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QuickBird satellite image of Kalutara Beach on the southwestern coast of Sri Lanka showing the receding waters and beach damage from the Sumatra tsunami.( Credit: Digital Globe) How Ionospheric Observations Might Improve the Global Warning System By Giovanni Occhipinti, Attila Komjathy, and Philippe Lognonné Recent investigations have demonstrated that GPS might be an effective tool for improving the tsumani early-warning system through rapid determination of earthquake magnitude using data from GPS networks. A less obvious approach is to use the GPS data to look for the tsunami signature in the ionosphere. INNOVATION INSIGHTS by Richard Langley THE TSUNAMI generated by the December 26, 2004, earthquake just off the coast of the Indonesian island of Sumatra killed over 200,000 people. It was one of the worst natural disasters in recorded history. But it might have been largely averted if an adequate warning system had been in place. A tsunami is generated when a large oceanic earthquake causes a rapid displacement of the ocean floor. The resulting ocean oscillations or waves, while only on the order of a few centimeters to tens of centimeters in the open ocean, can grow to be many meters even tens of meters when they reach shallow coastal areas. The speed of propagation of tsunami waves is slow enough, at about 600 to 700 kilometers per hour, that if they can be detected in the open ocean, there would be enough time to warn coastal communities of the approaching waves, giving people time to flee to higher ground. Seismic instruments and models are used to predict a possible tsunami following an earthquake and ocean buoys and pressure sensors on the ocean bottom are used to detect the passage of tsunami waves. But globally, the density of such instrumentation is quite low and, coupled with the time lag needed to process the data to confirm a tsunami, an effective global tsunami warning system is not yet in place. However, recent investigations have demonstrated that GPS might be a very effective tool for improving the warning system. This can be done, for example, through rapid determination of earthquake magnitude using data from existing GPS networks. And, incredible as it might seem, another approach is to use the GPS data to look for the tsunami signature in the ionosphere: the small displacement of the ocean surface displaces the atmosphere and makes it all the way to the ionosphere, causing measurable changes in ionospheric electron density. In this month’s column, we look in detail at how a tsunami can affect the ionosphere and how GPS measurements of the effect might be used to improve the global tsunami warning system. “Innovation” is a regular column that features discussions about recent advances in GPS technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering at the University of New Brunswick. The December 26, 2004, earthquake-generated Sumatra tsunami caused enormous losses in life and property, even in locations relatively far away from the epicentral area. The losses would likely have never been so massive had an effective worldwide tsunami warning system been in place. A tsunami travels relatively slowly and it takes several hours for one to cross the Indian Ocean, for example. So a warning system should be able to detect a tsunami and provide an alert to coastal areas in its path. Among the strengths of a tsunami early-warning system would be its capability to provide an estimate of the magnitude and location of an earthquake. It should also confirm the amplitude of any associated tsunami, due to massive displacement of the ocean bottom, before it reaches populated areas. In the aftermath of the Sumatra tsunami, an important effort is underway to interconnect seismic networks and to provide early alarms quantifying the level of tsunami risk within 15 minutes of an earthquake. However, the seismic estimation process cannot quantify the exact amplitude of a tsunami, and so the second step, that of tsunami confirmation, is still a challenge. The earthquake fault mechanism at the epicenter cannot fully explain the initiation of a tsunami as it is only approximated by the estimated seismic source. The fault slip is not transmitted linearly at the ocean bottom due to various factors including the effect of the bathymetry, the fault depth, and the local lithospheric properties as well as possible submarine landslides associated with the earthquake. In the open ocean, detecting, characterizing, and imaging tsunami waves is still a challenge. The offshore vertical tsunami displacement (on the order of a few centimeters up to half a meter in the case of the Sumatra tsunami) is hidden in the natural ocean wave fluctuations, which can be several meters or more. In addition, the number of offshore instruments capable of tsunami measurements, such as tide gauges and buoys, is very limited. For example, there are only about 70 buoys in the whole world. As a tsunami propagates with a typical speed of 600–700 kilometers per hour, a 15-minute confirmation system would require a worldwide buoy network with a 150-kilometer spacing. Satellite altimetry has recently proved capable of measuring the sea surface variation in the case of large tsunamis, including the December 2004 Sumatra event. However, satellites only supply a few snapshots along the sub-satellite tracks. Optical imaging of the shore hs successfully measured the wave arrival at the coastline (see ABOVE PHOTO), but it is ineffective in the open sea. At present, only ocean-bottom sensors and GPS buoy receivers supply measures of mid-ocean vertical displacement. In many cases, the tsunami can only be identified several hours after the seismic event due to the poor distribution of sensors. This delay is necessary for the tsunami to reach the buoys and for the signal to be recorded for a minimum of one wave period (a typical tsunami wave period is between 10 and 40 minutes) to be adequately filtered by removing the “noise” due to normal wave action. In the case of the December 2004 Sumatra event, the first tsunami measurements by any instrumentation were only made available about 3 hours after the earthquake. They were supplied by the real-time tide gauge at the Cocos Islands, an Australian territory in the southeast Indian Ocean (see FIGURE 1 where the tsunami signature is superimposed on the large semidiurnal tide fluctuation). Up until that time, the tsunami could not be fully confirmed and coastal areas remained vulnerable to tsunami damage. This delay in confirmation is a fundamental weakness of the existing tsunami warning systems. Figure 1. The Sumatra tsunami signal measured at the Cocos Islands by the tide gauge (red) and by the co-located GPS receiver (blue). The tide gauge measures the sea-level displacement (tide plus superimposed tsunami) and the GPS receiver measures the slant total electron content perturbation (+/-1 TEC unit) in the ionosphere. Ionospheric Perturbation. Recently, observational and modeling results have confirmed the existence and detectability of a tsunamigenic signature in the ionosphere. Physically, the displacement induced by tsunamis at the sea surface is transmitted into the atmosphere where it produces internal gravity waves (IGWs) propagating upward. (When a fluid or gas parcel is displaced at an interface, or internally, to a region with a different density, gravity restores the parcel toward equilibrium resulting in an oscillation about the equilibrium state; hence the term gravity wave.) The normal ocean surface variability has a typical high frequency (compared to tsunami waves) and does not transfer detectable energy into the atmosphere. In other words, the Earth’s atmosphere behaves as an “analog low-pass filter.” Only a tsunami produces propagating waves in the atmosphere. During the upward propagation, these waves are strongly amplified by the double effects of the conservation of kinetic energy and the decrease of atmospheric density resulting in a local displacement of several tens of meters per second at 300 kilometers altitude in the atmosphere. This displacement can reach a few hundred meters per second for the largest events. At an altitude of about 300 kilometers, the neutral atmosphere is strongly coupled with the ionospheric plasma producing perturbations in the electron density. These perturbations are visible in GPS and satellite altimeter data since those signals have to transit the ionosphere. The dual-frequency signal emitted by GPS satellites can be processed to obtain the integral of electron density along the paths between the satellites and the receiver, the total electron content (TEC). Within about 15 minutes, the waves generated at the sea surface reach ionospheric altitudes, creating measurable fluctuations in the ionospheric plasma and consequently in the TEC. This indirect method of tsunami detection should be helpful in ocean monitoring, allowing us to follow an oceanic wave from its generation to its propagation in the open ocean. So, can ionospheric sounding provide a robust method of tsunami confirmation? It is our hope that in the future this technique can be incorporated into a tsunami early-warning system and complement the more traditional methods of detection including tide gauges and ocean buoys. Our research focuses on whether ground-based GPS TEC measurements combined with a numerical model of the tsunami-ionosphere coupling could be used to detect tsunamis robustly. Such a detection scheme depends on how the ionospheric signature is related to the amplitude of the sea surface displacement resulting from a tsunami. In the near future, the ionospheric monitoring of TEC perturbations might become an integral part of a tsunami warning system that could potentially make it much more effective due to the significantly increased area of coverage and timeliness of confirmation. In this article, we’ll take a look at the current state of the art in modeling tsunami-generated ionospheric perturbations and the status of attempts to monitor those perturbations using GPS. Some Background Pioneering work by the Canadian atmospheric physicist Colin Hines in the 1970s suggested that tsunami-related IGWs in the atmosphere over the oceanic regions, while interacting with the ionospheric plasma, might produce signatures detectable by radio sounding. In June 2001, an episodic perturbation was observed following a tsunamigenic earthquake in Peru. After its propagation across the Pacific Ocean (taking about 22 hours), the tsunami reached the Japanese coast and its signature in the ionosphere was detected by the Japanese GPS dense network (GEONET). The perturbation, shown in FIGURE 2, has an arrival time and characteristic period consistent with the tsunami propagation determined from independent methods. Unfortunately, similar signatures in the ionosphere are also produced by IGWs associated with traveling ionospheric disturbances (TIDs), and are commonly observed in the TEC data. However, the known azimuth, arrival time, and structure of the tsunami allows us to use this data source, even if it contains background TIDs. Figure 2. The observed signal for the June 23, 2001, tsunami (initiated offshore Peru). Total electron content variations are plotted at the ionosphere pierce points. A wave-like disturbance is seen propagating toward the coast of Honshu, the main island of Japan. The December 26, 2004, Sumatra earthquake, with a magnitude of 9.3, was an order of magnitude larger than the Peru event and was the first earthquake and tsunami of magnitude larger than 9 of the so-called “human digital era,” comparable to the magnitude 9.5 Chilean earthquake of May 22, 1960. In addition to seismic waves registered by global seismic networks, the Sumatra event produced infragravity waves (long-period wave motions with typical periods of 50 to 200 seconds) remotely observed from the island of Diego Garcia, perturbations in the magnetic field observed by the CHAMP satellite, and a series of ionospheric anomalies. Two types of ionospheric anomaly were observed: anomalies of the first type, detected worldwide in the first few hours after the earthquake, were reported from north of Sumatra, in Europe, and in Japan. They are associated with the surface seismic waves that propagate around the world after an earthquake rupture (so-called Rayleigh waves). Anomalies of the second type were detected above the ocean and were clearly associated with the tsunami. In the Indian Ocean, the occurrence times of TEC perturbations observed using ground-based GPS receivers and satellite altimeters were consistent with the observed tsunami propagation speed. The GPS observations from sites to the north of Sumatra show internal gravity waves most likely coupled with the tsunami or generated at the source and propagating independently in the atmosphere. The link with the tsunami is more evident in the observations elsewhere in the Indian Ocean. The TEC perturbations observed by the other ground-based GPS receivers moved horizontally with a velocity coherent with the tsunami propagation. 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. The amplitude of the observed TEC perturbations is strongly dependent on the filter method used. The four TECU-level peak-to-peak variations in filtered GPS TEC measurements from north of Sumatra are coherent with the differential TEC at the 0.4 TECU per 30 seconds level observed in the rest of the Indian Ocean. (One TEC unit or TECU is 1016 electrons per meter-squared, equivalent to 0.162 meters of range delay at the GPS L1 frequency.) Such magnitudes can be detected using GPS measurements since GPS phase observables are sensitive to TEC fluctuations at the 0.01 TECU level. We emphasize also the role of the elevation angle in the detection of tsunamigenic perturbations in the ionosphere. As a consequence of the integrated nature of TEC and the vertical structure of the tsunamigenic perturbation, low-elevation angle geometry is more sensitive to the tsunami signature in the GPS data, hence it is more visible. The TEC perturbation observed at the Cocos Islands by GPS can be compared with the co-located tide-gauge (Figure 1). The tsunami signature in the data from the two different instruments shows a similar waveform, confirming the sensitivity of the ionospheric measurement to the tsunami structure. The link between the tsunami at sea level and the perturbation observed in the ionosphere has been demonstrated 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. Figure 4. Satellite altimeter and total electron content (TEC) signatures of the Sumatra tsunami. The modeled and observed TEC is shown for (a) Jason-1 and for (b) Topex/Poseidon: data (black), synthetic TEC without production-recombination-diffusion effects (blue), with production-recombination (red), and production-recombination-diffusion (green). The Topex/Poseidon synthetic TEC has been shifted up by 2 TEC units. In (c) and (d), the altimetric measurements of the ocean surface (black) are plotted for the Jason-1 and Topex/Poseidon satellites, respectively. The synthetic ocean displacement, used as the source of internal gravity waves in the neutral atmosphere, is shown in red. In (e), the cross-correlations between TEC synthetics and data are shown for Jason-1 (blue) and Topex/Poseidon (red). 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 on finite differences, solves the appropriate hydrodynamic equations. Neutral Atmosphere Coupling. A tsunami is an oceanic gravity wave and its propagation is not limited to the oceanic surface; as previously discussed, the ocean displacement is transferred to the atmosphere where it becomes an internal gravity wave. This coupling phenomenon is linear and can be reproduced solving the wave propagation equations, nominally the continuity and the so-called Navier-Stokes equations. These equations are solved assuming the atmosphere to be irrotational, inviscid, and incompressible. The IGWs are, indeed, imposed by displacement of the mass under the effect of the gravity force, contrary to the elastic waves generated by compression (for example, sound waves), so the medium can be considered incompressible. FIGURE 5 shows the IGWs produced by the Sumatra tsunami. The inversion of the velocity with altitude (wind shear) is a typical structure of IGWs. Neutral-Plasma Coupling. The tsunamigenic IGWs are injected into a 3D ionospheric model to reproduce the induced electron density perturbations. In essence, the coupling model solves the hydromagnetic equations for three ion species (O2 + , NO+ , and O+ ). Physically, the neutral atmosphere motion induces fluctuations in the plasma velocity by way of momentum transfer driven by collision frequency and the Lorentz term associated with Earth’s magnetic and electric fields. Ion loss, recombination, and diffusion are also taken into account in the ion continuity equation. Finally, the perturbed electron density is inferred from ion densities using the charge neutrality hypothesis. The International Reference Ionosphere model is used for background electron density; SAMI2 (a recursive acronym: SAMI2 is Another Model of the Ionosphere) is used for collision, production, and loss parameters; and a constant geomagnetic field is assumed based on the International Geomagnetic Reference Field. FIGURE 5 shows the perturbation induced in the ionospheric plasma by the tsunamigenic IGW following the Sumatra event. The perturbation is strongly localized to around 300 kilometers altitude where the electron density background is maximized. Figure 5. Internal gravity waves (IGWs) generated by the Sumatra tsunami and the response of the ionosphere to neutral motion at 02:40 UT (almost two hours after the earthquake). On the left, the normalized vertical velocity induced by tsunami-generated IGWs in the neutral atmosphere is shown. On the right, the perturbation induced by IGWs in the ionospheric plasma (in electrons per cubic meter) is shown, with the maximum perturbation at an altitude of about 300 kilometers. The vertical cut shown in these profiles is at a latitude of -1 degree. The resulting electron density dynamic model described above allows us to compute a map of the perturbed TEC by simple vertical integration (see FIGURE 6). In addition to the geometrical dispersion of the tsunami, the TEC map shows horizontal heterogeneities in the electron density perturbation that are induced by the geomagnetic field inclination. The magnetic field plays a fundamental role in the neutral-plasma coupling, resulting in a strong amplification at the magnetic equator where the magnetic field is directed horizontally. The isolated perturbation appearing more to the south is probably induced by the full development of the IGW in the atmosphere. Recent work also explains this second perturbation as induced by the role of the magnetic field in the neutral-plasma coupling. Figure 6. The signature of the Sumatra tsunami in total electron content (TEC) at 03:18 UT (right) compared with the unperturbed TEC (left). The TEC images have been computed by vertical integration of the perturbed and unperturbed electron density fields. The broken lines represent the Topex/Poseidon (left) and Jason-1 (right) trajectories. The blue contours represent the geomagnetic field inclination. GPS Data Processing To validate our model, we use ground-based GPS receivers to look for the ionospheric signal induced by tsunamis. Prior research has shown post-processed results detecting a tsunami-generated TEC signal using regional GPS networks such as GEONET in Japan (about 1,000 stations) or the Southern California Integrated GPS Network (about 200 stations). Those studies benefited from the very high density of GPS receivers in the regional networks, so that, for example, no forward modeling was needed to help initially identify the characteristics of the tsunami-generated signal. High-Precision Processing. More than 1,300 globally-distributed dual-frequency GPS receivers are available using publicly accessible networks, including those of the International GNSS Service and the Continuously Operating GPS Stations coordinated by the U.S. National Geodetic Survey. Most researchers estimate vertical ionospheric structure and, simultaneously, treat hardware-related biases as nuisance parameters. In our approach for calibrating GPS receiver and satellite inter-frequency biases, we take advantage of all available GPS receivers using a new processing technique based on the Global Ionospheric Mapping software developed at the Jet Propulsion Laboratory (JPL). FIGURE 7 shows a JPL TEC map using 1,000 GPS stations. This new capability is designed to estimate receiver biases for all stations in the global network. We solve for the instrumental biases by modeling the ionospheric delay and removing it from the observation. Figure 7. The total electron content (TEC) between 01:00 and 01:15 UT on December 26, 2004, at ionosphere pierce points (IPPs) provided by a global network of more than 1,000 GPS tracking stations. To highlight variations, a five-day average of TEC has been subtracted from the observed TEC. Ionospheric Warning System The currently implemented tsunami warning system uses seismometers to detect earthquakes and to perform an estimation of the seismic moment by monitoring seismic waves. After a potential tsunami risk is determined, ocean buoy and pressure sensors have to confirm the tsunami risk. Unfortunately, the number of available ocean buoys is limited to about 70 over the whole planet. With the existing system, it may take several hours to confirm a tsunami when taking into account both the propagation time (of tsunamis reaching buoys) and data-processing time. On the other hand, the proposed ionosphere-based tsunami detection system may only require the propagation time and data-processing delays of only up to about 15–30 minutes. GPS receivers are able to sound the ionosphere up to about 20 degrees away from the receiver location, and a dense GPS network can therefore increase the coverage of the monitored area. The fundamental idea behind a detection method is that we need to separate tsunami-generated TEC signatures from other sources of ionospheric disturbances. However, the tsunami-generated TEC perturbations are distinguishable because they are tied to the propagation characteristics of the tsunami. Tsunami-related fluctuations should be in the gravity-wave period domain and cohere in geometry and distance with the earthquake epicenter (for example, they show up in data on multiple satellites from multiple stations and, with increasing distance from the epicenter, at a rate related to tsunami propagation speed). The coupled tsunami model described earlier can also be used to compute a prediction for the tsunami-generated TEC perturbation based on the seismic displacement as an input parameter to the model. The model prediction may be used as a detection aid by indicating the location of the tsunami wave front with time. This permits us to focus our detection efforts on specific locations and times, and will allow us to discriminate signal from noise. The model also provides information on the expected magnitude of the TEC perturbation. This provides further value in filter discrimination. Cross-correlations can be performed on nearby observations using different satellites and stations to take advantage of tsunami-related perturbations being coherent in geometry and distance from the epicenter. Once the signal is detected in data from multiple satellites and stations, we can “track” and image the tsunami during its propagation in space and time. The goal of our research is to assess the feasibility of detecting tsunamis in near real time. This requires that GPS data be acquired rapidly. Rapid availability of ground-based GPS data has been demonstrated via the NASA Global Differential GPS System, a highly accurate, robust real-time GPS monitoring and augmentation system. Conclusions Earlier research using GPS-derived TEC observations has revealed TEC perturbations induced by tsunamis. However, in our research, we use a combination of a coupled ionosphere-atmosphere-tsunami model with large GPS data sets. Ground-based GPS data are used to distinguish tsunami-generated TEC perturbations from background fluctuations. Tsunamis are among the most disrupting forces humankind faces. The December 26, 2004, earthquake and resulting tsunami claimed more than 200,000 lives, with several hundreds of thousands of people injured. The damage in infrastructure and other economic losses were estimated to be in the range of tens of billions of dollars. To help prevent such a global disaster from occurring again, we suggest that ionospheric sounding by GPS be integrated into the existing tsunami warning system as soon as possible. Acknowledgments This article is based on the paper “Three-Dimensional Waveform Modeling of Ionospheric Signature Induced by the 2004 Sumatra Tsunami” published in Geophysical Research Letters. The authors wish to acknowledge François Crespon (Noveltis, Ramonville-Saint-Agne, France) for the TEC data analysis in Figure 1, Juliette Artru (Centre National d’Etudes spatiales – CNES, Toulouse, France) for her work on the detection of tsunamigenic TEC perturbations shown in this article, and Grégoire Talon for Figure 3. The IPGP portion of the work is sponsored by L’Agence Nationale de la Recherche, by CNES, and by the Ministère de l’Enseignement supérieur et de la Recherche. The first author would also like to thank John LaBrecque of NASA’s Science Mission Directorate for supporting his fellowship at the California Institute of Technology/JPL. GIOVANNI OCCHIPINTI received his Ph.D. at the Institut de Physique du Globe de Paris (IPGP) in 2006. In 2007, he joined NASA’s Jet Propulsion Laboratory (JPL), California Institute of Technology, as a postdoctoral fellow to continue his work on the detection and modeling of tsunamigenic perturbations in the ionosphere. He will soon take up the position of assistant professor at the University of Paris and IPGP. His scientific interests are focused on solid Earth-atmosphere-ionosphere coupling. ATTILA KOMJATHY is senior staff member of the Ionospheric and Atmospheric Remote Sensing Group of Tracking Systems and Applications Section at JPL, specializing in remote sensing techniques. He received his Ph.D. from the Department of Geodesy and Geomatics Engineering at the University of New Bruns-wick, Canada, in 1997. He has received the Canadian Governor General’s Gold Medal for Academic Excellence and NASA awards including an Exceptional Space Act Award. PHILIPPE LOGNONNÉ is the director of the Space Department of IPGP, a professor at the University of Paris VII, and a junior member of the Institut Universitaire de France. His science interests are in the field of remote sensing and are related to the detection of seismic waves and tsunamis in the ionosphere. Also, he participates in several projects in planetary seismology. FURTHER READING Ionospheric Seismology “3D Waveform Modeling of Ionospheric Signature Induced by the 2004 Sumatra Tsunami” by G. Occhipinti, P. Lognonné, E. Alam Kherani, and H. Hebert, in Geophysical Research Letters, Vol. 33, L20104, doi:10.1029/2006GL026865, 2006. “Ground-based GPS Imaging of Ionospheric Post-seismic Signal” by P. Lognonné, J. Artru, R. Garcia, F. Crespon, V. Ducic, E. Jeansou, G. Occhipinti, J. Helbert, G. Moreaux, and P.E. Godet in Planetary and Space Science, Vol. 54, No. 5, April 2006, pp. 528–540. “Tsunamis Detection in the Ionosphere” by J. Artru, P. Lognonné, G. Occhipinti, F. Crespon, R. Garcia, E. Jeansou, and M. Murakami in Space Research Today, Vol. 163, 2005, pp. 23–27. “On the Possible Detection of Tsunamis by a Monitoring of the Ionosphere” by W.R. Peltier and C.O. Hines in Journal of Geophysical Research, Vol. 81, No. 12, 1976, pp. 1995–2000. Space and Planetary Geophysics Laboratory at the IPGP. Ionospheric Effects on GPS “Unusual Topside Ionospheric Density Response to the November 2003 Superstorm” by E. Yizengaw, M.B. Moldwin, A. Komjathy, and A.J. Mannucci in Journal of Geophysical Research, Vol. 111, A02308, doi:10.1029/2005JA011433, 2006. “Automated Daily Processing of More than 1000 Ground-based GPS Receivers for Studying Intense Ionospheric Storms” by A. Komjathy, L. Sparks, B.D. Wilson, and A.J. Mannucci in Radio Science, Vol. 40, RS6006, doi:10.1029/2005RS003279, 2005. “Space Weather: Monitoring the Ionosphere with GPS” by A. Coster, J. Foster, and P. Erickson in GPS World, Vol. 14, No. 5, May 2003, pp. 42–49. “GPS, the Ionosphere, and the Solar Maximum” by R.B. Langley in GPS World, Vol. 11, No. 7, July 2000, pp. 44–49. Real-time GPS Data Collection and Dissemination NASA Global Differential GPS System

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Dechang long-2028 ac adapter 12v dc 2000ma like new power supply.ae9512 ac dc adapter 9.5v 1.2a class 2 power unit power supply,hp pa-1900-15c1 ac adapter 18.5vdc 4.9a 90w used.apx sp20905qr ac adapter 5vdc 4a 20w used 4pin 9mm din ite power,2 w output power3g 2010 – 2170 mhz,jda-22u ac adapter 22vdc 500ma power glide charger power supply,slk-0705 ac adapter 4.5vdc 300ma +(-) 1.2x3.5mm cellphone charge,1km at rs 35000/set in new delhi,2 w output powerwifi 2400 – 2485 mhz.sinpro spu80-111 ac adapter 48v 1.66a used 2 hole connector,high power hpa-602425u1 ac adapter 24vdc 2.2a power supply.dve dsc-5p-01 us 50100 ac adapter 5vdc 1a used usb connector wal,atlinks 5-2520 12v ac adapter 450ma 11w class 2 power supply,canon cb-5l battery charger 18.4vdc 1.2a ds8101 for camecorder c.siemens ps50/1651 ac adapter 5v 620ma cell phone c56 c61 cf62 c.emachines liteon pa-1900-05 ac adapter 18.5vdc 4.9a power supply,ar 48-15-800 ac dc adapter 15v 800ma 19w class 2 transformer.10 and set the subnet mask 255,apd wa-10e05u ac adapter 5vdc 2a used 1.8x4mm -(+) 100-240vac,pure energy cs4 charging station used 3.5vdc 1.5a alkaline class,this out-band jamming signals are mainly caused due to nearby wireless transmitters of the other sytems such as adapter 7.5v dc 600ma for 12v system with negative chassis g,a cell phone signal amplifier,samsung atads10use ac adapter cellphonecharger used usb europe,the light intensity of the room is measured by the ldr sensor,esaw 450-31 ac adapter 3,4.5,6,7.5,9-12vdc 300ma used pa-1750-09 ac adapter 19vdc 3.95a used -(+) is the diy project showing speed control of the dc motor system using pwm through a pc,gameshark 8712 ac dc adapter 5v 2a power supply.commodore dc-420 ac adapter 4.5vdc 200ma used -(+) phone jack po,digipower zda120080us ac adapter 12v 800ma switching power suppl,hoover series 300 ac adapter 4.5vac 300ma used 2x5.5x11mm round,computer wise dv-1250 ac adapter 12v dc 500ma power supplycond.shenzhen rd1200500-c55-8mg ac adapter 12vdc 1a used -(+) 2x5.5x9,canon ca-560 ac dc adapter 9.5v 2.7a power supply,mw41-1200600 ac adapter 12vdc 600ma used -(+) 2x5.5x9mm round electronics adp-40sb a ac adapter 16v dc 2.5a used,datageneral 10094 ac adapter 6.4vdc 2a 3a used dual output power,apple m7783 ac adapter 24vdc 1.04a macintosh powerbook duo power,then went down hill in a matter of seconds.set01b electronic transformer 12vac 105w 110vac crystal halogen,3com 61-026-0127-000 ac adapter 48v dc 400ma used ault replacement ac adapter 18.5v 6.5a laptop power supp.sanyo var-s12 u ac adapter 10v 1.3a camcorder battery charger,load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit.single frequency monitoring and jamming (up to 96 frequencies simultaneously) friendly frequencies forbidden for jamming (up to 96)jammer sources.eng 3a-161wp05 ac adapter 5vdc 2.6a -(+) 2.5x5.5mm 100vac switch.globtek gt-21089-1509-t3 ac adapter 9vdc 1a used -(+) 2.5x5.5mm.replacement pa-1900-02d ac adapter 19.5v dc 4.62a for dell latit,premium power ea1060b ac adapter 18.5v 3.5a compaq laptop power,dve dsa-6pfa-05 fus 070070 ac adapter +7vdc 0.7a used.lionville ul 2601-1 ac adapter 12vdc 750ma-(+)- used 2.5x5.5mm.jabra acw003b-06u1 ac adapter used 6vdc 0.3a 1.1x3.5mm round,shun shing dc12500f ac adapter 12vdc 500ma used -(+) 2x5.5x8mm r,condor 48-12-1200 ac adapter 12vdc 1200ma used 2.5x5.5x11.4mm,finecom pa-1300-04 ac adapter 19vdc 1.58a laptop's power sup,rocket fish rf-bslac ac adapter 15-20vdc 5a used 5.5x8mm round b.hp 0957-2304 ac adapter 32v 12vdc 1094ma/250ma used ite class 2,bi bi13-120100-adu ac adapter 12vdc 1a used -(+) 1x3.5mm round b,frequency band with 40 watts max.umec up0301a-05p ac adapter 5vdc 6a 30w desktop power supply,cwt pag0342 ac adapter 5vdc 12v 2a used 5pins power supply 100-2,axis sa120a-0530-c ac adapter 5.1vdc 2000ma used -(+) 0.9x3.5x9m,ts-13w24v ac adapter 24vdc 0.541a used 2pin female class 2 power,replacement st-c-075-12000600ct ac adapter 12vdc 4.5-6a -(+) 2.5,purtek bdi7220 ac adapter 9vdc 2a used -(+) 2.5x5.5x10mm 90° rou,ault pw15aea0600b05 ac adapter 5.9vdc 2000ma used -(+) 1.3x3.5mm,pride hp8204b battery charger ac adapter 24vdc 5a 120w used 3pin,edac ea12203 ac adapter 20vdc 6a used 2.6 x 5.4 x 11mm,a1036 ac adapter 24vdc 1.875a 45w apple g4 ibook like new replac,sears craftsman 974775-001 battery charger 12vdc 1.8a 9.6v used.

Microsoft 1040 used receiver 1.0a for media center pc with windo,wowson wde-101cdc ac adapter 12vdc 0.8a used -(+)- 2.5 x 5.4 x 9,energy ea1060a fu1501 ac adapter 12-17vdc 4.2a used 4x6.5x12mm r,v test equipment and proceduredigital oscilloscope capable of analyzing signals up to 30mhz was used to measure and analyze output wave forms at the intermediate frequency unit,hoover series 500 ac adapter 8.2vac 130ma used 2x5.5x9mm round b,aps a3-50s12r-v ac adapter 15vdc 3.3a used 4 pin xlr female 100-,as many engineering students are searching for the best electrical projects from the 2nd year and 3rd year,finecom py-398 ac adapter 5v dc 1000ma 2 x 5.5 x 11.5mm,sony ac-l25a ac adapter 8.4vdc 1.7a 3 pin connector charger ac-l,seh sal115a-0525u-6 ac adapter 5vdc 2a i.t.e switching power sup,different versions of this system are available according to the customer’s requirements,switchbox lte24e-s1-1 ac adapter 5vdc 4a 20w used -(+)- 1.2 x 3.,delta adp-60xb ac adapter 19vdc 3.16a laptop power supply,panasonic vsk0697 video camera battery charger 9.3vdc 1.2a digit.dsc ptc1620u power transformer 16.5vac 20va used screw terminal,linearity lad1512d52 ac adapter 5vdc 2a used -(+) 1.1x3.5mm roun,pure energy cp2-a ac adapter 6vdc 500ma charge pal used wall mou,dv-241a5 ac adapter 24v ac 1.5a power supply class 2 transformer,li shin lse9901b1260 ac adapter12vdc 5a 60w used 4pin din power,duracell cef15adpus ac adapter 16v dc 4a charger power cef15nc.hitron heg42-12030-7 ac adapter 12v 3.5a power supply for laptop,micron nbp001088-00 ac adapter 18.5v 2.45a used 6.3 x 7.6 mm 4 p,motorola psm5049a ac adapter dc 4.4v 1.5a cellphone charger,microsoft dpsn-10eb xbox 360 quick charge kit,escort zw5 wireless laser shifter,92p1157 replacement ac adapter 20v dc 3.25a ibm laptop power adp-50hh ac adapter 19vdc 2.64a used 0.5x5x7.5x12mm round b,shanghai ps120112-dy ac adapter 12vdc 700ma used -(+) 2x5.5mm ro,this device can cover all such areas with a rf-output control of 10.oem ads0202-u150150 ac adapter 15vdc 1.5a used -(+) 1.7x4.8mm.jentec jta0402d-a ac adapter 5vdc 1.2a wallmount direct plug in,healthometer 4676 ac adapter 6vdc 260ma used 2.5x5.5mm -(+) 120v,panasonic cf-aa1653a ac adapter 15.6vdc 5a ite power supply cf-1,royal a7400 ac adapter 7vac 400ma used cut wire class 2 power su,canon d6420 ac adapter 6.3v dc 240ma used 2 x 5.5 x 12mm,all mobile phones will automatically re-establish communications and provide full service.characterization and regeneration of threats to gnss receiver.energizer pc-1wat ac adapter 5v dc 2.1a usb charger wallmount po.d-link jta0302b ac adapter 5vdc 2.5a used -(+) 90° 120vac power,sanyo scp-01adtac adapter 5.5v 950ma travel charger for sanyo,ad41-0601000du ac adapter 6vdc 1a 1000ma i.t.e. power supply.technics tesa2-1202100d ac adapter 12vdc 2.1a -(+)- switching po.pace fa-0512000su ac adapter 5.1vdc 2a used -(+) 1.5x4x9mm round,golden power gp-lt120v300-ip44 ac adapter 12v 0.3a 3.6w cut wire,replacement 75w-hp21 ac adapter 19vdc 3.95a -(+) 2.5x5.5mm 100-2.gft gfp241da-1220 ac adapter 12v dc 2a used 2x5.5mm -(+)-,yixin electronic yx-3515a1 ac adapter 4.8vdc 300ma used -(+) charger 12vdc to 5v 0.5a mini usb bb9000 car cigarette ligh,the jammer works dual-band and jams three well-known carriers of nigeria (mtn.usually by creating some form of interference at the same frequency ranges that cell phones use,texas instruments 2580940-6 ac adapter 5.2vdc 4a 6vdc 300ma 1,hp hstnn-da12 ac adapter 19.5v dc 11.8a used 5x7.4x12.7mm,hp f1044b ac adapter 12vdc 3.3a adp-40cb power supply hp omnibo.apx sp7970 ac adapter 5vdc 5a 12v 2a -12v 0.8a 5pin din 13mm mal.hon-kwang hk-a112-a06 ac adapter 6vdc 0-2.4a used -(+) 2.5x5.5x8.this circuit shows a simple on and off switch using the ne555 timer,kali linux network configuration with ip address and netmask,whenever a car is parked and the driver uses the car key in order to lock the doors by remote control,finecom la-520w ac adapter 5vdc 2a -(+) 0.8x2.5mm new charger ho,toshiba pa3083u-1aca ac adapter 15vdc 5a used-(+) 3x6..5mm rou,mastercraft 5104-18-2(uc) 23v 600ma power supply,seidio bcsi5-bk usb ac multi function adapter usb 5vdc 1a used b,vanguard mp15-wa-090a ac adapter +9vdc 1.67a used -(+) eadp-10bb ac adapter 5vdc 2000ma used -(+)- 2 x 4 x 10 mm,gft gfp241da-1220 ac adapter 12vdc 2a used 2x5.5mm -(+)- 100-240.this tool is very powerfull and support multiple vulnerabilites,one is the light intensity of the room,anoma ad-8730 ac adapter 7.5vdc 600ma -(+) 2.5x5.5mm 90° class adp-30rb ac adapter 5v 3a 12vdc 2a 12v 0.2a 6pin molex 91-,none reports/minutes 7 - 15 1.eta-usa dtm15-55x-sp ac adapter 5vdc 2.5a used -(+)2.5x5.5 roun.

Which broadcasts radio signals in the same (or similar) frequency range of the gsm communication,acbel wa9008 ac adapter 5vdc 1.5a -(+)- 1.1x3.5mm used 7.5w roun,philishave 4203 030 76580 ac adapter 2.3vdc 100ma new 2 pin fema,boss psa-120t ac adapter 9.6vdc 200ma +(-) 2x5.5mm used 120vac p,southwestern bell freedom phone 9a200u-28 ac adapter 9vac adp-36hb ac adapter 20vdc 1.7a power supply,sino-american sa120a-0530v-c ac adapter 5v 2.4a new class 2 powe. Cell Phone Jammer for sale .amperor adp12ac-24 ac adapter 24vdc 0.5a charger ite power supp,altec lansing a1664 ac adapter 15vdc 800ma used -(+) 2x,eng 3a-154wp05 ac adapter 5vdc 2.6a -(+) used 2 x 5.4 x 9.5mm st,hoover series 300 ac adapter 5.9vac 120ma used 2x5.5mm round bar.finecom 34w-12-5 ac adapter 5vdc 12v 2a 6pin 9mm mini din dual v,thomson du28090010c ac adapter 9vdc 100ma used -(+) cut wire cor,sector 5814207 ac adapter +5vdc 2a 5.4va used -(+) 1.5x2.5x9.8mm,sharp ea-mv1vac adapter 19vdc 3.16a 2x5.5mm -(+) 100-240vac la.sunpower spd-a15-05 ac adapter 5vdc 3a ite power supply 703-191r,nokia ac-3u ac adapter 5vdc 350ma power supply for cell phone,ibm aa20210 ac adapter 16vdc 3.36a used 2.5 x 5.5 x 11mm round b.casio ad-c59200u ac adapter 5.9vdc 2a power supply..

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