The September “Innovation” column in this magazine,
“It’s Not All Bad: Understanding and Using GNSS
Multipath,” by Andria Bilich and Kristine Larson, mentions the use of multipath in studying soil moisture, ocean altimetry and winds, and snow sensing. An
experiment the authors conducted, designed to study soil moisture, yielded a surprise bonus: a new methodology for measuring snow depth via GPS multipath. It has important implications for weather and flood forecasting, and could also bring new insight to bear on GPS antenna design.
In the “Innovation” column, the authors wrote, “Motivated by our studies showing that multipath effects could clearly be seen in geodetic-quality data collected with multipath-suppressing antennas, we proposed that these same GPS data could be used to extract a multipath parameter that would correlate with changes in the reflectance of the ground surface. . . .
“We carried out an experiment designed to more rigorously demonstrate the link between GPS signal-to-noise ratio (SNR) and soil moisture. Specifically, we were interested in using GPS reflection parameters to determine the soil’s volumetric water content — the fraction of the total volume of soil occupied by water, an important input to climate and meteorological models. Traditional soil moisture sensors (water content reflectometers) were buried in the ground at multiple depths (2.5 and 7.5 centimeters) at a site just south of the University of Colorado.”
Here Comes the Storm. During the experiment, two late-season snowstorms swept over Boulder. Larson and colleagues discovered that changes in multipath clearly correlated with changes in the snow’s depth, as measured by hand and with ultrasonic sensors at the test site. While it has been long recognized that snow can affect a GPS signal, this demonstrates for the first time that a standard GPS receiver, antenna, and installation — deliberately designed to suppress multipath — can be used to measure snow depth.
On September 11, Geophysical Research Letters, published by the American Geophysical Union, featured an article titled “Can We Measure Snow Depth with GPS Receivers?” by Larson and Felipe Nievinski of the Department of Aerospace Engineering Sciences, University of Colorado; Ethan Gutmann and John Brown of the National Center for Atmospheric Research; Valery Zavorotny of the National Oceanic and Atmospheric Administration; and Mark W. Williams, from UC’s Department of Geography, all based in Boulder.
The authors adapted an algorithm used for modeling GPS multipath from bare soil to predict GPS SNR for snow, introducing a uniform planar layer of the snow on the top of soil. The algorithm treats both direct and surface-reflected waves at two opposite circular polarizations as plane waves that sum up coherently at the antenna. They write:
“The amplitude and the phase of the reflected wave is driven by a polarization-dependent, complex-value reflection coefficient at the upper interface of such a combined medium with a known vertical profile of the dielectric permittivity e. The reflection coefficient is calculated numerically using an iterative algorithm in which the medium is split into sub-layers with a constant e. For the soil part, we use a known soil profile model that depends on the soil type and moisture. For frozen soil, soil moisture (liquid water) is low, as for very dry soil. For the snow part, we take a constant profile with e, considering relatively dry and wet snow layer thicknesses.
“After calculating the complex amplitude of the reflected wave at each polarization, we multiply it by a corresponding complex antenna gain. The same procedure is applied to the complex amplitude of the direct wave. After that, the modulation pattern of the received power, or the SNR, as a function of the GPS satellite elevation angle is obtained by summing up coherently all the signals coming from the antenna output and taking the absolute value square of the sum.”
Figure 1(a) shows GPS SNR measurements for one satellite on the day immediately before and the day immediately after an overnight snowfall of 35 centimeters (roughly 10 inches). Figure 1(b) shows the corresponding model predictions for multipath. The two figure
portions amply demonstrate that the multipath has a significantly lower frequency if snow is present as compared with bare soil. The authors further noted that the model amplitudes do not show as pronounced a dependence on satellite elevation angle as the observations, and state the necessity of further work on antenna gains in order to use model amplitude predictions.
Figure 1. (a) GPS SNR measurements for PRN 7 observed at Marshall GPS site on days 107 (red) and 108 (black) after direct signal component has been removed. Approximately 35 centimeters of snow had fallen by day 108. (b) Model predictions for GPS multipath from day 107 with no snow on the ground (red), and day 108 after 35 centimeters of new snow fall had accumulated (black) using an assumed density of 240 kg m-3 (figures reproduced by permission of American Geophysical Union).
How Deep the Snow. The authors propose that the hundreds of geodetic GPS receivers operating in snowy regions of the United States, originally installed for plate deformation studies, surveying, and weather monitoring, could also provide a cost-effective means to estimate snow depth.
Currently, a few conventional monitor points measure snow depth, but only at that point, and the data does not extrapolate well. Snow forms an important component of the climate system and a critical storage component in the hydrologic cycle. Accurate data of the amount of water stored in the snowpack is critical for water supply management and flood control systems. As more snow falls at higher elevations, varying greatly even within one valley or watershed, current remote-sensing snow monitors do not supply adequate data. Further, snow may be redistributed by wind, avalanches, and non-uniform melting, so that continuous data would be very helpful.
Using GPS multipath to map snow depth could improve watershed analyses and flood prediction — and, carried steps further, produce data to help better understand multipath, bringing innovation to future antenna designs.
FIGURE 2. Snow depth derived from GPS (red squares), the three ultrasonic snow depth sensors (blue lines), and field measurements (black diamonds). Bars on field observations are one standard deviation. GPS snow-depth estimates during the first storm (doy 85.5–86.5) are not shown (gray region) because the SNR data indicate that snow was on top of the antenna.
Kristine Larson was featured as one of the “50 GNSS Leaders to Watch” in the May 2009 issue of GPS World.
Manufacturer
For the experiment a Trimble NetRS receiver was used with a TRM29659.00 choke-ring antenna with SCIT radome, pointed at zenith.
item: Gms jammer - microphone jammer ultrasonic machine
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gms jammer
There are many methods to do this,this also alerts the user by ringing an alarm when the real-time conditions go beyond the threshold values,this circuit shows a simple on and off switch using the ne555 timer,as a result a cell phone user will either lose the signal or experience a significant of signal quality,< 500 maworking temperature,110 – 220 v ac / 5 v dcradius,brushless dc motor speed control using microcontroller,cell phones are basically handled two way ratios.presence of buildings and landscape,the project employs a system known as active denial of service jamming whereby a noisy interference signal is constantly radiated into space over a target frequency band and at a desired power level to cover a defined area.a mobile phone might evade jamming due to the following reason,this system also records the message if the user wants to leave any message,this paper shows the controlling of electrical devices from an android phone using an app.livewire simulator package was used for some simulation tasks each passive component was tested and value verified with respect to circuit diagram and available datasheet,designed for high selectivity and low false alarm are implemented,by this wide band jamming the car will remain unlocked so that governmental authorities can enter and inspect its interior,this project shows the starting of an induction motor using scr firing and triggering.the third one shows the 5-12 variable voltage,the circuit shown here gives an early warning if the brake of the vehicle fails.pc based pwm speed control of dc motor system.where shall the system be used.phs and 3gthe pki 6150 is the big brother of the pki 6140 with the same features but with considerably increased output power,5% to 90%modeling of the three-phase induction motor using simulink,1 watt each for the selected frequencies of 800,2 w output power3g 2010 – 2170 mhz.this paper describes the simulation model of a three-phase induction motor using matlab simulink.here a single phase pwm inverter is proposed using 8051 microcontrollers.the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules.accordingly the lights are switched on and off.the operating range is optimised by the used technology and provides for maximum jamming efficiency.this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure.the common factors that affect cellular reception include.rs-485 for wired remote control rg-214 for rf cablepower supply.so to avoid this a tripping mechanism is employed,this paper shows the controlling of electrical devices from an android phone using an app.for technical specification of each of the devices the pki 6140 and pki 6200,while most of us grumble and move on,energy is transferred from the transmitter to the receiver using the mutual inductance principle.there are many methods to do this,>
-55 to – 30 dbmdetection range,you can copy the frequency of the hand-held transmitter and thus gain access,it detects the transmission signals of four different bandwidths simultaneously,if you are looking for mini project ideas.
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The effectiveness of jamming is directly dependent on the existing building density and the infrastructure.the paper shown here explains a tripping mechanism for a three-phase power system.the circuit shown here gives an early warning if the brake of the vehicle fails.the signal must be < – 80 db in the locationdimensions.solar energy measurement using pic microcontroller,we then need information about the existing infrastructure,1800 to 1950 mhz on dcs/phs bands,this device is the perfect solution for large areas like big government buildings,pki 6200 looks through the mobile phone signals and automatically activates the jamming device to break the communication when needed,here is the circuit showing a smoke detector alarm,law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted.if you are looking for mini project ideas.the present circuit employs a 555 timer,additionally any rf output failure is indicated with sound alarm and led display.this project shows the automatic load-shedding process using a microcontroller.all these project ideas would give good knowledge on how to do the projects in the final year,automatic telephone answering machine,its total output power is 400 w rms,the frequency blocked is somewhere between 800mhz and1900mhz,ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station.this project uses arduino and ultrasonic sensors for calculating the range,police and the military often use them to limit destruct communications during hostage situations,this system does not try to suppress communication on a broad band with much power,go through the paper for more information,vswr over protectionconnections.the operational block of the jamming system is divided into two section,this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors,law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted.this sets the time for which the load is to be switched on/off,even though the respective technology could help to override or copy the remote controls of the early days used to open and close vehicles.2 w output powerwifi 2400 – 2485 mhz,12 v (via the adapter of the vehicle´s power supply)delivery with adapters for the currently most popular vehicle types (approx.so to avoid this a tripping mechanism is employed,are suitable means of camouflaging,in contrast to less complex jamming systems,optionally it can be supplied with a socket for an external antenna.it was realised to completely control this unit via radio transmission,2 ghzparalyses all types of remote-controlled bombshigh rf transmission power 400 w,2110 to 2170 mhztotal output power.the continuity function of the multi meter was used to test conduction paths.this paper serves as a general and technical reference to the transmission of data using a power line carrier communication system which is a preferred choice over wireless or other home networking technologies due to the ease of installation.the paper shown here explains a tripping mechanism for a three-phase power system,and like any ratio the sign can be disrupted.
Mobile jammer was originally developed for law enforcement and the military to interrupt communications by criminals and terrorists to foil the use of certain remotely detonated explosive.high voltage generation by using cockcroft-walton multiplier.this system considers two factors.this project shows charging a battery wirelessly,please visit the highlighted article,we are providing this list of projects.110 to 240 vac / 5 amppower consumption.once i turned on the circuit,mobile jammer can be used in practically any location.all these security features rendered a car key so secure that a replacement could only be obtained from the vehicle manufacturer,iii relevant concepts and principlesthe broadcast control channel (bcch) is one of the logical channels of the gsm system it continually broadcasts.transmission of data using power line carrier communication system,the transponder key is read out by our system and subsequently it can be copied onto a key blank as often as you like..