HY-2A Altimeter Data Initial Assessment and Corresponding Two-Pass Waveform Retracker

Abstract

The accuracy and resolution of the marine gravity field derived from multisatellite altimeter data sets mainly depend on the corresponding range precision and spatial distribution. Here, we preliminarily investigate the performance of HY-2A altimeter data by analyzing cross-mission sea surface height discrepancies with SARAL/AltiKa and calculating correlation coefficients with respect to tide gauge measurements. We also explore the improved range precision that can be achieved using a two-pass weighted least squares retracker which was proposed for the purpose of optimal gravity field recovery. Firstly, both the exact repetitive mission and the geodetic mission for HY-2A provide new track orientations and different data coverage for recovering the marine gravity field, and these dense geographical distributions are more greatly attributed to the geodetic mission in recent years. Secondly, HY-2A provides reliable sea surface height measurements based on exterior verifications by SARAL/AltiKa geophysical data records and tide gauge measurements, although the accuracy level is slightly lower than SARAL/AltiKa. Another more exciting finding is that the statistics of along-track sea surface heights in one-second intervals show that the two-pass retracking does further improve the range precision by a factor of 1.6 with respect to 20 Hz retracked results in sensor data records. In conclusion, the HY-2A mission can substantially improve the global accuracy and resolution of the marine gravity field and will reveal new tectonic features such as microplates, abyssal hill fabric, and new uncharted seamounts on the ocean floor.

Inversion and Validation of Improved Marine Gravity Field Recovery in South China Sea by Incorporating HY-2A Altimeter Waveform Data

“…NC_A and NC_B denote the number of crossover points after and before deleting outliers, respectively. Unit: m. Compared to crossover statistic values in earlier HY-2A studies [18,19] for the ERM, the latest GM measurements stay at a consistent accuracy level with respect to ERM observations. A noticeable decrease in standard deviation (STD) values is observed for measurements within 1 day compared to those with no time limit.…”

“…HY-2A started its geodetic mission in March 2016, and the revisiting period extended to 168 days from the original 14 days during exact repeat mission (ERM). has verified that HY-2A provides reliable measurements and shown that the two-pass waveform retracker enhances the range precision by a factor of 1.6 [18]. A previous study, conducted by Zhu et al (2019) indicated that HY-2A can provide similar marine gravity recovery to other altimeters on the basis of 1 Hz measurements [19].…”

“…The thermal noise and square of the antenna mis-pointing angle are treated as constant parameters but need suitable pre-determination. In the second step, the rise time parameter is smoothed along-track and being fixed, before retracking the waveforms again using a two-parameter Brown model (arrival time and amplitude) [18]. Either the former three parameters or the latter two parameters will be solved during a weighted least squaring procedure.…”

“…The power M(t) in HY-2A waveforms can be modeled by Equation 9, where A is the amplitude, t 0 is the arrival time, t is time for each sample gate, σ is the effective pulse length, and α is the trailing edge decay factor relate to the antenna mis-pointing angle [18]. The effective pulse length σ can be calculated from…”

Global Bathymetry and Topography at 15 Arc Sec: SRTM15+

“…The first was the integration of global shipboard sounding compilations, which are used to calibrate the predicted depths (Smith & Sandwell, ) and as ground‐truthed “pins” (e.g., Becker et al, ; Smith & Sandwell, ) to provide high‐resolution mapping where available. The second was the development of custom waveform picking algorithms, tuned for optimal sea surface slope recovery (e.g., Garcia et al, ; Sandwell & Smith, , ; Zhang & Sandwell, ; Zhang et al, ).…”