Towards development of a consistent orbit series for TOPEX, Jason-1, and Jason-2

International audienc

OSTM/JASON-2 Cal/Val results from the Eastern Mediterranean altimeter calibration network - eMACnet

Summarization: The eastern Mediterranean altimeter calibration network (eMACnet) is the result of the expansion of ongoing collaborative efforts in the Aegean area. By 2003 we had established the Gavdos permanent absolute calibration facility, a joint EU, NASA, and the Swiss Federal Government effort. This was further expanded with NASA funding over the past three years to include a second site at Kasteli, Crete, Greece, both of these sites operating with the collaboration and efforts of the local team from the Tech. Univ. of Crete. The two sites at Karave, Gavdos, and Kasteli, Crete are located under the OSTM/JASON-2 ground-tracks (pass 018 and passes 018 and 109 respectively). The Gavdos "Karave" facility is now being relocated to its final and originally intended location, on a new pier, a move that will improve vastly the protection of the facility from heavy winter storms and minimize the need for maintenance. Over the past year our team expanded to include the Nation. Tech. Univ. of Athens (NTUA), the Hellenic Center for Marine Research (HCMR) and the Hellenic Navy Hydrographic Service (HNHS), in an attempt to obtain at a minimal cost data from existing facilities operated by these groups and future sites that are now being deployed. The primary purpose of the extended network is the calibration and validation of altimeter data from current and future altimetric missions. The location of some of our sites though is such that they are also of interest to tsunami warning network operators and we thus intend to provide our observations in real-time from these sites to the European Tsunami Warning System (TWS). Some of the new sites are HCMR open sea buoys that we will collaboratively instrument with additional equipment to allow their data to contribute to the calibration/validation process. In addition to an overview of the project, we will present initial results from the expanded network, covering the tandem flight phase of JASON-1 & -2 based on the latest release of JASON-1 GDRs (C).Presented on

Space Applications

Signals transmitted by global navigation satellite system (GNSS) satellites are not confined to the surface of the Earth but can likewise be used for navigation in space. Satellites in low Earth orbits, in particular, benefit from a similar signal strength and experience a full-sky visibility. On the other hand, the harsh space environment, long-term reliability requirements and the high dynamics of the host platform pose specific challenges to the design and operation of space-borne GNSS receivers. Despite these constraints, satellite manufacturers and scientists have early on started to exploit the benefits of GNSS technology. From the first flight of a Global Positioning System (GPS) receiver on Landsat-4, GNSS receivers have evolved into indispensable and ubiquitous tools for navigation and control of space vehicles. Following a general introduction, the chapter first describes the specific aspects of GNSS signal tracking in space and highlights the technological challenges of space-borne receiver design. Subsequently, the use of GNSS for spacecraft navigation is discussed taking into account both real-time navigation and precise orbit determination. Relevant algorithms and software tools are discussed and the currently achieved performance is presented based on actual missions and flight results. A dedicated section is devoted to the use of spaceborne GNSS for relative navigation of formation flying satellites. The chapter concludes with an outlook on special applications such as spacecraft attitude determination, GNSS tracking of ballistic vehicles as well as GNSS radio science