Aerial Survey and Remote Sensing & GIS

 Aerial Survey and Remote Sensing & GIS

*Acrial survey:

Aerial surveying, aerial photography and arial photogrammetry are used to designate the taking of photographs from the air depicting, a portion of the earth surface. The term aerial survey is used to cover both photogrammetry and photo interpolation, photogrammetry may be defined as the science and art of producing a map by compiling the photographs. It is the task of drawing inferences from the qualities of photographed objects.

Aerial photogrammetry was utilized in the first world war. Since then lot of improvements have been made in the development of aerial cameras, and in reducing the photographic information to maps, which has led to the replacement of terrestrial photogrammetry by aerial one. Speed of work and the degree of precision achieved are much higher in aerial photogrammetry. Vertical photographs of the ground are taken with a camera fixed in an aircraft flying along predetermined parallel flight lines. It is essential to establish some ground control. A few points on the ground are located, which can be easily identified on the aerial photographs.

*Aerial photographs:

These are the photographs obtained as a result of photograph of ground from air with a camera mounted on an aircraft. The image of the ground photographed is formed on the focal plane of the camera's objective, where a sensitive film is placed. Various objects in the photograph are distinguished due to distribution of lights and shade and with the aid of some other factors.

Any representation of objects on a plane constructed according to definite matheinatical law is forined by straight rays of light from ground points and passing through the camera objective with the optical centre of the objective as the centre of projection. Therefore an aerial photograph may be regarded as a gnomonic or perspective projection. From the mathematical point of view, however, the plan of the ground is an orthographic projection, which is produced on a plane by projecting the ground points through straight lines perpendicular to the plane.

Long Answer type Questions 

1. What is Remote Sensing?

Answer:

Remote Sensing is the science and art of obtaining information about an object, phenomenon through the analysis of data acquired by a device that is not in contact with the object area or phenomenon under investigation. It consists of collecting, processing and interpreting information about a target without being in physical contact with it.

2. What do you mean by Electromagnetic energy? 

Answer:

Sun is most obvious source of electromagnetic radiation remote sensing. All the objects having temperatures above OK are also sources of this radiations, but with different magnitudes and spectral compositions than that of Sun. Electromagnetic energy is a form of energy which moves with the velocity of light (3x10⁸m/S) in a harmonic pattern Consisting of sinusoidal waves. It has two fields -- the electrical and magnetic fields both orthogonal to each other. Some of other familiar forms are radio waves, ultraviolet rays  ×  rays and heat.

3. Write about Remote Sensing Sensor system?

Answer:

Remote Sensing is concerned with the detection and recording of electromagnetic radiation. The instrument for recording electromagnetic radiation are called Sensor.

Passive system: 

A system that uses an existing source of energy, e.g. sun rays is called a passive system. Such as taking photographs with a camera on clear bright day. It emitted and reflected radiation from ground surface. When the energy source is independent of recording instrument without illumination from the sun no photographs can be taken with camera can be taken with camera.

Examples: 

photographic cameras, television cameras, electro - optical Scanners etc.

Active system:

 System which utilizes man made sources of energy for data collection is called an active system, e.g. taking photographs in dark places with the help of flash bulb. The other examples are rader and laser scanner. It is possible to devise an active sensing system in which waves are propagated near the sensor and bounce on the earth surface.

4. Write about application of Remote Sensing?

 Answer:

Remote Sensing affords a practical means for accurate monitoring of the earth's natural and other resources and of determining the impact of man's activities or air, water and Lands.

Environmental Application: 

It is a vital source and the best means of acquiring basic information, particularly on regional scale. Environmental satellites have been launched for this purpose. The Indian INSAT series of satellites are currently being used for weathering forecasting. Pollution in the form of oil spills and thermal plumes can easily be monitored. Scientists are keeping a continuous watch on such important phenomena as ozone layer depletion and global warning, by using remote sensors.

Mineral Exploration:

Remote Sensing techniques have great promise both for reconnaissance and detailed exploration of non renewable resources like minerals and fossil fuels. It is appropriate where 

(a) Mapping regional lineaments along which an individual group of mining districts may occur.

(b) Mapping local fracture patterns that may control individual ore deposit.

(c) Detecting hydrothermally altered rocks associated with ore deposits. 

(d) Providing basic geological data.

Land use / Land cover analysis

With the rapidly growing population of the world, land use and land cover patterns also undergoing a sea change . Agricultural land is being used for urban purposes forests are being stripped 10 provide land for cultivation. Many of these changes harmful to human interests and may prove to be dangerous. To prevent this damage necessary to plan and regulate these changes. 

 The reasons for the uses of remote sensing are: 

(a) Image of large areas can be acquired rapidly.

(b) the problem of access, that generally hampers ground survey is eliminated. 

(C) Image provide a perspective which is lacking in the ground survey. 

(d) Image interpretation is faster and cheaper than ground surveying.

Natural Hazards:

Earthquake, landslides, Volcanic eruptions, flood are the naturals hazards that cause colossal losses – both material well as human. Remote Sensing can definitely minimize the damage in the following ways.

(a) By analyzing the geological formation of the area.

(b) By providing specific warning of certain natural hazards. 

(c) Assess the damage caused and thereby help in the rescue and aid operations.