This article throws light upon the top eight applications of remote sensing. The applications are: 1. Application to Atmospheric Studies 2. Application to Geospheric Survey 3. Biospheric Survey 4. Hydrospheric Survey 5. Cryospheric Survey 6. Environmental Studies 7. Geo-Botanical Exploration 8. Oceanography.
Application # 1. Atmospheric Studies:
Weather forecasters need access to information from large areas as quickly and as often as possible because weather observations rapidly become out of date. Satellites are best able to provide this kind of data that satisfy the requirements in terms of both coverage and immediacy.
ADVERTISEMENTS:
A good description of the current weather situation is essential to successful short-period weather forecasting, particularly for forecasting the movements and development of precipitation in the next six hours.
Satellite pictorial data are particularly useful as they provide precision and detail for short-period weather forecasting. Thus, meteorologists have been making increasing use of weather satellite data as aids for the analysis of synoptic and small-scale weather systems.
Weather radars make it possible to track even small-scale weather patterns and individual thunderstorms. Many countries have now developed a good network of weather forecasting by the application of remotely sensed data, termed as METEOSAT imagery system.
In pictorial form, weather satellite data are also capable of revealing excellent resolution in the position, extent and intensity of cloud systems and troposphere temperature changes with adequate precision. Wind speed, cloud movement, tornado, etc. can also be forecasted by these data’s.
On the whole, remotely sensed data, a broad based data base including inventories of the following parameters, can be obtained:
1. The earth/atmospheric energy and radiation, particularly the net radiation balance at the top of the atmosphere, which is the primary driving force of the earth’s atmospheric circulations.
ADVERTISEMENTS:
2. Global moisture distribution in the atmosphere, which relates to the distribution of energy in the atmosphere.
3. Global temperature distribution over land and sea and, accordingly, the absorption and radiation of heat.
4. Distribution of cloud cover, which is a major influence on the albedo of the earth/atmosphere system and its component parts and indicates horizontal transport patterns of latent heat.
5. Sea surface temperature, which relates directly to the release of latent heat through evaporation.
ADVERTISEMENTS:
6. Wind flow and air circulations, which relate to energy transfer within the earth/atmospheric system.
7. The climatology of synoptic weather systems including their frequencies and spatial distribution over extended periods.
The analysis of NIMBUS-7 satellite picture for determination of ozone hole in the atmospheric region during the month of October added a new dimension of application of remote sensed data in forecasting atmospheric changes.
The stratospheric aerosol measurement (SAM II) instrument on the NIMBUS-7 satellite provides a measurement of the optical depth of the atmosphere and accordingly is able to provide information on air quality.
Application # 2. Geospheric Survey:
ADVERTISEMENTS:
During the past decades, LA NDSAT imagery, in particular, laid a profound application in analysis of geological structures, identification of rock types and their mapping and also in determining the mineralized deposits on earth’s surface. In addition to LANDSAT, TM data are also very useful for these kinds of studies.
Geothermal mapping using scanner data is mainly carried out in geothermal energy exploration studies as part of investigations of alternative energy resources or for the monitoring of active volcanoes— particularly in the case of eruption prediction studies.
Using infrared lines canner it is also possible to denote the extent of fire in coal mining industries. Radar imagery is also very useful for determination of lineament features. Since 1990s, SONAR, a major sensor, was used in sea floor mapping.
Application # 3. Biospheric Survey and Analysis:
Even in the most technologically advanced countries, up to date and accurate assessments of the total acreage of different crops in production, anticipated yields, stages of growth and condition (health and vigour) are often incomplete or non-timely in relation to the information needed by agricultural managers.
These managers are continually faced with decision on planting, fertilizing, watering, control of pests and diseases, harvesting, storage, evaluation of crop quality, and planning for new cultivation areas. Remotely sensed information is used to predict marketing factors, to evaluate effects in case of crop failure, to assess damage from natural disasters or to aid farmers in determining when to plough, water, spray, or reap.
The need for accurate and timely information is particularly acute in agricultural information systems because of the very rapid changes in the condition of agricultural crops and the influence of crop yield predictions on the world market.
It is for these reasons that, as remote sensing technology has developed, the potential for the technologies to be used has received widespread attention. Previously aircraft surveys were used for crops to assist managers in gathering useful data; with the advent of multi-spectral repetitive satellite imagery, the possibility of an auto monitored crop inventory is now approaching reality.
Colour-infrared film is sensitive to green, red and near infrared (500-900 µm) portions of the spectrum and is widely used in aerial and space photographic surveys for land use and vegetation analysis.
Living vegetation reflects light in the green portion of the visible spectrum to which the human eye is sensitive. Additionally, it reflects 10 times as much in the near infrared (700-1,100 nm) portion of the spectrum which is just beyond the range of human vision.
When there is a decrease in photosynthesis, whether caused by normal maturation or stress, there is a corresponding decrease in near infrared reflectance. Living or healthy vegetation appears as various hues of red colour in infrared film.
If diseased or stressed, the colour response will shift to brown or yellow due to the decrease in near infrared reflectance. This film is also effective for haze penetration because blue light is eliminated by filtration.
Crops are best identified from computer-processed digital data that represents quantitative measures of radiance. In general, all leafy vegetation’s have a similar reflectance spectrum regardless of plant or crop species.
The differences between crops by which they are separated and identified depend on the degree of maturity and percentage of canopy cover, although differences in soil types and soil moisture may serve to confuse the differentiation.
However, if certain crops are not separable at one particular time of the year, they may be separable at a different stage of the season due to difference in planting, maturing, and harvesting dates. The degree of maturity and the yield for a giver crop also influence the reflectance at any stage of growth. This maturity and yield can be assessed by the history of any crop, traced in terms of its changing reflectance.
The three year large crop inventory experiment, using LANDSAT MSS imagery demonstrated that the global monitoring of food and fibre production by satellite was possible. In forestry, the LANDSAT MSS have proved effective in recognising and locating the broadest classes of forest land finer and in separating deciduous, evergreen and mixed communities.
More discrete classifications are possible with data from the Thermatric Mapper. Further possibilities include measurement of total hectare age given to forests and changes in these amounts.
Timber volume, age of forests and presence of disease or pest infections can also be determined. Heat-sensitive channels on the LANDSAT Thermatric Mapper and the AVHRR are also used in forestry because of their ability to detect fires.
Recently IRS-IA LISS-II scenes were very often used for forest survey works in India.
A generalized scheme for forest cover mapping through image processing is given in Fig. 26.22.
Application # 4. Hydrospheric Studies:
Fortunately, many of the hydrological features of interest for improved water resource management are easily detected and measured with remote sensing systems. Although water sometimes reflects light in the visible wavelength in a similar manner to other surface features, it strongly absorbs light in the near infrared.
As a consequence, standing water is very dark in the near infrared contrasting with soil and vegetation which appear bright in this part of the spectrum. Thus, in the absence of cloud, surface water can easily be distinguished and monitored in the optical wavebands.
Efficient management of marine resources and effective management of activities within the coastal zone is dependent, to a large extent, upon the ability to identify, measure and analyse a number of processes and parameters that operate or react together in the highly dynamic marine environment.
In this regard, measurements are required of the physical, chemical, geometrical, and optical features of coastal and open zones of the oceans.
These measurements would include sea, ice, temperature, current suspended sediments, sea state bathymetry, and water and bottom colour. Different remote sensing capabilities exist for the provisions of the required information involving one of the combinations of measurement techniques.
The phenomenon of wind-driven coastal upwelling and the resulting high biological productivity off the west coast of North America were dramatically revealed in the images of sea-surface temperature and chlorophyll pigments from NOAA and NASA satellites.
Application # 5. Cryospheric Studies:
Floating ice appears on many of the world’s navigation routes for part of the year, while in the case of the high Arctic regions it is present for all the year. It interferes with, or prevents, a wide variety of marine activities, including ships in transit, offshore resource exploration and transportation and offshore commercial fishing.
In addition, it can be a major cause of damage, resulting in loss of vessels and equipment, loss of life (as in the case of Titanic sinking) and major ecological disasters. Remote sensing techniques are particularly useful for gathering this ice information, both from aircraft and satellite platforms.
The aircraft are specially equipped with transparent domes for visual observations. Side Looking Airborne Radar (SLAR) is used for gathering all weather information about capability and lesser profilometers for accurate measurement of surface roughness.
Application # 6. Environmental Applications:
Remote sensing provides information related in some way or other to the quality, protection and improvement of land and water resources.
At the same time, information is obtained about man’s effect on the environment, allowing monitoring to take place where this may be required:
Of course not all adverse effects on the environment are due to man. Remote sensing can also facilitate the timely response to naturally occurring phenomena such as volcanic eruptions, earthquakes, hurricanes, tornadoes, and forest fires.
Examples of the use of thermal imagery for environmental monitoring include investigations of heat loss from buildings, septic tank seepage into water-supply and sewage outfall. Thermal infrared image of the city of Dundee, Scotland, showed light grey tones depicting warm areas and dark tones depicting cool areas. The detention of contrasting thermal signals was useful for a cattle survey made in summer in west Texas.
Oil pollution through leakage in pipelines or accidental spillage is an all too familiar example of the harmful effects man can have on the environment. For oil pollution monitoring from satellites the spectral resolution is often a serious problem, although, under favourable conditions, it is possible to observe and monitor oil slicks using this data.
Spatial Information Systems, Land use and Land Cover Mapping:
In recent years satellite data have been incorporated into sophisticated information systems of a geographical nature allowing the synthesis of remotely sensed data with existing information.
The growing complexity of society has increased the demand for timely and accurate information on the spatial distribution of land and environmental resources, social and economic indicators, landownership and value and their various interactions.
Land and Geographic Information System (GIS) attempt to model, in time and space, these diverse relationships so that, at any location, data on the physical, social and administrative environment can be accessed—interrogated and combined—to give valuable information to planners, administrators, resource scientists, and researchers.
Land use refers to the current use of the land surface by man for his activities, while land cover refers to the state or cover of the land only. Current remotely sensed data of the earth’s surface generally provide information about the land cover, with interpretation or additional information being needed to ascertain the land use.
Land use planning is concerned with achieving the optimum benefits for mankind in the development and management of the land for various purposes, such as food production, urbanisation, manufacture, supply of raw materials, farmer production, transport, and recreation.
This planning aims to match land use with land capacity and specific uses with appropriate natural conditions so as to provide adequate food and material supply without significant damage to the environment.
Land use planning has previously been severely hampered both by the lack of up to date maps, showing which categories are present and changing in an area or large region and the inadequacies of the means by which the huge quantities of data involved were handled.
The cost involved in producing land cover, land use and land capabilities maps have prohibited their acquisition at useful working scales. Vast areas of Africa, Asia and South America remain poorly-and often incorrectly-mapped. Land use can be deduced or inferred indirectly from the identification and distribution patterns of vegetation; surface materials and cultural features are interpreted from imagery.
With supplementary information which may be extracted from a appropriate data base or information system but is simply the accumulated knowledge of the interpreter, specific categories of surface features can be depicted in the map form.
Application # 7. Detecting Geo-botanical and Biogeochemical Anomalies:
Remote sensing has immense role in the field of mineral exploration in vegetated terrain. The use of remote sensing in this context is a recent addition to the sciences of geo-botany and biochemistry. Geo-botany is concerned with the affinity of particular plants, plant associations or plant morphological aberrations to soil containing higher than normal contents of heavy metals, such as copper, lead, zinc, or tin.
Biochemistry enables the analysis of plant tissue to assess its heavy metal content. Geo-botanical indicator species, plant association changes and biogeochemical anomalies can all be distinguished from the synoptic view of remote sensing platform. So, during the last so many years, remote sensing, as an exploration tool, has become increasingly popular.
The introduction of high resolution spectro-radiometers to detect plant spectra associated with heavy metals has yielded results of great significance to mineral exploration in vegetated terrain.
Healthy green leaves have a low visible and a high near infrared reflectance, while physiological disturbances- such as excess of heavy metals-cause changes in leaf pigmentation, structure and water content which lead to aberrant leaf reflectance.
The most successful detection of biogeochemical stress has been achieved with high spectral resolution spectro-radiometers.
Collins (1976) and Collins et al, (1979, 1980) have developed such an instrument which scans in 500 narrow bands between 0.4 nm and 1.1 nm. In addition to allowing studies of reflectance change in each narrow band this instrument also allows for an interpretation of reflectance changes that occur on the red edge.
Many case studies, which have utilized remote sensing as an aid to mineral exploration in vegetated terrain, have adapted an insular approach in that they have made studies of only single sets of imagery rather than taking multi-temporal approach to the problem of anomaly detection.
Application # 8. Oceanography:
Satellites with their potential to cover vast areas of land and oceanic areas on a repetitive basis are ideal for coastal and oceanic studies. Satellite data are also economical in comparison with other sources of data
For a nation like India with a long coastline and extensive exclusive economic zone, satellite based remote sensing can potentially provide substantial economic benefits; with the use of satellite data it is now possible to determine the location of potential fishing grounds, river meandering pattern and upwelling zone of coastal shelves.
Since 1990s, with the use of NOAA, IRS, LISSJ data, many features of coastal water and land mass were detected. However, it is proposed to continue these efforts when the wide field sensor (WIFS) data becomes available in future from the IRS-IC/ID satellites.
Once the technique is perfected and relationships between various levels of production are established, the remotely sensed data could be utilized for:
(i) Studying migratory patterns of the pelagic fish;
(ii) Preparation of spatial distribution of chlorophyll-a charts and fishery forecasting; and
(iii) Ecosystem modelling.