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Introduction to Aerial Photography and Photogrammetry

T.SrinivasaRao

Study of Aerial photography - Whether it may be photogrammetry or interpretation - is subset of a large discipline called "Remote Sensing"

What is Remote Sensing?

• Remote sensing is the science and art of

obtaining information about an object, area, or

phenomenon through the analysis of data

acquired by a device that is not in contact with

the object, area, or phenomenon under

investigation

Aerial Photography• The term "photography" is derived from two Greek

words meaning "light" (phos) and "writing" (graphien).

• Photography is production of permanent images by

means of the action of light on sensitized surfaces (film

or array inside a camera), which finally giving rise to a

new form of visual art.

• Aerial Photography means photography from the air

Aerial Photography• Aerial Photography is one of the most common,

versatile and economical forms of remote sensing.

• It is a means of fixing time within the framework of space (deLatil, 1961).

• Aerial photography was the first method of remote sensing and even used today in the era of satellite and electronic scanners. Aerial photographs will still remain the most widely used type of remote sensing data.

• 1858 - Gasper Felix Tournachon "Nadar" took the first aerial photograph from a captive balloon from an altitude of 1,200 feet over Paris.

Aerial Photography

Aerial Photography

1908, Julius Neubronner

• Between 1887 and 1889, Arthur Batut took aerial shots of the South of France using just a kite, a camera.

1887 and 1889, Arthur Batut

Aerial photography

• Between 1887 and 1889, Arthur Batut took aerial shots of the South of

France using just a kite, a camera.

• In 1908, Julius Neubronner, who had used carrier pigeons in his work as an

apothecary, filed a patent for a miniature camera that could be worn by a

pigeon and would be activated by a timing mechanism.

• Pigeons were also used by the French to capture the position of the

German army in the First World War.

• Ref: http://www.newyorker.com/culture/photo-booth/origins-aerial-photography?

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Characteristics of Aerial Photography

1. Synoptic Viewpoint: Aerial photographs give a bird's eye view of large areas enabling us to see surface features in their spatial context. They enable the detection of small scale features and spatial relationships that would not be found on ground.


2. Time freezing ability: They are virtually permanent records of the existing conditions on the Earth’s surface at one point in time, and used as an historical document.

3. Capability to stop action: They provides a stop action view of dynamic conditions and are useful in studying dynamic phenomena such as flooding, moving wildlife, traffic, oil spills, forest fires


4. Three dimensional perspective: It provides a stereoscopic view of the Earth’s surface and make it possible to take measurements horizontally and vertically - a characteristic that is lacking for the majority of remotely sensed data.

5. Spectral and spatial resolution: Aerial photographs are sensitive to radiation in wavelengths that are outside of the spectral sensitivity of the human eye (0.3 µm to 0.9 µm versus 0.4 µm to 0.7 µm).


6. They are sensitive to objects outside the spatial resolving power of human eye.

7. Availability: Aerial photographs are readily available at a range of scales for much of the world.

8. Economy: They are much cheaper than field surveys and are often cheaper and more accurate than maps.

Photogrammetry - Introduction

• Photogrammetry is the science and technology of obtaining spatial measurements and other geometrically reliable products from photographs.


• The principal application of photogrammetry is to determine the spatial position of the natural and man-made features situated on the earth's surface (topographic application).

• Photogrammetry is also used as a measuring tool in architecture, industrial design, deformation studies of structures, accident investigation, medicine etc. These operations are referred to as non-topographic applications.


• Based on the location of sensor– Terrestrial photogrammetry: Images aquired

by a ground based stationary sensor• close range photogrammetry: Sensor present in

close vicinity to the target object.– Aerial photogrammetry: Sensors mounted on

airborne platforms– Space photogrammetry: Mounted on satellites

Methods for photogrammetric measurements and processing

data

– Method 1: Requires complex instruments, which physically model the geometric relationship between the image and object at the time of data acquisition.

– These instruments act as analogue computers and the method is called as analogue or instrumental photogrammetry.

Methods for photo..contd..!

– Method 2: Photogrammetric operations are performed by mathematical modelling.

– This method is called analytical, numerical or computational photogrammetry.

– The use of digital images is a special case here. And because of the wide range of data processing techniques available and the type of instrumentation used here this class is called as digital or softcopy photogrammetry.

• Objectives and priciples of surveying adheres well with the photogrammetric principles and hence, the images acquired using photogrammetric principles can be used for surveying complementing the on-site surveys.

• Imaging has distinct advantages over data acquisition by direct, on-site, measurement.:– An image is a complete, comprehensive record of a scene or

situation as it existed at the instant of acquisition.

– It is a multilevel data set which can provide both quantitative and qualitative information.

– Data acquisition can be accomplished within a short time over large areas by imaging from the air or space.

– Processing and analysis of this data can be made at an appropriate time and place, .distant from the scene and can be repeated or augmented at will.

– The direct observation of directions and distances means point-by-point measurement, while on images continuous measurements can be made by tracing or delineating objects.

The weather and the seasons can place severe restrictions on the primary data

acquisition. On the other hand, under favorable conditions, images can be acquired over a large tract of land within a short period oftime from the air or from space.

It is not feasible to use aerial photography for the survey of small areas.

Equipment needed for the acquisition and processing of the data is more expensive and more complex to operate than those used for surveying on site.

Photogrammetry is not an entirely selfsufficient spatial positioning process. A certain amount of on-site observations are needed to control and verify the analysis.

At the current state of the art, direct in situ measurements can provide the highest possible accuracy for determining spatial positions.

Disadvantages

Applications of photogrammetry

Topographical mapping:• The plotting of map detail and contours is normally carried out using

aerial photogrammetric methods• These methods are used for both original survey and revision, and

replace classical ground methods except where the task is so small that flying is uneconomical

• The technique needs a certain amount of ground surveyed control, but this requirement is being continually reduced with the improvement of aerial triangulation techniques to provide supplementary control.

• A final Field check is necessary


Large Scale Plans:• Large scale plans can be produced

accurately and quickly by air survey methods, but requires thorough checking.

• For large tasks such as road building and major constructions, air survey methods are quicker and cheaper than ground methods.

• profiles for determination of earthwork quantities can be simply obtained using aerial photographs.

• Land use maps• Hydrographic maps: mapping coast lines

etc.,• Exploration and reconnaissance• Terrestrial and Scientific uses

– Detailed surveying of historic buildings– Traffic accidents– Medical applications etc.,

• Stereoscopic applications and measurements


• Cadastral Maps:• Similar types advantages compared

to large scale maps can be gained here.

• Ground techniques are accurate but not required in all cases.

• Air photo techniques provides necessary information with adequate accuracy.