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The utilization of the altimetric satellite’s on-board radiometer for atmospheric observation is demonstrated. This study uses the Wet Tropospheric Correction (WTC) data from the Topex/Jason altimetry mission series (Topex/Poseidon, Jason-1, Jason-2/OSTM, and Jason-3). The data spans nearly 30 years, making them sufficient for climate study. Precipitable Water Vapor (PWV) is derived from the WTC and used to study the water vapor variability over the Tropical Indian Ocean (TIO). Standard EOF (Empirical Orthogonal Function) analysis on the derived PWV anomaly (PWVA) in the TIO generates two leading modes. The first mode has a dipole spatial structure that explains 18.3% of the total variance, and the second one has a basin-wide homogeneous structure that explains 12.3% of the total variance. Correlation analysis with IOD and ENSO monitoring indices has shown that these two modes are associated with the two interannual variabilities. Further analyses using composite techniques are done to distinguish the different of mechanism and impact between the two. A new monitoring index is proposed here which uses the altimetry-derived PWV anomaly data. The index is computed from the difference of PWV anomaly between the dipole regions in TIO, which effectively describes the activity of the Indian Ocean Walker Circulation (IOWC). This research showcased the feasibility of using the data measured by the radiometer of altimetric satellites for atmospheric studies, a potential continuation of this research would be the use of the synchronous altimeter-radiometer measurement for more advanced analysis such as the ocean-atmosphere coupling.

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Geodetic observation methods, e.g., satellite gravimeter and Global Navigation Satellite System (GNSS), are mainly used for determining the Earth’s gravity field and reference system. However, many efforts have been made to adopt the mentioned methods for estimating hydrological dynamics. The satellite gravimeter of the Gravity Recovery and Climate Experiment and its Following-On missions (GRACE/GRACE-FO) have proven to capture the terrestrial hydrological variation. Also, thanks to its signal propagation through the atmosphere medium, GNSS can be used for sensing the hydrology variation in the atmosphere, i.e., troposphere medium. This study aims to explore GRACE/GRACE-FO and GNSS observations to estimate the respective terrestrial and atmospheric hydrological variation in Bandung, Indonesia. Monthly solutions of GRACE/GRACE-FO provided by three agencies were used to estimate the terrestrial hydrological variation. We also used the continuous GNSS site of ITB1 and calculated the atmospheric hydrological series in the form of precipitable water vapor. We found that the terrestrial hydrological series varies approximately ±20 cm, while the precipitable water vapor ranges between 1 to 5 centimeters. Further, we observed long-wavelength components from terrestrial and atmospheric hydrological variations that correspond to dry and wet seasons. However, we only sensed shorter wavelength components of hydrological dynamic from GNSS observation and not for the GRACE as the estimated hydrological variations were estimated monthly. At the same time, delays were calculated every two hours using GNSS observations. Nevertheless, this study shows the potential uses of geodetic approaches such as satellite gravity and GNSS observations to capture the hydrological dynamic.