dhanalakshmi college of engineering, … in detail about horizontal control & its methods...
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DHANALAKSHMI COLLEGE OF ENGINEERING, CHENNAI
DEPARTMENT OF CIVIL ENGINEERING
CE6404 SURVEYING -II
UNIT – 1: CONTROL SURVEYING
PART – A (2 Marks)
1. What do you understand by reduction to centre? (M-14) If the true station were occupied by computing the corrections and apply them algebraically to the observed values is generally known as reduction of centre
2. Name the instruments used for base line measurement. (M-14)
Marking stakes or tripod
Straining device
Supporting stakes or tripod
Steel tape
Six number of thermometer.
3. List out any four corrections that may be necessary when measuring the length of a baseline
Correction for absolute length
Correction for temperature
Correction for pull or tension
Correction for Sag
Correction for Slope
4. Triangulation networks for covering a large area are composed of any one or a combination of basic figures arranged as a series of chains or a connected centralized network: Enumerate any two such arrangements. (M-12)
Single chain of triangles
When the control points are required to be established in a narrow strip of terrain such as a valleybetween ridges, a layout consisting of single chain of triangles is generally used.
Double chain of triangles
This arrangement is used for covering thelarger width of a belt. This system also has disadvantages of single chain of triangles system.
5. What is meant by control surveying? (D-12) A control survey is a survey that provides positions horizontal or vertical points to which
supplementary surveys are adjusted.
6. What is satellite station? (D-12) A subsidiary station is established as near the true or principal station as possible, the station so established is called a satellite station or eccentric station or false station.
7. What is the principle involved in second order triangulation? (D-11) The secondary triangulation consists of a number of points fixed within the framework of primary triangulation. The stations are fixed at close intervals so that the sizes of the triangles formed are smaller than the primary triangulation.
8. What is the main principle involved in triangulation? (D-10)
The method of surveying called triangulation is based on the trigonometric proposition that if one side and two angles of a triangle are known, the remaining sides can be computed. Furthermore, if the direction of one side is known, the directions of the remaining sides can be determined.
A triangulation system consists of a series of joined or overlapping triangles in which an occasional side is measured and remaining sides are calculated from angles measured at the vertices of the triangles. The vertices of the triangles are known as triangulation stations.
9. Define – Base net A series of triangles connecting the baseline to the main triangulation is called base net.
10. Give the specifications of first order triangulation. (M-09) Average triangle closure : Less than 1 second Maximum triangle closure : Not more than 3 seconds Length of base line : 5 to 15 kilometres Length of the sides of triangles : 30 to 150 kilometres Actual error of base : 1 in 300,000 Probable error of astronomic azimuth : 0.5 seconds
11. What do you mean by figure adjustment in triangulation? (M-09) The determination of the most probable values of the angles involved in any geometrical figure so as to
fulfill geometrical conditions is called figure adjustments.
12. Mention the equipments for base line measurement.
Marking stakes or tripod
Straining device
Supporting stakes or tripod
Steel tape
Six number of thermometer.
13. Give the classification of triangulation system.
First order or Primary Triangulation
Second order or Secondary Triangulation
Third order or Tertiary Triangulation
14. What is well-conditioned triangle? The shape of the triangle should be such that any error in the measurement of angle shall have a minimum effect upon the lengths of the calculated side. Such a triangle is then called well-conditioned triangle.
15. What is meant by triangulation system? Triangulation is nothing but the system consists of not of interconnected triangles. In this method, knowing the length of one side and three angles, the length of other two sides of each triangle can be computed.
16. Define - Base Line The Base line is laid down with great accuracy of measurement & alignment as it forms the basis for the computations of triangulation system the length of the base line depends upon the grades of the triangulation.
17. Enumerate sag correction. A steel tape not supported along its entire length sags in the form of a catenary's, may results. Sag shortens the horizontal distance between end graduations, because the tape length remains the same. Sag can be diminished but not eliminated unless the tape is supported throughout.
The following formulas are used to compute the sag correction:
Where Cs: is the correction for sag, in meter.
Ls: the unsupported length of the tape, in meter. w: weight of the tape per meter of length. W: total weight of the tape between the supports, Kg. P1: is the pull on the tape, in Kg.
18. Define – Trigonometrical Leveling Trigonometrical leveling is the process of determining the differences of elevation of the given station from observed vertical angles and known distance.
19. What are the factors to be considered while selecting the site for base line? The following points should be taken into consideration while selecting the site:
The site should be fairly level. If, however, the ground is sloping, the slope should be uniform and gentle.
The site should be free from obstructions throughout the whole of the length. The line clearing should be cheap in labour and compensation.
The extremities of the base should be intervisible at ground level.
20. Enumerate the points to be borne in mind while selecting the triangulation station.
The triangulation station should be intervisible.
They should form well-shaped triangles. In general, no angles should be smaller than 30º or greater than 120º.
They should be selected that the length of sight is neither too small nor too large.
21. Write short notes on correction for temperature. If the temperature in the field is more than the temperature at which the tape was standardized, the length of the tape increases, measured distance becomes less, and the correction is therefore, additive.
Similarly, if the temperature is less, the length of the tape decreases, measured distance becomes more and the correction is negative. The temperature correction is given by
Ct = α (Tm-T0) L Where α = coefficient of thermal expansion Tm = mean temperature in the field during measurement T0 = temperature during standardization of the tape L = measured length.
22. Define – Permanent Bench mark
A benchmark is a point of reference by which something can be measured. In surveying, a "bench mark" (two words) is a post or other permanent mark established at a known elevation that is used as the basis for measuring the elevation of other topographical points.
23. What is Temporary Bench mark?
A temporary benchmark (TBM) is a fixed point with a known elevation used for level control during construction works and surveys
24. Define -– Arbitrary Bench Mark Arbitrary benchmarks are assumed to be equal to 100 meters generally and then the elevations with respect to assumed benchmark are determined. ... The datum surface may be real or imaginary location with a nominated elevation of zero. The commonly used datum is mean sea level.
25. Define – Extension of baseline In surveying, a baseline is a line between two points on the earth's surface and the direction and distance between them. In the United States Public Land Survey System, a baseline is the principal east-west line upon which all rectangular surveys in a defined area are based.
PART – B (16 Marks)
1. What are the different corrections to be applied while measuring baseline in geodetic surveying? 2. A steel tape 30m long, standardized at 10 o c with a pull of 100N was used for measuring a baseline. Find the correction per tape length, if the temperature at the time of measurement was 20oc and pull applied was 150 N. Density of steel = 3000 kg/m3. Weight of tape=5.88N.
2. What is meant by a “satellite station”? Explain briefly.
3. In a trignometrical measurement of the difference in level of two stations P and Q, 10480 m apart, the following data were obtained. Instrument at P, angle of elevation of Q = 0‟ 15”
Instrument at Q, angle of depression of P = 3‟ 33”
Height of instrument at P = 1.42 m.
Height of instrument at Q = 1.45 m.
Height of signal at P = 3.95 m.
Height of signal at Q = 3.92 m Find the difference in level between P and Q and the curvature and refraction correction.
4. From an eccentric Station S, 12.25 meters to the west of the main station B, the following angles were measured BSC = 760251; CSA = 540321 2011. The stations S and C are to the opposite sides of the line AB. Calculate the correct angle ABC if the lengths AB and BC are 5286.5 and 4932.2m respectively.
5. What are the methods of measurement of the base line and explain any two with neat sketch.
6. A steel tape is 30 m long at a temp of 15ºc when lying horizontal on the ground. Its c/s area is 0.08 cm2 and weight of 18.kg (18N) and. Co-efficient of expansion is 117 x10-7/ºc. The tape is stretched over 3 supports which are at the same level and at equal intervals. Calculate the actual length between the end graduations under the following conditions. Temp = 25ºc, Pull -180 kg, E = 2.1 x 105 N/cm2.
7. Explain in detail about Horizontal control & its methods andVertical Control & its Methods.
8. State the factors to be considered while selecting base line and also explain with neat sketches how to extend the base line in the field.
9. Explain in detail about the Classification of triangulation system.
10. What is meant by a “satellite station”? Explain briefly.
UNIT – II: SURVEY ADJUSTMENTS
PART – A (2 Marks)
1. State the principle of least square. (M-14,13) The most probable value of an observed quantity available from a given set of observations is the one for which the sum of the squares of the residual errors is a minimum.
2. What is weight of an observation? (M-14,13)
The weight of an observation is a number giving an indication of its precision and trust worthiness, when making a comparison between several quantities of different worth.
If a certain observation of weight 4 it means that it is 4 times as much reliable as an observation of weight 1. When two quantities (or) observations are assumed to be equally reliable, the observed values are said to be of equal weight (or) of unit weight.
3. Define – Correlates (M-13) Correlates are the unknown multiples or independent constants used for finding most probable values of unknowns.
4. Define - most probable value (M-13) It is defined as the quantity which added to and subtracted from the most probable value, fixes the limit within which it is an even chance the true value of the measured quantity must lie.
5. Distinguish between the observed value and the most probable value of a quantity. (M-12)
Observed value Most probable value
An observed value of a quantity is the value obtained when it is corrected for all the known errors.
The most probable value of a quantity is the one which has more chances of being true than has any other.
6. What are normal equations? (M-12)
A normal equation is the one which is formed by the multiplying each equation by the coefficient of the unknown, whose normal equation is to be formed out by adding the equation thus formed
7. What are the kinds of error possible in survey work? (M-12)
Mistakes
Systematic error
Accidental error
True error
Residual error
Most probable error
8. Differentiate between most probable error from residual error. (M-11)
Most probable error Residual error
It is defined as the quantity which added to and subtracted from the most probable value, fixes the limit within which it is an even chance the true value of the measured quantity must lie.
A residual error is the difference between most probable value of the quantity and its observed value.
9. What are the classifications of errors? (M-12)
Errors of measurement are of three kinds:
Mistakes
Systematic errors
Accidental errors
10. Write a note on accidental errors. (N-10) The Accidental Errors are those which remain after mistakes and systematical errors have been eliminated and are caused by the combination of reasons beyond the ability of the observer to control.
11. Give any four random errors occur in linear measurements. (N-10)
Mistakes
Systematic errors
Accidental errors
12. Define – conditioned quantity (M-10) It is the one whose value is dependent upon the values of one (or) more quantities. Its values bear a rigid relation to some other quantities. It is also called “dependent quantities”
13. Distinguish between true error and residual error. (M-09)
True Error Residual Error
A true error is the difference between the true value of a quantity and its observed value.
A residual error is the difference between most probable value of the quantity and its observed value
14. Give an account on method of equal shifts. (M-09) The method of equal shifts indicates that any shift which is necessary to satisfy the local equation should be the same for each triangle of the polygon. Similarly any shifts necessary to satisfied side equation should be the same for each triangle.
15. Give the rules of assigning weight age to the field observations.
The weight of the angle varies directly as the number of the observations made for the measurement of that angle.
The corrections to be applied to various observed quantities are in inverse proportion to their weights.
16. Define – Systematic and accidental errors. Systematic Error The systematic error is an error that under the same conditions will always be of the same size and sign. It is simply due to the error in instrument. These errors may be regarded as positive or negative according with whether they make the result too small (or) too great. This effect is cumulative. Accidental error The Accidental Errors are those which remain after mistakes and systematical errors have been eliminated and are caused by the combination of reasons beyond the ability of the observer to control.
17. Define - true error A true error is the difference between the true value of a quantity and its observed value.
18. Differentiate between conditioned quantity and conditioned equation.
Conditioned quantity Conditioned equation
A conditioned quantity is the one whose value is dependent upon the values of one or more quantities.
A conditioned equation is the equation expressing the relation existing between the several dependent quantities.
19. What are the conditions to be satisfied when correcting the measured angles?
Conditions imposed by the station of observation, known as the station adjustment
Conditions imposed by the figure, known as the figure adjustment.
20. What do you mean by figure adjustments in triangulation? The determination of the most probable values of the angles involved in any geometrical figure so as to fulfill geometrical conditions is called the figure adjustment.
21. Distinguish between true and most probable values.
True value Most probable value
o The true value of a quantity is the value which is absolutely free from all the errors.
o It is indeterminate since the true error is never known.
o The most probable value of a quantity is the one which has more chances of being true than has any other.
o It is deduced from the several measurements on which it is based.
22. State the law of accidental errors. This law defines the occurrence of errors and can be expressed in the form of equation which is used
to compute the probable value of a quantity. 23. Mention the adjustments of simple triangulation networks.
Single angle adjustment
Station adjustment
Figure adjustment
24. Define – Systematic Errors The systematic error is an error that under the same conditions will always be of the same size and
sign. It is simply due to the error in instrument. These errors may be regarded as positive or negative according with whether they make the result too small (or) too great. This effect is cumulative.
25. State Accidental Errors. The Accidental Errors are those which remain after mistakes and systematical errors have been
eliminated and are caused by the combination of reasons beyond the ability of the observer to control.
PART - B (16 Marks)
1. What are the temporary adjustments of dumpy level? How is it done?
2. What is reciprocal leveling and why is it employed? What errors will be eliminated by this?
3. Enumerate the principle of least squares as applied to observations of equal weight and to those for which different weights are assigned
4. Explain the methods of correlates.
5. What do you mean by station adjustment? Explain.
6. The following are the three angles α β and γ observed at a station P closing the horizon, along with their probable errors of measurement. Determine their corrected values α = 78o 12‟ 12” ± 2” β = 136o 48‟ 30” ± 4” γ = 144o 59‟ 08” ± 5”
7. What do you mean by figure adjustment? Explain
8. Adjust the angles by method of correlates.
9. Explain in detail about errors sources and error classification.
10. What are the precautions and correction can be applied in error reduction.
UNIT – III: TOTAL STATION SURVEYING
PART – A (2 Marks)
1. What are the advantages of a total station over conventional surveying instruments?
Relatively quick collection of information
Multiple surveys can be performed at one set-up location.
Easy to perform distance and horizontal measurements with simultaneous calculation of project coordinates (Northings, Eastings, and Elevations).
Layout of construction site quickly and efficiently.
2. What are the fundamental parameters of a total station? A total station is a digital theodolite with an EDM and a microprocessor. The theodolite measures the horizontal angle and the vertical angle of the line of sight from a center of the total station to the center of a target on a point to measure.
3. What are the precautions to be taken while using a total station?
Always carry a total station in a locked hard case even for a very short distance.
Do not move or carry a tripod with the total station fixed on it, except for centering.
Use both hands to hold the total station handle.
4. Write short notes on atmospheric and scale corrections factors of total stations. The scale factor (in ppm) is a sum of atmospheric correction (ΔD1 in ppm), in reduction to mean sea level (ΔD2 in ppm) and the projection scale factor(ΔD3 in ppm). The atmospheric correction factor is a function of temperature, atmospheric pressure and humidity. Using the formulae narrated below, the atmospheric correction can be calculated very easily.
Where ΔD1 = atmospheric correction in ppm
P = atmospheric pressure(hPa) t = temperature (°C) at the time of observation h = Relative humidity (%)
= 1/273.16
5. Write the application of total station?
Updating mapping
Topographic survey
Hydrographic survey
Cadastral survey
Project construction survey
Road, Rail Survey
Mining survey
6. List out the equipment inventory required for a total station. The minimum equipment inventory required is as follows Total station set
Total station instrument in a a hard case
Battery charger
Extra batteries
Memory module/Card, serial cable
Rain cover
User manuals
Tripod
Tape measure
7. How is a total station set up over a point during the field work?
Tripod Setup
Mount instrument on tripod
Focus on survey point
Leveling
Electronically verify Leveling
Adjust image & Reticle focus
8. What is total station surveying?
A form of an electronic theodolite combined with an electronic distance measuring device (EDM).
The primary function is to measure slope distance, vertical angle, and horizontal angle from a setup point to a foresight point.
9. List out the types of EDM.
Electro-optical instruments: They transmit light having wavelengths in the range of 0.7 to 1.2 micrometers within or slightly beyond the visible region of the spectrum.
Microwave instruments: They transmit microwaves with frequencies in the range of 3 to 35 GHz corresponding to wavelengths of about 1.0 to 8.6 millimeters.
10. State the principle of EDM. Electromagnetic energy propagates through to atmosphere in accordance with the following equation:
V = f. Where V is the velocity of electromagnetic energy, in meters per second; f the modulated frequency
of the energy, in hertz; and the wavelength, in meters. This propagation can be represented by the sinusoidal curve illustrated in the following figure, which shows one wavelength or cycle. Portions of wavelengths or the positions of points along the wavelength are given by phase angles.
11. Define – EDM Electro-magnetic distance measurement is a general term used collectively in the measurement of distances applying electronic methods. Basically the EDM method is based on generation, propagation, reflection and subsequent reception of electromagnetic waves.
12. Classify total station surveying
Manual Total Station
Semi Automated Total Station
Automated Total Station
Advanced Total station o Servo driven Total station & o Robotic Total station o
13. State the advantage of visible light EDM over microwave EDM.
The advantage of visible light EDM over microwave EDM instruments is that only one instrument is required, which work in conjugation with the inexpensive corner tube reflector.
14. What is Azimuth mark? An azimuth mark is a back sight without a prism. An azimuth mark is a distal point or an object with a sharp and clear vertical edge to be taken as a reference of orientation from the station.
15. Define – Tellurometer
Tellurometer comes under microwave instruments.
In this high frequency radio waves(or micro waves) are used instead of light waves.
It can be worked with a light weight 12 or 24 old battery.
Observations can be taken both during day as well as night.
16. Write down the types of EDM instruments. The types of EDM instruments are
Microwave instruments
Visible light instruments
Infrared instruments.
17. Define – Geodimeter
A geodimeter comes under category of visible light principles.
These instruments use visible light as carrier way with higher frequency of the order of 5*1014Hz.
Here the observations are normally restricted in the night.
18. List out the disadvantages of total station surveying.
Vertical elevation accuracy not as accurate as using conventional survey level and rod technique.
Horizontal coordinates are calculated on a rectangular grid system. However, the real world should be based on a spheroid and rectangular coordinates must be transformed to geographic coordinates if projects are large scale. Eg: Highways, large buildings etc.
19. What are the two types of accuracy related to total station? The accuracy of a total station is dependent on instrument type.
Angle Accuracy (Horizontal or Vertical) can range from 2” to 5”
Distance Accuracy can range from: +/- (0.8 + 1 ppm x D) mm to +/- (3 + 3 ppm X D) mm Where D = distance measured
20. List out the sources of errors for total station.
Circle eccentricity
Horizontal collimation error
Height of standards error:
Circle graduation error
Vertical circle error
Pointing errors
Uneven heating of the instrument.
Vibrations
Collimation errors
Vertical angles and elevations
21. What are the two types of traversing? Open traverse: It starts at a point of known position and terminates at a point of Unknown position. Closed traverse: It originates at a point of known position and close on another point of known
horizontal position. 22. Give the application of traversing.
a. Omitted Measurements b. Area of A Closed Traverse
By the coordinate method
By the double meridian distance method
23. Define – Traverse A traverse consists of a series of straight lines connecting successive points. The points defining the ends of the traverse lines are called traverse stations or traverse points.
24. Distinguish between triangulation and trilateration
Triangulation Trilateration
The positions of the points of interest are computed based on measured angles and two know points. From those angles, the distances are computed which are in turn used to calculate coordinates for the target points.
In trilateration, we work with distances. From those distances, we compute the angles. Once computed, we can use them in conjunction with the distances to get the position of the target points.
25. State the principle of triangulation. Triangulation is nothing but the system consists of not of interconnected triangles. In this method, knowing the length of one side and three angles, the length of other two sides of each triangle can be computed.
PART – B (16 Marks)
1. Explain in detail about Electromagnetic Spectrum and its applications?
2. Explain in detail about the properties of electromagnetic waves?
3. Explain in detail about the different types of EDM?
4. Explain the working principle of EDM?
5. Why phase comparison and modulation is preferred over time measurement in EDM?
6. Explain the working principle of “Tellurometer
7. Explain the working principle of “Geodimeter”
8. Explain the working principle of “Wild Distomats”
9. Explain in detail about the sources of errors in Total station and EDM.
10. How is Traversing and Trilateration done using Total station?
UNIT – IV: GPS SURVEYING
PART – A (2 Marks)
1. Define – GPS GPS, which stands for Global Positioning System, is a radio navigation system that allows land, sea, and airborne users to determine their exact location, velocity, and time 24 hours a day, in all weather conditions, anywhere in the world.
2. Write short notes on basics of GPS? NAVSTAR GPS refers to a group of US Department of Defense satellites constantly circling the earth. The satellites transmits very low-power radio signals, allowing anyone with a GPS receiver to determine their location on the earth. The GPS is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations operated by US Department of Defense.
3. List out the component of GPS. GPS systems rely on three main components: the satellite component, the ground component and the user component.
4. What are the advantages of GPS over total station?
Inter-station visibility between points is not required.
Can be used at any time of the day or night and in any weather.
Produces results with very high geodetic accuracy.
More work can be accomplished in less time with fewer people.
5. Explain the application of GPS.
Automobile Navigation
Fleet Tracking
Mapping and surveying
Mining
Recreational Use
6. Write the observation techniques of GPS.
In surveying applications, accepted method is relative positioning although Differential GPS with code receivers could be used in projects that require a very low order of accuracy, e.g. locating cellular phone transmission towers
In relative positioning, two or more receivers make simultaneous phase measurements on the carrier frequencies from four or more satellites
Only the data collected from the same satellites by the receivers occupying the ends of a baseline can be used in the computation of this baseline
7. What is meant by segment and classify its types.
The Space Segment -Satellites orbiting the earth.
The Control Segment -Stations positioned on the earth’s equator to control the satellites
The User Segment -Anybody that receives and uses the GPS signal.
8. Define -- Control Segment The control segment tracks the satellites and then provides them with corrected orbital and time information. The control segment consists of five unmanned monitor stations and one Master control station. The five unmanned stations monitor GPS satellite signals and then send that information to the Master Control station where anomalies are corrected and sent back to the GPS satellites through ground antennas.
9. Define – Space segment The space segment consists of at least 24 satellites and is the heart of the system. The satellites are in a high orbit about 20,200 km above the earth’s surface. Operating at such a high altitude allows the signals to cover a greater area. The satellites are arranged in their orbits so a GPS receiver on the earth can always receive signals or information from at least four of them at any given time.
10. Define – User segment The user segment consists of the users and their GPS receivers. The number of simultaneous users is limitless.
11. Comparison between Control and Space segment.
Space segment Control segment
The Space Segment consists of constellation of space craft, and the signals that are broadcast by them, which allow user to determine position, velocity and time.
The space segment consists of at least 24 satellites and is the heart of the system.
The control segment consists of facilities necessary for satellite health monitoring, telemetry tracking, command and control and satellite orbit and clock error computations.
The control segment consists of five unmanned monitor stations and one Master control station.
12. Distinguish between Space and User segment.
Space segment User segment
The Space Segment consists of constellation of space craft, and the signals that are broadcast by them, which allow user to determine position, velocity and time.
The user segment consists of the users and their GPS receivers. The number of simultaneous users is limitless.
13. Draw the signal structure
14. Give short notes on Task of control segment.
All five stations are monitor stations, tracking the satellites and sending the tracking data to the Master Control Station. Falcon Air Force Base, Colorado Springs, is the site of the Master Control Station (MCS), where the tracking data is processed in order to compute the satellite ephemerides and satellite clock corrections.
15. What is meant by Receiver and list out its type? GPS receivers take information transmitted from the satellites and uses triangulation to calculate a user’s exact location. Types: o Hand held Receiver o Geodetic Receiver
16. Define – Hand Held Receiver
Handheld GPS receivers are used for absolute positioning or for relative positioning using DGPS-services or WAAS/EGNOS signals. The positioning is realized using code pseudo-ranges.
Moreover it is well known that some of the handheld receivers use phase-smoothed code for positioning. This means that the phase signal is available and may be used for Precise Differential GPS (PDGPS) positioning.
17. Define – Geodetic Receiver
Geodetic GPS receivers have the advantage of providing additionally the P-code observations, with a noise level smaller than the noise on the C/A code.
The accuracy requirements of geodetic receivers are usually about 1-5 cm (or even better).
18. Write Short notes on triangulation in GPS.
The basis of GPS is "triangulation" from satellites.
Triangulation is a process by which the location of a radio transmitter can be determined by measuring either the radial distance, or the direction, of the received signal from two or three different points.
19. Define – GPS data processing Data processing is simply the conversion of raw data to meaningful information through a process. Data is manipulated to produce results that lead to a resolution of a problem or improvement of an existing situation. Similar to a production process, it follows a cycle where inputs (raw data) are fed to a process (computer systems, software, etc.) to produce output (information and insights).
20. Write down the steps of GPS data processing?
Collection of Data
Preparation of data and analysis
Verification of input data
Processing
Output and Interpretation
Storage of Data
21. What is meant by Anti spoofing? Anti-spoofing (AS) is a protection against “fake” transmissions by encrypting the P-code to form the Y-code. This ensures that the GPS signals cannot be disturbed (spoofed) by a GPS-like transmitter on the Earth. The anti-spoofing procedure converts the P-code to the Y-code which is only usable when a secret conversion algorithm is available to the receiver.
22. Define – Selective Availability Selective Availability is a process applied by the U.S. Department of Defense to the GPS signal. This is intended to deny civilian and hostile foreign powers the full accuracy of GPS by subjecting the satellite clocks to a process known as .dithering. which alters their time slightly.
23. What is Orbit determination & write its type. Orbit determination is the process to estimate the position and velocity of a satellite at a specific epoch based on models of the forces acting on the satellite, integration of satellite orbital motion equations and measurements to the satellites. Orbit determination (OD) is generally divided into two categories: preliminary orbit determination and precise orbit determination(POD).
24. What are the limitations of GPS? In order to operate with GPS it is important that the GPS Antenna has a clearview to at least 4 satellites. Sometimes, the satellite signals can be blocked by tall buildings, trees etc. Hence, GPS cannot be used indoors. It is also difficult to use GPS in town centers or woodland. Due to this limitation, it may prove more cost effective in some survey applications to use an optical total station or to combine use of such an instrument with GPS.
25. What is Orbit Representation? Orbit Representation is a means of representing a satellite orbit as a continuous trajectory with discrete observation data at the time of interest. The simplest orbit representation is the “osculating Keplerianelements” method, which describes an orbit as an ellipse.
26. Why are differential GPS data more accurate than handheld GPS data?
GPS satellites send out two different signals: L1 and L2. Differential GPS receivers measure both L1 and L2, whereas handheld GPS receivers measure only L1.
Differential GPS uses antennas specially constructed to reduce multipath error.
Differential GPS receivers store position data. Handheld GPS receivers do not.
Differential GPS data are processed at data storage facilities and corrected for errors. Handheld GPS data are not processed.
PART – B (16 Marks)
1. Briefly explain fundamentals of GPS surveying ?
2. Write about electro- optical system?
3. What is total station, briefly explain?
4. Write on notes on infrared GPS? Briefly Explain.
5. Write about briefly explain signal?
6. Explain signal structures? Briefly
7. Write short notes on orbit?
8. Explain portable GPS and advantages?
9. How does GPS work? Explain
10. What is IS – 95? Explain
UNIT – V : ADVANCED TOPIC IN SURVEYING
PART – A (2 Marks)
1. Define - celestial sphere and Azimuth axis (M-14) Celestial sphere The millions of stars that we see in the sky on a clear cloudless night are all at varying distances from us. Since we are concerned with their relative distance rather than their actual distance from the observer. It is exceedingly convenient to picture the stars as distributed over the surface of an imaginary spherical sky having its center at the position of the observer. This imaginary sphere on which the star appears to lie or to be studded is known as the celestial sphere. Azimuth axis The azimuth of a heavenly body is the angle between the observer’s meridian and the vertical circle passing through the body.
2. What is the use of station pointer? (M-14) The station pointer is a three-armed protractor and consists of a graduated circle with fixed arm and two movable arms to the either side of the fixed arm. All the three arms have beveled edges.
3. What do you understand by echo-sounding? (M-14)
A fathometer is used for ocean sounding where the depth of water is too much, and to make a continuous and accurate record of depth of water below the boat or ship at which it is installed.
It is an echo-sounding instrument in which water depths are obtained by determining the time required for the sound waves to travel from a point near the surface of the water to the bottom and back.
4. List out the generally used methods for determining the latitude of a place (M-14) The most generally used methods are
By meridian altitude of sun or star.
By Zenith pair observation of stars.
By meridian altitude of star at lower and upper culminations.
By ex-meridian observation of star or sun.
By determining the altitude of the pole star.
By prime vertical transits.
5. Define – Hydrographic surveying (M-13) Hydrographic surveying is that branch of surveying which deals with the measurement of bodies of water. It is used for making nautical charts for navigation and determinations of rocks, sand bars, lights and buoys.
6. Define – Azimuth (M-13)
The azimuth of a heavenly body is the angle between the observer’s meridian and the vertical circle passing through the body. The determination of azimuth or the direction of meridian at survey station consist in obtaining the azimuth or true bearing of any line from the station, so that the azimuth of all the survey lines meeting there may be derived.
7. Define – Equation of Time (M-13) At any instant the difference between apparent solar time and mean solar time is known as the equation of time. Values of equation of time are sometimes prefixed with the plus sign (sun after clock) or minus sign (sun before clock). Equation of time = R.A. of the mean sun – R.A. of the sun
8. Define – Right Ascension (R.A) (M-12) It is the equatorial angular distance measured eastward from the first point of Aries to the hour circle through through the heavenly body.
9. Define – Hour angle
The hour angle of a heavenly body is the angle between the observer’s meridian and the declination circle passing through the body. The hour angle is always measured westwards.
10. Name the different equipments needed for soundings. The equipment needed for soundings are:
Sounding boat
Sounding rods or poles
Lead lines
Sounding machine
Fathometer
11. What is meant by sounding? The measurement of depth below the water surface is called sounding. Here the horizontal line or the datum is the surface of water, the level of which continuously goes on changing with time.
12. Distinguish between terrestrial and aerial photogrammetry Terrestrial photogrammetry: Photographs taken from a fixed position on or near the ground and the branch deals on such aspects are called terrestrial photogrammetry. Aerial photogrammetry: Aerial photogrammetry is the other branch wherein the photograph are taken by cameras mounted on an aircraft flying over the area.
13. State three point problem in hydrographic surveying.
If a sounding is located by two angles from the boat by observations to three known points on the shore, the plotting can be done adopting three-point problem. The three point problem may be solved by mechanical, graphical or analytical methods.
14. What are the applications of photogrammetry?
Construction of planimetric and topographic maps.
Mountainous and hilly areas with less number of trees can be very satisfactorily surveyed.
Aerial surveying is most suitable for reconnaissance.
Acquisition of military intelligence.
Interpretation of geology and soil details.
Largely used for the surveys of buildings.
15. What is Tides? List out the types of tides? All celestial bodies exert a gravitational force on each other. These forces of attraction between earth and other celestial bodies (mainly moon and sun) cause periodical variations in the level of a water surface, commonly known as tides.
Types of tides: a. Lunar tides
b. Solar tides
c. Spring and neap tide (combined effect)
d. Other effects
16. Define – Mean Sea Level Mean sea level may be defined as the mean level of the sea, obtained by taking the mean of all the height of the tide as measured at hourly intervals over some states period covering a whole number of complete tides.
17. What do you understand by route surveying? Surveys along a comparatively narrow strip of territory for the location, design and construction of any route of transportation, such as highways and rail road’s, aqueduct, canals, pipe line for water, sewage, oil and gas, cable ways and belt conveyors and power, telephone and telegraph transmission is called route surveying.
18. What is reconnaissance? Reconnaissance survey is a rapid but through examination of an area or a strip of territory between the termine of the project to determine which of the several possible routes may be worthy of a detailed survey.
19. Define – Simple and Compound curve. Simple:Simple curve is the one which consists of a single arc of a circle. It is tangential to both the straight lines. Compound:It consists of two or more simple arcs that turn in the same direction and join at common tangent point.
20. Distinguish between compound and reverse curves. Compound: It consists of two or more simple arcs that turn in the same direction and join at common tangent point. Reverse: It consists of two simple curves of opposite direction join at a common tangent point called the point of reverse curvature. It is used in mountainous countries in cities and in the layout of railway spur tracks and cross over.
21. List the functions of transition curves. A curve having a gradual varying radius is called a transition curve. For example a curve with infinite radius in the beginning and varying gradually to a finite radius. Transition curves are provided in railway tracks to ensure safe running of the trains without overturning or derailment. These curves provide comfort to passengers both on roads and on railways.
22. Define – Transition Curve A transition curve is a curve of varying radius introduced between a straight and circular curve, or between two branches of a compound curve or reverse curve.
23. Define – Super Elevation
Super elevation or cant is the amount by which the outer end of the road or outer rail is raised above the inner line
24. Define – Sight Distance It is the length of roadway ahead visible to the driver. The stopping sight distance is the total distance travelled during the three time intervals: a. the time for the driver to perceive the hazard b. the time to react c. the time to stop the vehicle after the brakes is applied.
25. What is vertical curve? A Vertical curve is used to join two intersecting grade lines of the rail roads, highways or other routes to smooth out the changes in vertical motion. The vertical curve contributes to the safety, comfort and appearance.
26. Name the instrumental methods for setting out a circular curve.
The following are the instrumental methods commonly used for setting out a circular curve: a. Rankine’s method of tangential angle b. Two theodolite method & c. Tacheometric method.
27. What are the corrections to be applied for the observed altitude of sun? The observed altitude has to be corrected to obtain the true altitude. The corrections to be applied are 1. Instrumental corrections
a. Index error
b. Bubble error
2. Observational corrections
a. Correction for parallax
b. Correction for refraction
c. Correction for dip of the horizon
d. Correction for semi-diameter 28. Define – Sidereal Time
The sidereal time at any instant is the hour angle of the first point of arises reckoned westward from 0h to 24h. The right ascension of the meridian of a place is known as Local sidereal time (L.S.T). Local sidereal time (L.S.T) = Right ascension of a star + westerly hour angle of a star.
29. What are lunar and solar tides? Lunar tides:
The periodical variations in natural water level are called as tides. The resultant force between the earth and moon causes lunar tides. Solar tides:
The production of solar tides is due to force of attraction between earth and sun which is similar to the lunar tides.
30. What is the relation between right ascension and hour angle? Right ascension of the sun = local sidereal time – Hour angle of the sun.
PART – B (16 Marks)
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1. Explain briefly components of hydrographic survey?
2. Comparison between Aerial photographs and maps
3. List the different methods of locating soundings. Explain any two methods.
4. Define stereoscope and list out the types of stereoscopes?
5. State the equipment used for soundings and explain them.
6. State stereoscope and explain briefly the basic types of stereoscopes.
7. Explain briefly about the Electro-Magnetic Distance measurement.
8. What is a three point problem in hydrographic surveying? What are the various solution for the
Problems? Explain any one method.
9. What is Echo-sounding? Explain their advantages.
10. What do you understand by tides? How do they form? Explain the effects of tides.