wind energy resource evaluation in a site of central italy ... - WindSim

Table 4.2: Description of the colors used in the overlaid map.DESCRIPTIONRocks, stones and plowed terrainForestUrban areasCOLORBlueTransparentRedThe analysis of the previous picture shows a good agreement between theroughness map and the satellite picture, demonstrating that the whole area is welldescribed. Anyhow, there is evidence of some particular zones which are not exactlydescribed by the contour lines. In fact, the yellow color of the picture (relative to thesatellite image) should be totally covered by the blue color (relative to theroughness map), equal to Z 0 = 0,03 m.Some disagreement in the zones far from the plateau is not important and errors inthe roughness should not influence in a strong way the final results in the area ofinterest. Nevertheless, the better the area very close to the plateau is described themore precise the result are.A more detailed comparison between the two maps can be accomplished by theimage 4.7, showing the roughness contours drawn upon the satellite image at themaximum possible resolution (30 meters).It is confirmed that some zones are not covered by vegetation as converselyrepresented in the roughness map. Despite of this slight disagreement, theroughness map has not been modified.Finally, a further consideration should be done: the satellite map, extracted fromGoogle Earth software, can contain irregularities and be some years old.54