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What is Remote Sensing? / INSAT Series/ IRS Series/ PSLV Series

What is Remote Sensing?

Remote Sensing is the technology used to obtain information about an object or area without coming into physical contact with it. This is achieved through sensors mounted on satellites or aircraft.

Technically, it is the art and science of gathering data about an object, area, or phenomenon. Common examples include human vision and photography, where light energy—either natural (Sun) or artificial (Electricity)—strikes an object. Light energy consists of electromagnetic waves of varying lengths and intensities. When these waves hit an object, they are:

Absorbed
Scattered
Transmitted
Reflected

Indian Satellite and Launch Vehicle Series (INSAT, IRS, PSLV)

The Indian Space Research Organisation (ISRO) has developed specific series for surveying and communication:

1. INSAT Series (Indian National Satellite System)

Purpose: Primarily used for communication, meteorology (weather), and disaster management.
Features: These are Geostationary satellites located approximately 36,000 km above Earth, helping in accurate weather forecasting.

2. IRS Series (Indian Remote Sensing)

Purpose: This series is dedicated to Earth observation and natural resource management.
Features: These satellites operate in Sun-synchronous orbits. They are used for agriculture, water resources, and precision mapping.

3. PSLV Series (Polar Satellite Launch Vehicle)

What is it? It is a rocket (launch vehicle), not a satellite.
Function: PSLV is used to carry remote sensing satellites like the 'IRS' into their designated orbits. It is known as the "Workhorse of ISRO" due to its extreme reliability.

How Does Remote Sensing Work?

The process is primarily based on Electromagnetic Radiation:

Energy Source: The Sun or an artificial light source.
Interaction: Light waves strike an object and are reflected.
Recording: Sensors on the satellite record these reflected waves.
Image Processing: Data is sent to ground stations where it is analyzed using computer software (like GIS).

Applications in Engineering

Resource Exploration: Detecting minerals and underground water.
Land Use: Mapping forests, urban areas, and agricultural land.
Site Investigation: Selecting the right locations for dams, bridges, and tunnels.
Disaster Management: Assessing damage after floods, droughts, or earthquakes.

Active vs. Passive Remote Sensing

To understand remote sensing deeply, it is vital to distinguish between Active and Passive systems. The difference lies in where the "Energy" comes from.

1. Passive Remote Sensing

This technology relies on an external energy source. The sensor does not produce its own light.

Source: Primarily the Sun. It waits for solar radiation to reflect off the Earth.
Time: Can only function during daylight.
Example: A standard camera or satellites taking photos in sunlight (like certain INSAT sensors).

2. Active Remote Sensing

The satellite or aircraft has its own energy/illumination source. It sends out rays and measures the time and intensity of the signal that bounces back.

Source: The instrument's own energy (e.g., Radar microwaves).
Time: Can function during both day and night.
Specialty: It can see through clouds, fog, and smoke.
Example: RADAR and LiDAR.

Comparison Table

Feature	Passive Remote Sensing	Active Remote Sensing
Energy Source	Natural (Sunlight)	Artificial (Sensor's own energy)
Time	Only during the day	Both day and night
Weather Effect	Blocked by clouds/fog	Works through clouds and rain
Complexity	Simple and cost-effective	Complex and expensive
Usage	Vegetation studies, Land use	Topography, sea wave mapping

NTS Study Pro-Tip: In civil engineering surveying projects involving dense forests or regions perpetually covered by clouds, Active Remote Sensing (Radar/Lidar) is considered the best choice.

🏗️ Surveying: Complete Study Guide & Index

📔 Part 1: Fundamentals of Surveying

Surveying: A Bird's Eye View – Meaning and significance of land surveying.
Fundamental Principles – Classification and types of surveying.
Primary Division – Understanding Plane vs. Geodetic Surveying.
Representative Fraction (RF) – Utilization of scales and reduction factors.

📏 Part 2: Linear Measurement & Chain Survey

Chain Surveying – Basic procedures and workflow.
Errors & Adjustments in Chaining – Deficiencies in measurement and their remedies.
Distance Measurement Methods – Detailed discussion on linear surveying tools.
Tape Corrections – Adjustments for Sag, Temperature, and Pull.

🧭 Part 3: Angular & Instrumental Survey

Compass Surveying – Magnetic bearing survey and its applications.
Plane Table Surveying – Equipment used and graphical methods.
Theodolite Surveying – Horizontal and vertical angle measurement.
Total Station – Components, features, and modern digital use.

🏔️ Part 4: Levelling & Elevation

Need for Levelling – Why vertical measurement is vital in civil engineering.
Key Concepts: RL & Datum – Definitions of Reduced Level, Datum, and Benchmarks.
Operating Levelling Instruments – Handling Auto Level and Tilting Level.

🛰️ Part 5: Modern Technologies

Remote Sensing – Information on INSAT and IRS Series satellites.
GIS & LIS Systems – Geographic data management and functionality.
Laser Scanning – Advanced application and control.
Geoid & Ellipsoid – Understanding the mathematical shape of the Earth.

📝 Part 6: Practice & Quizzes (MCQs)

Surveying Quiz 1 (01-25) – GPS, Remote Sensing, and Photogrammetry.
Surveying Quiz 2 (26-50) – Ranging, EDM, and Tacheometry.
Surveying Quiz 3 (51-75) – Contouring and HI Method Levelling.
Surveying Quiz 4 (76-100) – Transition Curves and Bowditch Rule.
Surveying Quiz 5 (101-125) – Plane table and Compass
Surveying Quiz 6 (125-150) – Theodolite Surveying and Levelling
Surveying Quiz 7 (151-175) – Tacheometry, Curves, Modern Surveying Instruments (EDM/GPS)
Surveying Quiz 8 (175-200) – Area & Volume Calculation, Minor Instruments

📚 Quick Revision Resources

Surveying IS Codes with Latest Revision Years

1. General Surveying & Instruments

IS 1491:1959 – Specification for Prismatic Compass (Liquid and Non-liquid).
IS 1963:1981 – Specification for Bubbles for Surveying Instruments.
IS 2988:1995 – Glossary of Terms Relating to Surveying Instruments.
IS 1634:1992 – Code of Practice for Design and Construction of Storage for Surveying Instruments.

2. Chain and Tape Surveying

IS 1492:1970 – Specification for Metric Surveying Chains.
IS 1269 (Part 1):1997 – Material and Construction of Steel Tapes.
IS 1269 (Part 2):1997 – Woven Metallic and Glass Fibre Tapes.
IS 1659:2006 – Specification for Invar Tapes for High Precision Measurement.

3. Theodolite and Tacheometry

IS 8002:1976 – Specification for Surveying Chain Vertical Vernier Theodolite.
IS 8330:1976 – Specification for Tilting Levels (Optical).
IS 8636:1977 – Specification for Tacheometers.

4. Leveling and Contouring

IS 9128:1992 – Specification for Tilting Levels.
IS 9573:1980 – Specification for Automatic Levels.
IS 1779:1961 – Specification for 4-metre Leveling Staff (Folding Type).

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