| Title | Seasonal Change in Wetland Coherence as an Aid to Wetland Monitoring |
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| Author | Brisco, B; Ahern, F; Murnaghan, K; White, L; Lancaster, P |
| Source | Remote Sensing of Environment vol. 9, no. 158, 2017., https://doi.org/10.3390/rs9020158  Open Access |
| Image |  |
| Year | 2017 |
| Alt Series | Earth Sciences Sector, Contribution Series 20130057 |
| Publisher | MDPI AG |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Ontario |
| NTS | 31G/05 |
| Area | Ottawa valley |
| Lat/Long WENS | -76.0000 -75.5000 45.5000 45.2500 |
| Subjects | environmental geology; hydrogeology; radar imagery; ground probing radar; radar methods; satellite imagery; LANDSAT; satellites; floods; flood potential; wetlands; swamps; soils; vegetation; change
detection |
| Illustrations | Landsat images; location maps; tables; graphs |
| Program | Remote Sensing Science |
| Released | 2017 02 15 |
| Abstract | Water is an essential natural resource, and information about surface water conditions can support a wide variety of applications, including urban planning, agronomy, hydrology, electrical power
generation, disaster relief, ecology and preservation of natural areas. Synthetic Aperture Radar (SAR) is recognized as an important source of data for monitoring surface water, especially under inclement weather conditions, and is used operationally
for flood mapping applications. The canopy penetration capability of the microwaves also allows for mapping of flooded vegetation as a result of enhanced backscatter from what is generally believed to be a double-bounce scattering mechanism between
the water and emergent vegetation. Recent investigations have shown that, under certain conditions, the SAR response signal from flooded vegetation may remain coherent during repeat satellite over-passes, which can be exploited for interferometric
SAR (InSAR) measurements to estimate changes in water levels and water topography. InSAR results also suggest that coherence change detection (CCD) might be applied to wetland monitoring applications. This study examines wetland vegetation
characteristics that lead to coherence in RADARSAT-2 InSAR data of an area in eastern Canada with many small wetlands, and determines the annual variation in the coherence of these wetlands using multi-temporal radar data. The results for a
three-year period demonstrate that most swamps and marshes maintain coherence throughout the ice-/snow-free time period for the 24-day repeat cycle of RADARSAT-2. However, open water areas without emergent aquatic vegetation generally do not have
suitable coherence for CCD or InSAR water level estimation. We have found that wetlands with tree cover exhibit the highest coherence and the least variance; wetlands with herbaceous cover exhibit high coherence, but also high variability of
coherence; and wetlands with shrub cover exhibit high coherence, but variability intermediate between treed and herbaceous wetlands. From this knowledge, we have developed a novel image product that combines information about the magnitude of
coherence and its variability with radar brightness (backscatter intensity). This product clearly displays the multitude of small wetlands over a wide area. With an interpretation key we have also developed, it is possible to distinguish different
wetland types and assess year-to-year changes. In the next few years, satellite SAR systems, such as the European Sentinel and the Canadian RADARSAT Constellation Mission (RCM), will provide rapid revisit capabilities and standard data collection
modes, enhancing the operational application of SAR data for assessing wetland conditions and monitoring water levels using InSAR techniques. |
| Summary | (Plain Language Summary, not published)
Information about surface water can help a number of applications including hydrology, meteorology, ecology, and agronomy. Ample quantities of water are
needed for healthy wetlands. Synthetic Aperture Radar (SAR) satellite imagery is as an important data source for monitoring surface water, especially under inclement weather conditions. This paper evaluates methods to determine if RADARSAT-2,
Canada's SAR satellite, can be used to monitor wetland water levels. The results identify that coherence (the degree which surfaces are identical measured on a scale of 0 (low) to 1 (high)) offers promise as a monitoring tool for flagging wetland
changes. The cause of this change can then be determined and remedied. This paper identifies additional research needed for operational implementation of this technology for future SAR satellite missions, e.g. the RADARSAT Constellation
Mission. |
| GEOSCAN ID | 292590 |
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