Monitoring Wetlands Ecosystems Using ALOS PALSAR (L-Band, HV) Supplemented by Optical Data: A Case Study of Biebrza Wetlands in Northeast Poland

Abstract

Abstract:The aim of the study was to elaborate the remote sensing methods for monitoring wetlands ecosystems. The investigation was carried out during the years 2002-2010 in the Biebrza Wetlands. The meteorological conditions at the test site varied from extremely dry to very wet. The authors propose applying satellite remote sensing data acquired in the optical and microwave spectrums to classify wetlands vegetation habitats for the assessment of vegetation changes and estimation of wetlands' biophysical properties to improve monitoring of these unique, very often physically impenetrable, areas. The backscattering coefficients (σ°) calculated from ALOS PALSAR FBD (Advanced Land Observing Satellite, Phased Array type L-band Synthetic Aperture Radar, Fine Beam Dual Mode) images registered at cross polarization HV on 12 May 2008 were used to classify the main wetland communities using ground truth observations and the visual interpretation method. As a result, the σ° values were distributed among the six wetlands' vegetation classes: scrubs, sedges-scrubs, sedges, reeds, sedges-reeds, rushes, and the areas of each community and changes were assessed. Also, the change in the biophysical variable as Leaf Area Index (LAI) is described using the information from PALSAR data. Strong linear relationships have been found between LAI and σ° derived for particular wetland classes, which then were applied to elaborate the maps of LAI . Differences of almost double T s between "dry" and "wet" years were noticed that reflect observed weather conditions. The highest values of NDVI occurred in years with a sufficient amount of precipitation with the lowest in "dry" years. NDVI values variances within the same wetlands class resulted mainly from the differences in soil moisture. The results of this study show that the satellite data from microwave and optical spectrum gave the repetitive spatial information about vegetation growth conditions and could be used for monitoring wetland ecosystems.

Assessment of Carbon Flux and Soil Moisture in Wetlands Applying Sentinel-1 Data

“…In this study we decided to apply microwave and optical data for the classification of wetland vegetation habitats. Compared to the classification results undertaken using ALOS PALSAR HV [43], in the present study it was possible to distinguish wetland habitat types more precisely. The obtained classification results of wetland habitat types (two forest and five non-forest habitats) presented in Figure 2 were not found in the literature before and are promising in wetland changes monitoring.…”

“…RMSE was equal to 1.8 dB and MBE was equal to −0.37 dB for the test containing 63 observations. LAI can be estimated by applying optical or microwave satellite data [31,43,44]. In the present study the analysis between LAI and the backscattering coefficient calculated from Sentinel-1A data has been investigated by means of regression models.…”

“…Santoro et al [51] who studied ALOS PALSAR (Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar) data found that better classification results were obtained from HV than from HH polarization. Dabrowska-Zielinska et al [43] and Conforth et al [52] also presented wetland classification using ALOS PALSAR data acquired in HV polarization. Flores De Santiago et al [53] found that a combination of HH and HV polarization modes from ALOS PALSAR data was better at separating forested wetlands using an object-based classification approach.…”

“…Dorigo et al [64] presented the evaluation of CCI (Climate Change Initiative) soil moisture product using ground based observations. Soil moisture for the Biebrza Wetland has been investigated by authors in a previous study using microwave data acquired by ERS-1/2 SAR VV, ENVISAT ASAR IS2 HH, and ALOS PALSAR HH [25,43,44,65,66]. In the present study Sentinel-1 IW VV and VH data have been applied for the assessment of soil moisture (there was no S1 acquisition in HH polarisation).…”

Wetland Mapping Using SAR Data from the Sentinel-1A and TanDEM-X Missions: A Comparative Study in the Biebrza Floodplain (Poland)

“…In this area, the problems of soil moisture and biomass estimation have been intensively studied in the past [2,3]. The main hydrological concern in this area is how to retain the water for longer periods from early spring flooding.…”