NCERT Solutions for Class 11 Geography Practical Work in Geography I Chapter 6: Introduction to Remote Sensing

Chapter at a glance

Exercise Questions

Question 1 (i)

Remote sensing of objects can be done through various means such as A. remote sensors, B. human eyes and C. photographic system. Which of the following represents the true order of their evolution.
(a) ABC (b) BCA (c) CAB (d) None of the above

Answer

Human eyes were used first, then photographic systems (aerial photography), and finally modern remote sensors (scanners on satellites).

2. BCA

Question 1 (ii)

Which of the following regions of Electromagnetic spectrum is not used in satellite remote sensing.
(a) Microwave region (b) Infrared region (c) X-rays (d) Visible region

Answer

X-rays are absorbed by the atmosphere and are not used.

3. X-rays

Question 1 (iii)

Which of the following is not used in visual interpretation technique?
(a) Spatial arrangements of objects (b) Frequency of tonal change on the image (c) Location of objects with respect to other objects (d) Digital image processing

Answer

Digital image processing is a computer-based technique, not a visual one.

4. Digital image processing

Question 2 (i)

Why is remote sensing a better technique than other traditional methods?

Answer

1. It covers large areas quickly, including inaccessible regions (mountains, forests, deserts, oceans).
2. It provides repetitive coverage (temporal resolution), helping monitor changes over time (crops, floods, deforestation).
3. It records data in many spectral bands, revealing features invisible to the eye.
4. It is faster and cheaper per unit area than ground surveys, and data are in digital form for analysis with GIS.

It gives quick, repeated, multi-spectral coverage of large and inaccessible areas at lower cost than ground surveys, in digital form.

Question 2 (ii)

Differentiate between IRS and INSAT series of satellites.

Answer

IRS satellites are sun-synchronous polar-orbiting earth-resource satellites; INSAT satellites are geostationary communication and weather satellites.

Question 2 (iii)

Describe in brief the functioning of pushbroom scanner.

Answer

A pushbroom scanner has a linear array of many detectors arranged across the track. The number of detectors equals the swath width divided by the spatial resolution (e.g. SPOT HRV-1: 60 km ÷ 20 m = 3,000 detectors). Each detector records the energy reflected from one ground cell (pixel), so a whole line is imaged at once; as the satellite moves forward, successive lines build up the image like a broom pushed along the ground.

A linear array of detectors (swath ÷ resolution) images an entire line of ground cells at once, and the satellite’s forward motion builds up the image line by line.

Question 3 (i)

Describe the operation of a whiskbroom scanner with the help of a diagram. Explain how it is different from pushbroom scanner.

Answer

Whiskbroom (across-track) scanner

• It uses a rotating or oscillating mirror and a single detector (or a few detectors).
• The mirror sweeps the ground from side to side, across the flight track, through a wide angle of 90° to 120° (the Total Field of View, TFOV), collecting energy pixel by pixel.
• At any instant the sensor sees one small area — the Instantaneous Field of View (IFOV).
• The reflected energy is split into many narrow spectral bands (visible to middle infrared).
• As the satellite moves forward, successive scan lines build up the image.

Differences

A whiskbroom scanner uses an oscillating mirror and single detector to sweep the ground pixel by pixel across the track (TFOV 90°–120°, IFOV per pixel); a pushbroom scanner has a fixed linear detector array that images a whole line at once without moving parts.

Question 3 (ii)

Identify and list the changes that can be observed in the vegetation of Himalayas (Fig. 6.9).

Answer

Fig. 6.9 shows IRS false colour images of the Himalayas and northern plains taken in May (left) and November (right). In FCC images, healthy vegetation appears red.

1. May image: only patches of red appear, mainly on higher slopes — these are coniferous (evergreen) forests, which retain leaves throughout the year. Most of the rest appears dark, since deciduous trees have shed leaves in the dry season and fields are bare after the rabi harvest.
2. November image: the area appears largely red:
   • additional red patches show deciduous forests, which are green and leafy after the monsoon;
   • light red areas in the plains show crops (kharif/rabi crops in fields).
3. Hence the images reveal seasonal changes: increase in green cover from May to November, the distinction between coniferous and deciduous forests, and the presence of crops in the plains after the monsoon.

In May only coniferous forests show red; in November extra red patches show leafy deciduous forests and light red shows crops — revealing seasonal growth after the monsoon and the difference between coniferous and deciduous vegetation.

Topic checklist

• Meaning and stages of remote sensing
• Electromagnetic spectrum and spectral signatures
• Sensors: photographic, whiskbroom and pushbroom scanners
• Resolutions and satellites (IRS, INSAT)
• Visual interpretation and false colour composites

Total questions answered: 8 of 8