4 Final Report - Emits - ESA

3 Final
Report
Manoeuvre Times and Image Acquisition Times
The manoeuvre times can be separated into two contributors:
• Actual manoeuvre time;
• S/A tranquillisation time.
The actual manoeuvre time depends on the size of manoeuvre, chosen technology (wheel size, etc.)
and manoeuvre strategy.
The S/A tranquillisation time depends mostly on the pointing drift required for the image acquisition
(the more challenging the requirement, the longer the tranquillisation time). An allocation of 70
seconds per manoeuvre has been considered.
3.4 Cloud Coverage Analysis
Two of the key features of Geo-Oculus, the possibility for real-time commanding and the capability for
short revisit cycles have been found to give an essential asset in order to maximise the mission
performance - the optimisation of mission planning for cloud cover. The intention of this analysis has
been to identify the potential of Geo-Oculus that can be gained, to validate the system requirements,
to identify a possible optimisation strategy and to assess the performance compared to reference
missions.
Due to its geostationary orbit, Geo-Oculus has the capability to access every spot within its footprint at
the time the spot becomes cloud free. Considering the applied FOV and the possible agility of the
system, this capability confined. In result only a certain image acquisition frequency is achieved;
hence a selection of the images is required. This leads to the point that the system will have to apply a
permanently updated optimisation of the mission planning, to gain maximum possible ground
coverage. This optimisation should take into account the current cloud cover situation, possibly
supplied by MTG and Metop, the changing illumination conditions throughout the entire day, nowcasting
and short range forecasting information on the expected cloud cover situation and the
constraints placed by the on-demand missions.
In the analysis described in here, a simplified optimisation strategy and mission planning have been
used, considered to represent a realistic approach. This strategy accounts for the illumination
conditions and maximises the achieved ground coverage.
The entire cloud coverage analysis is based on cloud mask data from MSG with a revisit time of 15
min. The time span, considered in this analysis range from 01/2004 to 05/2007. In a preliminary low
level analysis representative days for a detailed evaluation of the cloud coverage are filtered out of the
complete dataset. To gain representative results from the analysis, representative days are indicated
by analysing every day concerning:
• Cloud amount
• Cloud coverage changes
• Time of sufficient illumination conditions
By comparing the values of each day with the mean value of the whole data set, several days for
detailed analyses have been indicated.
Page 3-22 Doc. No: GOC-ASG-RP-002
Issue: 2
Astrium GmbH Date: 13.05.2009