Results from the First Year of Swarm GPS Receiver and Accelerometer Data.

Thursday, 18 December 2014: 2:00 PM
Eelco Doornbos1, Christian Siemes2, Radek Peřestý3, Jiri Kraus3, Aleš Bezděk4, Jose van den IJssel1, Joao Encarnacao5, Pieter N Visser1 and Sean Bruinsma6, (1)Delft University of Technology, Aerospace Engineering, Delft, Netherlands, (2)European Space Research and Technology Centre, Noordwijk, Netherlands, (3)VZLU, Prague, Czech Republic, (4)Academy of Sciences of the Czech Republic, Astronomical Institute, Prague, Czech Republic, (5)Delft University of Technology, Aerospace Engineering, Delft, 5612, Netherlands, (6)CNES French National Center for Space Studies, Toulouse Cedex 09, France
One of the mission objectives for Swarm is to study the dynamics of the upper atmosphere, under the influence of the Sun and Earth's magnetic field. For this purpose, each of the three satellites carries a sensitive three-axis accelerometer, an accurate GPS receiver and a laser retroreflector. The GPS receiver data is used both for calibration of the acceleration data, as well as for precise orbit determination. Validation of the precise orbits with independent satellite laser ranging data confirms that the location of each of the three satellites is known to within 2 cm.
The data from both the accelerometer and GPS receiver can be used to derive a data set of thermospheric density along the satellite tracks, in a similar way as has been done using CHAMP, GRACE and GOCE. The acceleration data is combined with information on the satellite attitude from the star cameras, and models of the aerodynamic and radiation pressure forces. When density and drag levels are high enough in the future, possibly data on the neutral wind speed in the satellite's cross-track direction can be derived as well.
During commissioning, it was found that the accelerometer observations are affected by a large number of bias jumps, as well as a much larger than expected sensitivity to variations in on-board temperature. This presentation will provide details on investigations into corrections for these effects, as well as on the quality of the density data resulting from the acceleration measurements from the three Swarm satellites.