Design and performance analysis of a future satellite gravity mission for monitoring mass transport in the Earth’s system

PhD student: Pedro Inácio

The success of the recent GRACE satellite gravity mission has demonstrated the feasibility to directly measure mass redistribution in the Earth’s system from space. In particular the redistribution of water can be observed, which is critical for monitoring key climate indicators such as ice-sheet mass balance, terrestrial water-storage change, sea-level rise, and ocean circulation.

The designed mission lifetime of GRACE is 5 years; currently, GRACE is in its 10th year of operation, and it is unlikely that it will last beyond 2013. The unique capability of SG missions to directly monitor mass transport processes in the Earth’s system, some of which are key indicators of climate change, have initiated activities within space agencies towards a next generation of SG missions.

The objective of this project is to study the key elements of a future global mass transport observation system based on Satellite Gravity (SG) which will allow the observation of mass transport processes with unprecedented spatial resolution. The backbone of the project is a systematic inventory and analysis of the limitations that play a role in future SG missions along with an investigation of possibilities to overcome these limitations.

In defining the optimal set-up of the future satellite gravity mission, the SG data acquisition and processing will be reproduced as realistically as possible. This will include: (i) computation of satellite orbits on the basis of a realistic force model, including high-frequency gravity field variations associated with rapid mass transport in the Earth’s system; (ii) computation of primary observables, including a realistic simulation of sensor noise on the basis of available information about current and future sensors (typically provided in the form of a power spectral density); (iii) conversion of the observed quantities into parameters describing temporal variations of the Earth’s gravity field and the associated mass transport; and (iv) assessment of the obtained results, including the optimal filtering of the computed solutions (for an efficient suppression of noise) and a comparison with “true” gravity and mass variations in the global and regional context. The latter item will allow analyzing the effect of the mission design on the need for filtering and the implications this has for filter design.

In the course of the project, the GRACE mission set-up will be consistently used as a benchmark. Real data acquired by this mission are routinely available, so that results of simulations can always be compared with those data for validation and calibration purposes. It is foreseen that the following issues will be the subject of the primary concern during the project: (i) temporal aliasing; (ii) inaccurately known satellite orbits; (iii) anisotropic sensitivity; (iv) limited spatial resolution (v) choice of satellite formation type.

The proposed studies will allow the optimal concept of a future SG-based mass transport observation system to be defined. At the final stage, the identified concept will be critically evaluated and its parameters will be fine-tuned to ensure that the best performance can be reached with the minimal technical risks and costs.

RHOME, Design Synthesis Exercise 2010