NCERT Solutions for Class 11 Geography Chapter 6 - Introduction to Remote Sensing

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    36. Choose the right answer from the four alternatives given below:

    (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 these

    Ans. (b) BCA

    (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

    Ans. (c) X-Rays

    (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

    Ans. (a) Spatial Arrangement of Objects

    37. Answer the following questions in about 30 words.

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

    Ans. Remote sensing is a better technique than traditional methods because:

    (a) It presents a concise picture of a large area.

    (b) It provides real or nearly real pictures on time baseline.

    (c) It is less expensive as compared to land surveys, and we can easily collect information by using it.

    (d) It converts energy received into a photographic/digital form of data.

    (e) It is not affected by bad weather and inaccessible land.

    (ii) Differentiate between IRS and INSAT series of satellites.


    IRS series INSAT series
    It is a Sun Synchronous Satellite. It is a Geostationary Satellite.
    It places at an altitude of 700 – 900 km. It places at an altitude of 36,000 km.
    It covers 81 N to 81 S. It covers 1/3rd of the Globe.
    Its orbital period is 14 orbits per day. Its orbital period is 24 hours.
    Its resolution is fine. Its resolution is coarse.

    (iii) Describe in brief the functioning of push broom scanner.

    Ans. The number of detectors used in push broom scanners is equal to the number found by dividing the sensor’s swath by the size of the spatial resolution. Each detector in a push broom scanner is linearly arranged and captures the energy reflected by a ground cell (pixel) with dimensions of 20 metres from a nadir’s perspective. For example, the swath of High- Resolution Visible Radiometer – 1 (HRVR -1) of the French remote sensing satellite SPOT is 60 km, and the spatial resolution is 20 metres. If we divide 60 km × 1000 metres/20 metres, we get a number of 3000 detectors that are deployed in SPOT HRV – 1 sensor.

    38. Answer the following questions in about 125 words.

    (i) Describe the operation of a whiskbroom scanner with the help of a diagram. Explain how it is different from push broom scanner.

    Ans. The whiskbroom scanners consist of a single detector and a rotating mirror. In order to produce pictures in a large number of small spectral bands spanning the visible to middle infrared sections of the spectrum, the mirror is angled in such a way that when it completes a revolution, the detector sweeps throughout the field of vision between 90° and 120°. The scanner’s total Field of View (IFOV) refers to the whole area covered by the oscillating sensor. The sensor’s optical head is always positioned at a certain dimension known as the Instantaneous Field of View while scanning the whole field (IFOV).


    (a) In a whiskbroom scanner, a single mirror is used to reflect light onto a single detector. The mirror moves back and forth to collect measurements from one pixel in the image at a time, whereas, in a push broom scanner, a line of detectors is arranged perpendicular to the flight direction. The image is collected one line at a time, with all of the pixels in a line measured simultaneously.

    (b) A push broom scanner receives a stronger signal than a whiskbroom scanner because it looks at each pixel area for a long time.

    (c) Push broom scanner is more sensitive than whiskbroom scanner. So it is needed to calibrate perfectly.

    (ii) Identify and list the changes that can be observed in the vegetation of Himalayas (Fig. 7.9).

    Ans. The Himalayan ranges show a succession of vegetation from the tropical to the tundra, changing with altitude. Deciduous forests are found in the foothills of the Himalayas. It is succeeded by the wet temperate type of forests between an altitude of 1,000-2,000 m. After 3000 metres of altitude, conical forests with sharp leaves are found. Important trees in this region  are Chid, Fur, Pine, Spurs etc.

    The red patches in the May image refer to Coniferous vegetation. In the November image, the additional red patches refer to Deciduous plants, and the light red colour is related to the crops.

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