An Advanced Concept Of Radar Altimetry Over Oceans With Improved Performances And Improved Ocean Sampling : AltiKa
- Paper number
IAC-07-B1.3.06
- Author
Mr. Jacques Richard, AAS-F, France
- Coauthor
- Coauthor
Mr. Eric Caubet, Thales Alenia Space, France
- Year
2007
- Abstract
Space observation and numerical prediction of the ocean surface topography is now considered as an operational service which bring a better understanding of the large and mesoscale ocean phenomena. It is however recognised that the user needs for mesoscale circulation is to further improve the spatial and temporal sampling upon existing systems, with typical objectives of the order of 100 km and 10 days. This goal can be achieved either by a single radar interferometer altimeter operating with a small-off nadir angle to provide swath, or by a constellation of conventional nadir looking altimeter satellites (typically 3 satellites with convenient orbits). The first concept has been proposed by JPL and is known as Wide Swath Ocean Altimetry (WSOA). The swath altimetry concept is inherited from mono-pass interferometric side looking radar. The side looking geometry provides a swath as for SAR imagery for instance. Two spaced antennas and receiving chains provides two complex images with slightly different incidence angles in the across-track direction. The two images are complex multiplied to provide an interferogram. For each radar range gate, the phase of the complex interferogram is related to the angle of arrival in the across-track direction. The radar range and the angle of arrival allows to retrieve the ocean surface elevation. Such a concept is quite challenging given the suggested size of each antenna (2.2 m x 0.3m), the length of the baseline (10 m), the required antenna subsystem geometry stability and the necessity to unfold the full antenna system after launch. CNES (French Space Agency) has been considering the second solution presenting lower technical difficulties, development costs and risks than WSOA concept. It is based on a new class of altimeter allowing the compatibility of the altimetric payload (altimeter, localisation system, radiometer) with a micro-satellite. The key feature of the altimetric payload has been the selection of the Ka-band for the single-frequency altimeter. The selection of the Ka-band (around 35 GHz) for the altimeter avoids the need for a second frequency (necessary when using Ku-band) to correct the ionosphere delay and allows the same antenna to be shared by the altimeter and the radiometer. This single antenna solves the problem of accommodation of a conventional altimetric payload on a micro-satellite (150 kg class). This concept allows also the improvement of the range measurement accuracy in a ratio of 3:1 thanks to the use of a wider bandwidth and to a better pulse to pulse echo decorrelation. This mission concept is named AltiKa. The development of AltiKa payload has started in January 2005 for a delivery in 2008 and a launch by mid 2009. The paper will describe the AltiKa program : the mission, the instrument design, the key technologies involved, the altimeter parameters, the anticipated performances, the whole payload design and budgets, and the micro-sat configuration. A status of AltiKa development will be given.
- Abstract document
- Manuscript document
IAC-07-B1.3.06.pdf (🔒 authorized access only).
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