Coastal Zone Monitoring with RADARSAT-1
Gordon C. Staples, Jeff Hurely, and R. Shawan Burns
RADARSAT International
Richmond, B.C., CANADA
Fax 1-604-231-4940
E-mail : gstaples@rsi.ca
Abstract
Coastal zone application of RADARSAT imagery include monitoring of land-use and land-use change, ship sureillance of sovereignty control and fisheries management, detection of oil slicks due to shipping accidents and natural oil seeps, flood monitoring, ocean feature detection, and coastal mapping. The focus monitoring, ocean feature detection, and coastal mapping. The focus of this paper is on a subset of these applications, namely aquaculture detection, coastline mapping, ship surveillance and oil spill monitoring. Optimal conditions for aquaculture detection, coastline mapping, and ship surveillance are large incidence angles and no-wind. In the case of aquaculture detection, imagery acquired under similar wind conditions indicated that the aquaculture notes were using a large incidence angle. In contrast, oil spill detection is optimized at small incidence angles and moderate wind speeds. However, a study of the 1997 Nakhodka oil spill indicated that oil detection was primarily dependent on wind speed and to a lesser degree on incidence angle.
1.Introduction
A large percentage of the world's population and industrial activity is concentrated along the coastal zone. These environmentally sensitive areas are under intense pressure from natural processes, urban growth, resources development, and pollution. These events, originating from both anthropogenic and natural sources, are highly dynamic, and effective monitoring is ideally suited to synthetic aperture radar (SAR) satellite Earth observation techniques because of the synoptic coverage provided, and the ability of SAR to provide reliable monitoring independent of light and weather conditions. Within the context of radar monitoring of the coastal zone, applications of RADARSAT SAR imagery include monitoring of land-use and land-use change, ship surveillance for sovereignty control and fisheries management, detection of oil slicks due to shipping accidents and natural oil seeps, flood monitoring, ocean feature detection, and coastal mapping. The focus of this paper is on a subset of coastal zone application , namely coastal zone land use with a specific emphasis on aquaculture detection, coastline mapping, ship sureveillance, and oil spill monitoring.
RADARSAT represents a new tool for coastal zone monitoring and is viable for applications where traditional optical sensors have met with limited success. While RADARSAT employs a single frequency SAR sensor, it offers many benefits either as a Stand along source of information or in conjunction with multi-spectral system addition, through the use of on-board tape recorders and a world-wide network of ground stations, RADARSAT has capability to provide near-real-time (NRT) data delivery for time sensitive monitoring applications such as ship surveillance, flooding, and oil spill detection.
2.0 RADARSAT SAR
The operational focus of the planned five-year RADARSAT-1 program (a seven-year life-span is projected) is in contrast to other spaceborne SAR programs (ERS and NASA for example) which have a strong research focus. One of the initial objectives for the RADARSAT mission was for ice monitoring, but early in the spacecraft design period, the utility of the RADARSAT SAR was realized and the mission was expanded to include the development of world-wide operational applications.
RADARSAT is equipped with a C-band (5.6 cm wavelength) horizontally-polarized (HH SAR (Raney et al., 1991). The orbit, which is sun-synchronous, near polar, with a 800 km nominal altitude, was configured to give a maximum SAR on-time of approximately 28 minutes per orbit (one orbit is about 108 minutes). Unique to RADARSAT, and the cornerstone for coastal zone monitoring application development, is the availability of user-selectable beam modes via electronic steering of the SAR antenna. RADARSAT has seven beam modes that span a range of incidence angles from 10°C in the near range ot 60oC in the far range.
A given RADARSAT beam mode is defined by a range of incidence angles resolution, and spatial coverage. For example, the Fine mode has a range of incidence angles from 36 to 48 degrees, 8 m nominal resolution, and a 50 km nominal swath width. In contrast, ScanSAR Wide has a range of incidence angles from 20 to 50 degrees, 100 m resolution, and a 500 km swath width. Although RADARSAT's variable beam modes can be exploited to provide imaging at a variety of resolution's there is a trade-off between high resolution and spatial coverage: high resolution coverage is available at the expense of reduced spatial coverage, and similarly, increased spatial coverage is available at the expense of resolution. Therefore, depending on the particular application, beam mode selection can be optimized for a given application.
3.0 Coastal Zone Monitoring
3.1 Coastal Zone Land Use
Encompssing the area that extends offshore to the edge of the continental shelf and inshore to the extent of tidal influence, coastal zones are key areas of economic and biological diversity, affected by both natural and anthropogenic processes. For developed countries, coastal zone management programs are established, with activities such as urban expansion, coastal erosion/accretion, and biological processes routinely monitored.In addition, regions are heavy ship traffic are continually monitored for the presence of oil slicks, both from illegal dumping of oil and accidental oil spills.
In the case of developing countries, eager to implement coastal zone management plants a balance must be struck between economic growth through exploitation of the coastal zone resources and maintenance of coastal zone biodiversity. This dichotomy is evident in many areas of the world where economic expansion and the development of coastal zone resources are pronounced. For example, low-typing coastal regions are prime areas for mangrove forests which are biologically diverse and important natural fish-rearing grounds, but at the same time are key areas for the development of aquaculture sites.
