AU2020103096A4 - Movements/shifts/displacements monitoring SMART box of Earth Retaining Structures in Landslides Mitigation - Google Patents

Abstract

Our Invention "Movements/shifts/displacements monitoring SMART box of Earth Retaining Structures in Landslides Mitigation" is a Geodetic GNSS (Global Navigation Satellite System) receivers are conventionally used in these applications because of a high level of accuracy. Due to the very high investment in geodetic receivers at the unstable slopes may damage or destroy the receivers and hence slopes are monitored sporadically only. But due to this we couldn't manage to monitor the minute displacement at ERS sites. The invented technology also includes landslides are disastrous natural hazards, accountable for considerable loss of property and lives worldwide. In Landslide Susceptible Areas many people have died due to this natural phenomenon since past 15+ years. Landslides are causing due to heterogeneous nature of soil as a main constituents having great affinity towards water. Climate and raining pattern are some other major key features who govern the landslides. The Government is now a days mitigating the landslide susceptible areas by Constructing Earth Retaining Structures (ERS)/Retaining walls. But, unfortunately the Earth Retaining Structures which are planned initially for say 30 +years effective service span gets washed out within one or two rainy seasons only. This may lead to loss of property and lives. The prime important indicator for stability assessment of sliding slopes is usually movements/shifts/displacements which must be monitored with accuracy in the millimetre to integrated centimetre range to have at least sufficient time in hand for safe evacuation in such tragedies. The invented technology also includes A method for locating GNSS-defined points, distances, directional attitudes and closed geometric shapes includes the steps of providing a base with a base GNSS antenna and providing a rover with a rover GNSS antenna and receiver. The invented technology also includes a receiver is connected to the rover GNSS antenna and is connected to the base GNSS antenna by an RF cable and the receiver thereby simultaneously processes signals received at the antennas. The method includes determining a vector directional arrow from the differential positions of the antennas and calculating a distance between the antennas, which can be sequentially chained together for determining a cumulative distance in a "digital tape measure" mode of operation. The invented technology also includes a localized RTK surveying method uses the rover antenna for determining relative or absolute point locations. A system includes a base with an antenna, a rover with an antenna and a receiver, with the receiver being connected to the antennas and also a processor is provided for computing positions, directional vectors, areas and other related tasks. 29 A c 10 16 18 eo18 8 18 18 A A'i 11~ MCK IN SLAV RECEIVERS.

Description

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Movements/shifts/displacements monitoring SMART box of Earth Retaining Structures in Landslides Mitigation

FIELD OF THE INVENTION

Our invention "Movements/shifts/displacements monitoring SMART box of Earth Retaining Structures for Landslides Mitigations relates generally to positioning and more particularly to positioning with selected accuracy having high integrity.

BACKGROUND OF THE INVENTION

Each country is now-a-days mitigating the landslide susceptible areas by constructing Earth Retaining Structures (ERS)/Retaining walls. But, unfortunately the ERS which are planned initially, for say 30 years effective service span, get washed out within one or two rainy seasons only. The sudden / early failure of earth retaining structure is disastrous hazards, accountable for considerable loss of property and lives worldwide. These structures are constructed to control the slips, movement of boulders and landslides on habituated regions. A large number of structures are build, and their physical maintenance is carried out by local authorities, however the frequency of monitoring the stresses generated upstream side of the structure is not enough. The physiographic, topographic, meteorological and hydrologic parameters induce forces on upstream side of the structure. Sometimes, therefore, such structures could not resist these stresses and fail. The process is very slow and steady, and difficult to monitor through naked eyes.

The prime important indicator for stability assessment of sliding slopes is usually movements/shifts/displacements which must be monitored with accuracy in the millimetre to centimetre range to have at least sufficient time in hand for safe evacuation in such tragedies. Monitoring of minute displacement in the structure is possible through differential interferometric synthetic aperture radar (DInSAR) technique of remote sensing. However, the technique is constraint by availability of SAR data at very high temporal scale.

Therefore, Geodetic GNSS (Global Navigation Satellite System) receivers are conventionally used in these applications because of a high level of accuracy. Due to the very high investment in geodetic receivers at the unstable slopes may damage or destroy the receivers and hence slopes are monitored sporadically only. But due to this we couldn't manage to monitor the minute displacement at ERS sites.

This trigger need to opt cost effective and simplified technological permanent set-up to understand Earth Retaining Structures movements 24X7 throughout the service life. Early warning of displacement monitoring requires a permanently active monitoring and measuring system on site.

Thus low-cost GNSS receivers can be used for such tough challenges. Over the last twenty years, positioning with low-cost GNSS sensors have rapidly developed around the world at both commercial and academic research level.

The objective of this development is to give the solution for landslides monitoring system using the performance of low-cost GNSS receivers with IRNSS/NavIC Navigation system, with the purpose of serving for the society. To achieve the target, both geodetic and low cost receivers are used in the experiment: IRNSS/NavIC Receiver with L5 and S band dual frequency along with u-blox receivers.

To simulate the displacement of landslides, a sliding device built by us shall be used. The antenna of low-cost receiver will be placed on the sliding device, which can be moved on both vertical and horizontal direction. The antenna of u-blox M8T receiver shall move by mm increments alternating the horizontal and vertical direction every two hours. In total, the antenna shall be moved 10 cm both in the horizontal and vertical direction. Then the data will have processed by our developed algorithm and RTKLIB. This experiment will prove that u-blox M8T receiver are capable in detecting displacements at centimetre level, even sub centimetre level for horizontal direction giving the solution for landslide alert and monitoring system for the society.

The various soil properties and metrological data sensors are also incorporated while noting down the results in above stated experiment to validate the reasons, occurrence and intensity of landslide. High resolution DEM may also be generated using DGPS survey in the vicinity of the structure.

The invention relates generally to Global Navigation Satellite System (GNSS) receivers and more particularly to a method and an apparatus for computing multiple precise locations using differential carrier phases of a GNSS satellite signal by synchronizing the clocks between the master receiver and the slave receiver. It further relates to a technique of connecting a plurality of antennas to the slave receiver, which can be switched on to measure each antenna's relative location to the master antenna for monitoring long-term deformation. Still further, the invention relates to surveying and measuring applications of a multi-antenna, single-receiver vector GNSS system using RTK techniques.

GNSS includes the Global Positioning System (GPS), which was established by the United States government, and employs a constellation of 24 or more satellites in well-defined orbits at an altitude of approximately 26,500 km. These satellites continually transmit microwave L-band radio signals in two frequency bands, centered at 1575.42 MHz and 1227.6 MHz, denoted as Li and L2 respectively. These signals include timing patterns relative to the satellite's onboard precision clock (which is kept synchronized by a ground station) as well as a navigation message giving the precise orbital positions of the satellites. GPS receivers process the radio signals, compute ranges to the GPS satellites, and by triangulating these ranges, the GPS receiver determines its position and its internal clock error. Different levels of accuracies can be achieved depending on the techniques deployed. This invention specifically targets the sub-centimeter accuracies achievable on a remote and possibly mobile GPS receiver by processing carrier phase observations both from the remote receiver and from one or more fixed-position reference stations. This procedure is often referred to as Real Time Kinematic or RTK.

To gain a better understanding of the accuracy levels achievable by using the GPS system, it is necessary to understand the two types of signals available from the GPS satellites. The first type of signal includes both the Coarse Acquisition (C/A), which modulates the Li radio signal and precision (P) code, which modulates both the Li and L2 radio signals. These are pseudorandom digital codes that provide a known pattern that can be compared to the receiver's version of that pattern. By measuring the time-shift required to align the pseudorandom digital codes, the GPS receiver is able to compute an unambiguous pseudo range to the satellite. Both the C/A and P codes have a relatively long "wavelength," of about 300 meters (1 microsecond) and 30 meters (0.1 microsecond), respectively. Consequently, use of the C/A code and the P code yield position data only at a relatively coarse level of resolution.

The second type of signal utilized for position determination is the carrier signal. The term "carrier", as used herein, refers to the dominant spectral component which remains in the radio signal after the spectral content caused by the modulated pseudorandom digital codes (C/A and P) is removed. The Li and L2 carrier signals have wavelengths of about19 and 24 centimeters, respectively. The GPS receiver is able to "track" these carrier signals, and in doing so, make measurements of the carrier phase to a small fraction of a complete wavelength, permitting range measurement to an accuracy of less than a centimeter.

In stand-alone GPS systems that determine a receiver's position coordinates without reference to a nearby reference receiver, the process of position determination is subject to errors from a number of sources. These include errors in the satellite's clock reference, the location of the orbiting satellite, ionospheric refraction errors (which delay GPS code signals but advance GPS carrier signals), and tropospheric induced delay errors. Prior to May 2, 2002, a large portion of the satellite's clock error, referred to as Selective Availability (SA) was purposefully induced by the U.S. Department of Defense to limit GPS accuracy to non-authorized users. SA would often cause positioning errors exceeding 40 meters, but even today, with SA off, errors caused by the ionosphere can be tens of meters. The above mentioned error sources (satellite clock and satellite position errors, ionosphere refraction, tropospheric delay and SA) are common-mode errors for two receivers that are nearby. That is, the errors caused by these sources are nearly the same for eachreceiver

Another error source, which is present in the carrier phase measurements, is the clock difference between the two receivers. This clock difference applies to all satellite measurements equally, and as such, can be eliminated by what is known as double differencing. This is where one of the satellites is used as a reference and the other satellite measurements are compared to it. This reduces the number of usable satellite measurements by one. As will be explained later, the more measurements available the better the final solution.

To overcome the common-mode errors of the stand-alone GPS system, many kinematic positioning applications make use of multiple GPS receivers. A reference receiver located at a reference site having known coordinates receives the satellite signals simultaneously with the receipt of signals by a remote receiver. Depending on the separation distance, the common-mode errors mentioned above will affect the satellite signals equally for the two receivers. By taking the difference between signals received both at the reference site and at the remote location, common-mode errors are effectively eliminated. This facilitates an accurate determination of the remote receiver's coordinates relative to the reference receiver's coordinates.

The technique of differencing signals is known in the art as differential GPS (DGPS) or differential GNSS (DGNSS). The combination of DGPS with precise measurements of carrier phase leads to position accuracies of less than one centimeter root-mean-squared (centimeter-level positioning). When DGPS/DGNSS positioning utilizing carrier phase is done in real-time while the remote receiver is potentially in motion, it is often referred to as Real-Time Kinematic (RTK) positioning. One of the difficulties in performing RTK positioning using carrier signals is the existence of an inherent ambiguity that arises because each cycle of the carrier signal looks exactly alike. Therefore, the range measurement based upon carrier phase has an ambiguity equivalent to an integral number of carrier signal wavelengths. Various techniques are used to resolve the ambiguity,which usually involves some form of double-differencing of the carrier measurements. Once ambiguities are solved, however, the receiver continues to apply a constant ambiguity correction to a carrier measurement until loss of lock on that carrier signal or partial loss of lock that results in a carrier cycle slip.

Regardless of the technique deployed, the problem of solving integer ambiguities, in real time, is always faster and more robust if there are more measurements upon which to discriminate the true integer ambiguities. Robust means that there is less chance of choosing an incorrect set of ambiguities. The degree to which the carrier measurements collectively agree to a common location of the GPS receiver is used as a discriminator in choosing the correct set of ambiguities. The more carrier phase measurements that are available, the more likely it is that the best measure of agreement will correspond to the true (relative to the reference GPS) position of the remote GPS receiver. One method, which effectively gives more measurements, is to use carrier phase measurements on both Li and L2. The problem though is that it is relatively difficult to track L2 because it is modulated only by P code and the United States Department of Defense has limited access to P code modulation by encrypting the P code prior to transmission. Some receivers are capable of applying various cross-correlation techniques to track the P code on L2, but these are usually more expensive receivers than Li only capable receivers.

This invention relates generally to navigation systems and more specifically to a system for positioning radiosondes, sonobuoys, aircraft, ships, land vehicles, and other objects on or near the earth's surface using satellites of the Global Positioning System (GPS). The GPS is a multiple-satellite based radio positioning system in which each GPS satellite transmits data that allows a user to precisely measure the distance from selected ones of the GPS satellites to his antenna and to thereafter compute position, velocity, and time parameters to a high degree of accuracy, using known triangulation techniques. The signals provided by the GPS can be received both globally and continuously. The GPS comprises three major segments, known as the space, control, and user segments.

The space segment, when fully operational, will consist of twenty-one operational satellites and three spares. These satellites will be positioned in a constellation such that typically seven, but a minimum of four, satellites will be observable by a user anywhere on or near the earth's surface. Each satellite transmits signals on two frequencies known as Li (1575.42 MHz) and L2 (1227.6 MHz), using spread spectrum techniques that employ two types of spreading functions. C/A and P pseudo random noise (PRN) codes are transmitted on frequency L1, and P code only is transmitted on frequency L2. The C/A or coarse/acquisition code, is available to any user, military or civilian, but the P code is only available to authorized military and civilian users. Both P and C/A codes contain data that enable a receiver to determine the range between a satellite and the user. Superimposed on both the P and C/A codes is the navigation (Nav) message. The Nav message contains 1) GPS system time; 2) a handover word used in connection with the transition from C/A code to P code tracking; 3) ephemeris data for the particular satellites being tracked; 4) almanac data for all of the satellites in the constellation, including information regarding satellite health, coefficients for the ionospheric delay model for C/A code users, and coefficients used to calculate universal coordinated time (UTC).

The control segment comprises a master control station (MCS) and a number of monitor stations. The monitor stations passively track all GPS satellites in view, collecting ranging data and satellite clock data from each satellite. This information is passed on to the MCS where the satellites' future ephemeris and clock drift are predicted. Updated ephemeris and clock data are uploaded to each satellite for re-transmission in each satellite's navigation message. The purpose of the control segment is to ensure that the information transmitted from the satellites is as accurate as possible. GPS is intended to be used in a wide variety of applications, including space, air, sea, and land object navigation, precise positioning, time transfer, attitude reference, surveying, etc. GPS will be used by a variety of civilian and military organizations all over the world. A number of prior art GPS receivers have been developed to meet the needs of the diverse group of users. These prior art GPS receivers are of a number of different types, including sequential tracking, continuous reception, multiplex, all in view, time transfer, and surveying receivers.

A GPS receiver comprises a number of subsystems, including an antenna assembly, an RF assembly, and a GPS processor assembly. The antenna assembly receives the L-band GPS signal and amplifies it prior to insertion into the RF assembly. The RF assembly mixes the L-band GPS signal down to a convenient IF frequency. Using various known techniques, the PRN code modulating the L-band signal is tracked through code-correlation to measure the time of transmission of the signals from the satellite. The doppler shift of the received L band signal is also measured through a carrier tracking loop. The code correlation and carrier tracking function can be performed using either analog or digital processing.

The Global Positioning System (GPS) is operated by the United States government for providing free GPS positioning signals to all users around the world. Standalone GPS receivers can use a coarse/acquisition (C/A) code in these signals for computing unaided positions having typical accuracies of about five to twenty meters. These accuracies are sufficient for some applications including most navigation applications. However, there are positioning applications, such as survey, mapping, machine control and agriculture, where greater accuracy or integrity is needed. Some of these needs are met by differential GPS systems that provide GPS code phase corrections. A GPS receiver that is constructed for differential GPS operation can use the code phase corrections for computing positions having typical accuracies of a few tens of centimeters to a few meters. These accuracies are sufficient for many positioning applications. However, a user cannot be altogether confident in the accuracies of standalone or differential GPS positions because the integrity of the positions is affected by multipath. Multipath reflections of the GPS signals can cause occasional large errors of tens to hundreds of meters or even more depending on the extra distances that are traveled by reflected signals. Fixed ambiguity real time kinematic (RTK) systems provide highly accurate GPS carrier phase measurements in order to provide greater accuracy and at the same time avoid most of the effects of multipath. A rover GPS receiver that is constructed for RTK operation can use the carrier phase measurements for determining relative positions having typical accuracies of about a centimeter to a few tens of centimeters. The term "fixed ambiguity" refers to the fact that an integer number of cycles of carrier phase is resolved (fixed) for the RTK carrier phase measurements between the reference phase and the phase measured by the rover. The resolution of the carrier cycle integer traps multipath signal errors that are greater than a portion of the wavelength of the carrier of the GPS signal, resulting in a high confidence and integrity for the RTK-based positions.

PRIOR ART SEARCH

This application is a continuation-in-part of and claims the benefit of: U.S. patent applications Ser. No. 12/355,776 (4007.2), filed Jan. 17, 2009, which is a continuation-in part of and claims the benefit of Ser. No. 12/171,399 (4007.1), filed Jul. 11, 2008, which is a continuation-in-part of and claims the benefit Ser. No. 10/804,758 (4007), filed Mar. 19, 2004, now U.S. Pat. No. 7,400,956; and Ser. No. 12/171,399 (4011.1), filed Jul. 11, 2008, which is a continuation-in-part of and claims the benefit of Ser. No. 10/828,745 (4011), filed Apr. 21, 2004 now abandoned; and U.S. Provisional Patent Applications No. /456,146, filed Mar. 20, 2003, and No. 60/464,756, filed Apr. 23, 2003. The contents of all of the aforementioned applications are incorporated by reference herein in their entireties.

OBJECTIVES OF THE INVENTION

1. The objective of the invention is to a Geodetic GNSS (Global Navigation Satellite System) receivers are conventionally used because of a high level of accuracy. Due to the very high investment in geodetic receivers at the unstable slopes may damage or destroy the receivers and hence slopes are monitored sporadically only. But due to this we couldn't manage to monitor the miute displacement at ERS sites. 2. The other objective of the invention is to a landslides are disastrous natural hazards, accountable for considerable loss of property and lives worldwide. In Landslide Susceptible Areas many people have died due to this natural phenomenon since past 15+ years. 3. The other objective of the invention is to a climate and land surface parameters are some other major key features who govern the landslides. The Government is now a days mitigating the landslide susceptible areas by Constructing Earth Retaining Structures (E RS)/Retaining walls. But, unfortunately the Earth Retaining Structures which are planned initially for say 30 +years effective service span gets washedout within one or two rainy seasons only. 4. The other objective of the inventionis to the prime important indicator for stability assessment of sliding slopes is usually movements/shifts/displacements which must be monitored with accuracy in the millimetre to integrated centimetre range to have at least sufficient time in hand for safe evacuation in such tragedies. 5. The other objective of the invention is to a method for locating GNSS-defined points, distances, directional attitudes and closed geometric shapes includes the steps of providing a base with a base GNSS antenna and providing a rover with a rover GNSS antenna and receiver. The invented technology also includes a receiver is connected to the rover GNSS antenna and is connected to the base GNSS antenna by an RF cable and the receiver thereby simultaneously processes signals received at the antennas. 6. The other objective of the invention is to determining a vector directional arrow from the differential positions of the antennas and calculating a distance between the antennas, which can be sequentially chained together for determining a cumulative distance in a "digital tape measure" mode of operation. 7. The other objective of the invention is to localized RTK surveying method uses the rover antenna for determining relative or absolute point locations. A system includes a base with an antenna, a rover with an antenna and a receiver, with the receiver being connected to the antennas and also a processor is provided for computing positions, directional vectors, areas and other related tasks.

SUMMARY OF THE INVENTION

Disclosed herein in an exemplary embodiment is a method for measuring relative position of fixed or slow-moving points in close proximity comprising: receiving a set of satellite signals with a first receiver corresponding to a first position; receiving a related set of satellite signals with a second receiver corresponding to a second position; and computing a position of the second position based on at least one of code phase and carrier phase differencing techniques. At least one of: a clock used in the first receiver and a clock used in the second receiver are synchronized to eliminate substantial clock variation between the first receiver and the second receiver; and the first receiver and the second receiver share a common clock.

Also disclosed herein in another exemplary embodiment is a system for measuring relative position of fixed or slow-moving points in close proximity comprising: a first receiver in operable communication with a first antenna configured to receive a first plurality of satellite signals at a first position; and a second receiver in operable communication with a second antenna configured to receive a second plurality of satellite signals at a second position; and at least one of the first receiver and the second receiver computing a position corresponding to a position of the second antenna based on at least one of code phase and carrier phase differencing techniques. At least one of: a clock used in the first receiver and a clock used in the second receiver are synchronized to eliminate clock variation between the first receiver and the second receiver, and the first receiver and the second receiver share a common clock.

Further, disclosed herein in yet another exemplary embodiment is a system for measuring relative position of fixed or slow-moving points in close proximity comprising: a means for receiving a set of satellite signals with a first receiver corresponding to a first position; a means for receiving a related set of satellite signals with a second receiver corresponding to a second position; and a means for computing a position of the second position based on at least one of code phase and carrier phase differencing techniques. At least one of: a clock used in the first receiver and a clock used in the second receiver are synchronized to eliminate clock variation between the first receiver and the second receiver, and the first receiver and the second receiver share a common clock. Also disclosed herein in yet another exemplary embodiment is a storage medium encoded with a machine-readable computer program code, the code including instructions for causing a computer to implement the abovementioned method for measuring relative position of fixed or slow moving points in close proximity.

An alternative to the GPS receiver known in the prior art is the GPS translator or Transdigitizer, as described in U.S. Pat. No. 4,622,557, for example. These translators or transdigitizers typically include only the antenna assembly and RF assembly portions of a GPS receiver. Translators are typically employed in missile tracking applications where small, lightweight, expendable sensors are required. The GPS C/A code spread spectrum signals received by the translator are combined with a pilot carrier and transmitted at S band frequencies (2200 to 2400 MHz). A GPS translator processor located at the telemetry tracking site receives these translated GPS C/A code signals and estimates the position and velocity of the object. The Transdigitizer retransmits the digitally sampled GPS signal at 2 Msps using Quadra phase modulation at 149 to 170 MHz.

Known variants of the GPS translator are the digital translator and the Transdigitizer. An object-borne GPS digital translator or Transdigitizer operates to convert the GPS C/A code spread spectrum signals to base band and perform in-phase and quadrature phase sampling at a rate of about 2 MHz. Transdigitizer or translated GPS signals are processed in a ground based translator processing system in a similar manner to GPS signals.

A third variant of the GPS translator is the codeless GPS receiver, as typified by the teachings of U.S. Pat. No. 4,754,283. This receiver ignores the bi-phase code and recovers the carrier frequency of all satellites in view of the receiving antenna. A telemetry transmitter transmits a signal that contains the GPS carrier frequency information to a ground-based telemetry receiver. This data is used to derive the speed of the sonde. Since the GPS code is not tracked, the position of the sonde cannot be computed using this method. This system uses a telemetry link at 403 MHz with a bandwidth of 20 KHz and has the advantage of requiring less bandwidth than the Transdigitizer but the disadvantage of only providing velocity data instead of both position and velocity data.

In summary, prior art GPS receivers may be one of three types. In the first type, all navigation processing activities occur at the receiver, which outputs the position and velocity of the tracked object using either a single computer or an RPC and navigation computer, in which there is substantial interconnection between the RPC functions and the navigation functions for satellite selection and acquisition. In the second type of GPS receiver, the GPS signal is remoted by translation or variations thereof and the signal is tracked at a ground processing facility where the object position and velocity are derived. In accordance with this latter approach, significant bandwidth is required to transmit the translated signal. In the third type, the carrier frequency of the GPS signals is measured and retransmitted to the ground processing facility where only the velocity of the object can be derived.

It is therefore the principal object of the present invention to provide a low cost tracking system for radiosondes, sonobuoys, aircraft, ships, land vehicles, and other objects, using GPS satellites, that is capable of providing the position and velocity of multiple objects without requiring a 2 MHz bandwidth data link.

This and other objects are accomplished in accordance with the illustrated preferred embodiment of the present invention by providing a GPS sensor module that supplies the data required to locate a particular object, a one-way telemetry link, and a data processing workstation to process the data and display the object position and velocity. The GPS sensor module comprises an antenna and a sensor. The sensor operates autonomously following application of operating power. The sensor digitally samples the signals from visible GPS satellites and stores this data in a digital buffer. No processing functions are performed by the sensor, thereby permitting significant reductions in the cost thereof. The raw satellite data stored in the buffer, interleaved with other telemetry data from the sonde or other object, are transmitted back to the data processing workstation. Using this set of raw satellite data, the position and velocity of the sensor can be determined at the time the data was recorded by the sensor to a precision of 100 meters.

If differential corrections are also provided at the data processing workstation, the accuracy of the position fix can be improved to better than 10 meters. If a 20 kHz data link is used and the GPS signals are sampled at 2 Mbps, a 1-second set of GPS data can be provided every 100 seconds, or a 0.5-second set of GPS data every 50 seconds, or a 0.1 second set of data every 10 seconds. The principal advantage afforded by the present invention is its ability to provide extremely accurate position, velocity, and time information for radiosondes, sonobuoys, and other objects using a low cost sensor and a conventional data telemetry link. By eliminating all processing functions performed in prior art GPS sensors, significant cost reductions are achieved over existing GPS receiver designs. By reducing the data link bandwidth from the 2 MHz required of prior art transdigitizers, conventional telemetry links may be employed to retransmit the data. For low cost data applications, such as sonobuoys or radiosondes, a position and velocity fix is only required at a low rate (e.g. every 10 seconds), a requirement that is accommodated by the present invention. The disclosure describes ways of providing high integrity positioning with controlled accuracies for a rover station either by providing synthetic reference phases for a GPS reference system or by dithering a secure rover position.

Briefly, several systems are disclosed using measurements of or including one or more real time kinematic (RTK) reference stations for receiving GPS signals at one or more actual reference positions and for measuring reference phases. When three or more reference stations are used, virtual reference phases may be determined for a virtual reference position. A synthetic offset vector is generated in a reference station, a server in the reference system, an RTK rover station, or a synthetic phase processor interacting between the reference stations and the rover station. Reference phase measurements are used with the synthetic offset vector for inferring synthetic reference phases for a synthetic position where the synthetic position is not equal to any of the actual or virtual reference positions. The rover station uses the actual or virtual reference position with the synthetic reference phases in place of the actual or virtual reference phases for computing a rover position with respect to the actual or virtual reference position having an added positional error that is proportional to the synthetic offset vector. In another approach a secure RTK rover station uses a synthetic offset vector directly for dithering a secure rover position determined from the actual or virtual reference phase. The synthetic offset vector may be generated in a reference station, a server in the reference system, the rover station, or a processor acting between the reference system and the rover station. The positions determined by the rover station have the integrity of the RTK system with accuracy controlled by the synthetic offset vector.

One embodiment is a secure rover station having a controlled accuracy for a geographical position, comprising: a rover global navigation satellite system (GNSS) receiver for determining a secure position not available to a user of the rover station; and a position dither processor for dithering the secure position with a selected non-zero synthetic offset vector for issuing a rover position available to the user having an added position error proportional to the synthetic offset vector.

Another embodiment is a method for controlling accuracy of a geographical position, comprising: receiving a global navigation satellite system (GNSS) signal; using the GNSS signal for determining a secure position not available to a user of the rover station; and dithering the secure position with a selected non-zero synthetic offset vector for providing a rover position having an added position error proportional to the synthetic offset vector to the user.

Another embodiment is a tangible medium containing a set of instructions for causing a processor to carry out the following steps for controlling accuracy of a geographical position, comprising: receiving a global navigation satellite system (GNSS) signal; using the GNSS signal for determining a secure position not available to a user of the rover station; and dithering the secure position with a selected non-zero synthetic offset vector for providing a rover position available to the user having an added position error proportional to the synthetic offset vector.

Another embodiment is a computer apparatus for post positioning with a selected precision, comprising: a GNSS post processor to post process reference GNSS carrier phases from a reference system and rover GNSS carrier phases from a rover receiver to compute a secure position for the rover receiver not available to a user; and a random process generator to generate a sequence of offset vectors to dither the secure position according to a computed dither level to provide the selected precision for a user-available position for the rover receiver.

Another embodiment is a method for post positioning with a selected precision, comprising: post processing reference GNSS carrier phases from a reference system and rover GNSS carrier phases from a rover receiver for computing a secure position for the rover receiver, the secure position not available to a user; and generating a sequence of offset vectors to dither the secure position according to a computed dither level for providing the selected precision for a user-available position for the rover receiver.

Another embodiment is a computer-readable medium having computer-executable instructions stored or carried thereby that when executed by a processor perform a method comprising steps of: post processing reference GNSS carrier phases from a reference system and rover GNSS carrier phases from a rover receiver for computing a secure position for the rover receiver, the secure position not available to a user; and generating a sequence of offset vectors to dither the secure position according to a computed dither level for providing the selected precision for a user-available position for the rover receiver.

BRIEF DESCRIPTION OF THE DIAGRAM

FIG. 1: is a diagram of a system embodying an aspect of the invention and including combined master and slave receivers. FIG. 1A: is a diagram of a system embodying an alternative aspect of the invention and including separate master and slave receivers. FIG. 2: is a vertical, cross-sectional view of an application of the invention, shown in connection with a dam for monitoring the locations of various points thereon. FIG. 3: is top plan view of another application of the invention, shown in connection with a marine vessel. FIG. 4 is a diagram of a real-time kinematic (RTK) system embodying another aspect of the present invention and using single frequency (L1) receivers. FIGS. 5-9: show a positioning system comprising another aspect of the invention, which is adapted for use in connection with localized RTK surveying for GIS procedures and 3-D measuring with a "digital tape measure" configuration of the invention. FIG.10: solar panel for electricity at remote area. FIG.11: SMART box in ERS FIG.12: cushioning to absorb minor shock. FIG.13: SMART Box- antenna movement and bubble tube arrangement as per requirements. FIG.14: slider to change the angle as per requirements. Fig.15: bubble tube with various angles. FIG.16: Connection low cost GNSS receivers with IRNSS/ NAVIC Navigation System with receivers (recording- Temporal latitude, Longitude, Ground Position)

DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Certain terminology will be used in the following description for convenience in reference only and will not be limiting. For example, up, down, front, back, right and left refer to the invention as oriented in the view being referred to. The words "inwardly" and "outwardly" refer to directions toward and away from, respectively, the geometric center of the embodiment being described and designated parts thereof.

Global navigation satellite systems (GNSS) are broadly defined to include the global positioning system (GPS, U.S.), Galileo (proposed), GLONASS (Russia), Beidou (China), Compass (proposed), the Indian Regional Navigational Satellite System (IRNSS), QZSS (Japan, proposed) and other current and future positioning technology using signals from satellites, with or without augmentation from terrestrial sources. Inertial navigation systems (INS) include gyroscopic (gyro) sensors, accelerometers and similar technologies for providing output corresponding to the inertia of moving components in all axes, i.e. through six degrees of freedom (positive and negative directions along transverse X, longitudinal Y and vertical Z axes). Yaw, pitch and roll refer to moving component rotation about the Z, X and Y axes respectively. Said terminology will include the words specifically mentioned, derivatives thereof and words of similar meaning.

In a first alternative embodiment, this invention includes two receivers, which either share the same clock, or have a clock synchronization technique to eliminate the receiver clock errors. The reference receiver (herein called the master or base) is connected to a single antenna whereas the slave receiver, which is clock synchronized with the master, has a multitude of antennas connected to it, which are switched in and out to take a measurement at each antenna location.

The GPS slave (e.g., rover) receiver computes the location vector from a double or single difference of the GPS rover and reference carrier phases for a plurality of GNSS satellites. As the receivers are either co-located or have a link, the raw measurements from the slave antennas are sent to the master for computation (of course any receiver or even a separate computer could perform this computation). This eliminates the need for a radio link between the master and slave receivers as is required in prior art RTK.

According to a more specific aspect of the present invention, in order to solve the integer ambiguity problem, the master selects the slave antenna to be measured based on the GPS satellite almanac to provide the best geometry (or one of the best) and based on its time slot. The master also has the slave antenna's position stored to provide an immediate calculation of the carrier cycle ambiguity to each satellite. Position calculation then follows conventional RTK GPS practice of using single or double difference equations involving the total phase distance to each satellite to solve the relative location of the slave antenna with respect to the master antenna. As previously described, there is no clock difference between the two receivers (or the clock difference is known and nearly constant) so double differencing may not be required. There may however be a significant delay through the coaxial cable to each slave antenna. This also can be stored and the delay removed to the measurements. A temperature drift may be noticed which will gradually change the delay, but this too can be eliminated by the addition of a thermocouple to determine the ambient temperature around the cable and antennas. By doing this, all satellite measurements may be used in the solution.

Another advantage of eliminating double differencing is that ambiguity search routines will not have to form linear combinations to decorrelate the measurement data. When it is possible to use single differences, they are generally preferred over double difference equations. The double difference cross-correlations are more difficult to deal with mathematically, say in a measurement covariance matrix of a Kalman filter. Single difference equations result in a measurement covariance matrix having zero cross correlation. However, accuracy can be achieved with both approaches. Referring now to FIG. 1, a simplified block diagram of a GNSS positioning system 10 embodying an aspect of the present invention is depicted. In an exemplary embodiment, a method and system use two receivers, which either share the same clock, or include a clock synchronization technique to eliminate a receiver clock. Further, the reference receiver (hereinafter also called the master or base receiver) 12 is connected to a master antenna 16 (Am), whereas the rover or slave receiver 14, which is clock synchronized with the master receiver 12, has a multitude of antennas 18 (Al-An) connected to it, which are switched in and out to take a measurement at each antenna location.

As shown in FIG. 1, the master receiver 12 and the slave receiver 14 are combined in a single receiver unit 11 on a common printed circuit board (PCB), which also includes a central processing unit (CPU) 13, a temperature sensor 15, a clock 17 and an antenna switch control 23. Collocating the receivers 12, 14 facilitates communication between them. It will be appreciated that while an exemplary embodiment is described and illustrated with respect to measuring movement of a dam, dike or beam, the disclosed invention is readily applicable to other applications where fixed or slow moving phenomena are tracked. Such applications may include roadways, bridges, building motion, glacier and iceberg travels and the like. It is also applicable to conventional RTK applications that require relatively short distances between master and slave receivers and where it is desirable to take advantage of a common clock for added robustness and the elimination of a radio for cost and robustness. For example, one application is local surveying or measuring distance at a construction site, or leveling (such as required for foundation placement) at that site.

The master and slave receivers 12, 14 are configured to either share the same clock 17, or include a clock synchronization system (SYNC connection). This technique facilitates elimination of the receiver clock errors. The CPU 13 computes a location vector based on a double or single difference of the GNSS code and/or carrier phases for the master receiver 12, the slave receiver 14 and a plurality of GPS satellites 8. As the master and slave receivers 12 and 14 are either co-located or have a link, the raw measurements from the slave antennas are sent to the CPU 13 for computation (of course any receiver or even a separate computer could perform this computation). This eliminates the need for a radio link between the master and slave receivers 12, 14 as is required in existing RTK applications. Moreover, in another exemplary embodiment, satellite signals from multiple antennas with a known dimensional separation may be combined to achieve receiving an optimal set of satellite 8 signals for a given location. Such an approach will be beneficial for instances when insufficient data is available from a single antenna or a less desirable set of satellite 8 signals is all that is available. In this way, a location may still be computed despite poor satellite 8 geometry, obstructions, and the like.

Advantageously, in an exemplary embodiment, rather than increasing the number of measurements, a reduction in the number of unknowns is achieved by eliminating the clock errors between the reference receiver 12 and the rover 14 (or master and slave). This approach yields an even greater advantage than adding measurements, unless a substantial number of measurements could readily be added. In addition, an exemplary embodiment as disclosed herein significantly improves the ability to calculate the integer ambiguities to each satellite 8. It will be appreciated that because the slave antennas 18 are presumed to move far less than a fraction of a carrier cycle (e.g., 19 cm) between measurements, the positions of each slave antenna 18 location may be stored and then later retrieved as needed to facilitate the immediate calculation of the integer ambiguities.

In order to solve the integer ambiguity problem with current RTK applications, the master receiver 12 selects a particular slave antenna 18 to be measured based on the GPS satellite almanac to provide the best geometry (or one of the best) and based on its time slot. The master receiver 12 also has the slave antenna's position stored (as stated above) to provide an immediate calculation of the carrier cycle ambiguity to each satellite 8. Position calculation then follows RTK GNSS practice of using single or double difference equations involving the total phase distance to each satellite 8 to solve the relative location of slave antenna 18 with respect to the master antenna 16. One such methodology for GNSS positioning employing RTK is taught by Whitehead, U.S. Pat. No. 6,469,663 the contents of which are incorporated by reference herein in their entirety. As previously described, there is no clock difference between the two receivers 12 and 14 (or the clock difference is known and nearly constant) so double differencing may not be required. It will however, be readily appreciated that there may be a significant delay through a coaxial cable 20 to each slave antenna 18. This delay is dependent upon the selected position for each antenna relative to the master (e.g., the length of cable 20 to reach each antenna 18).

Advantageously, the delay may readily be measured and stored and the delay mathematically removed to correct the measurements. Moreover, selected antennas 18 may exhibit a temperature drift that may result in a gradual change of the expected delay. However, advantageously, this too may be readily eliminated by the addition of a temperature sensor 15 connected to a thermocouple 22 to determine the ambient temperature around the cable 20 and the antennas 16 and 18. Advantageously, by employing the abovementioned correction and compensation schemes, all satellite 8 measurements may be used to formulate the solution.

Another advantage of eliminating double differencing is that ambiguity search routines will not have to form linear combinations to decorrelate the measurement data. When it is possible to use single differences, they are generally preferred over double difference equations. The double difference cross-correlations are more difficult to deal with mathematically, say in a measurement covariance matrix of a Kalman filter. Single difference equations result in a measurement covariance matrix with zero cross correlation, which facilitates computation of the ambiguities. The accuracy of both approaches should be substantially similar. However, single differencing is an easier process.

Yet another exemplary embodiment as an enhancement to the abovementioned embodiments uses the capability to take advantage of the slow dynamics of antenna motion by averaging over periods of time, thereby reducing multipath contributions (which are time varying) and poor satellite 8 geometries. In fact, it will be appreciated that the master receiver 12 is constantly tracking the satellites 8 and may further be employed to select the best time of day, e.g., the best constellation (the GNSS satellites 8 orbit in a 12-hour cycle), to perform the measurements based on its knowledge of the slave antennas' 18 positions and the satellites currently visible. Additionally, the master receiver 12 may select two separate times of day to provide two independent satellite position constellations for performing the measurements. This would reduce the amount of averaging time required, yet still provide the multipath and poor satellite geometry reduction benefits. Overall, such an approach may be employed to reduce power consumption requirements as the receiver 12 would not have to be averaging continuously for a twelve-hour period. Power consumption reduction can be beneficial, especially at remote sites.

Referring once again to FIG. 1, the system 10 is shown configured with a plurality of slave antennas 18 (also denoted as Al, A2 ... An) connected to the slave receiver 14. Each slave antenna 18 is switched (except the last one which is selected when all switches are connected through to it) with a switch box 24 (also denoted as S1, S2..).The switch(es) 24 are activated and the antennas 18 selected by an antenna switch controller 23, which can be incorporated on the receiver unit 11. The antenna switch controller 23 can send a tone or some other control signal 30 on the cable 20 to activate a particular desired switch 24 and thereby activate the slave antenna 18 connected thereto. It will be appreciated that in order to provide fault protection, the switch(es) 24 may be designed and configured so that in the event a switch 24 fails, the connection through to the next switch 24 is made. Advantageously, in this way, if one switches 24 should fail, it will still permit measurements on the remaining slave antennas 18. Smart reset circuitry can be employed to insure that the master receiver 12 and the slave receiver 14 will start up at the same instant and therefore the samples will be aligned as well. This approach substantially eliminates any receiver clock biases.

As mentioned previously, phase drift and delay can result from the coaxial cables 20, which may be removed and/or compensated by using a temperature sensor 15 connected to a thermocouple 22 to measure the temperature. A look-up table may be employed by the CPU 13 that has stored (alternatively a simple formula may be used to save memory) phase delay difference versus ambient temperature. An alternative embodiment could use equivalent coaxial cable 20 lengths to all antennas 16, 18 so that any temperature or other loss and drift effects would be matched and therefore cancelled in the single difference calculation. Normally in order to solve for integer ambiguities from GNSS satellite 8 signals, double differencing is used to bring forth the integer nature of the ambiguities by removing other non-integer sources of error such as clock and atmospheric delays from the measurements. To illustrate, consider four equations describing pseudo-ranges resulting from measurements of carrier phase on receivers denoted m and n for the slave and master, respectively: (pm i=Rmi+rsvi+Ai+Bm+Nm (pnB=R ni+-rsv i=A i +B n +N n i (pnk=R mk+rsv k=Ak+B m+N mk <pn k=R n k+Tsv k=A k +Bn+N n k

Here pm i is the measured pseudo range from rover receiver m to satellite i,pn is the measured pseudorange from reference receiver n to satellite i, pm k is the measured pseudorange from rover receiver m to satellite k, and pn kis the measured pseudorange from reference receiver n to satellite k. Each pseudorange is actually a measure of the summation a number of different physical quantities all of which shall be expressed in units of carrier cycles at L1 (roughly 19 cm).

Specifically, in the first of these equations, the term Rm i is the true geometric range from receiver m to satellite i, Tsvi is the clock error of satellite i, Ai is the atmospheric delays, which are associated with satellite i, Bm is the clock error of receiver m, and Nm i is the integer ambiguity in the range measurement from receiver m to satellite i. Similar notation applies to the remaining three equations. For simplicity, these equations do not show noise effects such as errors caused by receiver thermal noise or multipath noise.

Consider first applying the single difference. If the first two equations are differenced: - N m'-(pni=R mi -R n+B m-B n+N mi n

Similarly, differencing the second two equations yields:

Wmk-n k=Rmk-R k+Bm-Bn+Nmk-N k

The satellite common errors, such as satellite clock,.tau.sv.sup.i and atmosphere, A.sup.i (atmosphere is common if we assume relative close proximity of receivers m and n) are removed in the single difference. As the clock errors B.sub.m are common these term will also cancel out, leaving:

mi-Wi=R mi -R ni+N m Since the ambiguities are all integers that can be lumped together into a single term, it may be written:

(mi-ni-Rmi-Rni+Nmn where Nmn=NmiNni

This shows that single differencing the pseudorange measurements removes common atmospheric errors from the equations while leaving simple combinations of the geometric ranges and integer ambiguities, and clock errors drop out due to the synchronization of the two receivers. For N satellites in common view of the master (reference) and slave (remote) receivers 12 and 14 respectively, there are N such single-difference equations that can be formed without causing mathematical redundancy. Whereas double differencing, to eliminate clock biases in receivers, which are not clock synchronous, results in only N-1 equations. This gives rise to N unknown integer ambiguities that must be solved in addition to the 3 unknown coordinates (X, Y, Z) of the GPS receiver. Note that each geometric range term, for example R.sub.m.sup.i, is a function only of the receiver's position and the transmitting satellite's position. Specifically:

Rmi=(X-recvm-Xsati)2+(Yrecvm-Ysati)2+(Zrecvm-Zsat1)2

where Xrecvm, YrecvmZrecvm are the Cartesian coordinates of the receiver m at the time reception of the signal from satellite i, whose coordinates are Xsati, Ysati, Zsati at the time of signal transmission. In the problem at hand, only the selected slave's antenna's 18 position is unknown. Once the ambiguities are determined, only the selected antenna's 3 coordinates of position are unknown and these are easily solved using a mathematical approachsuchas LeastSquares.

Every time a new slave antenna 18 is selected, the integer ambiguities must be solved. This is a complex process and can be very time consuming if the position is unknown. However, in this instance, it will be appreciated that the movements to be measured are on the order of less than a quarter of a wavelength (5 cm) between measurements. This limitation permits a rapid calculation of the integer ambiguities since the master receiver 12 or the CPU 13 "knows" the satellite's position and the selected antenna's position well enough to directly calculate ambiguities. Such an approach will greatly reduce the time utilized to solve for the integer from up to 10 minutes to a second or less. Cycle slips, which result usually from motion which the receiver failed to track properly and therefore slipped from one ambiguity to another is also greatly reduced due to the very low dynamics of the selected antenna location. An added benefit of the low dynamics is the receiver can integrate the measurements over a long period of time and narrow the carrier tracking loop bandwidth to reduce noise.

As mentioned previously, it should be appreciated that another source of error in applying RTK positioning, especially when solving for integer ambiguities over long baselines, is non-common atmospheric propagation delays on the signals received by the slave (rover) 14 and master (reference) receivers 12. Since differencing cannot eliminate these non-common delays, the next best alternative is to estimate or model their effects. However, in an exemplary RTK embodiment, the slave antennas 18 and the master antenna 16 will most likely be within 5 kilometers of each other and at this distance the atmospheric effects are minimal and may readily be ignored. An orientation device 32, such as a compass or some other non-GNSS orientation device, can be affixed to a structure of interest to determine its attitude or orientation and to provide a corresponding signal to the CPU 13 for processing in connection with GNSS ranging data received via the receivers 12,14.

A further advantage of this technique is that it permits a carrier phase based solution even when a large portion of the sky, and therefore the visible satellites, are obscured by a wall, dam (FIG. 2) or other structure. This is because, as described above, the receivers 12, 14 will still have one more measurement than previously due to the utilization of single differencing rather than double differencing techniques. In addition, the fixed or very slow moving nature of the problem permits long-term measurements.

FIG. 1A shows a GNSS positioning system 40 comprising an alternative aspect of the present invention with a master receiver unit 42 and a separate slave receiver unit 44, which can be connected by a clock-synchronizing connection (SYNC) 46 of the receivers 12, 14, a clock-sharing connection 48 and a link 50, which can comprise a cable or an RF connection between suitable transmitters and receivers. An optional orientation device 32 can be connected to either or both of the receiver units 42, 44, e.g., to the CPU 13 and/or an optional CPU 52 of the slave unit 42. Optionally, the slave unit 44 can include a clock 54, which can be synchronized with the master receiver unit clock 17.The slave receiver 14 is connected to a slave antenna array, which can comprise a single antenna or a multiple-antenna array as shown in FIG. 1.

Referring now to FIG. 2, in a GNSS dam-monitoring positioning system 60 comprising yet another exemplary embodiment, a technique is employed to utilize and take advantage of the master receiver's 12 knowledge of the satellites' locations in the sky, and a preprogrammed knowledge of the visibility of the sky for selected slave antennas 18. For example, FIG. 2 shows a configuration of satellites 8 and slave antennas 18 whereby the slave antenna Al receives ranging data transmissions from all four satellites (SAT 1-4), but slave antenna A2 only receives transmissions from satellites SAT 2-4 and slave antenna.

A 3 only receives transmissions from satellite SAT 1. The master receiver 12 and/or the CPU 13 may then choose the best time, that is, the time with the most satellites visible to the selected slave antenna 18, to perform the measurement at that location. The receiver(s) can then dwell for some time (say one half hour) to integrate and reduce noise, then move on to another slave antenna 18. Moreover, it will be appreciated that the master receiver 12 and/or the CPU 13 may direct that the slave receiver 14 return to the same location after some duration, e.g. a few hours, when another optimal/desirable geometry is available, which is uncorrelated to the first. By taking measurements at two (or more) different times (and geometries), and averaging the two (or more) measurements, multipath and atmospheric induced errors, typically correlated over time, will be reduced. This method will allow monitoring of the face of a dam or berm, or even a valleywall.

Further assumptions may be made of the anticipated motion of the monitoring point at the selected slave antenna 18 to further reduce the number of measurements required. For example, the motion is of a dam is generally horizontally away from the pressure excerpted by the body of water behind it. By performing the calculation only in this direction, a single satellite may be enough to perform a measurement. This is obvious when looking at this equation:

R m i = (Xrecv m - Xsat i) 2 + (Yrecv m - Ysat i) 2 + (Zrecv m - Zsat 1) 2

As explained previously the satellite position (Xsat, Ysat and Zsat) are known, and if the receiver assumes there is minimal motion in Y and Z, then there is only one unknown left. Of course, additional satellites are highly desired to reduce noise and errors and to help detect any false or erroneous readings from throwing the solution off. Another area of concern for runninga longlength of coaxial cable 20 to the antennas 16, 18, other than phase delay, which was addressed earlier, is attenuation. In yet another exemplary embodiment, the slave antennas 18 may be configured as active antennas, e.g., antennas that include an internal Low Noise Amplifier (LNA). In a receiver design, the noise figure is often important, and comprises a combination of the noise temperature before the first LNA, the LNA noise figure and subsequent losses divided by the LNA gain. Subsequent amplifier gains will reduce following noise temperature (T) contributions by their gain as is shown in the equation below:

As an example, a typical low loss coaxial cable (RG6 type) has 20 dB (CL=0.01) of attenuation every 100 meters. The noise temperature of the antenna and LNA is 170 K (2 dB noise figure), the gain of the first LNA is 30 dB (or 1000). Subsequent LNA's have the same noise temperature and a gain of 12 dB (15.8). If each antenna is 50 meters apart the losses are -10 dB. After five stages the noise temperature of the system is: T5=T1+T2/(CL1xG1)+T3/(CL1xC12xG1xG2)+T4/(CLlxCL2xCl3xG1xG2xG3)+T5/(CL1xC 12xC13xC14xG1xG2xG3xG4) T5=190+190/100+190/158+190/250+190/395 T5=194 K

F5=2.22 dB

This is compared to the first stage, which would have a noise figure of 2 dB. A GPS receiver such as the master receiver 12, or slave receiver 14 can operate with a noise figure of up to 3.5 dB without suffering significant degradation. As can be seen, additional stages will have diminishing contributions. The total gain will be increasing by only 2 dB each step, so after 1 km, in this example, the maximum gain will be 68 dB, the gain of the first stage is 30 dB, the Automatic Gain Control of the receiver can remove this difference easily. Also after 20 stages (1 km) the total noise temperature in this example would be T(1 km)=194.7 K, an insignificant increase.

Further, in a marine vessel (e.g., barge) 71 positioning system 70 comprising another exemplary embodiment shown in FIG. 3, multiple antennas 18 (Al, A2) could be used to compute a solution of a single point on a rigid body to which they are attached, using known geometry and distances. Such an approach may be employed, for example, when not any one antenna 18 provides enough useful information (satellites 8) to compute a location solution due to obstructions, e.g., a superstructure 72, but the constellation of satellites 8 could provide sufficient positioning data. In other words, the superstructure 72 partially blocks the antennas 16 (Al) and 18 (A2) from views of satellites 8 whereby each antenna 16, 18 receives GNSS positioning signals from some, but not all, of the satellite 8 constellation. It will be appreciated that the antennas 16, 18 are positioned in a predetermined, known relation (i.e. spacing and orientation) for determining attitude comprising yaw and roll, although the primary concern would be yaw because the antennas 16, 18 would normally remain at a relatively constant level in a marine application. The antennas 16, 18 are connected to a receiver unit 74, which can be similar to the receiver units described above.

Advantageously, a position solution employing this approach would not necessarily have to utilize carrier-phase based differencing (it could be code phase). An application might include positioning on a marine vessel 71, such as a barge, where the location of a reference point is needed but there are cranes, towers and/or a superstructure 72 blocking the satellite view so that there is not one optimum GNSS location. However, by placing an antenna 18 on either side of the barge 71, enough satellites 8 could be tracked by the combined antenna 16, 18 arrangements that a solution of the location of some reference point on the barge 71 could still be obtained. Furthermore, on a barge 71, the orientation device 32, such as a compass, could also be used to give orientation, thus removing another unknown from the relative location of two receivers (e.g., 12, 14 in the receiver unit 74) rather than solving a relative location of one receiver with respect to the other by using the combined receivers 12, 14 to produce one non-relative location. The system shown in

FIG 3 can also include an optional base unit 76 for RTK applications. A position solution microprocessor (CPU) can be provided in the receiver unit 74 for calculating position solutions.

FIG. 4: shows a GNSS positioning system 80 comprising another alternative aspect of the present invention, with a base receiver unit 82 and a rover receiver unit 84, which can be configured similarly to the master and slave receiver units 42, 44 described above. The base and rover receiver units 82, 84 include base and rover GNSS receivers 90, 92, clocks 93, 95 and CPUs 94, 96 respectively. The base and rover receiver units 82, 84 can be connected by a cable link 85 for relatively close operation, such as surveying. Alternatively, the base and rover receiver units 82, 84 can be wirelessly connected via a base RF transmitter 86 and a rover RF receiver 88. An optional orientation device 32 can be connected to the rover CPU 92 for providing orientation and attitude information with respect to a rover vehicle or piece of equipment.

The receivers 90, 92 can comprise Li-only receivers, which tend to be less expensive than the more sophisticated dual frequency (L1/L2) receivers, which are commonly used for RTK fine positioning. The base receiver unit 82 is preferably equipped with a single base antenna 98 and the rover receiver unit 84 is preferably equipped with at least two rover antennas 100. Although the base receiver unit 82 could be equipped with multiple antennas (e.g., for reducing multipath errors) and the rover receiver unit 84 could be equipped with a single antenna, the normal preferred configuration includes multiple rover antennas 100 (Ar1, Ar2,. . . Arn) whereby the attitude (orientation) of the rover can be determined using GNSS ranging techniques. Attitude/orientation of the base is not generally needed for rover positioning.

The rover attitude information facilitates resolving integer ambiguities in GNSS positioning solutions by first solving for locations of the rover antennas 100 with respect to each other (an attitude solution). Next, using the known rover antenna relative locations, and nonrelative ambiguities, the system 80 solves for the global ambiguities using observations taken at each antenna 98, 100. The number of observations is thereby significantly increased over conventional RTK systems. The global ambiguities are the ambiguities of one rover antenna 100 that allow it be located in a global sense, i.e. relative to the base receiver unit 82.

The steps of the GNSS positioning method using the system 80 comprise:

1. Transmit code and carrier phase data from a base station to a multiple-antenna rover system, such as would be done in a conventional RTK system that uses only one rover antenna.

2. At the rover side, determine the relative locations and relative ambiguities of the multiple antennas using an attitude solution that takes advantage of known constraints in geometry or clock as described in U.S. Pat. No. 7,388,539, which is incorporated herein by reference. The attitude solution is usually done much quicker than conventional RTK ambiguity resolution due to the use ofgeometry constraints and/or a common clock.

3. Optionally store off the attitude solution (locations and ambiguities) in step 2 for later retrieval so that the data can be time-tag matched with the data from the base station. Also store off the current GPS observations (carrier phase) for the same purpose. This step is not necessary, but time tag matching of base and rover data improves results by avoiding extrapolation errors (not so critical with selective availability (SA) off, except for possibly on the Wide-Area Augmentation System (WAAS) satellites which have been observed to have high phase jitter).

4. Form single or double difference equations and solve for the global ambiguities using knowledge of relative antenna locations/clocks and relative ambiguities. An example is provided below Example Using the Two Antenna Rover System 80

At antenna one (1) of the rover, we can write the equation: R1=[A]x1-N1,

Where R1 is a carrier phase observation vector (single or double difference) at antenna (1), A is a design matrix, X1 is the location vector of antenna 1 (may include clock if single differencing is used), and N1 is an ambiguity vector for antenna (1). Similarly, at antenna two (2) we can write: R2=[A]x2-N2,

Where R2 is a carrier phase observation vector at antenna (1), A is a design matrix, X2 is the location vector of antenna 2, and N2 is an ambiguity vector for antenna (2).

Not, that in this example, the design matrix A is taken to be the same in both antenna equations. But, this is true only if both antennas see the same satellites. A more general example would use separate Al and A2 for the two equations. Solving an attitude solution (see U.S. Pat. No. 7,388,539), we find the relative antenna displacement V, and the relative ambiguity M where: V=x2-xi And M=N2-N1 Thus, combining the above equations, we have: Ri=[A]x1-N1 R2=[A](x1+V)-(N1+M) Re-arranging gives: Ri=[A]xl-Ni R2-[A]V+M=[A]x1-Ni And, combining into a single vector equation gives: R=[Ajx1-N Where R=[R1,R2-[A]V+M]Tand N=[N1, N1]T Where 'T' denotes transpose.

Compared to conventional RTK techniques, the method described above provides twice as many equations (for a rover with two antennas 100) for the same number of unknowns x1 and N1. N1 is referred to as the global ambiguity, which is easier to solve for with more equations. For example, see Whitehead U.S. Pat. No. 6,469,663 for Method and System for GPS and WAAS Carrier Phase Measurements for Relative Positioning, which is incorporated herein by reference.

FIG. 5-10 show a localized RTK positioning system 110 comprising another aspect of the invention. The system 110 includes a base (which can also be designated a master, reference or datum) 112 including a base antenna 114 (Ab). The base 112 is adapted for placement at fixed locations, e.g., on a tripod 116, for localized surveying applications. A marking or locating device 118 is centrally located under the base antenna 114 and is adapted for placing a pin, paint mark, stake, benchmark or other suitable point-identifying device at a precise point, which can henceforth serve as a reference location. Of course, the reference location, or datum, can be a pre-determined, pre-marked point, e.g., a "point-of origin" in a surveying procedure.

The base 112 can optionally have a user interface 120, which can include a graphical user interface (GUI), such as an LED device, a display screen, indicator lights, digital readouts, a printer, etc. Input can also be provided at the user interface 120 via suitable switches, keys, etc. A rover 122 includes a rover receiver 124 connected to the base antenna 114 via an RF cable 125 and to a rover antenna 126 (Ar). The rover 122 can optionally include a graphical user interface (GUI) 128, as described above, a tripod 116 and a marking device 118. The receiver 124 can optionally be mounted on either the base 112 or the rover 122 and either or both of the base 112 and the rover 122 can include a suitable user interface 120 or 128, as described above. The base 112 location can be a specific, surveyed location if necessary for absolute positioning. If only relative accuracy is required, the absolute location of the base 112 is generally not required. The base antenna 114 is tethered to the rover receiver 124 by the RF cable 125, which can have a length of 100 meters or more as appropriate to accommodate surveying applications.

The system 110 is adapted for making localized surveys within the range of the RF cable 125. The GNSS ranging signals received by the two antennas 114 and 126 are processed by the same receiver 124 with a single clock, thereby avoiding the need for a second clock or clock synchronization associated with a second receiver. Signal delays associated with the RF cable 125 tend to be relatively constant due to its predetermined length and can be accommodated with a suitable offset value. Ambiguity resolution benefits from this arrangement because a clock offset, which would otherwise produce another unknown and increase the position solution complexity, is constant whereby the GNSS observations of the antennas 114, 126 can be more efficiently processed by the receiver 124 to provide a position solution (either relative or absolute) for the antennas 114, 126. Eliminating an unknown associated with a clock offset improves robustness and increases accuracy.

The effective range of the system 110 can be effectively increased by marking points130 with the marking device 118 of the rover 122 near the end of its tethered travel, and then placing the base 112 on the marked points 130 and repeating the marking procedure with the rover 122 from the newly redefined base point. User interfaces 120,128, which can include various I/O devices and displays, are adapted for uploading data files, such as computer aided drafting and design (CADD) files which can correspond to a surveyed project, such as a building or other structure. For example, a CADD file could be uploaded with a schematic of a building foundation. The user interface 128 could show the position of the rover 122 with respect to the schematic drawing. Key reference locations 130 of an outline 131 could then be marked at the base 112 and/or rover 122 locations, using ground stakes, paint or other suitable marking means applied with the marking devices 118.

The rover 122 can include a programmable microprocessor 134 for computing position solutions (e.g., using ranging information from the receiver 124 and various correction techniques, which are well-known in the art), computing distances, computing areas, storing information, running routines, interacting with the user interfaces 120, 128, etc. The base user interface 120 can be eliminated whereby the base 112 includes only an antenna 114, a device for locating it on a particular point, such as a tripod 116, and/or a point marking device 118. In this configuration all of the user interface operations can occur via the rover 122. Alternatively, the base user interface 120 can be connected to the microprocessor 132 and used alternately with the base 112 and the rover 122 exchanging functions as the system 110 stakes out a perimeter or sequentially measures a relatively long distance (i.e. longer than the RF cable 125) comprising a chain-linked series of individual measurements.

An example of a user interface 120, 128 is shown in FIGS. 6 and 7. The user interface 120, 128 includes a display 135 with the general configuration of a circular light bar 134 with circumferentially-spaced lights 136 for positioning through 360. As shown in FIG. 6, a light (e.g. LED, etc.) 137 is illuminated to indicate a relative direction via a directional arrow 138 for moving the rover 122. When the desired location is reached, the display 135 could change as shown in FIG. 7 whereby all lights 137 are illuminated. FIG. 8A shows a vector function of the system 110 whereby the base and rover 112, 122 are placed on marked points 130, the separation of which can be established by a fixed-length chain link 140 having a length "D." Such chains are commonly used in surveying. The antennas 114, 126 determine the GNSS-defined locations of the points 130, from which a baseline 142 (generally parallel with the chain link 140) is determined. A vector 144 is calculated in a direction perpendicular to the baseline 142 and generally represents the attitude of the system 110. Exemplary applications include laying out rectangles and other polygons (e.g., the outline 131 shown in FIG. 5) with predetermined side dimensions and using the vector function to establish and/or verify the proper directional orientation. FIG. 8B shows an LCD screen 146 with an outline 148 (e.g., a building perimeter) displayed thereon. From a rover 122 location a GNSS-defined vector directional arrow 150 points towards a predetermined point location 130, to which the user is directed for placement of the rover 122, whereupon the located point 130 can be appropriately marked as described above.

Another exemplary application involves laying out the configuration of a foundation, an in ground swimming pool or some other structure. The outline can be transferred as a.DXF (or some other suitable file format) file to the rover 122, which can comprise a handheld unit for maximum portability. The circular light bar 134 (FIG. 6) can guide the user as described above to the point locations 130 defining intersections of walls or other points of interest around the structure. Still further, the lights 136 could comprise different colors for signifying the magnitude of directional error. For example, a range of colors corresponding to degrees of directional error could be used with green indicating a correct course. Local differential corrections can also be transmitted to the system 110, for example with conventional RTK techniques.

FIG. 9: shows an application of the positioning system 110 for establishing required heights for a structure, such as a flat slab, being constructed with poured concrete. An elevation stakes 152 is shown at a location which can be determined with the rover 122, as described above. The application shown in FIG. 9 can utilize the 3-D positioning features of the system 110 for establishing elevations. For example, FIG. 10 shows a screen display for a computer running a "digital tape measure" application for locating multiple points with the system 110. GNSS-defined XYZ coordinates are available for all of the identified points, in addition to 2-D and 3-D distances between such points.

The locating system 110 is adaptable to a wide range of projects requiring precise point locations and attitude. For example, from a GNSS-defined CenterPoint reference location, circles and arcs with constant radii can be defined. 3-D capabilities can be useful for structures requiring vertical slope, e.g. paved surfaces requiring positive slopes for drainage purposes. Sports fields and courts can also be expeditiously laid out and relocated. Still further, retractable and adjustable-length flexible members, such as surveying chains, can be utilized for fixed-length applications as described above. The software installed on the microprocessor 132 can create a digital 2-D or 3-D model of the outline or structure laid out using the system 110, with GNSS-defined positions corresponding to nodes or intersections of structural elements, such as walls. In a digital tape measure mode of operation, straight lines and other shapes can be measured off to any desired length, radius, or other parameter.

Areas can be calculated from closed geometric shapes, such as polygons, circles, ellipses, etc. The captured and recorded data can be useful for creating as-built drawing files and recording material usages, such as yards of poured concrete. Surveying applications could include inputs comprising compass bearings with vertical slopes in expressed degrees or rise-over-run ratios. The I/O user interfaces 120, 128 can include "marking" functions activated by switches or simply placement of the base 112 or the rover 122. An audible signal can be provided for notifying the user of a "marked" location. Plotted outputs can include plans, elevation profiles, databases, etc.

The satellite systems as discussed herein may include but not be limited to Wide Area Augmentation System (WAAS), Global Navigation Satellite System (GNSS) including GPS, GLONASS and other satellite ranging technologies. The term WAAS is used herein as a generic reference to all GNSS augmentation systems which, to date, include three programs: WAAS (Wide Area Augmentation System) in the USA, EGNOS (European Geostationary Navigation Overlay System) in Europe and MSAS (Multifunctional Transport Satellite Space-based Augmentation System) in Japan. Each of these three systems, which are all compatible, consists of a ground network for observing the GPS constellation, and one or more geostationary satellites.

It will be appreciated that while a particular series of steps or procedures is described as part of the abovementioned process, no order of steps should necessarily be inferred from the order of presentation. For example, the process includes receiving one or more sets of satellite signals. It should be evident that the order of receiving the satellite signals is variable and could be reversed without impacting the methodology disclosed herein or the scope of the claims. It should further be appreciated that while an exemplary partitioning functionality has been provided, it should be apparent to one skilled in the art, that the partitioning could be different. For example, the control of the master receiver 12 and the slave receiver 14 could be integrated with either receiver, or in another unit. The processes may, for ease of implementation, be integrated into a single unit.

Claims (7)

1. WE CLAIM

   1 Our Invention "Movements/shifts/displacements monitoring SMART box of Earth Retaining Structures in Landslides Mitigation" is a Geodetic GNSS (Global Navigation Satellite System) receivers are conventionally used in these applications because of a high level of accuracy. Due to the very high investment in geodetic receivers at the unstable slopes may damage or destroy the receivers and hence slopes are monitored sporadically only. But due to this we couldn't manage to monitor the minute displacement at ERS sites. The invented technology also includes landslides are disastrous natural hazards, accountable for considerable loss of property and lives worldwide. In Landslide Susceptible Areas many people have died due to this natural phenomenon since past 15+ years. Landslides are causing due to heterogeneous nature of soil as a main constituents having great affinity towards water. Climate and raining pattern are some other major key features who govern the landslides. The Government is now a days mitigating the landslide susceptible areas by Constructing Earth Retaining Structures (ERS)/Retaining walls. But, unfortunately the Earth Retaining Structures which are planned initially for say 30 +years effective service span gets washed out within one or two rainy seasons only. This may lead to loss of property and lives. The prime important indicator for stability assessment of sliding slopes is usually movements/shifts/displacements which must be monitored with accuracy in the millimetre to integrated centimetre range to have at least sufficient time in hand for safe evacuation in such tragedies. The invented technology also includes A method for locating GNSS-defined points, distances, directional attitudes and closed geometric shapes includes the steps of providing a base with a base GNSS antenna and providing a rover with a rover GNSS antenna and receiver. The invented technology also includes a receiver is connected to the rover GNSS antenna and is connected to the base GNSS antenna by an RF cable and the receiver thereby simultaneously processes signals received at the antennas. The method includes determining a vector directional arrow from the differential positions of the antennas and calculating a distance between the antennas, which can be sequentially chained together for determining a cumulative distance in a "digital tape measure" mode of operation. The invented technology also includes a localized RTK surveying method uses the rover antenna for determining relative or absolute point locations. A system includes a base with an antenna, a rover with an antenna and a receiver, with the receiver being connected to the antennas and also a processor is provided for computing positions, directional vectors, areas and other related tasks.
2. 2. According to claim# the invention is to a Geodetic GNSS (Global Navigation Satellite System) receivers are conventionally used in these applications because of a high level of accuracy. Due to the very high investment in geodetic receivers at the unstable slopes may damage or destroy the receivers and hence slopes are monitored sporadically only. But due to this we couldn't manage to monitor the minute displacement at ERS sites.
3. 3. According to claim,2# the invention is to a landslides are disastrous natural hazards, accountable for considerable loss of property and lives worldwide. In Landslide Susceptible Areas many people have died due to this natural phenomenon since past 15+ years.
4. 4. According to claim,2,31# the invention is to a Climate and raining pattern are some other major key features who govern the landslides. The Government is now a days mitigating the landslide susceptible areas by Constructing Earth Retaining Structures (ERS)/Retaining walls. But, unfortunately the Earth Retaining Structures which are planned initially for say 30 +years effective service span gets washed out within one or two rainy seasons only.
5. 5. According to claim,3,5,2# the invention is to the prime important indicator for stability assessment of sliding slopes is usually movements/shifts/displacements which must be monitored with accuracy in the millimetre to integrated centimetre range to have at least sufficient time in hand for safe evacuation in suchtragedies.
6. 6. According to claim 1,2,5# the invention is to a method to decide the location of SMART box and in particularly the receivers according to Remote Sensing and Geographic Information System (RS-GIS) study incorporated in that area based on drainage pattern changes over the periods and geotechnical properties at site through field and lab experiments.
7. 7. According to claims, 2, 5,6# the invention is to a method to validate the results of Movements/shifts/displacements of ERS with High resolution DEM generated using DGPS or UAV survey in the vicinity of the structure. a According to claim,2,6# the invention is to a method to develop the prediction of geotechnical properties of soil through ANN or Python Soil Properties testing program and its effect on the ERS to give early warning for closely monitoring of ERS at that time. 9. According to claiml,2,4,5# the invention is to a method for locating GNSS-defined points, distances, directional attitudes and closed geometric shapes includes the steps of providing a base with a base GNSS antenna and providing a rover with a rover GNSS antenna and receiver. The invented technology also includes a receiver is connected to the rover GNSS antenna and is connected to the base GNSS antenna by an RF cable and the receiver thereby simultaneously processes signals received at the antennas. 1Q According to claim,2# the invention is to determining a vector directional arrow from the differential positions of the antennas and calculating a distance between the antennas, which can be sequentially chained together for determining a cumulative distance in a "digital tape measure" mode of operation. According to claim1,2,6# the invention is to localized RTK surveying method uses the rover antenna for determining relative or absolute point locations. A system includes a base with an antenna, a rover with an antenna and a receiver, with the receiver being connected to the antennas and also a processor is provided for computing positions, directional vectors, areas and other related tasks.

   FIG. 1: IS A DIAGRAM OF A SYSTEM EMBODYING AN ASPECT OF THE INVENTION AND INCLUDING COMBINED MASTER AND SLAVE RECEIVERS.

   FIG. 1A: IS A DIAGRAM OF A SYSTEM EMBODYING AN ALTERNATIVE ASPECT OF THE INVENTION AND INCLUDING SEPARATE MASTER AND SLAVE RECEIVERS.

   FIG. 2: IS A VERTICAL, CROSS-SECTIONAL VIEW OF AN APPLICATION OF THE INVENTION, SHOWN IN CONNECTION WITH A DAM FOR MONITORING THE LOCATIONS OF VARIOUS POINTS THEREON.

   FIG. 3: IS TOP PLAN VIEW OF ANOTHER APPLICATION OF THE INVENTION, SHOWN IN CONNECTION WITH A MARINE VESSEL.

   FIG. 4: IS A DIAGRAM OF A REAL-TIME KINEMATIC (RTK) SYSTEM EMBODYING ANOTHER ASPECT OF THE PRESENT INVENTION AND USING SINGLE FREQUENCY (L1) RECEIVERS.

   FIG. 5 SHOW A POSITIONING SYSTEM COMPRISING ANOTHER ASPECT OF THE INVENTION, WHICH IS ADAPTED FOR USE IN CONNECTION WITH LOCALIZED RTK SURVEYING FOR GIS PROCEDURES AND 3-D MEASURING WITH A “DIGITAL TAPE MEASURE” CONFIGURATION OF THE INVENTION.

   FIG.6: SHOW A POSITIONING SYSTEM COMPRISING ANOTHER ASPECT OF THE INVENTION, WHICH IS ADAPTED FOR USE IN CONNECTION WITH LOCALIZED RTK SURVEYING FOR GIS PROCEDURES AND 3-D MEASURING WITH A “DIGITAL TAPE MEASURE” CONFIGURATION OF THE INVENTION.

   FIG.7: SHOW A POSITIONING SYSTEM COMPRISING ANOTHER ASPECT OF THE INVENTION, WHICH IS ADAPTED FOR USE IN CONNECTION WITH LOCALIZED RTK SURVEYING FOR GIS PROCEDURES AND 3-D MEASURING WITH A “DIGITAL TAPE MEASURE” CONFIGURATION OF THE INVENTION.

   FIG.8-A: SHOW A POSITIONING SYSTEM COMPRISING ANOTHER ASPECT OF THE INVENTION, WHICH IS ADAPTED FOR USE IN CONNECTION WITH LOCALIZED RTK SURVEYING FOR GIS PROCEDURES AND 3-D MEASURING WITH A “DIGITAL TAPE MEASURE” CONFIGURATION OF THE INVENTION.

   FIG.8-B: SHOW A POSITIONING SYSTEM COMPRISING ANOTHER ASPECT OF THE INVENTION, WHICH IS ADAPTED FOR USE IN CONNECTION WITH LOCALIZED RTK SURVEYING FOR GIS PROCEDURES AND 3-D MEASURING WITH A “DIGITAL TAPE MEASURE” CONFIGURATION OF THE INVENTION.

   FIG.9: SHOW A POSITIONING SYSTEM COMPRISING ANOTHER ASPECT OF THE INVENTION, WHICH IS ADAPTED FOR USE IN CONNECTION WITH LOCALIZED RTK SURVEYING FOR GIS PROCEDURES AND 3-D MEASURING WITH A “DIGITAL TAPE MEASURE” CONFIGURATION OF THE INVENTION.

   FIG.10: SOLAR PANEL FOR ELECTRICITY AT REMOTE AREA.

   FIG.11: SMART BOX IN ERS.

   FIG.12: CUSHIONING TO ABSORB MINOR SHOCK.

   FIG.13: SMART BOX- ANTENNA MOVEMENT AND BUBBLE TUBE ARRANGEMENT AS PER REQUIREMENTS.

   FIG.14: SLIDER TO CHANGE THE ANGLE AS PER REQUIREMENTS.

   FIG.15: BUBBLE TUBE WITH VARIOUS ANGLES.

   FIG.16: CONNECTION LOW COST GNSS RECEIVERS WITH IRNSS/ NAVIC NAVIGATION SYSTEM WITH RECEIVERS (RECORDING- TEMPORAL LATITUDE, LONGITUDE, GROUND POSITION)