1) What is the importance of Geodesy for Surveying? Why do you think that Geomatics
Should students know about Geodesy? Discuss
Geology enables the determination of the alignment of land, including the position, territories, portion and shape through the application of theodolites, land data systems or other geodetic survey tools. Also, it is through geology that resulted in the creation of the GPS (Geo Information Satellite) systems which as a result has resulted in the optimal exploration of space and regionally associated information. Besides, geodesy for surveying, aids in the assessing the quality of control information to regulate the necessity for extra survey information for engineering, construction, and other projects. The geodetic surveyors and cartographers can and will get jobs in the private and public service, especially in the surveying firms, in the land registries as geodetic engineers. Also, the skills could land a person employment as a cartography personnel.
Through the Geodesy, the students are aware of the need and ability to apply the variety of the earth observations and space technologies which will contribute to the comprehension of the earth systems particularly its dynamics and geometry and gravity interactions. Also, students should gain an understanding regarding how the global geodetic facilities aid to improve the Global Positioning Systems (GPS).
2) Describe Earth Orientation Parameters (Precession, Nutation, Polar Motion and
The length of Day) in detail. While doing so explain the importance of these parametersfor Geodesy?
The present day geodetic methods have emerged to be sophisticated enough to call for precise, frequent determination of the earth orientation parameters. The parameter illustrates the orientation of the earth in the space. For this obligation, there are several geodetic methods that are available for this objective, such as GPS (Global Positioning System), the VLBI (Very Large Baseline Interferometry) just to name afew.
The earth orientation, which is explained as the rotation from the crust of the earth to a geocentric number of axes linked to the geocentric celestial system. The rotation, in particular,is divided into three elements:The precession-nutation; defined through the conventional precession-nutation designand the corrections established by the VLBI observations, the celestial pole offsets in accordance to the parametrization which has been embraced. The precession-nutation aspect and its corrections describe a fictitious axis, called the Celestial Intermediate Pole. On the other hand, the diurnal rotation in the celestial intermediate pole (it remains close to the immediate rotation axis). Besides, it can be disintegrated into an angle escalating with TAI and changes of the earth angular speed. The polar motion of the diurnal rotation around the celestial intermediate pole in accordance to the terrestrial crust. It is not easy to confuse the x and y-axes at the diurnal time scale.
3) a) Describe the different methods used by geodesists to measure gravity. You shouldinclude in your answer an assessment of the techniques; thus information such asaccuracy, thelength of observational period and field procedures should be included.
The geodesists can get the absolute gravity measurements by the means of estimating the time taken by a pellet to fall from some given distance in a vacuum. There is also the possibility to get the relative gravity estimations by the application of the mechanical balance equipment. The gravitational acceleration is 9.8m/s2 or 9.8m/s-2. The geodesists employ the negative notation in which the minus symbol does not imply a negative but instead is applied in place of ‘per’. This is the estimation of the gravitational field of the earth. Notably, the most estimations of the relative gravity were performed by the use of the reverse pendulums. It is as a result of this that a good accuracy was achieved. Through the use of gravimeters, highly desirable measurements can be ascertained at a particular site, called the gravity station. For most of the geodetic works, LaCoste-Romberg gravimeters are applied. It is noted that, there is a possibility to perform a 3,000 to 10,000 miles of gravity measurements monthly with a reasonably good accuracy.
B) Why do we consider Earth’s Gravity Field for surveying measurements? Be specificwith your answers.
The gravitational pull operates between the earth and any other object that is situated in or above the surface of the earth. Similarly, any object that exists within or on the surface of the earth needs the circular path with the rotation of the earth. Thus, the body on the earth’s surface follows the gravity field of the earth since it is held on the surface of the earth by the force of gravity.
4) Describe and explain the CHAMP, GRACE, and GOCE space missions. Discuss theimpact of these missions on geoid determination.
In their work, Flechtner et. al accords that, “The GRACE geoid mission was used to assimilate an MDT in an oceanic state measurement experiment. The study on the GRACE geoid model offered a noticeably higher accuracy than the previous geoid models. On the other hand, its level of accuracy was insufficient to offer extra data on the dynamics of the observations of the ocean when simulated with a dynamic ocean model (37)”. Conversely, with the GOCE mission, significant improvements in the estimation of the short scopes in the geoid height field were anticipated, with the target of 1-2 centimeter accuracy in a distance of 100km. The accuracy of the MDT’s by the use of the GOCE model has been researched in several case studies by drawing comparisons to products primarily by near earth surface drifters.
The CHAMP mission, for the first time, resulted in a concurrently highly accurate gravity and magnetic field estimations in more than a decade. The CHAMP mission was expected to be the opening of a new phase in geopotential studies and be a key contributor to the years of geopotential. The CHAMP mission permitted a comprehensive and integrated approaches to the geodesic structure and the dynamics of the earth. This is an improvement that will sternly improve research regarding the structure and elements of the core of the earth and pave theway for insights and application sectors in geodesy (Flechtner, 42).
5) Explain in detail why, theoretically, leveling loops will not close to zero and how thistheoretical non-closure is overcome.
This is because there are errors that emerge in the process of taking the measurements and since the field of the earth’s gravity is not entirely regular and has a constant gravity, the result is leveling loops that never close. The practical earth’s gravity field, takes place only approximately on small loops alike of the engineering projects, the closure of the loops is relatively small. Conversely, it is not the same in the larger loops that cover areas or continents. In replacement of the differences in height, the geopotential differences do not close in the levelling loops. The situation is overshadowed by applying the compensator that ascertains that the line of vision bears a horizontal view.
6) Describe the advantages and disadvantages of trigonometric leveling and differentialleveling as methods for precise lvelling
On advantages, Dzurisinnotes, “The trigonometric levelling is the most appropriate and adaptable to the rough and uneven topography where the direct levelling methods cannot be used.It is considerably reliable as long as a precise field procedure is maintained. Therefore, an accuracy of 1 to 2 centimeters can be retrieved (98)”. Besides, it is the fast technique in undertaking vertical control for profiling, particularly for the electrical power cables. On the other hand, trigonometric technique is time-consuming as one has to obtain both the horizontal and a vertical slope before using the trigonometric type of measurement. Also, the height difference is equivalent to a rise measured by the increase and reduction technique of spirit levelling. It is, however, relatively less accurate thanspirit levelling.According to Dzurisin (99), “Differential levelling is advantageous in that it is the most accurate leveling technique. Conversely, it can also be time-consumingas it involves shifting the level several times”.
7) Describe and justify the hierarchy for the geodetic network infrastructure for the USA.
In his work, Gupta pronounces that, “The GNSS methods changed the previous particular national reference system into being associated with the superior continental or international system. The national geodetic networks are required to offer a reliable usual coordinate model for the spatial data series and regionals data (128)”. Currently, several federal geodetic network infrastructure is composed of continuous operating referencestations (CORS), which is connected to the ITRF (International Terrestrial reference frame).
A GNSS CORS is composed of a GNSS recipient which has an antenna placed on a stable monument in a secure power supply place and is furnished with a reliable supply of electricity and link to the communication networks for dissemination of information. Various services make this infrastructure accessible to the users. The country’s coverage with the CORS is dependent on the available resources and of the tectonic conditions (Gupta, 136).
8) Explain why, in the past, geodetic networks were set up in a height and horizontalnetwork structure whereas nowadays national mapping authorities are moving to a heightand 4D structure.
The reason for the past use of the horizontal networks is that the horizontal networks were categorizedwith a given order and class. According to FGCC, “It was certified that the latitude and the longitude measurements of the given point could bear a relation to the specific accuracy of the coordinates of the other coordinates in the horizontal control system networks (86)”. The introduction and reasons for the shift to a height and 4D structure are that, in surveying large regions, it is initially important to create settings of horizontal, vertical and gravity management.
These offer a mutual ground for the surveying and mapping endeavors to ascertain an articulate product. The article explains that “A reference system, also called a datum is a basis for numerical amounts that offer a mutual ground. The current control network structures have been established by the country’s such as U.S to offer datum. The stations have a constant, recognizable points linked with the extremely precise observations” (FGCC, 88). From the observations, the values of the datum are calculated and printed. Consequently, the datum provides the basis which is crucial to surveying processes.
9) State Kepler’s three laws and describe the impact that these laws have on satelliteorbital motion.
Kepler’s first law, the laws of ellipses states that the planets are revolving around the sun in apath called an ellipse. The second law; the law of equal areas states that the rate at which a particular planet moves through space is continuously changing. The thirds law, also referred to as the law of harmonies draws a comparison between the orbital period and extent of the orbit of a planet to those of the other planets. Stern notes that “The impacts of the three laws extend to the movement of the natural and artificial satellites and also to the spacecraft which is not powered in orbit in stellar systems or the close planets.”As is stated by Kepler, the laws do not take into consideration the gravitational interactions of the planets. The challenge of accurately predicting the movements of more than two planets under the common attraction is relatively complex; empirical solutions of the three-body difficulties are not obtainable part from some special situations.
10) Explain what a map projection is and why a map projection is needed. Describe thethree principal cartographic criteria which are applied to map projections. Indicate thethree kinds of projection surfaces, how they may coincide and how their positions andalignments might be. State why conformal mappings are used exclusively in geodesy.
In his article, Dempsey affirms that “A map projection can be defined as one of the various techniques applied in the representation of thethe3-dimenstional surface of the earth or any other circular body printed on a 2-dimensional map.”The importance of the maps is that it offers an assumption that the person viewing the map has an orthogonal look at the map. If a surface can be changedto another surface without necessarily stretching, tearing, and or shrinking, then the surface is a suitable and appropriate for a projection surface. Dempsey continues to assert that, “The sphere or ellipsoid are not usable with a plane surface thus any projection that tries to give a projection on a flat sheet might misrepresent the image. The surface for the orientation of the images could be normal (parallel to the earth’s axis), transverse (perpendicular to the axis of the earth) or oblique (any angle between)”. The conformal mappings are used in geodesy because the Conformal projections preserve angles.
Works Cited
Dempsey, Caitlin. "What is Map Projection?" Gis Lounge (2002). Document .
Dzurisin, Daniel. Volcano Deformation: New Geodetic Monitoring Techniques. Springer Science & Business Media, 2006. Print.
FGCC. "Standards and Specifications." Federal Geodetic Control Committee (2001): 84-94. Document .
Frank Flechtner, Nico Sneeuw, Wolf-Dieter Schuh. Observation of the System Earth from Space - CHAMP, GRACE, GOCE and future missions: GEOTECHNOLOGIEN Science Report, Issue 20. Springer Science & Business Media, 2013. Print.
Gupta, Harsh. Encyclopedia of Solid Earth Geophysics. Springer Science & Business Media, 2011. Print.
Stern, David P. Kepler's Three Laws of Planetary Motion. 23 March 2005. document . 13 5 2016.
