High Spatial Resolution Water Level Time Series in the Florida Everglades Wetlands using Multi-track ALOS PALSAR Data
Hong, Sang-Hoon1; Wdowinski, Shimon2
1Korea Aerospace Research Institute, KOREA, REPUBLIC OF; 2University of Miami, UNITED STATES
Wetland InSAR (Interferometric Synthetic Aperture Radar) observations provide very high-resolution maps of water level changes that cannot be obtained by any terrestrial technique. We recently developed the Small Temporal Baseline Subset (STBAS) approach, which combines single-track InSAR and stage (water level) observations to generate high-resolution absolute water level time series maps (Hong et al., 2010). However, the temporal resolution of produced time series is coarse compared with in-situ stage observation and, hence, the usefulness of these maps is rather limited. To compensate for the low temporal resolution weakness of space-based water level time series, we propose using a multi-track STBAS technique, which utilizes all available Synthetic Aperture Radar (SAR) observations acquired over a certain wetland area. We use a four-year long L-band ALOS PALSAR dataset acquired during 2007-2011 to test the proposed method over the Water Conservation Area 1 (WCA1) in the Everglades wetlands, south Florida (USA) as shown in Fig. 1. A total of 37 images acquired with four tracks (two tracks are ascending and the rest are descending acquisition modes) were collected. Daily water level data at 12 stage stations, which are monitored by the Everglades Depth Estimation Network (EDEN) in WCA1 area, were used to calibrate the InSAR-derived water level data.
The proposed multi-track approach yielded a significant improvement of temporal resolution, which is dependent on the SAR satellite revisit cycle. Instead of the 46-day repeat orbit of ALOS, the multi-track method produces water level maps with temporal resolution of only 7 days. A quality control analysis of the methods indicates that the average root mean square error (RMSE) of the differences between stage water level and retrieved water level by InSAR technique is 4.0 cm (Fig. 2). The end products of absolute water level time series with improved temporal and very high spatial resolutions can be used as excellent constraints for high-resolution wetland flow models. Furthermore, the next generation of SAR satellites has been designed with shorter revisit cycles, which will provide temporally denser maps of water level changes.
Keywords: Wetlands, InSAR, Multi-track Small temporal baseline subset (STBAS), Temporal resolution, wetland surface flow, Everglades, Water Construction Area (WCA1).
 Hong, S.H., Wdowinski, S., Kim, S.W., and Won, J.S. 2010. Multitemporal monitoring of wetland water levels in the Florida Everglades using interferometric synthetic aperture radar (InSAR). Remote Sensing of Environment, Vol. 114, No. 11, pp. 2436 2447. doi: 10.1016/j.rse.2010.05.019.
Fig. 1. (a) Location map showing the SAR tracks used in this study, and (b) satellite image showing the location of stage stations in the WCA1 area. White squares mark station location along the peripheral canals and yellow squares mark location of stations located within the interior of the area.
Fig. 2. Comparison between stage (red) and InSAR (green: 148 track, purple: 149 track, black: 464 track and blue: 465 track) determined water level time series. The graphs show good agreement between InSAR and stage station measurements.