By:

AKSHITA KOHLI

Presentation on

AERIAL PHOTOGRAPHY

AND REMOTE SENSING

INTRODUCTION

Aerial Photography is the science of obtaining photographs from air

using various platforms, mostly aircrafts for studying the surface of earth. It is one of the most common,

versatile and economical forms of remote sensing.

Remote sensing can be broadly defined

as the collection or information about an

object or physical phenomenon without

being in physical contact with the object

or phenomenon.

HISTORY OF AERIAL PHOTOGRAPHY The word “aerial” originated in early 17th century.

[Formed from Latin aerius , from Greek aerios , from

air .] The term "photography" is derived from two Greek

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

Aerial photography dates to mid 1800, wherein the first photographs were taken using balloons and kites.

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

In India aerial photography has been in use since 1920 for aerial survey and interpretation in various fields like geology

FACTORS AFFECTING AERIAL PHOTOGRAPHY Scale Flight direction Time of photography Season of photography Atmospheric conditions Stereoscopic coverage

CHARACTERISTICS OF AERIAL PHOTOGRAPHY Synoptic view Time freezing ability Capability to stop action Three dimensional perspective Spatial and spectral resolution Availability Economy

AERIAL CAMERAS

Aerial photographs can be made with any type of camera (e.g. 35 mm small amateur or 70 mm or special cameras that are purpose built meant for mapping).

Many successful applications have employed aerial photography made from light aircraft with handheld 35 mm cameras.

For the aerial study of large areas, high geometric and radiometric accuracy are required and these can only be obtained from by using cameras that are purpose built.

• Aerial camera are precision built and specifically designed to expose a large number of films/photographs in rapid succession with the ultimate in geometric fidelity and quality.

• These cameras usually have a medium to large format, a high quality lens, a large film magazine, a mount to hold the camera in a vertical position and a motor drive.

• The first ever aerial cameras were mounted on peigions

TYPES OF AERIAL CAMERAS

There are many types of aerial cameras: Aerial mapping camera (single lens), Reconnaissance camera,

Strip camera, Panoramic camera, Multilens camera, the multi camera

array (multiband aerial camera) Digital camera

AERIAL MAPPING CAMERAS

AERIAL MAPPING CAMERAS

Aerial mapping cameras (also called as metric or cartographic cameras) are single lens frame cameras designed to provide extremely high geometric image quality.

They employ a low distortion lens system held in a fixed position relative to the plane of the film.

The film format size is commonly a square of 230 mm on a side. The total width of the film used is 240 mm and the film magazine capacity ranges up to film lengths of 120 metres.

A frame of imagery is acquired with each

opening of the camera shutter, which is tripped at a set frequency by an electronic device called an intervalometer.

They are exclusively used in obtaining aerial photos for remote sensing in general and photogrammetric mapping purposes in particular.

Single lens frame cameras are the most common cameras in use today

LENS ABERRATIONS IN AERIAL CAMERAS

Spherical aberration Coma Astigmatism Curvature of the field Chromatic aberration

CLASSIFICATION OF AERIAL PHOTOGRAPHS

Aerial photographs can be classified on the following basis

Scale Tilt Angular Coverage Film

SCALE

Large scale Medium scale Small scale The specifications of scales varies

from country to country.

TILT

VerticalObliqueHorizontal or Terrestrial

ANGULAR COVERAGE

Narrow AngleNormal AngleWide AngleSuper-wide Angle

FILM Black and white panchromatic Black and white infrared Color Color infra-red/ false color

COST OF AERIAL PHOTOGRAPHY

In India, the cost of aerial photography depends on the flying agency carrying out the operations; scale; area covered and whether the prints are supplied from fresh or existing photography.

E.g. In case of air survey company the cost is Rs. 75.20 per mile (the cost is also regularly revised)

APPLICATION OF AERIAL PHOTOGRAPHY

Mapping Interpretation Map substitute

REMOTE SENSING

Remote sensing refers to obtaining information about objects or areas at the Earth’s surface without being in direct contact with the object or area.

The Remote Sensing is basically a multi-disciplinary science which includes

a combination of various disciplines such as optics, spectroscopy, photography, computer, electronics and telecommunication, satellite launching etc.

All these technologies are integrated to act as one complete system in itself, known as Remote Sensing System.

REMOTE SENSING PROCESS

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TYPES OF REMOTE SENSING

ACTIVE remote sensing systems have their own source of energy (such as Lidar (Light Detection And Ranging), Radar (Radio Detection And Ranging)

PASSIVE remote sensing systems depend upon external source of illumination (such as SUN) Ex: Passive Microwave Radiometer that detects naturally emitted microwave energy & Radiometers

ADVANTAGES OF REMOTE SENSING

1. Relatively cheap and rapid method of acquiring up-to-date information over a large geographical area. Example: Landsat 5 covers each area of 185x160km at a ground resolution of 30m every 18 days, cost of the original digital data is $5 000 (6 200 ha $-1, each hectare contains approximately 11 observations. Even with the cost of ground truthing this is very economical.

2. It is the only practical way to obtain data from inaccessible regions, e.g. Antarctica, Himalaya,

3. At small scales, regional phenomena which are invisible from the ground are clearly visible. Examples: faults and other geological structures. A classic example of seeing the forest instead of the trees.

4. Cheap and rapid method of constructing base maps in the absence of detailed land surveys.

5. Easy to manipulate with the computer, and combine with other geographic coverage in the GIS.

DISADVANTAGES OF REMOTE SENSING

They are not direct samples of the phenomenon, so must be calibrated against reality. This calibration is never exact.

They must be corrected geometrically and georeferenced in order to be useful as maps, not only as pictures. This can be easy or complicated.

Distinct phenomena can be confused if they look the same to the sensor, leading to classification error. Example: artificial & natural grass in green light (but infrared light can easily distinguish them).

Phenomena which were not meant to be

measured (for the application at hand) can interfere with the image and must be accounted for. Examples for land cover classification: atmospheric water vapor, sun vs. shadow (these may be desirable in other applications).

Resolution of satellite imagery is too coarse for detailed mapping and for distinguishing small contrasting areas

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