KEYS TO ANALYZE ACTIVE LAHARS FROM PINATUBO ON SAR ERS IMAGERY

Two ERS-1 SAR scenes have been acquired over Mt. Pinatubo, before and during the rainy season, respectively on 9 July and 13 August 1993. Th e last one is coeval with typhoon and subsequent lahar activity. From field observations and consideration of physical properties of lahar s urfaces, we decipher keys to detect areas covered by recent and active lahars. The main physical characteristics to consider are surface rou ghness, soil moisture, and morphology. Color compositions show differe nces between the two dates. Recently deposited lahars may have high or low roughness at the surface and are wet. Running lahars have a tumul tuous rough surface. Recently deposited or running lahars have high ba ckscatter values which differ from low values of more ancient flat smo oth-surfaced dry lahar sediments or lahars covered by shallow quiet wa ter. Shallow quiet waters covering more ancient rough lahar surfaces a re also detected. Anastomotic streams, fanlike patterns, closure or in filling of lakes, and migration of streams are also morphologic expres sions of lahar deposits. Flooded areas during typhoons can be recogniz ed from their location in large coastal plains, while lahars occur alo ng main river beds and nearby. (C) Elsevier Science Inc., 1997.