x 500||1 / 20° – 50°||1:250,000|
|Extended High||25||75 x 75||6 / 49° – 59||1:100,000|
|Extended Low||35||170 x 170||1 / 10° – 23°||1:200,000|
|(RADARSAT International, 1995)|
RADARSAT 1 is the first EO satellite with a SAR remote sensing payload designed for global, operational applications on a commercial basis. In addition to the growing worldwide network of ground stations for its SAR data, RADARSAT 1 has two onboard tape recorders which enable SAR data acquisition even from areas outside the receiving range of ground stations. The RADARSAT 1 orbital and SAR system parameters are in tables 1 & 2. The unique feature of its SAR system is the wide choice of imaging modes (Fig. 1). There are w25 possible choices, depending on the selection of incidence angle (SAR beam position), ground resolution (SAR beam operation mode), and size of RADARSAT SAR scene (Ahmed et al., 1990; Parashar et al. l 993).
The choice of incidence angles at which the ground scene can be viewed by the RADARSAT’s SAR steerable antenna ranges from 10 to 59 degrees. This enables frequent coverage of selected areas, which is important for monitoring of impacts of natural disasters, such as floods. Furthermore, RADARSAT SAR image data can be recorded at 6 different ground resolutions ranging from 10m to 100m. The actual ground resolution is better than the specified nominal values. For example, the analysis of RADARSAT SAR images of forest clearcuts, recorded at the fine resolution, yielded an actual ground resolution of about 8m, rather than the nominal 10m (Ahern & Banner, 1996). The size of RADARSAT SAR scenes ranges from 40km x 50km (recorded at 10 m ground resolution) to 500km x 500km (recorded at 100m ground resolution). Such a wide choice of image recording parameters provides an adequate flexibility to select the imaging modes bet suited to a particular application.
The strongest benefits of satellite SR remote sensing systems are expected in monitoring applications, when data have to be recorded in frequent intervals, often under adverse weather conditions, unsuitable for optical sensors. For example, monitoring of natural or man-induced disaster, such as floods, landslides, damage caused by earthquakes and windstorms, oil spills, etc., requires timely coverage of the effected area during all weather conditions. A combination interpretability of land cover classes and other earth surface features, and thus results in higher information content and accuracies of mapping and monitoring products.
3. GlobeSAR program
Interpretation of SAR images requires different expertise and skills than the interpretation of images from optical sensors. There are not enough remote sensing officers trained in SAR image interpretation. This situation, if not corrected, would hinder the effective application of SAR image products, especially in developing countries where they are needed most. In order to overcome this problem CCRS, with funding support from CSA and the International
Development Research Centre (IDRC), has initiated, in 1993, an innovative GlobeSAR program for training prospective users of ADARSAT SAR image products in developing countries.
The GlobeSAR program, managed by CCRS and implemented jointly with private specter companies, was practically oriented, based on pilot projects and focused on application of SAR images to tasks defined by participants. Five Asian countries, China, Jordan, Malaysia, Thailand and Vietnam participated directly in the program. Several other Asian countries, Bangladesh, Cambodia, India, Indonesia, Kuwait, Laos, Mongolia, Nepal, Pakistan, papua New Guinea, and the Philippines participated in GlobeSAR workshops and training courses (Campbell, 1993 & 1994; Campbell et al., 1995). Taiwan participated, at its own cost, in the commercial part of the GlobeSAR program developed by Intera Information Technologies Corporation; its new name is Intermap Technologies (Brisco, 1996).
Since the GlobeSAR field activities were implemented before the launch of RADARSAT, an airborne SAR system had to be used for data recording. In the Fall of 1993, over 125,000 sq.km of airborne SAR image data were acquired during the GlobeSAR campaign (Petzinger, 1995). Thee data were processed into products simulating as closely as possible those to be obtained from RADARSAT. Application areas and test sites were selected by countries themselves, who also participated in data analysis. The results were reported in GlobeSAR workshops help in Bangkok, Thailand (Nov./Dec. 94), Amman, Jordan (Apr.95) and in Beijin, China (Oct.95).
GlobeSAR pilot studies included over twenty application fields in which the usefulness of RADARSAT SAR data was tested. These pilot studies were summarized by Brown et al., (1996). Their results demonstrate a strong potential of RADARSAT SAR data n a wide range of applications. Only few example of such applications are listed below:
- Agriculture. Promising application of particular interest to Asian countries are in mapping and monitoring soil moisture, drainage patterns, rice fields, and fruit-and cash-crops tree plantations such as the orchards, olive and rubber tree plantations. Fallow farmland could be easily differentiated from plowed fields. SAR data also facilitate assessment of soil erosion and delineation of individual land parcels;
- Forestry. Applications included successful stratification of forest cover, mapping of forest roads and old burns, monitoring of clear cuts and forest regeneration. However, rugged topography may reduce interpretability of land cover classes on SAR images. Heavy rain before SAR data recording may have a similar effect by reducing contrast between vegetation classes. Shifting cultivation could not be identified from SAR imagery alone;
- Coastal zones. Studies included successful interpretation of mangrove forest, aquaculture ponds, shrimp farms, drainage channels, as well as monitoring of land use, shore erosion, land accretion, oil slicks, and wave patterns. RADARSAT SAR recording modes optimizing detection of vessels and its accuracy are being studied;
- Hydrology. Mapping of rives and monitoring changes in their courses were successfully demonstrated. Mapping of abandoned river channels. Lakes and wetlands was also successful. Reliable delineation of floodplains requires availability of collateral data. Ground water studies have shown a good potential (Singhroy et al. 1996);
- Natural disasters. Assessment and monitoring of floods were successfully demonstrated. For example, the extent of flood caused by typhoon was immediately delineated in Vietnam.
Delineation of the extent of landslides was successfully accomplished in Malaysia and Thailand. Assessment of damage caused by earthquakes and volcanic eruptions is also promising.
In most of these applications the availability of multidate and multi sensor data, and their combined analysis with relevant collateral data in GIS system, will bring up the best results and increase the cost benefits (Brisco & Brown, 1995). Furthermore, steerable SAR antenna of RADARSAT enables data recording at different view angles. Combination of different “views” of the same ground scene will increase discrimination of land cover classes and geomorphologic features. Selection of SAR image enhancement technique appropriate for a given application is another essential requirement for successful application of SAR data (Singhrory, 1996).
GlobeSAR studies demonstrated not only the usefulness of RADARSAT SAR data over a wide range of applications, but also provided their participants with the necessary skills for their effective application and strengthened their interest in the use of EO for sustainable development of natural resources and environmental protection.
4. Application Development and Research Opportunity (ADRO)
ADRO is an international program, complementary of GlobeSAR, designed to encourage and support worldwide research studies based on RADARSAT SAR data. Its specific objectives are to achieve the effective use of RADARSAT SAR data under all operating modes and a wide variety of environments; development and demonstration of new RADARSAT SAR data applications; making contributions to better understanding of the Earth’s geophysical and biological processes; and obtaining information essential to improvement of future programs.
The ADRO program is jointly sponsored by CSA, the U.S. National Aeronautics and Space Administration, and RADARSAT International Inc. An ADRO Coordination Office has been established at CSA which has the overall responsibility for management of the program. CCRS has an advisory role, focusing on development, demonstration and promotion of new RADARSAT SAR data application.
Over 350 ADRO proposals have been accepted, out of which about 50 are from Asia. Universities, Government agencies and research institutes, and private sector companies are all represented in the approved proposals. Successful implementation of these research studies will further enhance the usefulness of microwave remote sensing from space platforms, and strengthen the RADARSAT position at the leading edge of space SAR technology for EO.
Use of satellite remote sensing in Asia has now been well established. The GlobeSAR program has demonstrated that RADARSAT will significantly expand the scope of EO applications relevant to Asian countries. RADARSAT is of particular interest to developing countries, as a reliable source of remote sensing data, for the following reasons:
- their urgent need for timely and reliable geospatial information required for completion and revision of inventories of natural resources, compilation of land cover maps, assessment of land degradation, mitigation of natural disasters, and environmental protection;
- reliability of RADARSAT SAR image data supply regardless of weather conditions, especially in view of large delays with delivery of remote sensing data from EO satellites with optical sensor systems because of frequent clouds in countries with humid tropical climate.
- Worldwide availability of RADARSAT SAR data. Its two onboard data recorders assure coverage for areas located outside the range of RADARSAT receiving stations;
- Short revisit time because of selectivity of RADARSAT SAR incidence angles. This is particularly important for monitoring of natural disasters, such as floods;
- Wide choice of RADARSAT SAR products, with ground resolution range 8m 1-100m, and scene size range 50km -500km;
- Possibility of producing stereo-image of the ground scene and producing digital elevation models (DEM);
- Operational status of RADARSAT and assurance of continuity of RADARSAT program the next 10-15 years.
The increasing capacities of EO satellites provide mankind with unprecedented global capability for natural resources surveys and environmental monitoring. Yet, developing countries are still lagging in their participation in full benefits derived from satellite remote sensing (Kalensky, 1996). This paper has outlined the Canadian approach towards rectifying this situation. However, greater international effort is required to assure that all countries family benefit from advances in earth observation. CCRS is looking forward to continue, and further expand its good cooperation with countries of this region to contribute towards and early achievement of this goal.
The authors gratefully acknowledge helpful comments by reviewers of his paper, Dr. B. Brisco, Dr. R.J. Brown, Dr. F.H.A. Campbell and Dr. V. Singhroy. Their respective contributions have been appreciated.
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