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;
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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.
