Surveying Test 4

A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present geographic data.

GIS has wide usage in the fields of science, government, business, and industry, with applications including real estate, public health, crime mapping, national defense, sustainable development, natural resources, climatology, landscape architecture, archaeology, regional and community planning, transportation and logistics.

Concept

Relief displacement (d) = r – r_o

Where,

‘r’ = Radial distance of top of tower from principal point

‘r_o’ = Radial distance of top of tower from principal point

The height of the tower (h) is given by

\(h = \frac{{d \times \left( {H - {h_1}} \right)}}{r}\)

Where

‘H’ = Height above datum from where photograph is taken

h₁ = Elevation of the bottom of the tower from datum

Calculation

Given

H = 1000 m

h₁ = 300 m

r = 100 m, r_o = 80 m

Relief displacement (d) = r – r_o

d = 100 – 80 = 20 m

Height of the tower (h) is given by

\(h = \frac{{d \times \left( {H - {h_1}} \right)}}{r}\)

\(h = \frac{{20 \times \left( {1000 - 300} \right)}}{{100}}\)

h = 140 m

We know that,

Arc (A) = Radius of the curve (R) × Angle subtend by the arc (θ)

Therefore,

\(Radius\;of\;the\;curve\;\left( R \right)\; = \frac{{{\rm{Arc\;}}\left( {\rm{A}} \right)}}{{{\rm{Angle\;subtend\;by\;the\;arc\;}}\left( {\rm{\theta }} \right)}}\)

The angle subtended by the arc (θ) = \(\frac{{5^\circ }}{{180^\circ }} \times \pi \)

\(\theta = 0.0872\;radians\)

\(Radius\;of\;the\;curve\;\left( R \right) = \frac{{10{\rm{\;}}}}{{0.0872}} = 114.6\;m\)

Hence, the radius of the curve for given arc length and angle between them is 114.6 m.

Remote sensing:

Remote sensing is the process of detecting and monitoring the physical characteristics of an area by measuring it's reflected and emitted radiation at a distance typically from satellite or aircraft. Special cameras collect remotely sensed images, which help researchers "sense" things about the Earth.

Types of remote sensing

1.Active Remote Sensing

Active sensors emit energy to scan objects and areas and a sensor then detects and measures the radiation that is reflected or backscattered from the target.

Examples:  RADAR and LiDAR 

2.Passive Remote Sensing

Passive sensors gather radiation that is emitted or reflected by the object or surrounding areas. Reflected sunlight is the most common source of radiation measured by passive sensors.

Examples: film photography, infrared, charge-coupled devices, and radiometers.

Concept:

Area covered by one photograph

\({\rm{a}} = \left( {1{\rm{}}-{\rm{}}{{\rm{P}}_{\rm{L}}}} \right){\rm{\;}}\left( {1{\rm{}}-{\rm{}}{{\rm{P}}_{\rm{S}}}} \right){\rm{\;}}\left( {{\rm{L}} \times {\rm{W}}} \right) \times {\rm{}}\frac{1}{{{{\rm{S}}^2}}}\)

L = length of photograph in the direction of flight

W = width of photograph normal to the direction of flight

S = scale of photograph

P_L = longitudinal overlap

P_S = side overlap

\({\rm{Number\;of\;photographs}} = \frac{{{\rm{total\;area\;to\;be\;covered\;}}\left( {\rm{A}} \right)}}{{{\rm{area\;covered\;by\;one\;photograph}}}}\)

Calculation:

N = 725

\(\frac{{{{\rm{P}}_{\rm{L}}}}}{{{{\rm{P}}_{\rm{S}}}}} = 3\)

P_S = 25%

P_L = 75%

L = 36 cm

W = 36 cm

\( {\rm{a }} = {\rm{ }}\left( {1{\rm{ }}-\frac{{75}}{{100}}} \right)\left( {1{\rm{ }}-\frac{{25}}{{100}}} \right)\left( {36{\rm{ }} \times {\rm{ }}36} \right) \times {10^{ - 10}} \times {\rm{ }}\frac{1}{{{{\rm{S}}^2}}} \)

\({\rm{a\;}} = \frac{{243 \times {{10}^{ - 10}}}}{{{{\rm{S}}^2}}}\left( {{\rm{k}}{{\rm{m}}^2}} \right)\)

A = 600 Km²

\(725 = {\rm{N}} = \frac{{\rm{A}}}{{\rm{a}}} = \frac{{600 \times {{\rm{S}}^2}}}{{243 \times {{10}^{ - 10}}}}\)

\({\rm{Scale}} = \frac{1}{{5835.84}}\)

i.e. 1 in 5835.84

Concept:

The distance AB on ground is given by:

\(AB = \sqrt {{{\left( {{X_B} - {X_A}} \right)}^2} + {{\left( {{Y_B} - {Y_A}} \right)}^2}} \) 

\(\begin{array}{l}{X_B} = \frac{{{x_b}}}{f}\left( {H - {h_B}} \right)\\{X_a} = \frac{{{x_a}}}{f}\left( {H - {h_a}} \right)\end{array}\) 

\(\begin{array}{l}{Y_B} = \frac{{{y_b}}}{f}\left( {H - {h_b}} \right)\\{Y_A} = \frac{{{y_a}}}{f}\left( {H - {h_a}} \right)\end{array}\) 

Calculation:

h_a = 502 m, h_b = 525 m

H = 1670 m

x_a = +15.50 mm

x_b = = +109.20 mm

y_a = -71.20 mm

y_b = -25.20 mm

\({X_b} = \frac{{109.20}}{{158}}\left( {1670 - 525} \right)\) 

X_b = 791.35 m

\({X_a} = \frac{{15.50}}{{158}}\left( {1670 - 502} \right)\) 

X_a = 114.58 m

\({Y_b} = - \frac{{25.20}}{{158}}\left[ {1670 - 525} \right]\) 

Y_b = -182.62 m

\({Y_a} = - \frac{{71.20}}{{158}}\left[ {1670 - 502} \right]\) 

Y_a = -526.34 m

\(AB = \sqrt {{{\left( {791.35 - 114.58} \right)}^2} + {{\left( { - 182.62 - \left( { - 526.34} \right)} \right)}^2}} \) 

AB = 759.05 m

Remote sensing survey:

It is the art and science of obtaining information about an object or feature without physically coming in contact with that object.

Characteristics of remote sensing

1. The data collected using it is in various forms such as variations in acoustic wave distributions (SONAR), variations in force distributions (gravity meter), variations in electromagnetic energy distributions.
2. The remote sensing is the process of inferring surface parameters from measurements of the electromagnetic radiation (EMR) from the Earth’s surface.
3. In space-borne remote sensing, sensors are mounted on a satellite orbiting the earth.

Advantages of remote sensing are:

1. Remote sensing provides data on large areas.
2. It can be used to obtain data of very remote and inaccessible regions.
3. With the help of remote sensing imagery of any area over a continuous period through which any natural changes in the landscape (earthquake) can be analyzed.
4. It is relatively cheap when compared to employing a team of surveyors.
5. Easy and rapid collection of data.
6. Rapid production of maps for interpretation.

The following table gives information regarding the Global Positioning System.