On the use of GRACE measurements of inter-satellite range-rate (aka L1B data) for exploring dynamics of surface water and soil moisture storage in the Amazon

To push the limit of the GRACE's capability to advance hydrology and climate sciences, we have been developing a novel approach exploiting instantaneous measurements of distance change between two GRACE satellites (aka L1B data product). By utilizing fundamental orbit perturbation data, the highest possible temporal and spatial resolution can be maintained in the respective geophysical analysis. Various post-processing techniques, often applied to monthly time-series of global gravity maps (aka L2 data product), are not required, because our method bypasses the gravity inversion process. For the most straightforward comparison and assessment of hydrology and other geophysical models, our approach suggests forward computation of inter-satellite orbit changes from hydrology and other geophysical models and direct comparison with the in situ L1B measurements from GRACE. In this talk, I overview our approach, highlight advantage, discuss limitation, and present the recent examples of what we have learned from our new approach over the Amazon basin. We quantified the amount of surface water in the channels and floodplains to be as large as soil moisture perturbing the motions of the satellites to a detectable amount by GRACE. We found the effective velocity for runoff routing throughout the Amazon basin over the years to be about 30 cm/s but with significant seasonal change. The lower velocity, during rising stages and peak water season, and the faster velocity, during falling stages, could be delineated from the GRACE L1B observations. Lastly, I explore a possibility of direct assimilation of GRACE L1B tracking data to improve land surface dynamic processes by resolving the average time scale of transport in rivers and streams.