## 2 Study Area
### Rice Phenomena  
The temporal observation of rice growth is important for understanding the radar responses of rice plots at different stages of growth. Camargue has a single cropping season of rice; the agricultural calendar is shown in Table 1.  
The rice crop in Camargue is an intensive type irrigated with direct seeding. Temperature and light are key factors in crop growth:  
* For levee, a minimum temperature of 12 \({}^{\circ}\)C;
* For flowering, a minimum temperature of 20 \({}^{\circ}\)C.  
There are three major periods of rice cultivation: the sowing period (starting according to the weather conditions from the end of April to middle May), the growth period (up to September) and the harvest period (end of September to the beginning of October).  
In Camargue, the sowing date is from 24 April to 16 May, followed by a germination stage from May to June. At the germination stage, water is not evacuated. If the surface is bumpy, two risks are present: (1) either the water height is too high and the seedling dies; (2) the land is bare and the seedling germinates badly. Constant monitoring of water levels, which have a significant role as thermal regulators, should be carried out. Continuous water movement compensates the variations of air temperature. A high water depth protects the seedling in case of cooling. However, it is necessary to rapidly lower the level as soon as the ambient conditions become again favorable.  
The growing period begins from the successful germination to the flowering/maturation stage. Figure 1 shows clearly the development of rice plants in Camargue.  
Three essential factors play a role in the success of seedling emergence: water temperature, with an average above 15 \({}^{\circ}\)C with the nocturnal minimum around 10 \({}^{\circ}\)C; the constancy of the insulation; the fight against parasites: larvae or algae. After the emergence, the rice plot is dried up to 10 or 12 times. Drying can last a day or sometimes half a day. Temporary drying inhibits the development of parasites and activates the rice rooting. Between 25 July and 25 August comes the flowering period. The height of crops does not increase much at this stage. Flowering period requires a warm climate, without wind, without rain. After flowering comes the ripening period where the farmers begin to evaluate their future harvest at the end of August. The harvest stage occurs from the end of September to the beginning of October, all ripening rice crops are reaped. At the end of the harvest, two options are possible. For the first option, rice farmers normally have a long period enough to prepare their rice plots. In irrigated rice farming, as is the case in the Camargue, special attention is paid to leveling, using a laser-guided blade. The use of this equipment aims to obtain perfectly  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Nature of Work and Vegetative Cycle** & **Executive Date** \\ \hline Stubble & October to November \\ Land preparation & March to April \\ Use of fertilizers and herbicides & Middle April \\ Watering and seeding & 25 April to 16 May \\ Lifting and sodding & May to June \\ Post-emergence herbicide & June to July \\ Earing-flowering & July to August \\ Maturation, harvest & 15–20 September to October \\ \hline \hline \end{tabular}
\end{table}
Table 1: Agricultural calendar and rice cycle in Camargue [40].  
Figure 1: Rice crop growth calendar in Camargue.  
flat plots, in order to manage water precisely. This method is also used after harvest period between seasons for maintenance of irrigation canals (\"waterways\"). In Spring, once the last surface preparation is carried out to obtain a suitable seedbed, ditches are dug in the plots to facilitate their filling and emptying during cultivation, and then watering is done; we have a continuous cultural cycle. For the second option, farmers work very quickly to sown as early as autumn, usually with wheat which is the second crop in rice farms in Camargue.