Lesson Note On GPS

What is GPS?

 The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the US government made the system available for civilian use. Prior to 1990, GPS signals were deteriorated so a user could not achieve accuracy better than 10 meters. However, this has been changed and now any standard GPS unit can provide a precision of 4 to5 meters or 12- 15 feet. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS. 

However, tall building s or thick forest cover may block the GPS signal and result in a less precise accuracy. 

The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are traveling at speeds of roughly 7,000 miles an hour. GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. 

The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map. 

As GPS receivers track satellites and calculate your position this process is referred to as Triangulation. Any organization or agency that requires accurate location information can benefit from the efficiency and productivity provided by GPS technology. GPS units are used to collect point, line or polygon data on program activities by recording the latitude and longitude of activity sites, or tacking roads or walking/driving perimeter locations. 

The type of GPS unit used by USAID/Malawi does not provide data measurements necessary for land tenure processes and data collected should not be used for any legal purposes or land dispute as it is not to the required accuracy.

Lesson Note On PROFILE LEVELING

PROFILE LEVELING

DEFINITION OF PROFILE LEVELING

The process of determining the elevations of a series of points at measured intervals along a line such as the centerline of a proposed ditch or road or the centerline of a natural feature such as a stream bed.
Normally we will assign an elevation of 100.00 to the datum rather using the mean sea level elevation.

AN EXTENSION OF DIFFERENTIAL LEVELING

·  Elevations are determined in the same manner.

·  The same definitions define the concepts and terms involved.

·  The same types of mistakes and errors are possible.

·  A page check should always be done.

·  A closure check should be done if the profile line runs between bench marks.

ACCURACY OF ROD READINGS

The backsights, foresights, and elevations of benchmarks and turning points should be recorded to the nearest 0.01 ft. Profile elevations of intermediate points are determined from "ground readings" and thus the foresight readings and subsequent elevations should be recorded to the nearest 0.1 ft.

THEORY

Add rod readings (BS) to benchmark or known turning point elevations to get the elevation of the line of sight (HI).
Subtract rod readings (FS) from the line of sight to establish elevations of unknown points.
Take any number of intermediate FS readings at points along the line until it is necessary to establish a turning point to move the level.
Repeat as required.

LOCATION OF INTERMEDIATE POINTS

A foresight is taken on a bench mark to establish the height of instrument.
A foresight is taken on the stations as required (such as every 100 ft).
Foresights are also taken at breaks in the ground surface and at critical points.
This is repeated until the limit of accurate sighting is reached, at which point a turning point is established and the level is moved.

SCHEMATIC

The level is usually set up off the center line.

PROFILE CROSS SECTIONS

Cross sections are lines of levels or short profiles made perpendicular to the center line of the project. (For example, taking a cross section profile of a stream bed while doing a profile survey of the stream.)
Cross sections are usually taken at regular intervals and at sudden changes in the center-line profile.

CROSS SECTION SCHEMATIC

CROSS SECTIONS

The cross sections must extend a sufficient distance on each side of the center line to provide a view of the surrounding terrain.
Rod readings should be taken at equal intervals on both sides of the center line and at significant changes in the terrain.
Example: for a stream cross section, rod readings could be taken at 15, 30, 45, and 60 ft on each side of the center line as well as the edge of the stream and the top of bank of the stream.

CROSS SECTION FIELD NOTES

·  Field notes for a cross section should include:

an elevation or difference in elevation from the center line
horizontal distance from the center line

Lesson Note On Leveling Survey (Longitudinal and Cross-section)

Leveling Survey (Longitudinal and Cross-section)

Learning Outcome

By the end of this practical work students should be able to:

1.           Setup level equipment

2.           Take back sight, intermediate sight and fore sight reading

3.           Make correct booking

4.           Calculate reduced level of all the point taken

5.           Perform correction to the reduced level

6.           Plot a longitudinal profile and cross section with a suitable scale

Theory

Leveling is the art of determining relative height or elevations of different points on the earth surface. The elevation of a point has been defined as its vertical distance above and below a given reference level surface and usually a mean sea level. The leveling work can be carried out by using direct method or indirect method. The main equipment needed to carry out leveling works is level and staffs. The elevation of the point is calculated using Height of Collimation Method or by using Rise and Fall Method. The final works of the leveling is to transform the numerical data into graphic form either in map or drawing.

Equipment

1. level
Automatic level is used to compare points on the surface of the earth and series of heights observed must be relative to a plane called datum. Automatic level is a device that gives a truly horizontal line. The telescope of this instrument need only be approximately level and the compensating device, usually a pendulum system inside the telescope corrects for the residual mislevelment. This instrument has no bubble tube; therefore preliminary leveling is carried out using the conventional three-screw leveling head and a small target bubble mounted on the tribach which brings the collimation to within 10’ of the horizontal. A prismatic compensator fitted between the eyepiece and the objective lens make correction of slight tilt automatically.

2. Leveling staff

The staff used for ordinary leveling work is sectional and assemble either telescopically or by slotting one another vertically. Most modern designs are manufactured in an aluminum alloy BS4484:Part1:1969 requires length of 3 m, 4m or 5m extension. The graduations are in the form of an E or F shape and the graduations in the 100mm interval.

3. Staff bubble

An instrument to ensure the staff is erected vertically. It is place at the side of the staff.

4. Tapes

Tape is made of synthetic material, glass fiber or linen. The length of the tape is 10m, 20, 30m and 50m are generally available. The tape is graduated at every 5mm and figures every 100mm. the first and the last meter lengths are graduated in millimeters. Whole meter figures are shown in red at every meter.

Procedures

·                     Longitudinal leveling (60m length)

1.           The suitable position for the level to be set up is selected

2.           The level is set up. The temporary adjustment is made

3.           The staff is placed at the bench mark and the reading is taken

4.           The reading is noted in the form provided

5.           Another staff is placed at the distance of 7.5m from the first staff

6.           The reading of second staff is taken and is noted as the intermediate sight

7.           A distance of 7.5m is measured and the third staff position is placed. The reading is noted in the field sheet as an intermediate sight

8.           Step 5 to 7 is repeated until the staff cannot be read. The last reading of the staff before the level is moved is noted in the column foresight. The staff at the foresight position must not move until the back sight reading is taken

9.           The level is moved to new suitable position and the temporary adjustment is made

10.        The back sight reading is taken

11.        A cross section reading is taken at every 15m

12.        Steps 5 to 10 are repeated until the work is completed

13.        A fly level is performed back to the benchmark

14.        The HOC and the reduced level of all the staff positions is calculate

15.        The longitudinal and cross section profile of the road is plotted

·                     Cross section leveling (0m, 40m, 80m, 120m, 160m and 200m)

1.           Five staff positions is selected perpendicular to the longitudinal line at position A, B, C, D and E

2.           The staff is placed at point A and the reading is taken

3.           The reading is entered as intermediate sight if the level is still not being moved from the previous position

4.           Taking reading for points B, C, D and E is continued

5.           After completed cross section leveling, taking the longitudinal leveling is continued until completed

Conclusion

From this practical, we were able to setup the compass survey stations and their equipment correctly. We have taken the reading of three points of static things that have at our location from station A. There are 3.25m, 1.80m and 3.35m from station A

We have calculated the misclosure as mentioned in the local attraction method table. The corrected bearing and the final bearing is determined by followed the correct steps

Discussion and Recommendations

1.           Avoid taking measurement near magnetic sources such as hand phone, watch, electric cable and etc

2.           Make sure the bubbles are properly level

3.           Triple check with the work and reading

4.           Make sure the plum bob properly centered over the peg

Lesson Note On How to establish controls in Hydrographic Surveying

How to establish controls in Hydrographic Surveying
	The first step in making a hydrographic survey is to control both horizontal and vertical. Horizontal Controls: In an extensive survey, the primary horizontal control is established primarily by running theodolite and tape traverse before the triangulation station. Tthe traverse lines being run to following the shore lines approximately. In survey of less extent the primary horizontal control only is required and is established by running a theodolite and tape traverse sufficiently close to shore line. For rough work, the control may be established by running a theodolite and staid traverse or plane table trader. Stadia Surveying: The distances are determined by angles there are stadia hairs from which angles and all calculations are determined without change. Vertical Controls: These are based upon a series of bench marks established near the shore line by spirit leveling and these serve for setting and checking tide gages etc to which the sounding are referred.
Shore Line Surveying: Purpose: To determine the shore lines. To locate the shore details, promise topographical feature, light house, pointt of reference etc. To determine the high and lower water lines for average spring. Both in please and elevations in the case of tidal waters. All irregularities in the shore line as well as the shore details are located by means of offsets measured with a tape form the traverse lines, by staid or plane table. The points of reference should be dearly risible form the water and should be near enough such wing mills, flag poles etc. buoys anchored off the shore and light houses are used reference points. The position of the high water line may be judged roughly form deposits an marks on rocks however to locate it accurately the elev of mean high water is determined and point are located on the shore at that elevation. The line connecting these points represent high water level.