Fundamental Of Remote Sensing - Unit 1

Unit Overview

Introduction to Remote Sensing

Concept and Physical Basics

  • Importance in daily life applications

  • Electromagnetic Spectrum

  • Radiation Law

  • Atmospheric Effects

  • Image Characteristics

  • Sources of Remote Sensing Information

  • Spectral Signatures and Characteristics of Spectral Reflectance Curves

Overview of Remote Sensing

Remote Sensing (RS) is defined as the science and art of gathering information about the Earth's surface without direct contact. This technology pervades daily life, illustrated by common activities such as listening to sounds and reading books, where energy and sensors play critical roles in data collection. RS methods can be divided into two types:

  • In-situ Measurements - e.g., using clinical thermometers that require physical contact.

  • Remote Sensing Observations - measurements taken without physical contact, often utilizing various energy sources and sensor technology.

Principles of Remote Sensing

Understanding basic principles can be enhanced through familiar experiences. For example, reading a book involves:

  • Target Object reflecting light

  • Eye acting as a sensor

  • Head as the platform for the sensor

Light serves as the energy source, leading to brain interpretation for identifying text. Modern RS extends from this natural analogy, with major objectives including improved natural resource management, land use efficiency, and environmental protection. Critical energy sources include visible light and various forms of electromagnetic radiation - from ultraviolet (UV) through to microwave regions. Key components of RS systems are:

  • Energy Source

  • Sensor

  • Platform

  • Target

  • Interpreter

Remote Sensing System Processes

A complete Remote Sensing System illustrates a process that includes:

  1. Energy Source

  2. Remote Sensor (Energy Detector)

  3. Target Interaction with the atmosphere

  4. Data Transmission and Reception

  5. Data Interpretation and Analysis

  6. Application of Data to resolve real-world issues.

Energy Interaction Stages




(A) Energy Source: Electromagnetic energy illuminates targets.(B) Atmosphere Interaction: Energy interacts with atmospheric particles before reaching targets, affecting its characteristics.(C) Target Interaction: Energy experiences reflection, absorption, and transmission depending on target properties.(D) Data Recording: Recorded energy is collected by sensors after interaction.

Further Processes



(E) Data Transmission and Processing: Energy captured is transmitted for processing into usable images.(F) Interpretation and Analysis: Processed images are analyzed to extract valuable information.(G) Applications: The final outcome is the application of this information for deepening understanding and solving issues.

Types of Remote Sensing

Passive Remote Sensing

  • Natural Energy Sources (e.g., sunlight) are utilized for data collection.

  • Operational limitations exist during night or cloudy conditions when natural thermal infrared may not be present.

Active Remote Sensing

  • Artificial Energy Sources, like in radar technology, allow observations to occur regardless of time and weather conditions.

  • Examples include SAR (Synthetic Aperture Radar) and various forms of imaging technology.

Satellites in Remote Sensing

  • Satellites, either natural (e.g., the moon) or artificial (humans made), serve various functions including: communication, military, and scientific studies regarding Earth and space.

Indian Satellite Systems

  • India’s NAVIC, similar to GPS, employs a set of 7 satellites to offer navigational and positioning services. Key historical satellites include Aryabhatta and BHASKAR-1, with many more such as INSAT and IRS series providing vital data for numerous applications.

The Electromagnetic Spectrum

Electromagnetic radiation consists of varying wavelengths where characteristics like wavelength and frequency are crucial. The visible spectrum for human eyes accounts for a minuscule portion of the total electromagnetic spectrum. Much radiation is utilized in RS, covering various categories from gamma rays to radio waves. Typical measurements of energy from the sun at the Earth’s surface reach approximately 343 W/m²/sec.

Interaction of EMR with Atmosphere

Before reaching the Earth’s surface, electromagnetic radiation undergoes scattering and absorption, influenced significantly by atmospheric composition. Scattering mechanisms include:

  • Rayleigh Scattering: Occurs with small particles compared to wavelengths, e.g., giving the sky its blue color.

  • Mie Scattering: Affects longer wavelengths due to larger particles, primarily in lower atmosphere conditions.

  • Nonselective Scattering: Occurs with large particles, scattering all wavelengths equally, causing cloud and fog appearances.

The Importance of Absorption

Various wavelengths interact differently with atmospheric gases, with water vapor, ozone, and carbon dioxide being significant absorbers.

Reflection, Absorption, and Transmission

  • Reflection occurs when light energy bounces back, crucial for RS;

  • Absorption transfers energy into other forms (e.g., heat);

  • Transmission allows some energy to pass through materials, impacting overall energy reaching the sensor.

Atmospheric Windows

Some EMR can pass smoothly through the atmosphere, while others are obstructed. These regions, known as atmospheric windows, are critical to sensor design and application in RS; they allow for maximum data collection with minimal interference.

Image Resolution in Remote Sensing

Image resolution is central to RS, with four types identified:

  • Spatial Resolution

  • Spectral Resolution

  • Radiometric Resolution


  • Temporal ResolutionEach impacts the kind of data collected and the level of detail available for analysis.

Spectral Reflectance and its Applications

Spectral Reflectance (Rλ) characterizes the energy ratio reflected by surfaces, measured across various wavelengths, serving as an identifier for different earth surface features. The graphical representation of spectral responses enables the analysis of these reflective characteristics, essential in selecting wavelengths for effective RS data acquisition.

Factors Influencing Reflectance

Factors influencing reflectance include environmental conditions, moisture levels, and type of surface.

Spectral Features of Vegetation, Soil, and Water

Vegetation: High reflectance in NIR due to leaf structure, chlorophyll absorption visible in specific light bands.

Soil: Reflectance values influenced by moisture, texture, and organic content. Key features include varying colors related to iron oxide and moisture percentages.

Water: Generally low reflectance due to absorption properties, but notable variations can occur based on depth and material presence. The reflectance can change based on conditions such as sediment presence, chlorophyll content, and surface conditions.

Summary of Key Concepts

Remote sensing is a comprehensive topic integrating various disciplines, requiring an understanding of physics, data collection methods, and interpretation skills. Applications are vast, impacting fields like agriculture, forestry, urban planning, and environmental monitoring. Understanding the principles of RS will enhance capabilities in natural resource management and scientific inquiry.