Abstract
HaiYang-2A (HY-2A, where ‘Haiyang’ means ‘Ocean’ in Chinese) has provided reliable sea surface height observations for gravity with uniform ocean data coverage on a global scale for more than 8 years, particularly with denser across track sampling during the geodetic mission since March 2016. This paper aims at modeling and evaluating the regional marine gravity field at 1′×1′ resolution by incorporating HY-2A altimeter waveform data from 7 complete 168-day cycles in the geodetic mission phase. Initial evaluation indicates that, firstly, the measurements in the geodetic mission stay at a consistent accuracy level with observations at the start-of-life stage according to statistics of discrepancies at crossover points cycle by cycle. Secondly, range precision improvement can be achieved using a two-pass weighted least-squares retracker. Thirdly, a downsampling procedure combined with a low-pass filter is designed for HY-2A 20 Hz data to obtain 5 Hz measurements with enhanced precision. We calculate the 1′×1′ marine gravity field model over the South China Sea area by using the EGM2008 model as a reference field with the remove/restore method. The verifications with published models and shipborne gravimetric data show that HY-2A GM data is capable of improving marine gravity field modeling. Results show slightly higher accuracy than other models with similar input datasets but not including HY-2A. The accuracy is also compared with the latest DTU17 and SIO V27.1 model.
Highlights
Accurate knowledge of marine gravity anomalies is essential for a range of scientific and engineering applications, such as earth gravity modeling, oceanic resources exploration, submarine topography inversion, and yielding insight into the structures of the lithosphere [1,2,3,4]
Similar to the HY-2A exact repeat mission (ERM) data [18], we find that the noise level for two-step retracked data is 1.6 times lower than that for one-step retracked data and retracked results from Sensor Data Records (SDR)
Two-pass waveform retracker, which was known for optimal gravity recovery, was adopted for HY-2A
Summary
Accurate knowledge of marine gravity anomalies is essential for a range of scientific and engineering applications, such as earth gravity modeling, oceanic resources exploration, submarine topography inversion, and yielding insight into the structures of the lithosphere [1,2,3,4]. Over the past few decades, satellite altimetry has evolved as an effective tool for recovering regional or global marine gravity fields. The improvement of the marine gravity field model mainly relies on the improvement to range precision and spatial resolution of accumulated multi-satellite altimeter measurements, especially those from geodetic missions (GM) [6,11]. Studies show that retracking techniques significantly improves the accuracy of the recovered marine gravity field, even in marginal seas and sea-ice covered regions [12,13,14,15,16]. Marine gravity field modeling has gone through huge improvement since the completion of the Jason-1 geodetic mission and accumulation of the CryoSat-2 data with a repeat period around
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