Waveform Classification and Water-Land Transition over the Brahmaputra River using SARAL/AltiKa & Jason-2 Altimeter

摘要

With technology development and reduced foot print size of recent altimeters, estimation of water level height of inland water bodies with sub-meter level accuracy at the global scale with reasonable temporal and spatial resolution is possible. SARAL/Altika is the first altimeter working in very high frequency of Ka (36.5GHz) band. SARAL has 500 MHz bandwidth so the pulse width is reduced to 2 ns and effective footprint is reduced to 1.3 km for calm surfaces. The Brahmaputra River is one of the biggest rivers of the India located in the northeastern part of the country. Here in this study we have done waveform classification of Ka band and Ku band waveforms for Saral and Jason 2 respectively. We have analysed total 3000 Ku band waveforms of Jason-2 and 1000 Ka band waveforms of SARAL. We have classified different types of waveforms like Brown shaped, spiked, double spiked, multi spikes in leading edge, multi spikes in trailing eadge, very low power waveforms on the basis of their shape. Here we have studied the land to water and water to land transition of satellite altimeter derived from the change in the shape of wavefrom as a first step towards the waveform retracking for the water level estimation. As satellite approches from land to water, midpoint of leading edge shifts, power increases and number of peaks in the trailing edge decreases. The reverse pattern can be seen the water to land transition. We also showed seasonal variability of water spread of the Brahmaputra River. Geophysical corrections have major impact on the retrieval of water level from altimeter waveforms. We have also analyzed DTC (Dry Tropospheric Correction), WTC (Wet Tropospheric Correction) and IC (Ionospheric Correction) which we have applied to the range for the water level estimation of Brahmaputra River.