The Normalized Difference Vegetation Index (NDVI) is a proxy for which of the following?

Chlorophyll content and plant health. Chlorophyll content and plant health is the answer. NDVI compares near-infrared and visible red light. Healthy leaves absorb red light for photosynthesis and reflect near-infrared light strongly. A higher NDVI therefore means denser, greener leaves. NDVI is a proxy, because it tracks leaf greenness and not chlorophyll itself. Land surface temperature needs thermal sensors. Methane needs gas-sensing instruments, and soil moisture needs other data. Memory hook: NDVI means a plant's green health score. Read more: What Satellite Remote Sensing Can Measure, Indian Remote Sensing Satellites: What IRS Can and Cannot Do.

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.

1, 2 and 3. All three statements are correct, so the answer is 1, 2 and 3. Statement 1 is correct because red-edge bands and NDVI-type data help estimate chlorophyll. Statement 2 is correct because sensors such as TROPOMI track methane over rice regions. Statement 3 is correct because thermal sensors such as Landsat TIRS measure land surface temperature. So options 1 only, 2 and 3 only, and 3 only each leave out a true statement. Memory hook: light gives chlorophyll, heat gives temperature, and gas gives methane. Read more: What Satellite Remote Sensing Can Measure, Indian Remote Sensing Satellites: What IRS Can and Cannot Do.

The Normalized Difference Vegetation Index compares which two kinds of reflected light?

Near-infrared and visible light. Near-infrared and visible light are the two kinds. The formula is NDVI = (NIR - VIS) / (NIR + VIS). Healthy leaves absorb visible light and reflect near-infrared light. So green plants give a high value. Ultraviolet, X-rays, microwaves and gamma rays are not used in this index. Thermal infrared is used for temperature, not for NDVI. Memory hook: NDVI is a near-infrared against visible contest. Read more: What Satellite Remote Sensing Can Measure, Indian Remote Sensing Satellites: What IRS Can and Cannot Do.

A very low NDVI value, such as 0.1 or below, most likely marks which surface?

Barren rock, sand or snow. Barren rock, sand or snow is the answer. NASA gives NDVI values of 0.1 or below for such surfaces. These surfaces have no green leaves to reflect near-infrared light. Rainforest is high, at about 0.6 to 0.8. Healthy crops and green forest are also well above 0.3. Shrub and grassland sit in between, at 0.2 to 0.3. Memory hook: little green means a low number. Read more: What Satellite Remote Sensing Can Measure, Indian Remote Sensing Satellites: What IRS Can and Cannot Do.

The Thermal Infrared Sensor on Landsat 8 is mainly used to measure which quantity?

Land surface temperature. Land surface temperature is the answer. The sensor has two thermal bands that separate the surface from the air above it. It sees patches about 100 metres wide every 16 days. Chlorophyll is read from visible and near-infrared light instead. Rainfall needs radar or gauge data. Soil acidity cannot be seen from orbit. Memory hook: TIRS is the satellite's thermometer. Read more: What Satellite Remote Sensing Can Measure, Indian Remote Sensing Satellites: What IRS Can and Cannot Do.

Which satellite sensor maps methane and other trace gases across the whole planet every day?

TROPOMI on Sentinel-5P. TROPOMI on Sentinel-5P is the answer. ESA says the satellite maps trace gases, including methane, with a swath of 2,600 kilometres. That wide swath lets it map the planet daily. Researchers used its data to study paddy methane. TIRS measures temperature. The Sentinel-2 red-edge bands estimate chlorophyll. A laser altimeter measures height. Memory hook: Sentinel-5P sniffs the air. Read more: What Satellite Remote Sensing Can Measure, Indian Remote Sensing Satellites: What IRS Can and Cannot Do.

About what share of world farm emissions comes from flooded rice, according to the AgLED estimate?

About 9 to 11 per cent. About 9 to 11 per cent is the answer. That is 493 to 723 million tonnes of carbon dioxide equivalent a year. Microbes in flooded fields make methane without oxygen, and it escapes through the rice plants. The share is far above 1 to 2 per cent. It is nowhere near 30 per cent or more. Draining fields can cut methane. Memory hook: rice is about a tenth of farm emissions. Read more: What Satellite Remote Sensing Can Measure, Indian Remote Sensing Satellites: What IRS Can and Cannot Do.

Which feature of Sentinel-2 improves satellite estimates of chlorophyll content?

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