## 2 Materials and Methods
### Data Sets  
Long-term changes in land use in the Ben Tre and Tra Vinh provinces were monitored using EO data. A long time series of satellite data with medium resolution was required in order to cover the target area. According to a careful inspection of EO data archives, historical images were available from the SPOT, Landsat and ENVISAT satellites. The ENVISAT ASAR images were used to detect changes during 2005-2011. One to three rice crops per year are harvested in the area [18]. Therefore, several SAR images acquired throughout the year were needed for each year in order to map rice areas and to get the number of rice crops. Long term land-use changes from 1979 were monitored by the optical Landsat images and from 1987 using the optical SPOT images. The long term changes were detected from optical images acquired at the same time of year in December to January.  
The following EO data (Tables 1 and 2) were acquired from European Space Agency (ESA) and United States Geological Survey (USGS) archives:  
Figure 1: A district map of the study area with the ground truth point (GTP) locations.  
* 38 ENVISAT ASAR Wide Swath Mode medium resolution images--2005, 2009, 2011
* Two Landsat images--1979 and 2002
* Six SPOT images--1987, 1998, 2005  
In order to get more data, in the 2011 SAR dataset, imagery from the end of 2010 and the beginning of 2012 were included. The pixel size of the SAR data is 75 m. The Landsat image resolution is 80 m for the MSS image and 30 m for the ETM image. The resolution of the SPOT multispectral images was 20 m. It should be noted that SPOT images did not cover the entire area of interest; however, with two images it was possible to cover 80%-90% of the area.  
In addition to the EO data, administrative boundaries, the official land-use map 2005 of the Mekong Delta from National Institute of Agricultural Planning and Projection (NIAPP) [18], scanned topographic maps from USGS [35] and the 3 arc-second digital elevation model (DEM) from the Shuttle Radar Topography Mission (SRTM) were used. The USGS topographic maps were geocoded and transformed to UTM48 WGS4 coordinate system.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**ID** & **Date** & **Orbit** & **Track** & **ID** & **Date** & **Orbit** & **Track** & **ID** & **Date** & **Orbit** & **Track** \\ \hline
1 & 16.12.2004 & 14,615 & 32 & 14 & 10.1.2009 & 35,886 & 261 & 29 & 15.12.2010 & 45,966 & 262 \\
2 & 19.12.2004 & 14,658 & 75 & 15 &  
Ground truth data were acquired by a field survey campaign on 7-10 October 2013 in Ben Tre and Tra Vinh provinces. At first, 180 ground truth points were randomly created within the study area. However, ground truth data collection was laborious because all locations need to be visited including the time reserved for discussions with local people. The final number and spatial distribution of ground truth points were limited due to resources, time and road accessibility and 75 points were finally collected (Figure 1). The 75 ground truth points covered all land-use classes included in the classification maps. A higher number of points would be needed for detailed accuracy assessment of each land-use class. However, 75 points was considered to be enough for a rough estimate of the classification accuracy. In addition, farmers were asked about the past changes in land use. The number of various land-use classes included in field survey points is presented in Table 3. Detailed information about the crop cycle and type of each location was acquired by interviewing local authorities and farmers _in situ_. The accurate location of each field survey point was captured using hand-held Garmin Etrex GNSS navigator with location accuracy less than 10 m.