Remote Sensing Role, Principles ,Platforms and applications

 Remote Sensing

Remote sensing is defined as the art and science of gathering information about objects or areas from a distance without having physical contact with objects/areas being investigated.

Role of Remote Sensing – Agricultural resources are important renewable dynamic natural resources. In India, agriculture sector alone sustains the livelihood of around 67% of the population. Increasing agricultural productivity has been the main concern since scope for increasing area for cultivation is rather limited.

This demands judicious and optimal management of both land and water resources. Hence, comprehensive and reliable information on land use/cover, forest area, soils, geological information, extent of wastelands, agricultural crops, water resources (surface and underground) and hazards/natural calamities like drought and floods is required.

Season-wise information on crops, their acreage, vigour and production enables the country to adopt suitable measures to meet shortages, if any, and implement proper support and procurement policies. Remote sensing systems, having capability of providing regular, synoptic, multi-temporal and multi-spectral coverage of the country, are playing an important role in providing such information.

Many experiments have been carried out in developing techniques for extracting agriculture related information from ground borne, air borne and space borne data.

Principles of Remote Sensing

Every material on the earth absorbs and reflects the solar energy. In addition, they emit certain amount of internal energy. The absorbed, reflected and emitted energy is detected by remote sensing instruments or sensors, which are carried in aircraft or satellites.

The detections are made by characteristic terms called “spectral signatures” and “images”. Remote sensing systems in common use, record radiation in the form of electromagnetic spectrum (sunlight), i.e., visible range (0.4–0.7 nm), near infrared (0.7–1000 nm) and microwaves (1nm–0.8 nm). Artificial sources of illumination such as radars are also used.

Sensors Used in Remote Sensing

Photography: Photographic systems are the most commonly used sensing systems. The film records the energy reaching it at the exposure time in the visible and near infrared ranges of the spectrum. The photographic technique is used to identify soil types, plants grown, disease incidence and drainage patterns.

Line scan and related system: The system uses the visible and near infrared portion of the spectrum. In this system, a mirror is rotated parallel to the direction of the movement of the aircraft or satellite. The mirror reflects the radiation received on to a detector and the data is recorded.

The multi spectral scanners have different channels for different colours of visible and IR portions. The IR sensors also record the thermal infrared radiation emitted by the earth proportional to the surface temperature. The infrared imagery is used to study the extent of vegetation, soil moisture, etc.

Microwave system: The microwave radiation emitted from earth’s surface in small quantities is used by microwave sensors in a wavelength of about 1 nm–1000 nm. The sensors record the microwave radiation through complex antennae.

These are used in weather satellites. The active microwave systems are known as radars. Radars are used to study soil characters, plant condition, soil moisture and runoff slopes.

Remote Sensing Platforms

Three platforms are generally used for remote sensing techniques. They are ground based, air based and satellite based. Infrared thermometer, spectral radiometer, pilot balloons and radars are some of the ground-based remote sensing tools while aircrafts are air based remote sensing tools. Since the ground based and air based platforms are very costly and have limited use, space based satellite technology has become handy for wider application of remote sensing techniques. The digital image processing, using powerful computers, is the key tool for analyzing and interpretation of remotely sensed data.

The advantages of satellite remote sensing are:

• Synoptic view – Wide area can be covered by a single image/photo (One scene of Indian Remote Sensing Satellite IRS series cover about 148 × 178 sq. km area).

• Receptivity – We can get the data of any area repeatedly (IRS series cover the same area every 16-22 days).

• Coverage – Inaccessible areas like mountains, swampy areas and thick forests are easily covered. Space based remote sensing is the process of obtaining information about the earth from the instruments mounted on the earth observation satellites (EOS).

The satellites are subdivided into two classes and the types of satellite are as follows:

(i) Polar orbiting satellites – These satellites operate at an altitude between 550 and 1,600 km along an inclined circular plane over the poles. These satellites are used for remote sensing purposes. LANDSAT (USA), SPOT (FRANCE), and IRS (INDIA) are some of the remote sensing satellites.

(ii) Geostationary satellite- These satellites have orbits around the equator at an altitude of 36,000 km and move with the same speed as the earth, so as to view the same area on the earth continuously. They are used for telecommunication and weather forecasting purposes. INSAT series are launched from India for the above purposes. All these satellites have sensors on board operating in the visible and near infrared regions of the electromagnetic spectrum. INSAT-3A was launched on 10th April, 2003.

Application

Remote sensing techniques are used in agricultural and allied fields for the following reasons:

• For collection of basic data for monitoring crop growth

• For estimating the cropped area

• For forecasting the crop production

• For mapping of wastelands

• For drought monitoring and its assessment

• For flood mapping and damage assessment

• For land use/cover mapping and area under forest coverage

• For soil mapping

• For assessing soil moisture condition, irrigation, drainage

• For assessing outbreak of pest and disease

• For ground water exploration.

Areas of general application:

(i) Agricultural land use mapping;

(ii) Agricultural population distribution;

(iii) Land use potential, and

(iv) Soil and water resource surveys.

Areas of specific application:

( i) Crop identification;

(ii) Crop acreage, vigour and density;

(iii) Crop growth rates and maturity;

(iv) Yield estimation and forecasting;

(v) Soil problems like salinity etc.;

(vi) Soil moisture, water quality and irrigation effectiveness;

(vii) Drought prediction;

(viii) Insects, diseases and nematodes;

(ix) Frost damage;

(x) Storm and flood warning;

(xi) Fire surveillance and control;

(xii) Water availability and location of canals;

(xiii) dates of planting and harvesting and

(xiv) Areas of fertilizer application and effect of fertilizers.

Application to range surveys

• Identification of forage species and their yield

• Delineation of forest types and condition of range

• Carrying capacity of ranges

• Soil fertility and soil erosion

• Identification of poisonous species

• Pest, disease and weed infestation

• Wild life inventory

• Fire surveillance.

Application of livestock surveys

• Population studies, distribution of animals

• Animal behaviour, health of animals

• Types of farm buildings.

Remote Sensing in India

India, with the experience gained from its experimental remote sensing satellite missions BHASKARA-I (1979) and BHASKARA-II (1981), has now established satellite based operational remote sensing system in the country with the launch of Indian Remote Sensing Satellite IRS-IA in 1988, followed by IRS-IB (1992), IRS-IC (1995) and IRS-ID (1997).

The Department of Space (DOS)/Indian Space Research Organization (ISRO) as the nodal agency for establishing an operation remote sensing system in the country initiated efforts in the early 1970s for assessing the potentials of remotely sensed data through several means. In order to meet the user requirement of remote sensing data analysis and interpretation, ISRO/DOS has set up a system to launch remote sensing satellites once in three or four years to maintain the continuity in data collection. 

In seventies, ISRO used remote sensing for resource inventory and launched Rohini–I (1981) and Rohini–II (1983).

Organizations using RS Techniques

• National Remote Sensing Agency (NRSA), Hyderabad

• Space Application Centre (SAC), Ahmedabad

• National Bureau of Soil Survey and Land Use Planning (NBSSLUP), Nagpur

• Central Ground Water Board ( CGWB)

• National Institute of Oceanography (NIO)

• All India Soil and Land Use Survey (AISLS), New Delhi.

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