GOCE – Specific Tasks on Fine Gravity Field Structure of the Earth
This grant project began in September 2007. It consists of 4 areas of simulations and preparation for the actual GOCE data (which will be available in summer 2010). The following items are studied:
1. Orbit choice and tuning for GOCE measuring phases.
2. Novel geodetic computational methodologies.
3. Comparison of detailed satellite and terrestrial data.
4. Detection of hidden impact (meteoritic) structures on the Earth surface.
1. Following the successful insertion of GOCE in its orbit on 17 March 2009, we closely followed the actual orbital decay of the spacecraft from the initial altitude of 280 km in a nearly “free-fall” regime, where the commissioning of the onboard instruments took place. We analyzed both this early orbit phase as well as the repeatability conditions of the planned GOCE orbits during the measurement operational phases (MOPs).
2. The modern computational capabilities will enable us to process the GOCE data in a full complexity allowing to determinate the geopotential parameters with the complete information about its inner accuracy stored in the covariance matrix. Such a matrix is a suitable tool for error estimation of the derived potential quantities. The main aim for the year 2010 is to continue both in the gradiometry itself and in the combination with the satellite altimetry data. Namely the second topic is now studied in a close cooperation with DGFI in Munich. Objectives for further study are outlined and will be presented at EGU 2010 in Vienna and at the ESA Living Planet symposium in Bergen. They concern research on the non-traditional parametrizations of of the GOCE observations (poster for Vienna), returning to Hotine’s formulae, and a testing of the methods upwarding the gravitational quantities from the ocean surface (given by satellite altimetry) to the GOCE altitude for the validation purposes.
3. The mathematical apparatus formulated in the initial phase of the project was coded and tested in various alternative settings by using both simulated (synthetic) and real gravity data. The gravity field model is being solved in terms of a database of discrete values of the gravity potential (or geoidal heights) in the grid of curvilinear coordinates (either spherical or Gauss-ellipsoidal coordinates). This solution is particularly advantageous for spatially limited gravity observations that represent functionals of the gravity potential, namely its first- (gravimetry) and/or second-order (gradiometry) directional derivatives (gradients). These data are collected in space and time by various sensors located at the Earth’s surface (ground/marine gravimetry), aircraft (airborne gravimetry) and spacecraft (spaceborne gravimetry and gradiometry).
4. We have surveyed the Earth with the 2160×2160 gravitational potential model EGM 08 using both its computed gravity anomalies in spherical approximation and second radial derivatives. Over most of the well known impact crater sites we find the second derivatives offer finer discrimination of the circular features than the anomalies themselves. We also find indications for double or multiple impact craters instead of single crater which need further ground verification by geophysicists and geologists.