4 Final Report - Emits - ESA

5 Final
Report
5 Recommendations on further Analysis
5.1 System Analysis
Detailed analysis of the manoeuvre times
A driving aspect of the mission performance is the manoeuvre time of the system to point from on
observation pattern to the next. Depending on the configuration of the AOCS, the limiting factor is the
settling time to achieve the desired level of stability after the active part of the manoeuvre. It has been
identified that especially the characteristics of the solar array are of relevance for the settling time.
It is highly recommended to analyse the manoeuvre times in more detail, especially concerning the
characteristics of large structures as the solar array, in order to consolidate this important aspect of
mission performance at a high level of confidence.
Detailed investigation of microvibration aspects
At the required level of attitude stability, the microvibrations from momentum wheels, solar array drive
and, if applicable, of an antenna pointing mechanism have to be minimized and/or compensated. A
detailed analysis of the microvibrations and the means of reductions is highly recommended for the
further study phases.
5.2 Mission Objectives and Data Processing
At least two major issues remain at this stage of the GEO study. First the need to strongly consolidate
the user’s requirement, second the temporal coverage specificity of the GEO (compute the optimal
revisit frequency to get one clear image per days, based on the Eumetsat cloud products archive and
taking into account ocean colour geometrical limitations).
Additional proposed tasks:
• Justification of the GEO concept for OC. A less demanding requirement on the temporal
coverage is to be able to detect the daily oceanic structures (like Chlorophyll gradient).
Contrary to purely numerical techniques of “optimal interpolation” trying to fill the gap of LEO,
the GEO concept could directly supply the physical data in a progressive way among the
day. It is proposed to analyse the progressive detection of Chlorophyll structure (i.e.
progressive improvement of the gradient computation with increasing clear zones along the
day), as a function of the number of acquisitions, and to derive the minimal revisit
requirement which suits current operational services in structure detection.
• Air mass issue and atmospheric correction. There is a big need to have a radiative
transfer modeling tool in spherical coordinates, in order to access the realistic air mass
requirements. To our knowledge such a code is not available to the Ocean Colour
community in Europe and could be developed.
• Coverage analysis The user requirement on temporal coverage refers to two main aspects:
− need to have several images per day in order to built one daily cloud-free synthesis (e.g.
phytoplancton map)
− need to have several clear images per day in order to follow rapid events (e.g. tides, NRT
water quality monitoring).
The analysis conducted so far on "availability coverage" used a very high revisit time (15
min) and is thus not exactly scaled to the requirements and potential of Geo-Oculus (agility
for pointing on cloud-free region). An acquisition scenario that would optimise the cloud-free
region, taking into account the realistic duration of acquisition, pointing and stabilization
Doc. No: GOC-ASG-RP-002 Page 5-87
Issue: 2
Date: 13.05.2009 Astrium GmbH