• Energy Source or Illumination (A)- An energy source that illuminates or provides electromagnetic energy to the target of interest is the first prerequisite for remote sensing.
  • Radiation and the Atmosphere (B)-  As energy moves from its source to its goal, it will interact with the atmosphere it travels through. As the energy moves from the target to the sensor, this interaction might happen again.
  • Interaction with the Target (C)-Depending on the characteristics of both the radiation and the target, the energy interacts with the target after traveling through the atmosphere to reach it.
  • Recording of Energy by the Sensor(D) -A sensor that is remote from the target and not in contact with it is needed to collect and record the electromagnetic radiation after it has been scattered by or emitted by the target.
  • Transmission, Reception, and Processing (E): The energy that the sensor has recorded must be sent, frequently in electronic form, to a station that will receive it and process it into an image (either in hard copy or digital form).
  • Interpretation and Analysis(F): To extract details about the lit target, the processed image is evaluated visually, digitally, or electronically.
  • Application(G): The final step in the remote sensing process is reached when we use the knowledge we have gained about the target from the imaging to better comprehend it, expose new knowledge, or help solve a specific issue.

Interaction process

interaction process

Interaction processes

  1. Reflection: A light beam will change direction at a point where two different media come together to reflect, returning the light to the original medium. 
  • Specular: Angle of incidence and angle of reflection are identical.
  • Diffused: Light scatters when it hits the surface of a (non-metallic) material because of many reflections from the microscopic imperfections within the material.
  • Lambertian: Light striking it is dispersed so that the surface’s apparent brightness to an observer is constant and independent of the angle of the observer’s view. According to Lambert’s cosine law, the radiant intensity seen from a “Lambertian” surface is inversely proportional to the cosine of the angle formed at 0 degrees between the observer’s line of sight and the surface normal.
    2. Transmission & Communication
    3. Absorption & Ingestion

Physical processes in the atmosphere

Scattering: Physical air-space procedures radiation that has been redirected from a straight route by the medium they are traveling through.

  • Rayleigh scattering
  • Mie scattering
  • Non-selective scattering

Absorption: A thermodynamically irreversible conversion of light energy to heat occurs during absorption.

Refraction: Refraction is a change in a radiation’s direction brought on by a change in its speed (caused by a change in the medium it travels through).

atmospheric windows

Atmospheric windows: Spectral regions through which the EMR passes with little attenuation.

  • A window between 0.4 and 2 pm in the visible and reflected infrared spectrum. This is the window through which the optical remote sensors operate.
  • Three windows in the thermal infrared region, namely two narrow windows between 3 and 5 pm and a third, relatively broad window between 8 and 2 pm.

Rayleigh scattering:

Where electromagnetic radiation interacts with particles smaller than the wavelength of the incoming light, Rayleigh scattering dominates. Dust specks and nitrogen (NO2) and oxygen (O2) molecules are examples of these particles. Rayleigh scattering has an effect that is inversely proportional to the fourth power of the wavelength: shorter wavelengths are scattered more than longer wavelengths.

Rayleigh scattering is the most important type of scattering in satellite remote sensing. When compared to measurements taken on the ground, it distorts the spectral characteristics of the reflected light: the shorter wavelengths are overestimated due to the Rayleigh effect. It accounts for the blueness of color photographs taken at high altitudes. In general, Rayleigh scattering reduces contrast in photos, limiting interpretation possibilities. When working with digital image data (as provided by multispectral scanners), the distortion of the surface’s spectral characteristics may limit image classification possibilities.

Mie scattering: 

When the wavelength of the incoming radiation is similar to the size of the atmospheric particles, Mie scattering occurs. Aerosols, a mixture of gases, water vapor, and dust, are the most important cause of Mie scattering.

Under overcast cloud conditions, Mie scattering is generally limited to the lower atmosphere, where larger particles are more abundant and dominate. Mie scattering affects the entire spectral region, from near-ultraviolet to near-infrared, and has a greater effect on longer wavelengths than Rayleigh scattering.

Non-selective scattering: 

When the particle size is much larger than the rediation wavelength, non-selective scattering occurs. Water droplets and larger dust particles are typical particles responsible for this effect.

Non-selective scattering occurs when all wavelengths are scattered about equally.

Spectral Signature

Vegetation: Chlorophyll, a chemical compound found in leaves, absorbs red and blue wavelengths but reflects green wavelengths. In the summer, when chlorophyll content is highest, leaves appear “greenest” to us. Because there is less chlorophyll in the leaves in autumn, there is less absorption and proportionately more reflection of red wavelengths, giving the leaves a red or yellow appearance (yellow is acombination of red and green wavelengths). Healthy leaves’ internal structure acts as an excellent diffuse reflector of near-infrared wavelengths. Trees would appear extremely bright to us if our eyes were sensitive to near-infrared wavelengths. In fact, scientists can determine how healthy (or unhealthy) vegetation is by measuring and monitoring near-IR reflectance.

Soil: The reflection properties of soils tend to increase approximately monotonically with wavelength. They have a high reflectance in all bands. This is, of course, dependent on factors such as color, constituents, and, most importantly, moisture content. Water, as previously stated, is a relatively strong absorber of all wavelengths, especially those longer than the red part of the visible spectrum. As a result, as a soil’s moisture content increases, its overall reflectance decreases. Soils rich in iron oxide reflect more red wavelengths than other visible wavelengths, making them appear red (rust color) to the human eye. A sandy soil, on the other hand, appears bright white in imagery because visible wavelengths are more or less evenly distributed.

Water: Water absorbs more visible and near-infrared radiation with longer wavelengths than with shorter wavelengths. Water appears blue or blue-green due to higher reflectance at shorter wavelengths, and darker when viewed at red or near-infrared wavelengths. If there is suspended sediment in the upper layers of the water body, the reflectivity and brightness of the water will improve. The visible color of the water will shift slightly to longer wavelengths. Suspended sediment (S) is easily confused with shallow (but clear) water due to their similar appearance. Algae chlorophyll absorbs more blue wavelengths and reflects more green wavelengths, making the water appear greener when algae are present. 

Spectral Response Pattern

Based on the spectral band with its reflectance, the spectral response was obtained from the spectral signature of features or objects such as vegetation, soil, water, asphalt, sand, concrete, cloud, and so on. The spectral reflectance pattern is determined by:

  1. Temporal effect (time)
  2. Spatial effect (location)
  3. Illumination effect (shadow)
  4. Solar elevation
  5. Azimuth angle
  6. Variation in terrain (slope & aspect)

Atmospheric influence on Spectral Response Pattern

The following factors influence the Spectral Response pattern in the atmosphere:
1. Radiance or brightness value recorded
2. Radiance along the path
3. Illumination ( reflected sunlight and diffuse skylight)
4 The weather situation
5. Seasonal variations
6. Dispersal

Ideal Remote Sensing System

1. Uniform energy source
2. A noninterfering atmosphere
3. A series of unique energy-matter interactions at the earth’s surface
4 A super sensor / powerfull sensor’s 
5. A real-time data processing and supply system
6. Multiple data users

Real Remote Sensing System

1. May or may not be a uniform energy source
2. Interaction with the atmosphere
3. Interaction with the earth’s surface
4. Malfunctioning of sensor
5. May or may not be real-time data processing and
supply system

engineeringthrive

By admin

Leave a Reply

Your email address will not be published. Required fields are marked *