# Assessment of Carbon Flux and Soil Moisture in Wetlands Applying Sentinel-1 Data
## 2 Materials and Methods
### Data Sets  
The datasets used for the study were: in-situ measurements, TerraSAR-X (TSX) and Landsat 8 OLI images used for vegetation habitat types classification, and Sentinel-1 (S1) data used for examining the relationship of backscatter to soil moisture, LAI, and NEE. Table 1 presents the list of microwave satellite data taken into the research: TerraSAR-X (X-band, wavelength 31 mm, frequency 9.65 GHz, ENL-1 (Effective Number of Looks), and Sentinel-1 (C-band, wavelength 5.55 cm, frequency 5.405 GHz, ENL-5).  
TerraSAR-X images were registered in ScanSAR imaging mode and single polarization--VV. The TSX acquired product type was Geocoded Ellipsoid Corrected (GEC) in UTM projection. Sentinel-1 images were registered in Interferometric Wide (IW) mode, incidence angle 35\({}^{\circ}\) and dual polarization--VV and VH. The S1 acquired product type was Ground Range Detected (GRD) in WGS4 ellipsoid. The optical data--Landsat 8 OLI (Operational Land Imager) image registered on 19 May 2013 was applied in combination with TSX images in the classification procedure. This image was registered in nine spectral bands from 0.43 to 1.38 \(\upmu\)m with a spatial resolution of 30 m for Bands 1 to 7 and 9, and 15 m for Band 8--panchromatic.  
The in-situ measurements have been done from April to October of the years 2013-2015 at nearly 25 points distributed in various sites of the Biebrza Wetland in order to assess the distribution of soil moisture, vegetation parameters, and CO\({}_{2}\) flux over various types of vegetation habitats. During the field campaigns, each of the sites was treated three times in three different localizations around a measurement point for the calculation of the mean value. The dates of in-situ measurements corresponded to the dates of Sentinel-1 overpasses. The positions of the measurement plots were determined using GPS. Instantaneous flow of CO\({}_{2}\) between the ground surface and the atmosphere was measured using a static chamber method [40]. The concentration of CO\({}_{2}\) (ppm) and air temperature (\({}^{\circ}\)C) inside the plastic transparent chamber (40 \(\times\) 40 \(\times\) 35 cm) was measured by a portable non-dispersive infrared sensor (SenseAir(r), SenseAir SE) in one minute intervals. With this set-up, carbon flux (NEE) was first measured under light conditions immediately followed by a measurement of ecosystem respiration (RESP) after darkening of the chamber. The ground measurements also involved simultaneously measured significant vegetation and soil parameters such as: soil moisture in the layer of 0-15 cm (there is strong relationship between 0-5 cm and 0-15 cm for the peat soil) using the TDR method (TRIME-FM, IMKO Micromodultechnik GmbH, Ettlingen, Germany), LAI (LAI 2000, LiCor Inc., Lincoln, NE, USA), wet and dry biomass (in the laboratory from samples harvested inside the whole surface covered by the chamber following the flux measurement). All in-situ and satellite data have been stored in ACCESS and EXCEL databases.  
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Platform** & **Band (cm)** & **Acquisition Date** & **Processing Level/Type** & **ENL 1** & **Beam Track** & **Spatial Resolution (m)** & **Polarization** \\ \hline TerraSAR-X & & 21 May 2013 & & & scan\_008 & & \\ SAR ScanSAR & & 7 June 2013 & & & scan\_003 & 18 & VV \\  & & 23 June 2013 & & & scan\_008 & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Microwave data acquisitions over the Biebrza Wetland test site.