Intercomparison of Geophysical Parameters From SARAL/AltiKa and Jason-2 Altimeters

Abstract

SARAL/AltiKa (AltiKa), a Ka-band altimeter is a joint Indo-French satellite mission launched on 25th February, 2013 by Indian Space Research Organization (ISRO). During the calibration/validation phase of the mission, it is essential to calibrate this altimeter and evaluate its performance for further use by the oceanographers’ community. With this objective, geophysical parameters namely significant wave height (SWH), wind speed (WS), and sea surface height anomaly (SSHA) from Jason-2 are used to assess the performance of AltiKa quantitatively. Additionally, certain supporting direct and indirect measurements from altimeters and radiometers onboard the two missions like normalized backscatter coefficient (Sigma0), brightness temperature ( ${{\rm T}_{\rm B}}$ ), water vapor (WV), and corresponding ionospheric corrections (IC) have also been analyzed. Global analyses show that the various parameters obtained from the two missions are in good agreement with each other even at 95% confidence level. Furthermore, ocean-wise regional analysis reveals that SWH from AltiKa is consistent with those from Jason-2. SSHA from AltiKa and Jason-2 shows a better agreement over the Indian Ocean with correlation coefficient (R) of 0.90 as compared to the Pacific or the Atlantic Oceans. Statistical analyses of other supporting parameters namely ${{\rm T}_{\rm B}}$ and WV from radiometers and IC from global ionosphere maps (GIM) model reveal that values for AltiKa and Jason-2 also compare well with bias [root-mean-square error (RMSE)] of 2.94 K (3.17 K), $\text{0}.\text{65}\;{\text {kg}}/{\text {m}^{2}}$ ( $\text{1}.\text{72}\;{\text {kg}}/{\text {m}^{2}}$ ), and 0.04 m (0.0008 m), respectively. The overall statistics are quite encouraging and envisage the great potential of AltiKa observations for oceanographic applications.