干旱区生态环境知识资源中心

Based on the GRACE Level 1b raw data from 2005 to 2010, we have successfully produced an unconstrained monthly gravity field model (Hust-IGG01) up to d/o 60. Unlike the official data-processing centers, we employ the kinematic orbits instead of the GPS measurements as the pseudo observations. Meanwhile, an alternative model (Hust-IGG02) using the reduced-dynamic orbits as the pseudo observations is provided as well. We aim to understand the impacts of orbit pseudo observations on the accuracy of the ultimate gravity products. To this end, Hust-IGG01 and Hust-IGG02 are fully compared to each other, such that we are able to identify which type of orbit pseudo observations is more desired for the gravity inversion. Experiments demonstrate that Hust-IGG01 performs better in terms of signal to noise level than Hust-IGG02 in the following aspects: (a) Hust-IGG01 improves the estimation of geopotential coefficients at low degrees, e.g., C-20 C-60 C-70 C-80 C-90 which are closer to SLR or CSR RL05 results; (b) the induced formal error of Hust-IGG01 is appropriate and comparable to that of GFZ RL05a, while Hust-IGG02 poses too optimistic formal error; (c) over three typical regions of interest (Amazon, Greenland and Sahara), the mass variation derived from Hust-IGG02 has been under-estimated by about 5%similar to 10% with respect to those from the official products, while Hust-IGG01 has achieved a fairly comparable accuracy. The latter is supported by the numerical results such as: the yearly trend of glacial melting over Greenland derived from Hust-IGG01, CSR RL05, GFZ RL05a and JPL RL05 are -125.4 Gt . a(-1), -125.4 Gt . a(-1), -127.3 Gt . a(-1) and -124.3 Gt . a(-1), respectively; the annual amplitude of mass change in terms of EWH (equivalent water height) over Amazon is 17.56 cm, 17.40 cm, 17.46 cm and 17.22 cm, respectively; the RMS of mass change over Sahara desert is 0.87 cm, 0.77 cm, 1.10 cm and 0.87 cm, respectively. An additional validation is undertaken as well, to investigate the performance of Hust-IGG01 on the scale of basins, and the results demonstrate that the induced annual amplitude, semi-annual amplitude and yearly trend of mass variations agree with those of CSR RL05 over the 32 selected major river basins. In summary, our comparisons above suggest that an appropriate kinematic orbit is more beneficial than the reduced dynamic orbits, for the accurate gravity recovery from the GRACE observations.