SARAL/AltiKa's main scientific objective is the observation of the ocean circulation at meso-scale.
Ocean meso-scale variability is defined as a class of high-energy processes, with a scale ranging from a few dozen to a few hundreds of kilometres and with periods of a few days to one year. Kinetic energy of meso-scale variability is one order of magnitude more than mean circulation’s one. Description of meso-scale is thus essential for understanding ocean dynamics, including mean circulation and its climatic effects (through interactions of meso-scale turbulence with the mean flow).
SARAL/Altika's main scientific objective is divided in sub-themes including:
- Intrinsic scientific studies of ocean at meso-scale dynamics: observations, theoretical analyses, modelling, data assimilation, parameterization, etc.
- Improvement of our understanding of the oceanic component in the climate system: investigation of local processes at small or medium scale poorly known and understood at present, but which have an impact on the modelling of climate variability at large spatial and temporal scales.
- Contribution to the study of coastal dynamic processes, especially small or medium scale phenomena, whose retrieval will enable to anticipate many downstream applications.
- Contribution to operational oceanography which is seeking large amounts of in situ and space observation data.
SARAL/Altika's secondary objectives are notably the monitoring of the main continental water levels (lakes, rivers, closed seas), the monitoring of mean sea level variations, the observation of polar oceans, the analysis and forecast of wave fields, the study of continental ices (thanks to improved performances of Ka-band) and sea ices, the access to low rain climatology (enabled in return for the sensitivity of Ka-band to clouds and low rains), and the marine biogeochemistry (notably through the role of meso and sub-meso-scale physics).
Altika, A high accuracy oceanographic altimeter
Radar altimetry by satellite is a technique used in oceanography to measure, globally over the oceans, the sea level needed to understand ocean circulation and its variability.
The Altika project developed by CNES is based on a large Ka-band altimeter (35.75 GHz, 500MHz), 1st oceanographic altimeter to use such a high frequency. The use of the Ka-band frequency will supply more accurate measurements (improvement of the spatial and vertical resolution) enabling a better observation of ices, coastal areas, continental water bodies as well as wave height.
The Altika project is part of the operational satellite altimetry system, jointly with Jason-2, and ensures the service continuity which is nowadays provided by the Envisat altimeter jointly with Jason-2 and Jason-1.
By ensuring observation continuity and widening the observation areas, CNES answers the wish of the oceanography community by bringing a description:
- for the meso-scale in open ocean,
- in coastal areas,
- for seasonal forecast,
- for climate studies.
Altika data will thus contribute, along with data from other altimetry missions, to the development of operational oceanography, to our understanding of the climate and to the development of forecasting capabilities through the improvement of data assimilation methods in ocean-atmosphere coupling models, bio-chemistry models, etc.
The high resolution altimeter Altika integrates a bi-frequency radiometric function to correct altimetry measurements from wet troposphere effects. Altika is coupled with the precise orbitography system, DORIS, associated to a laser reflector, in order to determine accurately the satellite position on its orbit.
With the ARGOS-3 mission instruments, the whole Altika payload has been set on board the SARAL satellite, developed in cooperation with ISRO (Indian Space Agency) which provides the platform and ensures the prime contractorship of the satellite, its launch, and the control/command operations. CNES provides the Altika payload and ensures the data reception and processing by using SALP services (Service d'Altimetrie et de Localisation Precise). Two other processing centres process Altika data: EUMETSAT for the real time, ISRO for the real and delayed-time data. The Saral Satellite was launched on 25 February 2013 at 12:31 UTC.