Prelims · Science & technology · 22 questions

Space technology

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Prelims 2019 · Q32

Easy

For the measurement/estimation of which of the following are satellite images/remote sensing data used?

1.Chlorophyll content in the vegetation of a specific location
2.Greenhouse gas emissions from rice paddies of a specific location
3.Land surface temperatures of a specific location

Select the correct answer using the code given below.

Answer & explanation

Answer: (d) 1, 2 and 3

All three can be measured or estimated from satellite data: leaf greenness and chlorophyll from visible and near-infrared reflectance, land surface temperature from thermal infrared, and paddy methane by combining satellite-derived rice area and temperature with models.

✓ 1. Chlorophyll strongly absorbs visible light and leaves reflect near-infrared, so satellite vegetation indices (such as MODIS NDVI and EVI) track canopy greenness, which depends on leaf area, chlorophyll and canopy structure.
✓ 2. Methane from rice paddies has been estimated with a model driven by satellite-mapped rice area, land surface temperature and evapotranspiration, for example over China's Sanjiang Plain.
✓ 3. Land surface temperature is retrieved from thermal infrared measurements, for example the MODIS daily product at 1 km pixels.

Remember · Remote sensing gives vegetation greenness and chlorophyll (NDVI), land surface temperature (thermal infrared), and, with models, methane from rice fields.

Sources

NASA MODIS: Vegetation Index Products (NDVI and EVI) ↗ “MODIS vegetation indices, produced on 16-day intervals and at multiple spatial resolutions, provide consistent spatial and temporal comparisons of vegetation canopy greenness, a composite property of leaf area, chlorophyll and canopy structure.”
NASA MODIS: Land Surface Temperature and Emissivity (MOD11) ↗ “The Land Surface Temperature (LST) and Emissivity daily data are retrieved at 1km pixels by the generalized split-window algorithm and at 6km grids by the day/night algorithm.”
Sun et al. (2017), PLoS ONE: satellite-data-based estimation of methane emissions from rice paddies, Sanjiang Plain, China (open-access copy on PubMed Central, NIH) ↗ “we estimated CH 4 emissions using a process-based model derived by rice area, CH 4 flux, land surface temperature (LST), and the ratio of precipitation (P) and evapotranspiration (ET) in rice paddies in the SJP”

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2019 · Q97

Easy

Recently, scientists observed the merger of giant 'blackholes' billions of light-years away from the Earth. What is the significance of this observation?

Answer & explanation

Answer: (b) 'Gravitational waves' were detected.

The merger of two black holes was significant because it produced gravitational waves, ripples in space-time that scientists detected directly for the first time on 14 September 2015 using the LIGO detectors. The waves, predicted by Einstein a hundred years earlier, travelled for 1.3 billion years before reaching Earth.

✓ (b) The Nobel Prize in Physics 2017 press release says the first observed gravitational waves came from a collision between two black holes. An Indian team was part of the group that announced the discovery in 2016.
✗ (c) NASA states that black holes do not provide shortcuts between different points in space, so nothing about travel through wormholes was confirmed.
✗ (a) The Higgs boson is a particle searched for in particle-physics experiments; the black-hole merger observation was about gravitational waves, not that particle.
✗ (d) The observation is remembered for detecting gravitational waves, not for explaining the 'singularity' inside a black hole.

Remember · First direct detection of gravitational waves (LIGO, 14 September 2015): two black holes merging about 1.3 billion light-years away; Nobel Prize in Physics 2017.

📘 Read it in NCERT: Class 11 Knowledge Traditions and Practices of India, Part I, Ch 5 (practise this chapter)

Sources

NCERT Class 11 · Knowledge Traditions and Practices of India, Part I, Chapter 5 “A team of Indian Scientists was a part of the group which announced in 2016, the discovery of gravitational waves predicted by Einstein.”
The Nobel Prize in Physics 2017, press release (Royal Swedish Academy of Sciences) ↗ “On 14 September 2015, the universe’s gravitational waves were observed for the very first time. The waves, which were predicted by Albert Einstein a hundred years ago, came from a collision between two black holes.”
NASA Science, Black Holes ↗ “They don’t provide shortcuts between different points in space, or portals to other dimensions or universes.”

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

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Read it in NCERT

Class 11 Knowledge Traditions and Practices of India, Part I, Chapter 5cited in 1 explanation