**7. Note**

216 Remote Sensing – Applications

Fig. 9. Automatic lava flow outline extraction of May 2004 (blue) compared with the

Lets considerate the example of the May 2004 lava flow (figure 9 and table 4). Three zones are sharply distinguished in the extraction: a very low reflectance and high thermal zone (1), a low reflectance with few or no thermal diffusion zone (2), and a various reflectance with few or no thermal diffusion zone (3). The weakest precision is for the first zone, for the second zone, the low reflectance is due to the substrate's nature and to luminosity issues in the zone, because the shadow projected by the rampart can interfere. A luminosity parameter is to be taken into consideration when choosing and time acquiring SPOT data. As for the extraction of the third zone, the thermal infrared band essentially obtains it, because the lava flow implemented in a vegetalized zone with a high spectral signature difference compared to the lava flow. It is the zone where the extraction is the most precise

The vectors of the outlines obtained by automatic extraction properly match with the referenced outlines since we obtain a mean exactitude producer of 80% for the "lava flow" class. If we compare our automatic extraction results to those obtained by DGPS, they are less precise. The DGPS has a precision of about one centimeter at its antenna, now it's the operator who transports it. The error is due to the positioning of the antenna regards to the outlines. The error then is about one meter, for pluri-meter in our extractions. Nevertheless, the effusion zones are not all accessible, and cannot let realizing the outlines in their integrality, especially in the Grandes Pentes. Computer assisted drawing methods are on the other hand less reliable than our methodology for the data' distortion are not taken into account and can provoke hundred of meters error. The results of our classification are close to those obtained in other contexts' literature. (Azerzaq et al., 1997 ; Messar et Messar, 1997 ;

The vectorization time by photo-interpretation can take several days, whereas the automatic method enables obtaining this vector in less than one hour. There is therefore a considerable

referenced outline (purple).

because only based on the SPOT data.

**5. Discussion and conclusion** 

Yüksel et al., 2008).

All the lava flow outlines' vectors will be available online on the Laboratoire de Geosciences Reunion website.
