REMOTE SENSING AND GIS BY GOWRI PRIYA GVHSS, VITHURA

REMOTE SENSING AND GIS

REMOTE SENSING
DEFINITIONS:-
Remote sensing is the science of acquiring, processing and interpreting images that record the interaction between electromagnetic energy and matter.
Remote sensing is the science and art of obtaining information about an object, area or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area or phenomenon under investigation.
The characteristics measured by the devices called sensors are the electromagnetic energy reflected or emitted by Earth’s surface, which can be visible light or Infra Red or radio waves.
Depending on the source of EM energy there are two types of remote sensingviz, passive and active. In passive remote sensing, we employ natural sources of energy such as the solar radiation. Therefore it can be used on during daytime and is also influenced by atmospheric conditions, like cloudiness.
In active remote sensing, the sensor has its own source of energy which it emits to the Earth’s surface and the measures the reflected energy. For e.g. Radar, Laser. It has the advantage of being capable of working both during day and night and is not affected by atmosphere.
Reflectance characters of some common land cover types:
Vegetation: Reflectance characters of vegetation depends on the properties of leaves, including the orientation and  structure of leaf canopy, leaf pigmentation, leaf thickness and composition ( cell structure) also the amount to water in leaf tissues. In visible portion of the spectrum, blue and red light are mostly absorbed by chlorophyll. So vegetation reflects more green light. At harvest stage, leaves dry out, plants change colour and photosynthesis is reduced, as a result, there will be more reflectance in the red portion as well as middle IR. So optical remote sensing data provide information about the type of plants and also about its health condition.
Bare soil: Factors influencing reflectance are: soil colour, moisture content, presence of carbonates, and iron oxide content.
 Water: Water has lower reflectance compared to vegetation and soils. Vegetation may reflect upto 50%, soil upto 30-40%, while water reflects at most 10% of the incoming radiation. Highest reflectance is given by turbid (silt loaded) water, and by water containing plants with a chlorophyll reflection peak at the green wavelength.
True colour and colour infrared photography:
There are 2 types of colour photography: true colour and false colour infrared. In true colour photography, the final image will have the same colours as that of the original object. In false colour infrared, the image will have blue for green objects, green for red objects and red for IR objects. This is because the film has a near-infrared sensitive layer and a colour must be assigned to this radiation to make it visible. This prevents the normal true- colour assignment of the three primary colours to their respective wave bands.
REMOTE SENSING IN SOIL STUDIES:-
Remote sensing allows for classification of soils, providing information on the productivity of forests, meadows, wildlife habitat conditions, land-use and recreational suitability.  This will result in the future protection of the environment.Remote sensing data can help to locate soil erosion, area under shifting cultivation, areas affected by salinity, area covered by ravines, waterlogged and marshy areas, land affected by desertification, mining etc. Precise information on the nature, extent, spatial distribution and magnitude of the problems in degraded lands forms a vital input with conservation, reclamation and scientific management of these lands. It’s also important to monitor these degraded lands at regular intervals to know the impact of the reclamation using multi satellite data.
GIS:-
A geographic information system or geographical information system (GIS) is a system for creating and managing spatial data and associated attributes. A GIS is a computer system capable of capturing, storing, analyzing, and displaying geographically referenced information; that is, data identified according to location. Most of the information we have about our world contains a location reference, placing that information at some point on the globe. When rainfall information is collected, it is important to know where the rainfall is located. This is done by using a location reference system, such as longitude and latitude, and perhaps elevation.   In a more generic sense, GIS is a "smart map" tool that allows users to create interactive queries (user created searches), analyze the spatial information, and edit data.
Uses:-Geographic information systems technology can be used for scientific investigations, resource management, asset management, development planning, cartography and route planning. For example, a GIS might allow emergency planners to easily calculate emergency response times in the event of a natural disaster, or a GIS might be used to find wetlands that need protection from pollution.
The role of remote sensing and GIS in crop studies can be broadly categorized into two groups- inventorying/ mapping and management. While RS data alone is mostly used for inventorying  (crop acreage estimation, crop condition assessment, crop yield forecasting, etc) purposes and the management ( cropping system analysis, precision farming etc.) need various other spatial physical/ environmental information which has to be integrated with RS  data, where the functionalities of GIS are used.