SARAL/AltiKa measurements for geodetic applications: Impact of drifting and mispointing phase data

Abstract

The Indo-French SARAL/AltiKa mission in Ka band has provided valuable information on global oceans to cater the needs of oceanographic community. The SARAL/AltiKa has been operating in three different orbital configurations, viz. Exact Repeat Mission (ERM, March 2013 – July 2016), Drifting Phase (DP, July 2016 – February 2019) and Mispointing Phase (MP, February 2019 – till date). We investigate the utility of the SARAL/AltiKa data for geodetic applications. Global crossover analysis of Sea Surface Height (SSH) measurements from SARAL/AltiKa suggests a stable performance throughout its life with similar range of standard deviations during ERM (5.8 cm), DP (5.9 cm) and MP (5.9 cm) configurations. Two separate Mean Sea Surface (MSS) models were retrieved by adding DP and MP data from SARAL/AltiKa to the ERM stacks of SARAL/AltiKa and Jason satellite series. The quality of MSS models were evaluated based on the crossover differences with the ERM database. It is observed that the crossover adjustments have reduced the deviations in SSH errors by ∼30% for both DP-MSS and MP-MSS models. Analysis of along-track sea surface slopes suggests that 99.9% of data in ERM and DP phases and 93.8% of data in MP phase are well within 1 μrad bound corresponding to an accuracy of ∼1 mGal in free-air gravity anomaly. Further, time-series analysis of Sea Level Anomaly (SLA) from SARAL/AltiKa showed a stable performance with no significant drifts throughout its phases. Deviations in daily SLA for SARAL/AltiKa DP (10 cm) is considerably lower than that of Jason-3 (10.2 cm) and CryoSat-2 (10.2 cm) satellites. However, daily SLA for the MP phase showed slightly larger deviation (10.4 cm), owing to the larger number of outliers, which could be easily removed using a simple median filter. The present study reveals the usefulness of MP data from SARAL/AltiKa for geodetic applications.