GeographyCBSE Class 11 · Introduction to Remote Sensing

Remote Sensing: Stages, Platforms and Sensors (Class 11 Practical Work in Geography, Chapter 6)

Updated 17 October 2026 · Fact-checked

Remote sensing is the process of acquiring and measuring information about objects and phenomena with a sensor that is not in physical contact with them. It has eight stages: source of energy, transmission, interaction with the surface, propagation through the atmosphere, detection by the sensor, conversion to data, extraction of information and conversion to maps or tables. Satellites are sun-synchronous (700-900 km, IRS) or geostationary (36,000 km, INSAT).

Understand Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors

Why this topic matters. This chapter carries 5 marks in the 30-mark practical exam; the stages, the satellite comparison and the sensor types are asked as short answers and tables.

1. Meaning. Human eyes and cameras respond to only a minute part of the energy that objects reflect, but remote sensing devices respond to a much wider range of radiation reflected, emitted, absorbed and transmitted by all objects above 0 K (minus 273 degrees C). The term was first used in the early 1960s. Remote sensing covers all the processes by which information about objects and phenomena is acquired and measured with a sensor that does not touch them. Three components: object surface, sensor and information-carrying energy waves.

2. Stages (a-d). (a) Source of energy: mainly the sun; also artificial, as in radar. (b) Transmission: energy travels at the speed of light (300,000 km/s) as electromagnetic radiation (EMR); the electromagnetic spectrum runs from gamma rays and X-rays through ultraviolet, visible, infrared and microwaves to radio waves, and remote sensing uses the visible, infrared and microwave regions. (c) Interaction with the surface: energy is absorbed, transmitted, reflected or emitted; each object has a spectral signature; fresh water absorbs red and infrared and looks dark, turbid water reflects blue and green and looks light. (d) Propagation through the atmosphere: gases, water molecules and dust absorb or scatter energy, so some properties go unrecorded.

3. Stages (e-h). (e) Detection by the sensor on a satellite. (f) Conversion into a digital image of digital numbers, sent to an Earth Receiving Station (in India at Shadnagar near Hyderabad). (g) Extraction of information by digital image processing or visual interpretation. (h) Conversion into maps or tables (thematic layers).

4. Platforms. Sun-synchronous remote sensing satellites at 700 to 900 km (the IRS series) cover 81 degrees N to 81 degrees S, make about 14 orbits a day, give fine resolution and are used for earth resources. Geostationary satellites at about 36,000 km (INSAT) move with the earth's rotation (24 hours), cover one-third of the globe, give coarse resolution (about 1 km) and are used for telecommunication and weather.

5. Sensors. Photographic (analogue) sensors are cameras recording at an instant of exposure; non-photographic (digital) sensors are scanners. Multispectral scanners use a mirror and detectors. A whiskbroom scanner has a rotating mirror with a single detector sweeping across the field of view (90 to 120 degrees); a pushbroom scanner has many detectors in a linear array, the number being swath divided by spatial resolution (for SPOT HRV-1: 60 km / 20 m = 3,000 detectors).

Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors: key facts

Stages: a Source
b Transmission
c Interaction
d Propagation
e Detection
f Conversion to data
g Extraction
h Maps and tables; Eight stages.
Spectrum used: Visible
Infrared
Microwave
Speed of light 300,000 km/s; EMR regions.
Satellites: Sun-synchronous: 700 to 900 km, about 14 orbits a day, fine resolution | Geostationary: about 36,000 km, 24 hours, one-third of globe, coarse; IRS and INSAT.
Pushbroom detectors: $N u mb er o f d e t ec t or s = s w a t h / s p a t ia l r eso l u t i o n ∣ E x am pl e 60 k m /20 m = 3, 000$; SPOT HRV-1.

How to answer Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors questions

A stage question is answered as a numbered list of eight stages.

1State the stage letter and name.
2Give one line on what happens.
3Include the example (sun, EMR, IRS, Shadnagar).
4Close with the end product (maps or tables).

Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Dark lake in a picture

Suppose a satellite image shows one lake very dark and another light blue.

What can be inferred about the water?

Try it first, then show the solutionSolution

Fresh water absorbs red and infrared strongly and looks dark.
Turbid water reflects more blue and green and looks lighter.

Answer: The dark lake is fresh water; the light blue one is turbid.

Memory hook: Clear is dark.

Daily weather picture

Suppose a weather channel shows cloud pictures of one-third of the globe every few minutes from a satellite that seems to stay above one spot.

Which kind of satellite is it?

Try it first, then show the solutionSolution

It moves with the earth's rotation at about 36,000 km.
Geostationary satellites provide weather and communication.

Answer: A geostationary satellite, such as INSAT.

Memory hook: Stays over one spot.

Tricks to remember Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors

Short memory aids. Say each one aloud once, then use it on a question the same day.

STIP DECE
Source, Transmission, Interaction, Propagation, Detection, Conversion, Extraction, End products
Use it when: Eight stages in order.
IRS low, INSAT high
Sun-synchronous 700-900 km, geostationary 36,000 km
Use it when: Altitudes.
Whisk one, push many
Whiskbroom single detector, pushbroom linear array
Use it when: Sensors.

Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Geostationary altitude · 1 mark · MCQBoard level

A geostationary satellite orbits at about:
(A) 800 km
(B) 8,000 km
(C) 36,000 km
(D) 360,000 km

Try it first, then show the solutionSolution

About 36,000 km (1 mark).

Answer: (C)

Example 2: Remote sensing definition · 2 marks · Very short answerBoard level

Define remote sensing. (2 marks)

Try it first, then show the solutionSolution

Acquiring and measuring information about objects and phenomena (1 mark).
Using a sensor not in physical contact (1 mark).

Answer: Remote sensing is the total process of acquiring and measuring information about objects and phenomena using a sensor that is not in physical contact with them.

Example 3: Sun-synchronous versus geostationary · 3 marks · Short answerHarder board level

Compare sun-synchronous and geostationary satellites on altitude, coverage and use. (3 marks)

Try it first, then show the solutionSolution

Altitude: 700 to 900 km versus about 36,000 km (1 mark).
Coverage: 81 degrees N to S versus one-third of the globe (1 mark).
Use: earth resources versus telecommunication and weather (1 mark).

Answer: Sun-synchronous satellites orbit at 700 to 900 km, cover 81 degrees N to 81 degrees S and are used for earth resources, like the IRS series. Geostationary satellites orbit at about 36,000 km, view about one-third of the globe and are used for telecommunication and weather, like INSAT.

Example 4: Assertion and reason: pushbroom · 1 mark · Assertion-reasonHarder board level

Assertion (A): A pushbroom scanner needs many detectors.
Reason (R): The number of detectors equals the swath divided by the spatial resolution.
(A) Both true, R explains A
(B) Both true, R does not explain A
(C) A true, R false
(D) A false, R true

Try it first, then show the solutionSolution

Each detector records one ground cell, so many are needed across the swath (1 mark).

Answer: (A)

Example 5: HOTS: detectors and swath · 5 marks · Long answerHOTS / competency

A hypothetical pushbroom sensor has a swath of 48 km and a spatial resolution of 12 m. Find the number of detectors, then the number if the resolution is improved to 6 m, and explain what an improvement in spatial resolution means for the picture. (5 marks)

Try it first, then show the solutionSolution

48 km = 48,000 m (1 mark).
Detectors = 48,000 / 12 = 4,000 (1 mark).
At 6 m: 48,000 / 6 = 8,000 detectors (1 mark).
Spatial resolution is the ability to separate closely spaced objects (1 mark).
Higher resolution identifies smaller objects, so more detectors are needed (1 mark).

Answer: Detectors = swath / resolution = 48,000 m / 12 m = 4,000. With a 6 m resolution the number doubles to 48,000 / 6 = 8,000. Better spatial resolution means the sensor can separate more closely spaced objects, so smaller objects can be identified, which requires more detectors across the same swath.

Where students lose marks in Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors

The slips examiners see most often, and what to write instead.

Mistake: Giving seven stages
One stage skipped.
Wrong working
Stages end at extraction.
Right working
Eight stages: add conversion into maps or tables.
Do this: Count to eight.
Usually costs: 1 mark.
Mistake: Mixing up satellite altitudes
Orbit names confused.
Wrong working
IRS is geostationary.
Right working
IRS is sun-synchronous; INSAT is geostationary.
Do this: Pair name and altitude.
Usually costs: 1 mark.
Mistake: Saying sensors touch objects
Misreading remote.
Wrong working
Sensor is placed on the object.
Right working
Sensor is not in physical contact.
Do this: Use "not in contact".
Usually costs: 1 mark.

Exam tips

Draw the eight stages as a flow chart.
Compare satellites in a table with at least four rows.
Use the pushbroom formula with units converted to metres.

Practice questions on Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
In India, remote sensing satellite data are received at:
(A) Mirzapur
(B) Shadnagar near Hyderabad
(C) Sriharikota
(D) Delhi
Hint
Earth Receiving Station.
Answer
(B)
Q2 · 2 marks · Very short answerBoard level
Name the regions of the electromagnetic spectrum used in remote sensing. (2 marks)
Hint
Three regions.
Answer
The visible, infrared and microwave regions.
Q3 · 3 marks · Short answerHarder board level
Explain the interaction of energy with the earth's surface. (3 marks)
Hint
Four possibilities.
Answer
Energy reaching a surface may be absorbed, transmitted, reflected or emitted. Objects differ in composition so they respond differently, and one object responds differently in different spectral regions, giving a spectral signature. For example, fresh water absorbs red and infrared and appears dark.
Q4 · 3 marks · Short answerHarder board level
How does the atmosphere affect remote sensing? (3 marks)
Hint
Absorb and scatter.
Answer
Reflected energy passes through gases, water molecules and dust. Carbon dioxide, hydrogen and water molecules absorb middle infrared, and dust scatters blue light. Energy that is absorbed or scattered does not reach the sensor, so some properties are not recorded.
Q5 · 4 marks · Short answerHOTS / competency
A student says "a camera and a scanner record in the same way". Evaluate this and describe the key difference between photographic and digital sensors and the parts of a whiskbroom scanner. (4 marks)
Hint
Instant versus bit by bit.
Answer
The statement is incorrect. A camera records a photograph at an instant of exposure (analogue), while a scanner is a non-photographic sensor that records bit by bit and gives a digital image. A whiskbroom scanner has a rotating mirror that sweeps a single detector across the field of view of 90 to 120 degrees.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What does EMR stand for?Show answer
Electromagnetic radiation.
2.Which satellites are the IRS?Show answer
Sun-synchronous remote sensing satellites.
3.Who receives the data in India?Show answer
Earth Receiving Station at Shadnagar.
4.What is a spectral signature?Show answer
The characteristic response of an object in each spectral region.

Remote Sensing: Meaning, the Eight Stages of Data Acquisition, Satellite Platforms and Sensors: frequently asked questions

What is a scene?

The ground area covered by an image.

What is a swath?

The length of the scan line set by the sensor's angular field of view.

What are IFOV and TFOV?

Instantaneous Field of View and Total Field of View of a whiskbroom scanner.