Evaluation of SARAL / AltiKa Measured Significant Wave Height and Wind Speed in the Indian Ocean Region

Abstract

Significant wave height (SWH) and wind speed (WS) estimated by AltiKa are evaluated using in situ measurements and Jason-2 observations over the Indian Ocean region (30°S – 30°N and 30°E – 120°E). SARAL carried a Ka-band altimeter (AltiKa) along with a dual frequency radiometer onboard. This is the first altimeter operating in such high frequency of 35.75 GHz. Advantage of this high frequency is the narrow foot print of the satellite, which is useful for studies related to coastal regions, with the limitation of high attenuation to rain. From the validation exercise with in situ data for 21 cycles of AltiKa high resolution 40 Hz data, it is observed that the SWH is good while little underestimation of WS is observed. The root mean square error (RMSE) and bias of SWH are 0.21 m, −0.04 m respectively with a scatter index of 0.13; whereas in the case of WS, the RMSE and bias are 1.75 m/s, 0.25 m/s respectively with scatter index of 0.30. Inter-comparison is carried out between AltiKa and Jason-2 at all the cross over points in the Indian Ocean region and the SWH and WS of these two altimeters are in good concurrence with each other with the bias and RMSE of 0.03 m and 0.35 m for SWH and 0.01 m/s and 1.45 m/s for WS. From this study of Ka-band altimeter, it is inferred that the quality of the products is extremely good which is also capable of picking up accurate SWH during extreme events.