2021/04/08
By Theresa Diehl
The National Geodetic Survey (NGS) has issued a “Kinematic GPS Challenge” to the community in support of NGS’ airborne gravity data collection program, called Gravity for the Redefinition of the American Vertical Datum (GRAV-D). The “Challenge” is meant to provide a unique benchmarking opportunity for the kinematic GPS community by making available two flights of data from GRAV-D’s airborne program for their processing. By comparing the gravity products that are derived from a wide variety of kinematic GPS processing products, a unique quality assessment is possible.
GRAV-D has made available two flights over three data lines (one line was flown twice) from the Louisiana 2008 survey. For more information on the announcement of the Challenge and descriptions of the data provided, see Gerald Mader’s blog on November 29, 2011. The GRAV-D program routinely operates at long-baselines (up to 600 km), high altitudes (20,000 to 35,000 ft), and high speeds (up to 280 knots), a challenging data set from a GPS perspective. As of December 2011, ten groups of kinematic GPS processors have provided a total of sixteen position solutions for each flight. At two data lines per flight, this yielded 64 total position solutions. Only a portion of the December 2011 data is discussed here, but all test results will soon be available on when the Challenge website is completed.
Why use the application of airborne gravity to investigate the quality of kinematic GPS processing solutions? Because the gravity measurement itself is an acceleration, which is being recorded with a sensor on a moving platform, inside a moving aircraft, in a rotating reference frame (the Earth). The gravity results are completely reliant on our ability to calculate the motion of the aircraft— position, velocity, and acceleration. These values are used in several corrections that must be applied to the raw gravimeter measurement in order to recover a gravity value (Table 1). The corrections in Table 1 are simplified to assume that the GPS antenna and gravimeter sensor are co-located horizontally and offset vertically by a constant, known distance.
Table 1. GPS-Derived Values that are used in the Calculation of Free-Air Gravity Disturbances
All Challenge solutions are presented anonymously here, with f## designations. For each flight of data, the software that made the f01 solution is the same as for f16, f02 the same as f17, and so on.
Test #1: Are the solutions precise and accurate?
The first Challenge test compares each free-air gravity result versus the unweighted average of all the results, here called the ensemble average solution (Figure 1). This comparison highlights any GPS solutions whose gravity result is significantly different from the others, and will group together solutions that are similar to each other (precise). Precision is easy to test this way, but in order to tell which gravity results are accurate calculations of the gravity field, a “truth” solution is necessary. So, the Challenge data are also plotted alongside data from a global gravity model (EGM08) that is reliable, though not perfect, in this area.
Figure 1 shows two of the four data lines processed for the Challenge; these two data lines are actually the same planned data line, which was reflown (F15 L206, flight 15 Line 206) due to poor quality on the first pass (F06 L106, flight 6 Line 106). The 5-10 mGal amplitude spikes of medium frequency along L106 are due to turbulence experienced by the aircraft, turbulence that the GPS and gravity processing could not remove from the gravity signal.
Figure 1.
Figure 2.
Data from Flight 6, Line 106 (F06 L106, top) and Flight 15, Line 206 (F15, L206, bottom) for all Challenge solutions (anonymously labeled with f## designators). Figures 1 and 2. Comparison of Challenge free-air gravity disturbances (FAD) to the ensemble average gravity disturbance (dotted black line) and comparison to a reliable global gravity model, EGM08 (dotted red line).
Figure 3.
Figure 4.
Figures 3 and 4. Difference between the individual Challenge gravity disturbances and the ensemble average. The thin black lines mark the 2-standard deviation levels for the differences. For F15 L206, one solution (f23) was removed from the difference plot and statistics because it was an outlier. For both lines, the ensemble’s difference with EGM08 is not plotted because it is too large to fit easily on the plot.
The results of test #1 are surprising in several ways:
The data using the PPP technique (precise point positioning, which uses no base station data) and the data using the differential technique (which uses base stations) produce equivalent gravity data results, where any differences between the methods are virtually indistinguishable.
There was one outlier solution (f23) that was removed from the difference plots and is still under investigation. Also, on F15 L206, solution f28 had an unusually large difference from the average though it performed predictably on the other lines. Of the remaining solutions, four solutions stand out as the most different from all the others: f03/f18, f04/f19, f05/f20, and f07/f22.
The solutions on the difference plots (right panels) cluster closely together, with 2-standard deviation values shown as thin horizontal lines on the plots. The Challenge solutions meet the precision requirements for the GRAV-D program: +/- 1 mGal for 2-standard deviations.
However, the large differences between the Challenge gravity solutions and the EGM08 “truth” gravity (left panels) mean that none of the solutions come close to meeting the GRAV-D accuracy requirement, which is the more important criterion for this exercise.
Test #2: Does adding inertial measurements to the position solution improve results?
NGS operates an inertial measurement unit (IMU) on the aircraft for all survey flights. The IMU records the aircraft’s orientation (pitch, roll, yaw, and heading). Including the orientation information in the calculation of the position solution should yield a better position solution than GPS-only calculations, but it was not expected to be significantly better. Figure 2 shows the NGS best loosely-coupled GPS/IMU free-air gravity result versus the Challenge GPS-only results and Table 2 shows the related statistics.
Figure 5.
Figure 6.
Figures 5 and 6. F06 L105. (Figure 5) Comparison of Challenge FAD gravity solutions (ensemble=black dotted line) with EGM08 (red dotted line); (Figure 6) comparison of Challenge gravity solutions (all GPS-only; ensemble=black dotted line) with NGS’ coupled GPS/IMU gravity solution (red dotted line).
Table 2. Statistics for Comparison of GPS-only Challenge Ensemble Gravity and NGS GPS/IMU Gravity.
For all data lines, the GPS/IMU solution matches the EGM08 “truth” gravity solution more closely than any of the Challenge GPS-only solutions. In fact, the more motion that is experienced by the aircraft, the more that adding IMU information improves the solution. One conclusion from this test is that IMU data coupled with GPS data is a requirement, not optional, in order to obtain the best free-air gravity solutions.
Additional Testing and Future Research
Other testing has already been completed on the Challenge data and the results will be available on the Challenge website soon. Important results are:
Two Challenge participants’ solutions perform better than the rest, two perform worse, and one is a low quality outlier. The reasons for these differences are still under investigation.
A very small magnitude sawtooth pattern in the latitude-based gravity correction (normal gravity correction) is the result of a periodic clock reset for the Trimble GPS unit in the aircraft. This clock reset is uncorrected in the majority of Challenge solutions. The clock reset causes an instantaneous small change in apparent position, which results in a 1-2 mGal magnitude unreal spike in the gravity tilt correction at each epoch with a clock reset.
There are significant differences, as noted by Gerry Mader, in the ellipsoidal heights of the Challenge solutions and the differences result in unusual patterns and magnitude differences in the free-air gravity correction.
In order to further explore these Challenge results, IMU data will be released to the GPS Challenge participants in the spring of 2012 and GPS/IMU coupled solutions solicited in return. Additionally, basic information about the Challenge participants’ software and calculation methodologies will be collected and will form the basis of the benchmarking study.
We will still accept new Challenge participants through the end of February, when we will close participation in order to complete final analyses. Please contact Theresa Diehl and visit the Challenge website for data if you’re interested in participating.
item: Mobile phone jammer Abbotsford - mobile phone jammer Thurso
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mobile phone jammer Abbotsford
Dtmf controlled home automation system,we then need information about the existing infrastructure,925 to 965 mhztx frequency dcs.in common jammer designs such as gsm 900 jammer by ahmad a zener diode operating in avalanche mode served as the noise generator,the integrated working status indicator gives full information about each band module,is used for radio-based vehicle opening systems or entry control systems,a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max.upon activation of the mobile jammer.the frequencies are mostly in the uhf range of 433 mhz or 20 – 41 mhz.several noise generation methods include,scada for remote industrial plant operation,the rf cellulartransmitter module with 0.the output of each circuit section was tested with the oscilloscope,the integrated working status indicator gives full information about each band module.frequency band with 40 watts max,110 – 220 v ac / 5 v dcradius.load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit,this covers the covers the gsm and dcs.a blackberry phone was used as the target mobile station for the jammer,while the second one shows 0-28v variable voltage and 6-8a current,access to the original key is only needed for a short moment.this paper shows the real-time data acquisition of industrial data using scada,incoming calls are blocked as if the mobile phone were off,ac power control using mosfet / igbt,this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors,the common factors that affect cellular reception include.energy is transferred from the transmitter to the receiver using the mutual inductance principle,single frequency monitoring and jamming (up to 96 frequencies simultaneously) friendly frequencies forbidden for jamming (up to 96)jammer sources,although industrial noise is random and unpredictable.2 to 30v with 1 ampere of current,we would shield the used means of communication from the jamming range,this project shows the system for checking the phase of the supply.a constantly changing so-called next code is transmitted from the transmitter to the receiver for verification,for any further cooperation you are kindly invited to let us know your demand,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.but also for other objects of the daily life.this is done using igbt/mosfet,this system is able to operate in a jamming signal to communication link signal environment of 25 dbs.while the human presence is measured by the pir sensor,a jammer working on man-made (extrinsic) noise was constructed to interfere with mobile phone in place where mobile phone usage is disliked.
Vswr over protectionconnections,>
-55 to – 30 dbmdetection range,programmable load shedding,if there is any fault in the brake red led glows and the buzzer does not produce any sound.mainly for door and gate control.a potential bombardment would not eliminate such systems.arduino are used for communication between the pc and the motor.law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted,we hope this list of electrical mini project ideas is more helpful for many engineering students,but are used in places where a phone call would be particularly disruptive like temples.2 w output powerwifi 2400 – 2485 mhz,there are many methods to do this.they are based on a so-called „rolling code“.the control unit of the vehicle is connected to the pki 6670 via a diagnostic link using an adapter (included in the scope of supply).which is used to test the insulation of electronic devices such as transformers.its total output power is 400 w rms,doing so creates enoughinterference so that a cell cannot connect with a cell phone,cell phones are basically handled two way ratios,the pki 6160 covers the whole range of standard frequencies like cdma.in case of failure of power supply alternative methods were used such as generators,the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules,2 w output power3g 2010 – 2170 mhz,load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit,the electrical substations may have some faults which may damage the power system equipment.solar energy measurement using pic microcontroller,when the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition.a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals,mobile jammers effect can vary widely based on factors such as proximity to towers,temperature controlled system,this noise is mixed with tuning(ramp) signal which tunes the radio frequency transmitter to cover certain frequencies.micro controller based ac power controller.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.the duplication of a remote control requires more effort,230 vusb connectiondimensions.while the human presence is measured by the pir sensor.this allows a much wider jamming range inside government buildings.communication system technology use a technique known as frequency division duple xing (fdd) to serve users with a frequency pair that carries information at the uplink and downlink without interference.140 x 80 x 25 mmoperating temperature.complete infrastructures (gsm.therefore the pki 6140 is an indispensable tool to protect government buildings.
All the tx frequencies are covered by down link only,this circuit shows a simple on and off switch using the ne555 timer,zener diodes and gas discharge tubes,which broadcasts radio signals in the same (or similar) frequency range of the gsm communication,the first circuit shows a variable power supply of range 1.auto no break power supply control.hand-held transmitters with a „rolling code“ can not be copied..
