class 11 notes

Class 11 Geography Notes Chapter 7 (Introduction To Remote Sensing) – Practical Work in Geography Book

Philoid

Philoid

— 6 min read

Practical Work in Geography
Detailed Notes with MCQs of Chapter 7, 'Introduction to Remote Sensing' from your Practical Work in Geography book. This is a crucial topic, not just for your Class 11 understanding, but also forms the basis for many questions in competitive government exams. Pay close attention as we break down the core concepts.

Chapter 7: Introduction To Remote Sensing - Detailed Notes

1. What is Remote Sensing?

  • Definition: Remote Sensing is the science and art of obtaining information about an object, area, or phenomenon through the analysis of data acquired by a device (sensor) that is not in physical contact with the object, area, or phenomenon under investigation.
  • Core Principle: It relies on measuring the Electromagnetic Radiation (EMR) that is reflected or emitted from the Earth's surface features.
  • Analogy: Think of your own eyes. You 'sense' objects remotely using the light reflected from them. Cameras work on a similar principle.

2. The Remote Sensing Process:

This is a fundamental sequence you must understand:

  • (a) Energy Source or Illumination (A): The process begins with an energy source. This can be:
    • Passive Systems: Rely on natural energy, primarily the Sun. Most remote sensing systems are passive.
    • Active Systems: Provide their own source of energy to illuminate the target (e.g., RADAR, LiDAR).
  • (b) Radiation and the Atmosphere (B): Energy travels from the source to the target. As it passes through the atmosphere, it interacts with atmospheric particles (gases, dust, water vapour). This interaction involves scattering and absorption, which can affect the energy reaching the target and the sensor.
    • Atmospheric Windows: These are specific wavelengths/regions of the EMR spectrum where the atmosphere is relatively transparent, allowing energy to pass through with minimal interference. Sensors are designed to operate within these windows.
  • (c) Interaction with the Target (C): Once the energy reaches the target (e.g., soil, water, vegetation), it interacts in three ways:
    • Reflection: Energy bounces off the target.
    • Absorption: Energy is absorbed by the target.
    • Transmission: Energy passes through the target.
    • Remote sensing primarily measures the reflected or emitted energy.
  • (d) Recording of Energy by the Sensor (D): A sensor mounted on a platform (aircraft, satellite) collects and records the electromagnetic radiation reflected or emitted from the target.
  • (e) Transmission, Reception, and Processing (E): The recorded data is transmitted (often electronically) to a receiving station on Earth. This raw data is then processed using computers to correct for geometric and radiometric errors, creating usable images.
  • (f) Interpretation and Analysis (F): Processed images are interpreted and analysed by specialists (visually or digitally using software) to extract meaningful information about the targets.
  • (g) Application (G): Finally, the extracted information is applied to solve problems, make decisions, or better understand a particular phenomenon (e.g., mapping land use, monitoring floods, assessing crop health).

3. Electromagnetic Spectrum (EMS):

  • Definition: The range of all possible frequencies of electromagnetic radiation.
  • Key Regions for Remote Sensing:
    • Visible Light (0.4 - 0.7 μm): The light our eyes can see (Violet, Blue, Green, Yellow, Orange, Red). Used extensively in photography and satellite imagery.
    • Infrared (IR) (0.7 - 100 μm): Divided into Near-IR, Mid-IR, and Thermal-IR.
      • Near-IR & Mid-IR: Useful for vegetation studies, moisture content. Measures reflected solar energy.
      • Thermal-IR: Measures emitted heat energy. Useful for temperature mapping (water bodies, urban heat islands, forest fires).
    • Microwaves (1 mm - 1 m): Longer wavelengths. Can penetrate clouds, haze, and light rain. Used by RADAR systems. Ideal for studying sea ice, soil moisture, and topography.

4. Sensors:

  • Definition: Devices that detect and record electromagnetic radiation.
  • Types:
    • Passive Sensors: Detect naturally available energy (reflected solar radiation or emitted thermal energy). Examples: Photographic cameras, multispectral scanners (like those on Landsat, IRS satellites).
    • Active Sensors: Generate their own energy pulse and record the 'echo' returned from the target. Examples: RADAR (Radio Detection and Ranging), LiDAR (Light Detection and Ranging). Advantage: Can operate day or night and often penetrate clouds.

5. Platforms:

  • Definition: The vehicles or carriers on which sensors are mounted.
  • Types:
    • Ground-based: Handheld devices, cranes, towers. Used for detailed studies and sensor calibration.
    • Airborne: Aircraft (planes, helicopters, drones). Used for acquiring high-resolution imagery for specific projects like mapping or surveying. Aerial photography is a classic example.
    • Spaceborne: Satellites orbiting the Earth. Provide large area coverage and repetitive observations.
      • Geostationary Satellites: Orbit at approx. 36,000 km, appearing stationary over the equator. Used primarily for weather monitoring and communications (e.g., INSAT series). Provide high temporal resolution but lower spatial resolution.
      • Sun-Synchronous Satellites: Orbit pole-to-pole at lower altitudes (typically 600-900 km). They pass over any given point on Earth at the same local solar time. Ideal for consistent illumination conditions, used for resource monitoring (e.g., Landsat, IRS, SPOT). Provide higher spatial resolution but lower temporal resolution compared to geostationary.

6. Resolutions in Remote Sensing:

This defines the capabilities of a sensor system and the characteristics of the data acquired.

  • (a) Spatial Resolution:
    • Refers to the size of the smallest object that can be distinguished on the image. It's related to the pixel size (the smallest unit of an image).
    • High Spatial Resolution: Smaller pixel size (e.g., 1m) - shows more detail, smaller features.
    • Low Spatial Resolution: Larger pixel size (e.g., 1km) - shows less detail, only large features.
  • (b) Spectral Resolution:
    • Refers to the number and width of the specific wavelength intervals (bands) in the EMS that the sensor can record.
    • Panchromatic: Single wide band (often visible spectrum), appears as black and white.
    • Multispectral: Records energy in several discrete bands (e.g., Blue, Green, Red, Near-IR). Most common type.
    • Hyperspectral: Records energy in hundreds of very narrow, contiguous bands. Allows very detailed spectral analysis.
  • (c) Radiometric Resolution:
    • Refers to the sensitivity of the sensor to differences in electromagnetic energy intensity (brightness levels).
    • Measured in bits (e.g., 8-bit, 10-bit, 12-bit). Higher radiometric resolution means the sensor can detect finer differences in reflected or emitted energy, resulting in more shades of grey (or colour levels). An 8-bit sensor records 2^8 = 256 brightness levels.
  • (d) Temporal Resolution:
    • Refers to the frequency with which a sensor acquires data over the same area. It's the revisit period of the satellite.
    • High Temporal Resolution: Frequent revisits (e.g., daily by weather satellites). Good for monitoring dynamic phenomena like floods, vegetation growth stages.
    • Low Temporal Resolution: Infrequent revisits (e.g., every 16 days like Landsat). Suitable for monitoring slower changes like land use change.

7. Spectral Signature:

  • Every object reflects or emits energy differently across various wavelengths. This unique pattern of reflectance/emittance across the spectrum is called its spectral signature.
  • Example: Healthy green vegetation strongly reflects Near-Infrared light and Green light, while absorbing Red and Blue light. Water absorbs most Near-Infrared light.
  • Spectral signatures are crucial for identifying and differentiating features in remote sensing imagery.

8. Advantages of Remote Sensing:

  • Synoptic View: Provides a view of large areas simultaneously.
  • Repetitive Coverage: Allows monitoring of changes over time (temporal analysis).
  • Accessibility: Can acquire data from remote or inaccessible areas.
  • Cost-Effective: Often cheaper than ground surveys for large areas.
  • Digital Data: Satellite data is readily available in digital format for computer analysis.

9. Applications in Geography and Beyond:

  • Land Use / Land Cover Mapping
  • Agricultural Monitoring (crop type, health, yield estimation)
  • Forestry (species identification, deforestation monitoring, fire mapping)
  • Water Resource Management (surface water mapping, flood monitoring, snow cover)
  • Geology (structural mapping, mineral exploration)
  • Urban Planning (monitoring urban sprawl)
  • Disaster Management (damage assessment for floods, earthquakes, landslides)
  • Oceanography (sea surface temperature, chlorophyll concentration)
  • Environmental Monitoring (pollution detection)

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on the chapter to test your understanding:

  1. Remote sensing primarily involves obtaining information about an object or area without:
    a) Using electromagnetic radiation
    b) Physical contact with the object
    c) Processing the data digitally
    d) Using a sensor device

  2. Which of the following is an example of an active remote sensing system?
    a) A photographic camera on an airplane
    b) The human eye
    c) A RADAR system on a satellite
    d) A multispectral scanner like Landsat's ETM+

  3. The specific wavelengths in the electromagnetic spectrum where the atmosphere allows radiation to pass through relatively easily are known as:
    a) Spectral signatures
    b) Atmospheric windows
    c) Radiometric resolutions
    d) Absorption bands

  4. The unique pattern of reflectance and emittance of an object across different wavelengths is called its:
    a) Spatial resolution
    b) Radiometric profile
    c) Platform characteristic
    d) Spectral signature

  5. Which type of satellite orbit is most suitable for continuous weather monitoring over a specific region?
    a) Sun-synchronous orbit
    b) Polar orbit
    c) Geostationary orbit
    d) Elliptical orbit

  6. The ability of a remote sensing system to distinguish small objects on the ground is determined by its:
    a) Spectral resolution
    b) Radiometric resolution
    c) Temporal resolution
    d) Spatial resolution

  7. A sensor that records data in hundreds of very narrow, contiguous spectral bands has a high:
    a) Spatial resolution
    b) Temporal resolution
    c) Spectral resolution (Hyperspectral)
    d) Radiometric resolution

  8. Which stage of the remote sensing process involves correcting the raw data for errors and converting it into usable images?
    a) Interaction with the Target
    b) Recording of Energy by the Sensor
    c) Transmission, Reception, and Processing
    d) Interpretation and Analysis

  9. Which part of the electromagnetic spectrum is particularly useful for sensing emitted heat energy from the Earth's surface?
    a) Visible light
    b) Near-Infrared
    c) Thermal Infrared
    d) Microwaves

  10. The frequency with which a satellite revisits the same location on Earth is known as its:
    a) Spatial resolution
    b) Spectral resolution
    c) Radiometric resolution
    d) Temporal resolution

Answer Key for MCQs:

  1. b
  2. c
  3. b
  4. d
  5. c
  6. d
  7. c
  8. c
  9. c
  10. d

Study these notes thoroughly. Understanding the process, the components like EMS, sensors, platforms, and especially the different types of resolutions is key. Good luck with your preparation!

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