Image Remote Sensing

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Image Remote Sensing is nothing but the identification and analysis of the different features of the Earth’s surface without any direct contact, by means of aerial photographs and satellite imageries.

How it is done?

Before taking leap into image Remote Sensing, one needs to be aware of the proceedings of image generation. The electromagnetic radiation (EMR) is reflected from the object which is to be remote sensed, and the sensor records that and an image is created. In this regard it must be noted that a sensor is a device which records or detect the electromagnetic radiation (EMR) which is emitted from the object concerned. These sensors are mounted mostly on an aircraft or satellite called platforms.

Development of the Image:

Image Remote Sensing is not all about image generation and interpretation. Image Remote Sensing also involves the image processing. After the sensor records the electromagnetic radiation (EMR), it is coded and converted into digital formats, from where the image is generated. After the image is generated, it is subjected to processing. This processing involves three steps:

1. Pre-processing: In this step, the geometric and radiometric properties of the image are corrected. Geometric transformation like reduction, enlargement and rotation are done. Radiometric correction are done for the various error due to the sensor sensitivity, angle of Sun, topography and atmospheric disturbances.
2. Image enhancement: This involves the color correction like adjustment of brightness & contrast and quantization. Any error regarding the registration or alignment of the images are corrected. Image editing, gray scale conversion, histogram conversion and segmentation of the image into different regions are also the part of image enhancement. The image is passed through visible wavelength to convert the True Color Composite (TCC) into False Color Composite (FCC) and vice versa for different application purposes. Image filtering is also an part of this image enhancement.
3. Image Analysis: This is the extraction of the information and data from the image. The extraction of Remote Sensing data from an image can be classified into five types. They are as follows:

• • • Classification
    • Detection of temporal change
    • Extraction of physical quantities
    • Extraction of indices
    • Identification of specific features

The following table shows the nature of image analysis with example:

TYPES OF IMAGE ANALYSIS	NATURE/EXAMPLE
Classification	Vegetation cover, Settlement cover, Land cover in totality
Detection of temporal change	Vegetation cover change through time by detailed observation of multi-dates images
Extraction of physical quantities	Height/elevation, temperature, atmospheric condition etc.
Extraction of indices	Vegetation index, Turbidity index
Identification of specific features	Identification of phenomenon like hurricane, forest fire, discovery of archaeological features.

These image analysis /interpretation is mainly done on the basis of some fundamental elements of the image or photography. They are as follows:

• Tone: This is one of the most effective element in interpretation of image/photo. Example- red color in L3 satellite image indicates vegetation.
• Size: This helps us to determine the size of the objects as well as the scale of the image /photo.
• Shape: This helps us to determine the particular shape of the object.
• Texture: The texture is the impression of the smoothness. Example- an abrupt smooth surface implies the presence of a water body.
• Pattern: This is the indicator of the spatial arrangement of the objects in totality.
• Shadow: This is particularly useful in case of aerial photographs, where shadows plays an important role in the identification of the objects.
• Association: This indicates the arrangement of a particular object in relation with the objects of the surrounding environment. This helps in understanding the mutual relationship shared by them.

Uses of Image Remote Sensing:

Image Remote Sensing are used in various field now a days. The uses of image Remote Sensing are enumerated below:

Environmental Study Disaster Management Ground Survey /Terrain Analysis Geological Survey Urban Planning Agricultural Planning Archeology

Thus, image Remote Sensing is one of the important tool of geographical analysis.