Maarg Manthan · Topic 12.12

Remote Sensing Applications and Ground Segment Services

Science & Technology › Space Technology and ISRO · Topic 12.12

Remote sensing is the science of getting information about the Earth's surface without touching it, by recording the energy that objects reflect or emit, mostly from satellites. Passive sensors use sunlight or the heat given out by the Earth, while active sensors such as radar and lidar send their own signal. Satellite data are described by four kinds of resolution: spatial, spectral, temporal and radiometric. The ground segment is the set of stations and centres that receive data from the satellite, control it and process the data into products. In India the National Remote Sensing Centre in Hyderabad receives and distributes Earth observation data, and applications include agriculture, forests, water, urban planning, geology, oceans, weather and disaster management.

5 min read · UPSC Prelims · Science & Technology · Space Technology and ISRO

At a Glance

Passive sensors Use sunlight or Earth emission
Active sensors Radar and lidar
Resolutions Spatial, spectral, temporal, radiometric
Data centre NRSC, Hyderabad
Public portal Bhuvan
Exam link UPSC Prelims, Science & Technology: Space Technology and ISRO

Where Does It Fit?

This topic follows the new technologies in space. It deals with the main use of Earth observation satellites, and with the ground based systems that make satellite data useful. Previous topic: Space Technology Innovations: Nanosatellites, Electric Propulsion, Satellite-Based Internet. Next topic: Deep Space Atomic Clock.

How Does Remote Sensing Work?

Item	Details
Energy source	The Sun for passive optical sensing, or the sensor’s own signal for active sensing
Interaction	Objects reflect, absorb or emit energy differently in each wavelength, which gives each a spectral signature
Sensors	Panchromatic (one broad band), multispectral (several bands), hyperspectral (hundreds of narrow bands), thermal infrared and microwave
Synthetic aperture radar	Active microwave sensor that images through cloud, rain and darkness
Spatial resolution	Size of the smallest object seen on the ground. Cartosat-3 about 0.25 m, Resourcesat LISS-IV about 5 m, AWiFS about 56 m
Spectral resolution	Number and width of wavelength bands
Temporal resolution	How often a place is imaged again. AWiFS revisits every 5 days. Geostationary satellites image every 15 to 30 minutes

What Is the Ground Segment and What Are the Uses?

Receiving stations: Shadnagar near Hyderabad is the main reception station for Indian remote sensing data, and a station is also in Antarctica
Telemetry, Tracking and Command: ISTRAC in Bengaluru tracks and controls satellites
Processing and archive: NRSC converts raw data into corrected images and keeps an archive
Bhuvan: a public geoportal with satellite maps and thematic data
Agriculture: crop area and yield estimates, drought assessment and the FASAL programme, run with the Agriculture Ministry
Forests and environment: forest cover, fire alerts and wetland maps
Water and hydrology: snow cover, glaciers, reservoir levels and flood mapping
Urban and rural planning: land use maps, Smart Cities and PM Gati Shakti planning

What Else Should You Remember?

Disaster management: ISRO’s Decision Support Centre gives flood, cyclone and landslide information to authorities, and the National Database for Emergency Management has data layers
Fisheries: potential fishing zone advisories use ocean colour and sea surface temperature data
Geology and minerals: satellite images help to find rock types and mineral zones
Weather: INSAT satellites give cloud images for forecasts and cyclone tracking
Hyperspectral images: identify crop types, minerals and pollution by their detailed spectrum, as in Hyperspectral Imaging Satellite and Water Propulsion System in CubeSats
Lidar: uses laser pulses to measure elevation and forests structure
Geographic Information System: software that stores and analyses spatial data along with satellite images
Indian Institute of Remote Sensing: Dehradun, a training institute for remote sensing and geoinformatics
Data policy: India has opened access to many remote sensing datasets for free or low cost, and the National Geospatial Policy 2022 liberalised mapping data
Open data: Landsat of the United States and Sentinel of Europe also give free data
Limits: cloud cover, resolution limits, and need for ground truth checking
Link: satellites used are described in INSAT, GSAT and IRS in Satellite Systems: INSAT, GSAT, IRS (Remote Sensing)
National Remote Sensing Centre: the National Remote Sensing Centre at Balanagar, Hyderabad, is a centre of the Department of Space that is responsible for acquiring, processing and distributing Earth observation data and for applications projects
Crop forecasting: satellite images are combined with weather data and field samples to forecast production of wheat, rice, cotton and other crops before harvest
Change detection: comparing images of two dates shows changes such as forest loss, urban growth, shoreline movement and glacier retreat
Vegetation index: the Normalised Difference Vegetation Index uses red and near infrared reflectance to show how green and healthy plants are

Why Does It Matter for the Exam?

Terms: four resolutions
Sensor types: passive versus active, SAR
Institutions: NRSC, ISTRAC, IIRS
Current affairs link: Bhuvan and geospatial policy
Common errors: confusing spatial with temporal resolution

As an analytical point, satellite data now support nearly every sector, but value is created at the ground, through processing, analysis and delivery to the user. Open data and trained analysts widen the benefits.

Why Is This Topic Important?

Resolutions Four types
Ground NRSC and Bhuvan
Uses Farm to disaster

What Came Next?

The next topic covers the Deep Space Atomic Clock. Next topic: Deep Space Atomic Clock.

Key People and Terms

Spectral signature Reflectance pattern of an object
Swath Width of image strip
Revisit time Time between images
Ground truth Field check
GIS Spatial data system
SAR Synthetic aperture radar

Exam Corner

Points to Remember

Passive sensors use sunlight; active use own signal.
Four resolutions: spatial, spectral, temporal, radiometric.
NRSC is in Hyderabad.
IIRS is at Dehradun.
Radar sees through clouds.

Do Not Confuse With

Spatial and spectral resolution Smallest object versus number of bands
Passive and active sensing Uses sunlight versus own signal
Multispectral and hyperspectral Few broad bands versus hundreds of narrow bands

Memory Hook

Passive waits for the sun, active sends its own; spatial, spectral, time and radiometric measure the view.

Mains Angle

Questions ask about terms, institutions and applications. These points help.

Applications Farm to disaster
System Ground segment
Policy Open data

A Question You May Face

An original practice question, not a past paper question.

“Discuss the applications of remote sensing in India and the importance of the ground segment in making satellite data useful.”

How to Answer

Principle Sensors and resolution.
Ground NRSC, ISTRAC.
Uses Agriculture, disasters.
Way Open data, skills.

GS Relevance

Prelims: types of remote sensing, resolutions, ground segment, Indian centres. GS Paper 3: science and technology, space applications, disaster management.

Frequently Asked Questions

What is remote sensing?

Remote sensing is the collection of information about the Earth's surface or atmosphere from a distance, usually by sensors on satellites or aircraft that record reflected or emitted energy. The data are processed into images and maps used for farming, forests, water resources, cities, oceans, weather and disaster management.

What are the types of resolution in remote sensing?

The four types are spatial resolution, which is the size of the smallest object that can be seen, spectral resolution, which is the number and width of wavelength bands, temporal resolution, which is how often a place is imaged, and radiometric resolution, which is the ability to detect small differences in brightness.

What is the difference between active and passive remote sensing?

Passive remote sensing records energy that is naturally available, such as sunlight reflected by the Earth, so it works only in daylight and clear weather. Active remote sensing, such as radar and lidar, sends out its own signal and records the return, so it can work at night and see through clouds.

What is the ground segment of a satellite system?

The ground segment consists of the stations and centres on Earth that track and control satellites, receive their data, process the data into usable products and distribute them to users. In India, ISTRAC controls satellites, Shadnagar receives data, and the National Remote Sensing Centre in Hyderabad processes and distributes images.

What is Bhuvan?

Bhuvan is a geoportal of ISRO that allows the public to view and use satellite maps and thematic data for India. It provides images, land use maps, village level information, disaster alerts and tools, and is used by government departments, researchers and citizens for planning and monitoring.

PYQ Practice — Statement Analysis

1 Synthetic aperture radar can image the Earth through cloud cover.

True

It is an active microwave sensor.

2 Temporal resolution is the size of the smallest object seen on the ground.

False

That is spatial resolution.

3 The National Remote Sensing Centre is located in Hyderabad.