RS - Remote Sensing

Remote Sensing (RS) is the acquiring of Data about an object without touching it.

RS is an art and science of obtaining information about an object or feature without physically coming in contact with that object or feature. The data collected can be of many forms: variations in acoustic wave distributions (sonar), force distributions (gravity meter), electromagnetic energy distributions (eye), etc.

What Remote Sensing is it used for?

The Remote Sensing process of inferring surface parameters from measurements of the Electromagnetic Radiation (EMR) from the Earth’s surface. EMR can either be reflected or emitted from the Earth’s surface.

Electromagnetic Radiation(EMR)

Electromagnetic Radiation(EMR) or Electromagnetic energy is the energy propagated in the form of an advancing interaction between electric and magnetic fields. It travels with the velocity of light. Visible light, ultraviolet, and infrared rays, heat, radio waves, X-rays all are different forms of electromagnetic energy.

Electromagnetic Spectrum

The Electromagnetic Spectrum is represented by Electromagnetic waves. It’s characterized by their wavelength or frequency, linked by the speed of light. The frequency is associated with energy. High frequency is high energy.

Elements of Remote Sensing

A. Emission of electromagnetic radiation. (The Sun or an EMR source located on the platform)

B. The Transmission of energy from the source to the object. (Absorption and scattering of the EMR while transmission)

C. Interaction of EMR with the object and subsequent reflection and emission

D. Transmission of energy from the object to the sensor

E. Recording of energy by the sensor. (Photographic or non-photographic sensors)

F. In Transmission of the recorded information to the ground station

G. Processing of the data into digital or hard copy image

H. Analysis of data

Active and Passive Remote Sensing

Active sensor– have its source of light or illumination and its sensor measures reflected energy.

In the case of Active Remote Sensing, energy is generated and sent from the RS platform towards the targets. The energy reflected from the targets are recorded using sensors onboard the RS platform. Most of the microwave RS is done through Active RS.

Passive sensor- measure reflected sunlight that was emitted from the sun.

Passive Remote Sensing, source of energy is that naturally available such as the Sun. Most of the RS systems work in passive mode using solar energy as the source of EMR. Solar energy reflected by the targets at specific wavelength bands is recorded using sensors onboard air-borne or space-borne platforms.

Remote Sensing Platforms

RS platforms can be classified as follows, based on the elevation from the Earth’s surface at which these platforms are placed.

1. Ground borne remote sensing

Ground-level remote sensors are very close to the ground.

They are used to develop and calibrate sensors for different features on the Earth’s surface.

2. Airborne remote sensing

 Low altitude aerial remote sensing

 High altitude aerial remote sensing

3. Spaceborne remote sensing

 Space shuttles

 Polar-orbiting satellites

 Geo-stationary satellites

Appplication of Remote Sensing

Forestry

  • Forest
  • Biodiversity management
  • Deforestation

Natural resource Management

 

  • Geomorphology
  • Environmental assessment
  • Water source management
  • Habitat analysis
  • Pest/disease outbreaks
  • Impervious surface mapping
  • Hydrology
  • Mineral province

Urbanization & Transportation

  • Urban planning
  • Roads network and transportation planning
  • City expansion
  • Wetland delineation

Agriculture

 

  • Soil sensing
  • Farm classification
  • Farm condition assessment
  • Agriculture estimation
  • Mapping of  farm and agricultural land characteristics
  • Mapping of land management practices

Advantages and Disadvantages of Remote Sensing

Advantages

a) Provides data from large areas

b) Provides data of very remote and inaccessible regions

c) Able to obtain imagery of any area over a continuous period time through which any anthropogenic or natural changes in the landscape can be analyzed

d) Relatively inexpensive when compared to employing a team of surveyors

e) Easy and rapid collection of data

Disadvantages

a) The interpretation of imagery requires a certain skill level

b) Needs cross verification with ground (field) survey data

c) Data from multiple sources may create confusion

d) Objects can be misclassified or confused

e) Distortions may occur in an image due to the relative motion of sensor and source

Sensor Resolution

Resolution is commonly used to describe the number of pixels display on a display device, or area on the ground that a pixel represents in an image file.

Four distinct types of the Resolution must be considered:
Spectral—specific wavelength intervals that a sensor can record
Spatial—area on the ground represented by each pixel
Radiometric—number of possible data file values in each band
Temporal—how often a sensor obtains imagery of a particular area

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