Notes on Basics of Remote Sensing

Introduction to Remote Sensing

• Remote Sensing: Collection of scientific data from a distance without physical contact.
• In Situ Data Collection: Data collected directly at the site (field data collection).
• Key Questions:
  • What is remote sensing?
  • Why is it used?
  • How does it work?

What is Remote Sensing?

• Definition: Science and art of obtaining information about objects, areas, or phenomena.
• Objects of Interest: Buildings, cities, weather phenomena (e.g., rainfall).
• Process Involves:
  • Scientific principles and technology.
  • Skill of the interpreter.

Why Use Remote Sensing?

Advantages Over Field Measurements

1. Systematic Data Collection:
   • Reduces human error.
   • Ensures objective data collection.
2. Three-Dimensional Information:
   • Offers stereo images and 3D representations (e.g., Google Earth).
3. Repeatability:
   • Data can be collected over time and space.
4. Global Coverage:
   • Ideal for inaccessible areas (e.g., disaster zones).
5. Multi-Purpose Information:
   • Data can be analyzed for various fields (agriculture, forestry, marine science).

Limitations of Remote Sensing

• Cannot completely replace field measurements.
• Calibration and validation of instruments require ground truth data.
• Some research, especially subsurface analysis, relies on field measurements.

Components of Remote Sensing Process

1. Source of Electromagnetic Radiation:
   • Can be natural (e.g., sunlight) or artificial.
2. Target:
   • The object or area being studied.
3. Sensor:
   • Combination of detector and platform (space-based, airborne, or ground-based).
4. Ground Receiving Station:
   • Data is transmitted from sensor to ground station.
   • Pre-processing is required (error correction, data formatting).

Types of Remote Sensing

Passive Remote Sensing

• Uses sunlight or natural radiation reflected from the target.
• Examples: Reflective remote sensing.

Active Remote Sensing

• The source of illumination is carried on board the platform.
• Examples: Radar.

Emissive Remote Sensing

• Detects radiation emitted by the target itself (thermal radiation).

Understanding Electromagnetic Radiation

• Wave Theory: Electromagnetic energy as sinusoidal waves (oscillating electric and magnetic fields).
• Particle Theory: Electromagnetic energy consists of discrete units called photons.
• Wave-Particle Duality: Light behaves both as a wave and a particle.

Measurement of Radiation

• Terms:
  • Irradiance: Incoming light flux density.
  • Excitance: Outgoing light.
  • Radiant Intensity: Energy per unit solid angle (for point sources).
  • Radiance: Flux density per unit solid angle.
• Spectral Measurement: Measured in specific wavelength ranges.

Interaction of Electromagnetic Radiation with Matter

Types of Interactions

1. At Boundary of Two Media: Reflection and refraction.
2. Within a Single Medium: Absorption and scattering.
   • Reflection: Specular (smooth surfaces) and diffuse (rough surfaces).
   • Rayleigh Criteria: Determines if a surface is rough or smooth based on average undulation and wavelength.

Spectral Signatures

• Unique identification of features based on their reflective properties.
• Different materials exhibit distinct spectral signatures.

Interaction with Atmosphere

• Atmospheric Windows: Spectral regions where electromagnetic radiation passes through with minimal attenuation.
• Scattering: Affects incoming and outgoing radiation, impacting image quality.
  • Types: Rayleigh, Mie, and non-selective scattering.

Summary of Lecture

• Overview of remote sensing concepts, advantages, and limitations.
• Introduction to electromagnetic radiation properties and interactions.
• Discussion on how electromagnetic radiation interacts with targets and the atmosphere.

Next Steps

• Further exploration of electromagnetic radiation properties and their importance in remote sensing.