Detectability of Water Level along Yaluzangbu River Demonstrated by Envisat, Jason-2, and SARAL/AltiKa

Abstract:

Periodic and flash flood is one of major natural disasters happened annually in mainland South Asia, especially for countries within the basin of Ganges, Brahmaputra, and Mekong River. The flood either caused by massive rainfall or melting glacier/snow water has combined with land subsidence and results in exacerbated economic loss in adjacent regions. A monitoring system based on satellite observation is thus necessary for early warning and precautionary estimate of inundation area since it is difficult to build river gauges and collect data in remote areas. The knowledge of water level along the river is thus important for monitoring the anomalous rise of water flow that potentially causes floods downstream. The satellite altimetry, which was widely used for open ocean sea-level measurements, had been applied for monitoring inland waters, such as rivers, reservoirs, and even glaciers surface elevation change. In this study, we utilized and compared a series of altimetry satellites along the Yaluzangbu River, upstream of the Brahmaputra River, located in the southern Tibetan Plateau with its origin located at Angsi Glacier. These satellites include Envisat, Jason-2, and SARAL/AltiKa. The detectability of water level has been examined in terms of the backscattering coefficient in radar echo, radar waveform pattern, height retrieval, stability of measurement over water surface, and percentage of detectable crossovers. Our preliminary result shows that the Ka-band AltiKa is more stable over narrow (<500 m) rivers section with height uncertainty in each cycle less than 10 cm, in contrast to Jason-2 and Envisat which are limited to tens of centimeters level.