GPS World - February 2008 - (Page 53)

System Design & Test | INNOVATION 400 km using a 3D numerical modeling based on the coupling between the ocean surface, the neutral atmosphere, and the ionosphere (see FIGURE 3). The modeling reproduced the TEC data with good agreement in amplitude as well as in the waveform shape, and quantified it by a cross-correlation (see FIGURE 4). The resulting shift of / 1 degree showed the presence of zonal and meridional winds neglected in the modeling. The presence of the wind can, indeed, introduce a shift of 1 degree in latitude and 1.5 degrees in longitude. Since modeling is an effective method to discriminate between the tsunami signature in the ionosphere and other potential perturbations, the GPS observations can be a useful tool to develop an inexpensive tsunami detection system based on the ionospheric sounding. Modeling TEC Perturbations A model to describe the effect of a tsunami on the ionosphere has been developed at the Institut de Physique du Globe de Paris (IPGP), France. It is comprised of three main parts. Firstly, it computes tsunami propagation using realistic bathymetry of, for example, the Indian Ocean. Secondly, an oceanic displacement is used to excite IGWs in the neutral atmosphere. Thirdly, it computes the response of the ionosphere induced by the neutral atmospheric motion resulting in enhanced electron densities. After integrating the electron densities, we obtain modeled (synthetic) TEC data. The modeling steps are as follows: Tsunami Propagation. Tsunami modeling is an established science and the propagation of tsunamis is generally based on a shallow-water hypothesis. Under this hypothesis, the ocean is considered as a simple layer where the ocean depth, h, is locally taken into account in the tsunami propagation velocity, v = hg, which directly depends on h and the gravity acceleration g. The modeling, usually based Neutral Ocean atmosphere Amplifier Ionosphere Detector 100 km IGW Tsunami Solid Earth Earthquake p FIGURE 3 The tsunamigenic earthquake mechanism and transfer of energy in the neutral and ionized atmosphere. The solid Earth displacement produces the tsunami and the sea surface displacement produces an internal gravity wave in the neutral atmosphere, which perturbs the electron distribution in the ionosphere. on finite differences, solves the appropriate hydrodynamic equations. Neutral Atmosphere Coupling. A tsunami is an oceanic gravity wave and its PLANS POSITION LOCATION AND NAVIGATION SYMPOSIUM TUTORIALS: MAY 5 TECHNICAL SESSION TRACKS Navigation Sensor Technologies Navigation Architectures and Systems Applications of Navigation Technologies Navigation & Positioning in GNSS Limited Environments Pre-Registration Discount Deadline: April 4, 2008 Exhibit Space Going Fast! Details at www.plansconference.org MONTEREY, CALIFORNIA • TECHNICAL MEETING: MAY 6–8 Co-sponsored by the IEEE AESS and The Institute of Navigation ION February 2008 | GPS World www.gpsworld.com 53 http://www.plansconference.org http://www.plansconference.org http://www.gpsworld.com

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GPS World - February 2008 Contents Out in Front Expert Advice Galileo's Second Coming Soon UPS First to Use ADS-B European Industry Group Galileo Validation 2008 Antenna Survey Tsumani Detection by GPS Classifieds Advertisers Index Seen + Heard

GPS World - February 2008

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