Search

SUMMARY: To ensure the global observability of next generation gravimetric mission (NGGM), different agencies have to repeatedly launch satellites to about 89.0° orbit inclination. However, due to the poor isotropy of observation system, only minor improvement in terms of temporal gravity field estimation can be obtained via these repeatedly launched polar pair missions. To ensure the global observability as well as the isotropy of observation system, a near-polar pair mission rather than a polar mission is likely an optimal selection, especially considering that the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission has been already in operation. In this study, for the upcoming NGGMs (for instance, the Chinese NGGM), we design a closed-loop simulation to assess the performance of a near-polar mission at a near-circular orbit with about 500 km altitude for detecting the Earth's temporal gravity field, and the main conclusions are summarized as follows. (1) Based on the statistic results, 85.0° is selected as the optimal orbit inclination for the near-polar mission, which provides 37 per cent noise reduction in terms of cumulative geoid height error in spectral domain, but also 31 per cent noise reduction in terms of mean oceanic root-mean-square (RMS) error in spatial domain when compared to the 89.0° polar mission (89-PM). (2) To figure out the reason of these noise reductions, we also compare the contribution of single error components [including instrument error, atmospheric and oceanic (AO) aliasing error, ocean tide error]. It indicates that the outperformance of the 85.0° near-polar mission (85-NPM) is mainly derived from the relatively smaller non-tidal atmospheric and oceanic mass variation error. (3) Although there are inevitable 5.0° polar gaps in the 85-NPM, the analysis result (including the comparison via in-orbit observations and simulated retrieved solutions) still demonstrates a comparable performance of the 85-NPM in tracking mass variations over the Antarctic, and even an outperformance with 12 per cent noise reduction over the Greenland when compared to the 89-PM. The result confirms the feasibility of implementing a near-polar mission as a stand-alone mission or a complementary observation system for the repeatedly launched polar missions, which offers an alternative option of launching the Chinese NGGM satellites to an 85.0° inclination orbit instead of 89.0°. [ABSTRACT FROM AUTHOR]

The Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE Follow-On mission have been estimating temporal gravity field models for various geoscience applications since 2002. While the errors in atmospheric and oceanic de-aliasing (AOD) model are still the key limitation for GRACE-type missions especially taking advantages of improved laser ranging interferometer (LRI), this paper explores the realistic assumption of continuously reducing AOD model error in global scale and regional scale (e.g. ocean, Greenland, Qinghai-Tibet plateau and South America) in the anticipated future. For this, using a realistic orbit scenario and error assumptions both for instrument and background model errors, the 5-yr full-scale simulations are implemented in the context of 26 scenarios with different AOD model errors. Our overall simulation results demonstrate that: (1) when the AOD model errors are reduced in the global scale, the corresponding gain in temporal gravity field determination is significant, with the cumulative geoid height error decrease from 11.28 to 6.25 mm in spectral domain, as well as 26.3–65.2 per cent noise reduction in terms of mean RMS residuals over ocean in spatial domain. (2) When the AOD model errors are reduced in the regional scale, the improvements of temporal gravity field estimations are diverse in different simulation scenarios. The most notable noise reduction, with 22.9–43.9 per cent noise reduction in spatial domain, is observed when the AOD model error decreases in ocean. The limited noise reductions (0.1 per cent and 1.3 per cent respectively in spectral and spatial domain) are observed in the temporal gravity field estimations if the AOD model is refined in other typical regions such as the Qinghai-Tibet plateau, the Greenland and the South America. (3) However, when the satellites passing over the AOD model refined regions, the along-orbit range rate analysis indicates that, there are visible differences by about 50.0 nm s−1 in terms of range rate residuals as well as 11.0–48.5 nm s−1 in terms of the mean RMS of range rate residuals. These results reflect the benefits of reducing AOD model error in both global and regional scale for improving GRACE-type temporal gravity estimation, especially considering the development of LRI technology. [ABSTRACT FROM AUTHOR]