UPSC Essentials brings to you its initiative for the practice of Mains answer writing. It covers essential topics of static and dynamic parts of the UPSC Civil Services syllabus covered under various GS papers. This answer-writing practice is designed to help you as a value addition to your UPSC CSE Mains. Attempt today’s answer writing on questions related to topics of GS-3 to check your progress.

LiDAR (Light Detection and Ranging) technology has been instrumental in archaeological discoveries. Explain the working principle of LiDAR.

Air Quality Index (AQI) is a critical measure for understanding air pollution levels and its impact on public health. Discuss the components of the AQI, with specific reference to PM2.5 and PM10 particles.

Introduction

— The introduction of the answer is essential and should be restricted to 3-5 lines. Remember, a one-liner is not a standard introduction.

— It may consist of basic information by giving some definitions from the trusted source and authentic facts.

Body

— It is the central part of the answer and one should understand the demand of the question to provide rich content.

— The answer must be preferably written as a mix of points and short paragraphs rather than using long paragraphs or just points.

— Using facts from authentic government sources makes your answer more comprehensive. Analysis is important based on the demand of the question, but do not over analyse.

— Underlining keywords gives you an edge over other candidates and enhances presentation of the answer.

— Using flowcharts/tree-diagram in the answers saves much time and boosts your score. However, it should be used logically and only where it is required.

Way forward/ conclusion

— The ending of the answer should be on a positive note and it should have a forward-looking approach. However, if you feel that an important problem must be highlighted, you may add it in your conclusion. Try not to repeat any point from body or introduction.

— You may use the findings of reports or surveys conducted at national and international levels, quotes etc. in your answers.

Self Evaluation

— It is the most important part of our Mains answer writing practice. UPSC Essentials will provide some guiding points or ideas as a thought process that will help you to evaluate your answers.

QUESTION 1: LiDAR (Light Detection and Ranging) technology has been instrumental in archaeological discoveries. Explain the working principle of LiDAR.

Note: This is not a model answer. It only provides you with thought process which you may incorporate into the answers.

Introduction:

— LiDAR, or Light Detection and Ranging, is a remote sensing technology that uses light in the form of a pulsed laser to measure ranges (or variable distances) of a sensor, usually mounted aboard an aircraft, to Earth’s surface.

— According to the US Geological Survey, LiDAR data can be used to generate high-resolution 3-D ground elevation models with vertical accuracy of up to 10 cm.

— LiDAR is used to generate precise three-dimensional data about the Earth’s shape and surface properties. This is undoubtedly valuable information for geographers, policymakers, conservationists, and engineers. In recent years, however, LiDAR has demonstrated potential as an archaeological discovery tool.

Body:

You may incorporate some of the following points in your answer:

Working principle of LiDAR

— LiDAR instrumentation comprises a laser, a scanner, and a GPS receiver. The rapidly firing laser travels to the ground where it hits vegetation, building, and various topographic features. This light is reflected or scattered, and recorded by the LiDAR sensor.

— The system determines the distance between the terrain and the sensor by calculating the two-way travel time of the light pulses. It combines this information with Global Positioning System (GPS) and Inertial Measurement System (IMS) data to generate an elevation map of Earth.

— LiDAR data is originally gathered as a “point cloud” consisting of all individual points reflected by anything on the surface, including structures and vegetation. However, knowing how much light energy was returned to the sensor enables for more accurate identification of various things, such as plants, buildings, and so on. For example, tree canopies, no matter how dense they are, allow some light to flow through and reach the ground.

Conclusion:

— LiDAR allows researchers to study much larger swathes of land quickly in the comfort of a home or lab. Auld-Thomas, the lead author of the latest research published in the journal Antiquity used publicly available LiDAR data taken for a forest monitoring project in 2013 to discover the city he named Valeriana in Mexico’s Campeche region.

— The LiDAR data can be further refined to produce what scientists call a “bare earth” Digital Elevation Model, in which structures and vegetation are stripped away.

(Source: How remote sensing system LiDAR helped discover a lost Mayan city)

Points to Ponder

What is the difference between terrestrial LiDAR and mechanical LiDAR?

How is RADAR different from LiDAR?

Related Previous Year Questions

How is the S-400 air defence system technically superior to any other system presently available in the world? (2021)

What do you understand about the ‘Standard Positioning System’ and ‘Precision Positioning System’ in the GPS era? Discuss the advantages India perceives from its ambitious IRNSS programme employing just seven satellites. (2015)

QUESTION 2: Air Quality Index (AQI) is a critical measure for understanding air pollution levels and its impact on public health. Discuss the components of the AQI, with specific reference to PM2.5 and PM10 particles.

Note: This is not a model answer. It only provides you with thought process which you may incorporate into the answers.

Introduction:

— The Air Quality Index (AQI) in New Delhi was approximately 351 on November 1, the day after Diwali. The arrival of winter and cool, dense air encircling the city, road dust and traffic pollution, and stubble burning in the neighbouring states of Punjab and Haryana all contribute to the decline in air quality.

— AQI is a number that indicates air quality: the higher the AQI, the worse the air. There are six categories of AQI, namely ‘Good’ (0-50), ‘Satisfactory’ (50-100), ‘Moderately polluted’ (100-200), ‘Poor’ (200-300), ‘Very Poor’ (300-400), and ‘Severe’ (400-500).

— The colour-coded AQI index was introduced in India in 2014, and it assists the public and the government in understanding the state of the air and the subsequent measures that will be done to tackle the problem based on its severity.

Body:

You may incorporate some of the following points in your answer:

Components of the AQI

— According to the Central Pollution Control Board, a division of the Ministry of Environment, Forests, and Climate Change, the AQI converts complex air quality data for multiple pollutants into a single number (index value), name, and colour. Pollutants measured include PM 10, PM 2.5, nitrogen dioxide, ground-level ozone, carbon monoxide, sulphur dioxide, ammonia, and lead.

— Each of these categories is determined by the ambient concentration levels of air contaminants and their potential health effects.

Impact of pollutants like PM 2.5 and PM 10

— Smaller pollutants, such as particulate matter (PM) 2.5, are among the most damaging. PM 2.5 is an atmospheric particulate matter with a diameter less than 2.5 micrometres. It causes breathing issues and impairs visibility. Because of their small size, the particles can only be identified using an electron microscope.

— Because of their size, PM 2.5 particles can readily travel via the nose and throat and into the circulatory system. The particles can also cause chronic ailments like asthma, heart attacks, bronchitis, and other respiratory issues.

Conclusion:

— Governments in cities such as Delhi declare actions in response to air quality problems. The Graded Response Action Plan (GRAP) has been specifically designed to implement emergency actions that would avoid further degradation of air quality in Delhi-NCR.

— Earlier, it resulted in a restriction on the use of coal and firewood, including tandoors in hotels, restaurants, and open eateries, as well as diesel generator sets (save for emergency and essential services). It also includes an increase in parking fees to discourage the usage of private vehicles.

(Source: What is AQI — and how is the air quality in Delhi after Diwali this year?)

Points to Ponder

Suggest some measures to reduce air pollution

How does ground level ozone impact human health?

Related Previous Year Questions

What are the key features of the National Clean Air Programme (NCAP) initiated by the government of India? (2020)

Describe the key points of the revised Global Air Quality Guidelines (AQGs) recently released by the World Health Organisation (WHO). How are these different from its last update in 2005? What changes in India’s National Clean Air Programme are required to achieve revised standards? (2021)

UPSC Essentials: Mains answer practice — GS 1 (Week 75)

UPSC Essentials: Mains answer practice — GS 1 (Week 74)

UPSC Essentials: Mains answer practice — GS 2 (Week 73)

UPSC Essentials: Mains answer practice — GS 2 (Week 74)

UPSC Essentials: Mains answer practice — GS 3 (Week 74)

UPSC Essentials: Mains answer practice — GS 3 (Week 75)

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