Error analysis for the Global Positioning System. Artists conception of GPS Block II F satellite in orbit. The analysis of errors computed using the Global Positioning System is important for understanding how GPS works, and for knowing what magnitude of errors should be expected. The Global Positioning System makes corrections for receiver clock errors and other effects but there are still residual errors which are not corrected. The Global Positioning System GPS was created by the United States Department of Defense DOD in the 1. It has come to be widely used for navigation both by the U. Global Haywire Online' title='Global Haywire Online' />S. GPS receiver position is computed based on data received from the satellites. Errors depend on geometric dilution of precision and the sources listed in the table below. Overviewedit. Geometric Error Diagram Showing Typical Relation of Indicated Receiver Position, Intersection of Sphere Surfaces, and True Receiver Position in Terms of Pseudorange Errors, PDOP, and Numerical Errors. User equivalent range errors UERE are shown in the table. There is also a numerical error with an estimated value,  numdisplaystyle sigma num, of about 1 meter. The impact of the global financial crisis on crossborder mergers and acquisitions a continental and industry analysis. Online periodical for British expatriates. Provides resources by region and includes finding mentors, latest news, finance, health care, property, education and a. Replicants, superheros, and reboots await you in our Fall Movie Guide. Plan your season and take note of the hotly anticipated indie, foreign, and documentary. NEW YORK TIMES BESTSELLER The single most important explanation, and the fullest explanation, of how Donald Trump became president of the. Its a wellworn fact that our round Earth is warming, and that human carbon emissions are the cause. Whats less wellknown is how much warming weve already. The standard deviations,  Rdisplaystyle sigma R, for the coarseacquisition CA and precise codes are also shown in the table. These standard deviations are computed by taking the square root of the sum of the squares of the individual components i. RSS for root sum squares. To get the standard deviation of receiver position estimate, these range errors must be multiplied by the appropriate dilution of precision terms and then RSSed with the numerical error. Electronics errors are one of several accuracy degrading effects outlined in the table above. When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 1. These effects also reduce the more precise PY codes accuracy. However, the advancement of technology means that in the present, civilian GPS fixes under a clear view of the sky are on average accurate to about 5 meters 1. The term user equivalent range error UERE refers to the error of a component in the distance from receiver to a satellite. These UERE errors are given as errors thereby implying that they are unbiased or zero mean errors. These UERE errors are therefore used in computing standard deviations. The best opinions, comments and analysis from The Telegraph. The standard deviation of the error in receiver position,  rcdisplaystyle sigma rc, is computed by multiplying PDOP Position Dilution Of Precision by  Rdisplaystyle sigma R, the standard deviation of the user equivalent range errors. Rdisplaystyle sigma R is computed by taking the square root of the sum of the squares of the individual component standard deviations. PDOP is computed as a function of receiver and satellite positions. A detailed description of how to calculate PDOP is given in the section, geometric dilution of precision computation GDOP. Rdisplaystyle sigma R for the CA code is given by 3R3. Rsqrt 32522. The standard deviation of the error in estimated receiver position  rcdisplaystyle sigma rc, again for the CA code is given by rcPDOP2R2num. PDOP22. 2. 21. 2mdisplaystyle sigma rcsqrt PDOP2times sigma R2sigma num2sqrt PDOP2times 2. The Seventh Dwarf Free Online Movie. The error diagram on the left shows the inter relationship of indicated receiver position, true receiver position, and the intersection of the four sphere surfaces. Signal arrival time measurementeditThe position calculated by a GPS receiver requires the current time, the position of the satellite and the measured delay of the received signal. The position accuracy is primarily dependent on the satellite position and signal delay. To measure the delay, the receiver compares the bit sequence received from the satellite with an internally generated version. By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about one percent of a bit pulse width, 0. CA code. Since GPS signals propagate at the speed of light, this represents an error of about 3 meters. This component of position accuracy can be improved by a factor of 1. PY signal. Assuming the same one percent of bit pulse width accuracy, the high frequency PY signal results in an accuracy of 0. Atmospheric effectseditInconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earths atmosphere, especially the ionosphere. Correcting these errors is a significant challenge to improving GPS position accuracy. These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the path through the atmosphere is longer see airmass. Once the receivers approximate location is known, a mathematical model can be used to estimate and compensate for these errors. Ionospheric delay of a microwave signal depends on its frequency. It arises from ionized atmosphere see Total electron content. This phenomenon is known as dispersion and can be calculated from measurements of delays for two or more frequency bands, allowing delays at other frequencies to be estimated. Some military and expensive survey grade civilian receivers calculate atmospheric dispersion from the different delays in the L1 and L2 frequencies, and apply a more precise correction. This can be done in civilian receivers without decrypting the PY signal carried on L2, by tracking the carrier wave instead of the modulated code. To facilitate this on lower cost receivers, a new civilian code signal on L2, called L2. C, was added to the Block IIR M satellites, which was first launched in 2. It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave. The effects of the ionosphere generally change slowly, and can be averaged over time. Those for any particular geographical area can be easily calculated by comparing the GPS measured position to a known surveyed location. This correction is also valid for other receivers in the same general location. Several systems send this information over radio or other links to allow L1 only receivers to make ionospheric corrections. The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems SBAS such as Wide Area Augmentation System WAAS available in North America and Hawaii, EGNOS Europe and Asia or Multi functional Satellite Augmentation System MSAS Japan, which transmits it on the GPS frequency using a special pseudo random noise sequence PRN, so only one receiver and antenna are required. Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the troposphere. This effect is both, more localized and changes more quickly than ionospheric effects, and is not frequency dependent. These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects. The Atmospheric pressure can also change the signals reception delay, due to the dry gases present at the troposphere 7. N2, 2. 1 O2, 0. 9 Ar. Its effect varies with local temperature and atmospheric pressure in quite a predictable manner using the laws of the ideal gases. Multipath effectseditGPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain buildings, canyon walls, hard ground, etc. These delayed signals cause measurement errors that are different for each type of GPS signal due to its dependency on the wavelength. A variety of techniques, most notably narrow correlator spacing, have been developed to mitigate multipath errors. For long delay multipath, the receiver itself can recognize the wayward signal and discard it. To address shorter delay multipath from the signal reflecting off the ground, specialized antennas e. Fantasyland by Kurt Andersen Penguin. Random. House. com. NEW YORK TIMES BESTSELLER The single most important explanation, and the fullest explanation, of how Donald Trump became president of the United States. I have read this year. Lawrence ODonnell. How did we get here In this sweeping, eloquent history of America, Kurt Andersen shows that whats happening in our country todaythis post factual, fake news moment were all living throughis not something new, but rather the ultimate expression of our national character. America was founded by wishful dreamers, magical thinkers, and true believers, by hucksters and their suckers. Fantasy is deeply embedded in our DNA. Over the course of five centuriesfrom the Salem witch trials to Scientology to the Satanic Panic of the 1. P. T. Barnum to Hollywood and the anything goes, wild and crazy sixties, from conspiracy theories to our fetish for guns and obsession with extraterrestrialsour love of the fantastic has made America exceptional in a way that weve never fully acknowledged. From the start, our ultra individualism was attached to epic dreams and epic fantasiesevery citizen was free to believe absolutely anything, or to pretend to be absolutely anybody. With the gleeful erudition and tell it like it is ferocity of a Christopher Hitchens, Andersen explores whether the great American experiment in liberty has gone off the rails. Fantasyland could not appear at a more perfect moment. If you want to understand Donald Trump and the culture of twenty first century America, if you want to know how the lines between reality and illusion have become dangerously blurred, you must read this book. Praise for FantasylandWith this rousing book, Kurt Andersen proves to be the kind of clear eyed critic an anxious country needs in the midst of a national crisis. San Francisco ChronicleThis is a blockbuster of a book. Kurt Andersen is a dazzling writer and a perceptive student of the many layers of American life. Take a deep breath and dive in. Tom BrokawThis is an important bookthe indispensable bookfor understanding America in the age of Trump. Its an eye opening history filled with brilliant insights, a saga of how we were always susceptible to fantasy, from the Puritan fanatics to the talk radio and Internet wackos who mix show business, hucksterism, and conspiracy theories.