A Review of Wetland Remote Sensing <s> Emergency Mapping <s> The authors find that interferometric processing of repeat-pass L-HH-band shuttle imaging radar (SIR-C) data reveals centimeter-scale changes in the elevations of water surfaces within flooded vegetation. Because radar pulses reflect specularly from the water surface, interferometric observations of open water are incoherent. However, within flooded forests and inundated shrubs, the L-band radar pulse penetrates the vegetation canopy and follows a double-bounce travel path that includes the water and vegetation-trunk surfaces. In these environments, the returned radar energy and associated phase coherence are both stronger than the surrounding nonflooded terrain, permitting determination of the interferometric phase. Phase errors related to atmospheric water vapor are usually longer in wavelength and spatially distinct from phase signatures related to stage changes in tributaries and floodplain lakes. The interferometrically measured stage decreases match gauge data, providing further verification. Water level changes across 150 m to 2.75 km-wide water bodies containing inundated vegetation can be reliably measured. The authors' results suggest that if future interferometric L-HH-band SAR missions are implemented with short temporal baselines, it is possible to measure the hydrologic response of wetlands and inundated floodplains to changes in mainstem water level. <s> BIB001 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> Multifrequency, polarimetric airborne synthetic aperture radar (SAR) survey of a salt marsh on the east coast of the UK is used to investigate the radar backscattering properties of emergent salt marsh vegetation. Two characteristics of flooded vegetation are observed: backscatter enhanced by approximately 1.2 dB at C-band, and 180° HH-VV phase differences at L-band. Both are indicative of a double bounce backscattering mechanism between the horizontal water surface and upright emergent vegetation. The mapping of inundated vegetation is demonstrated for both these signatures, using a statistical active contour model for the C-band enhanced backscatter, and median filtering and thresholding for the L-band HH-VV phase difference. The two techniques are validated against the waterline derived from tidal elevation measured at the time of overpass intersected with an intertidal DEM derived from airborne laser altimetry. The inclusion of flooded vegetation is found to reduce errors in waterline location by a factor of approximately 2, equivalent to a reduction in waterline location error from 120 to 70 m. The DEM is also used to derive SAR waterline heights, which are observed to underpredict the tidal elevation due to the effects of vegetation. The underprediction can be corrected for vegetation effects using canopy height maps derived from the laser altimetry. This third technique is found to improve the systematic error in waterline heights from 20 to 4 cm, but little improvement in random error is evident, chiefly due to significant noise in the vegetation height map. <s> BIB002 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> The Louisiana coast is subjected to hurricane impacts including flooding of human settlements, river channels and coastal marshes, and salt water intrusion. Information on the extent of flooding is often required quickly for emergency relief, repairs of infrastructure, and production of flood risk maps. This study investigates the feasibility of using Radarsat‐1 SAR imagery to detect flooded areas in coastal Louisiana after Hurricane Lili, October 2002. Arithmetic differencing and multi‐temporal enhancement techniques were employed to detect flooding and to investigate relationships between backscatter and water level changes. Strong positive correlations (R 2 = 0.7–0.94) were observed between water level and SAR backscatter within marsh areas proximate to Atchafalaya Bay. Although variations in elevation and vegetation type did influence and complicate the radar signature at individual sites, multi‐date differences in backscatter largely reflected the patterns of flooding within large marsh areas. Prelim... <s> BIB003 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> This paper discusses the contribution of multipolarization radar data in monitoring flooding events in wetland areas of the Delta of the Parana/spl acute/ River, in Argentina. The discussion is based on the comparison between radiative transfer model simulations and ENVISAT Advanced Synthetic Aperture Radar observations of two types of marshes: junco and cortadera. When these marshes are flooded, the radar response changes significantly. The differences in radar response between the flooded and nonflooded condition can be related to changes in the amount of emerged biomass. Based on this, we propose a vegetation-dependent flooding prediction scheme for two marsh structures: nearly vertical cylinders (junco-like) and randomly oriented discs (cortadera-like). <s> BIB004 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> Detailed analysis of C-band European Remote Sensing 1 and 2 (ERS-1/ERS-2) and Radarsat-1 interferometric synthetic aperture radar (InSAR) imagery was conducted to study water-level changes of coastal wetlands of southeastern Louisiana. Radar backscattering and InSAR coherence suggest that the dominant radar backscattering mechanism for swamp forest and saline marsh is double-bounce backscattering, implying that InSAR images can be used to estimate water-level changes with unprecedented spatial details. On the one hand, InSAR images suggest that water-level changes over the study site can be dynamic and spatially heterogeneous and cannot be represented by readings from sparsely distributed gauge stations. On the other hand, InSAR phase measurements are disconnected by structures and other barriers and require absolute water-level measurements from gauge stations or other sources to convert InSAR phase values to absolute water-level changes. <s> BIB005 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> The Brazilian Pantanal is a large continuous tropical wetland with large biodiversity and many threatened habitats. The interplay between the distribution of vegetation, the hydrology, the climate and the geomorphology nourishes and sustains the large diversity of flora and fauna in this wetland, but it is poorly understood at the scale of the entire Pantanal. This study uses multi-temporal L-band ALOS/PALSAR and C-band RADARSAT-2 data to map ecosystems and create spatial-temporal maps of flood dynamics in the Brazilian Pantanal. First, an understanding of the backscattering characteristics of floodable and non-floodable habitats was developed. Second, a Level 1 object-based image analysis (OBIA) classification defining Forest, Savanna, Grasslands/Agriculture, Aquatic Vegetation and Open Water cover types was achieved with accuracy results of 81%. A Level 2 classification separating Flooded from Non-Flooded regions for five temporal periods over one year was also accomplished, showing the interannual variability among sub-regions in the Pantanal. Cross-sensor, multi-temporal SAR data was found to be useful in mapping both land cover and flood patterns in wetland areas. The generated maps will be a valuable asset for defining habitats required to conserve the Pantanal biodiversity and to mitigate the impacts of human development in the region. <s> BIB006 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> This paper assesses the potential of using spaceborne X-band synthetic aperture radar (SAR) data for monitoring water-level changes over wetlands. Our analysis is based on three sets of TerraSAR-X (TSX) observations acquired over South Florida's Everglades wetlands during an eight-month period in 2008. The first set was acquired in single HH polarization stripmap mode over our northern study area, consisting of managed wetlands and urban environments. The second set was acquired in dual-polarization stripmap mode over the western half of the same area, consisting mostly of managed wetlands. The third set was also acquired with dual-polarization stripmap mode over our southern study area, consisting of natural flow freshand salt-water wetlands in the southern Everglades. The first data set was used for a proof-of-concept study to verify that X-band data can generate coherent interferograms in wetland areas. Interferometric processing of this data set shows a high level of coherence (> 0.35) over both wetland and urban regions, maintaining interferometric phase in all three interferograms spanning 11 days. Surprisingly, phase is maintained over some of the wetlands even for interferograms spanning 33 days. The other two data sets were used to evaluate interferometric coherence of all four polarization modes and to determine dominant scattering mechanism in each wetland environment. Our results show high coherence values (> 0.4) in all polarization modes, with highest values in HH, then VV, and lowest in HV or VH. Interferograms calculated from multipolarization data show very similar fringe patterns regardless of the polarization type, suggesting that the phase information in all polarization data reflects water-level changes in wetlands and that volume scattering may be less important than commonly believed. We also used the two multipolarization data sets to conduct the Pauli decomposition, finding a strong dependence of scattering mechanism on vegetation type. The high interferometric coherence level of all polarization data suggests that a significant part of the X-band scattered signal interacts with lower sections of the vegetation (trunks and branches), because scattering from wind-affected canopies cannot support such a high coherence level. The high spatial resolution of TSX, combined with its 11-day repeat orbit, makes this X-band sensor surprisingly suitable for wetland interferometric SAR applications. <s> BIB007 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> Inundation maps of coastal marshes in western Louisiana were created with multitemporal Envisat Advanced Synthetic Aperture (ASAR) scenes collected before and during the three months after Hurricane Rita landfall in September 2005. Corroborated by inland water-levels, 7 days after landfall, 48% of coastal estuarine and palustrine marshes remained inundated by storm-surge waters. Forty-five days after landfall, storm-surge inundated 20% of those marshes. The end of the storm-surge flooding was marked by an abrupt decrease in water levels following the passage of a storm front and persistent offshore winds. A complementary dramatic decrease in flood extent was confirmed by an ASAR-derived inundation map. In nonimpounded marshes at elevations ;80 cm during the first month after Rita landfall. After this initial period, drainage from marshes-especially impounded marshes-was hastened by the onset of offshore winds. Following the abrupt drops in inland water levels and flood extent, rainfall events coinciding with increased water levels were recorded as inundation re-expansion. This postsurge flooding decreased until only isolated impounded and palustrine marshes remained inundated. Changing flood extents were correlated to inland water levels and largely occurred within the same marsh regions. Trends related to incremental threshold increases used in the ASAR change-detection analyses seemed related to the preceding hydraulic and hydrologic events, and VV and HH threshold differences supported their relationship to the overall wetland hydraulic condition. <s> BIB008 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> Floodplain lakes and peatlands in the middle Mahakam lowland area are considered as ecologically important wetland in East Kalimantan, Indonesia. However, due to a lack of data, the hydrological functioning of the region is still poorly understood. Among remote sensing techniques that can increase data availability, radar is well-suitable for the identification, mapping, and measurement of tropical wetlands, for its cloud unimpeded sensing and night and day operation. Here we aim to extract flood extent and flood occurrence information from a series of radar images of the middle Mahakam lowland area. We explore the use of Phased Array L-band Synthetic Aperture Radar (PALSAR) imagery for observing flood inundation dynamics by incorporating field water level measurements. Water level measurements were carried out along the river, in lakes and in peatlands, using pressure transducers. For validation of the open water flood occurrence map, bathymetry measurements were carried out in the main lakes. A series of PALSAR images covering the middle and lower Mahakam area in the years 2007 through 2010 were collected. A fully inundated region can be easily recognized on radar images from a dark signature. Open water flood occurrence was mapped using a threshold value taken from radar backscatter of the permanently inundated river and lakes areas. Radar backscatter intensity analysis of the vegetated floodplain area revealed consistently high backscatter values, indicating flood inundation under forest canopy. We used those values as the threshold for flood occurrence mapping in the vegetated area. <s> BIB009 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> This paper explores our ability to map the extent of large floods in near real time using coarse resolution C-band radar remote sensing. The European Space Agency’s advanced synthetic aperture radar aboard the Envisat satellite, operating in global monitoring mode (GM), is considered for Australia due to its high temporal frequency, comprehensive coverage and ease of acquisition. Challenges are identified which relate both to the use of radar generally, and also in particular to GM data, in the demarcation of water and land. In Australia, the need for a better understanding of the expected backscatter response from inundated areas in tropical savanna, which covers one third of its landmass, is targeted. The backscatter responses to two large flood events in the tropical savanna of northern Australia are investigated, showing markedly different results. One flood allows the accurate classification of inundated extents, while the other is almost completely indistinguishable from the surrounding wet vegetation. Data from water height loggers established in the neighbouring Mitchell floodplain over a dry/wet season period provide an insight into the interaction of these particular vegetation conditions under flood. Results concur with the work of others, that backscatter response is a complex combination of effects depending on relative water height, vegetation spatial density, biomass, and verticality, or enmeshment, of super-surface grasses. Opportunities are also identified that relate to future space missions, the synoptic use with optical data, and better knowledge of the processes that govern the applicability of radar data for mapping large flood events. <s> BIB010 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> The Erguna floodplain, located on the boundary of China, Russia, and Mongolia, is a globally important breeding and stop-over site for many migratory bird species. However, it has a fragile ecosystem and is facing severe impacts from climate change and human activities. Motivated by the high demand for spatial and temporal information about flooding dynamics and vegetation patterns, six fully polarimetric RADARSAT-2 images acquired with the same configuration were explored to reveal the characteristics of the floodplain. The evaluation of a set of polarimetric observables derived from the series of polarimetric synthetic aperture radar (PolSAR) data was used to investigate the characteristics of the typical land-cover types in the floodplain. The behaviors of the polarimetric features highlight the benefits of interpreting the scattering mechanism evolutions at different phenological and inundation stages. The vegetation and inundation patterns were mapped by a random forest (RF) classifier with the input of these polarimetric observations. The results show that a multi-temporal classification can better capture the spatial distribution of the vegetation pattern than single-temporal classifications, which often show a large variability due to the effect of phenology and flooding. A hydroperiod map, which was generated by the time-series classification results of open water, illustrates the flooding temporal dynamics and the hydrological regime. The two main environmental factors that induced the changes in the backscattering – phenology and flooding – were identified based on the aggregated classification results of different phenological intervals. The spatial and temporal characteristics of the phenology- and flooding-induced changes were documented by the changes in the trajectories of three patch metrics at the class level. The polarimetric features' importance scores derived from the RF classifier indicate that the intensity-related features are important for land-cover mapping. The HV intensity, in particular, achieves the highest importance score. In addition, the volume scattering component shows a better performance among the composite features, revealing the importance of the quad-polarimetric information for floodplain interpretation and monitoring. <s> BIB011 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> Abstract Flooding is one of the most costly natural disasters and thus mapping, modeling and forecasting flood events at various temporal and spatial scales is important for any flood risk mitigation plan, disaster relief services and the global (re-)insurance markets. Both computer models and observations (ground-based, airborne and Earth-orbiting) of flood processes and variables are of great value but the amount and quality of information available varies greatly with location, spatial scales and time. It is very well known that remote sensing of flooding, especially in the microwave region of the electromagnetic spectrum, can complement ground-based observations and be integrated with flood models to augment the amount of information available to end-users, decision-makers and scientists. This paper aims to provide a concise review of both the science and applications of microwave remote sensing of flood inundation, focusing mainly on synthetic aperture radar (SAR), in a variety of natural and man-made environments. Strengths and limitations are discussed and the paper will conclude with a brief account on perspectives and emerging technologies. <s> BIB012 </s> A Review of Wetland Remote Sensing <s> Emergency Mapping <s> Abstract. Interferometric synthetic aperture radar (InSAR) techniques can monitor water-level changes in wetlands with suitable coherence. RADARSAT-2 has many beam modes with varying system parameters to satisfy a wide range of applications. During data acquisition the SAR signals are digitized using eight-bit analog-to-digital converters followed by block adaptive quantization (BAQ) coding. Most RADARSAT-2 beam modes use three-bit BAQ but some modes use two-bit BAQ to accommodate larger data sets, including the wide multilook fine and wide ultrafine modes. These modes are attractive for surface monitoring applications due to good resolution over a wide swath. The two-bit BAQ can have signal saturation due to the smaller dynamic range and an increased phase noise. The Everglades National Park (ENP) has been used for numerous InSAR investigations of water level monitoring. This study describes the results of an evaluation of RADARSAT-2 products from different modes for the monitoring of water-level changes... <s> BIB013
A flood is a natural disturbance of wetlands and information is needed immediately to create a destruction map and rescue plan BIB012 . Radar images are used for this purpose instead of optical images because of clouds and rain. In fact, SAR images have been proven useful for monitoring floods because of the all-weather, all-time capabilities in obtaining ground information. The backscattered signal of flooded and non-flooded vegetation in wetland regions is different; based on this, Grings et al. BIB004 developed a method to predict the flooded marsh. Radarsat-1 SAR data are an effective data sources for detecting flood extent in coastal marshes. The backscattered signal of SAR data have a positive correlation with water level BIB003 . Kiage et al. BIB003 also revealed that marsh flood can be best described by the changes of two flood images. It has been verified that the combinations of multitemporal ALOS PALSAR and RADARSAT-2 data are efficient in mapping land cover and flood patterns in wetland regions BIB006 . Airborne SAR images were used by Horritt et al. BIB002 to map the flooded vegetation in a salt marsh using two techniques: C-band backscatter-enhanced and L-band HH-VV phase differences. Their results showed that both methods improve the mapping of the emergent vegetation and can be used to reduce the errors of flood maps. Furthermore, RADARSAT-2 has different beam modes for different purposes. Brisco et al. BIB013 compared the results of water level changes and flooded vegetation from different modes of RADARSAT-2 and found that the wide-swath high-resolution modes are appropriate for wetland monitoring and water level estimates because of the appropriate coherence and backscatter. Zhao et al. BIB011 revealed the land cover characteristics of Erguna Floodplain in China using six polarimetric RADARSAT-2 images; they reported that multitemporal image classification can describe vegetation cover with better accuracy. They also concluded that the intensity of the backscatter signal is important for land cover mapping. JERS-1 SAR and Envisat ASAR data were also efficient for the classificaton of flooded wetland and flood monitoring BIB004  BIB008 . TerraSAR-X, ERS-1/ERS-2, Radarsat-1, and Shuttle Imaging Radar with Payload C (SIR-C) data have been used to reveal the water level changes in wetlands of different countries BIB001 BIB005 BIB007 . O'Grady and Leblanc BIB010 explored mapped flood areas nearly in real time using C-band radar data. Based on the comparison of notably different backscatter responses of the two large flood cases, they concluded that the backscatter signal is affected by many factors, such as the water level, vegetation density, and biomass, and shows complex changes. Hidayat et al. BIB009 used PALSAR data to derive the flood extent and flood occurrence information in tropical wetlands. They incorporated water level measurements in lakes and peatlands in their study and revealed that the flood under forest canopy corresponds to high backscatter values.