Rashid's Blog: A Place for Inquisitive Souls

The amount of water available per person in India is decreasing steadily – from 3450 cm in 1951, it fell to 1250 cm in 1999. According to the Ministry of Water Resources is expected to decrease further to 760 cm per person in 2050.8 Water scarcity is the single biggest threat to food production, as falling groundwater levels and shrinking rivers make less water available for agriculture. Water is a key productive resource for growing food and raising cattle. Sustained access to water for irrigation is a question of survival for about 70% of the Indian population.This number includes disadvantaged and marginalized farmers and those surviving by subsistence farming as well as agricultural labourers. The impact of a lack of access to water has been dramatically exposed during the last years in drought-prone areas throughout the country. Basically water is required for agriculture and domestic consumption. Apart from this water is used by industries.

Agriculture accounts for almost 80 per cent of water use in India.The FAO estimates that due to population growth there is a needfor additional 60 percent more food in the next 30 years. This estimate assumes that the current water intensive agriculture is continued. Hence a review of water use in agriculture is a must; demand management both in agriculture and industry is an imperative in this regard. Ground water is the major source of irrigation in India. It fulfils almost 60 percent of the country’s total irrigation needs, in rainless areas this rate being even much higher. Over 70 per cent of the value of farm produce depends on ground water. However, excessive depletion of groundwater

reserves has led to a dramatic decrease of the groundwater
level. Moreover crops that need more water (paddy, sugar cane) are being farmed replacing the traditional products consuming less water (millet). Industry too has become a huge consumer of ground water in agricultural areas.

Diverting water from domestic and agriculture to industries poses serious problems. In most parts of India, ground water mining is taking place at twice the rate of natural recharge causing aquifers to drop by 1 to 3 meters every year. Till date, many private corporations contribute to the excessive depletion of groundwater.

The ozone hole is a thinning of the stratosphere’s ozone layer, which is roughly 9 to 31 miles above the earth’s surface. The depletion of the ozone is due to man-made chemicals like chlorofluorocarbons (CFCs). A thinner ozone layer lets more harmful ultraviolet (UV) radiation to reach the earth’s surface.

Global warming, on the other hand, is the increase in the earth’s average temperature due to the buildup of CO₂ and other greenhouse gases in the atmosphere from human activities.

Climate change is any substantial change in Earth’s climate that lasts for an extended period of time.  Global warming refers to climate change that causes an increase in the average temperature of the lower atmosphere.  Global warming can have many different causes, but it is most commonly associated with human interference, specifically the release of excessive amounts of greenhouse gases. (EPA, 2006)

Greenhouse gases, such as carbon dioxide (CO₂), methane (CH₄), water vapor, and fluorinated gases, act like a greenhouse around the earth.  This means that they let the heat from the Sun into the atmosphere, but do not allow the heat to escape back into space.  The more greenhouse gases there are, the larger the percentage of heat that is trapped inside the earth’s atmosphere.  The earth could not exist in its present state (that is, with life) without the presence of some naturally occurring greenhouse gases, such as CO₂, CH₄, and water vapor. Without any greenhouse gases no heat would be trapped in atmosphere, so the earth would be extremely cold. (NASA, 2002)

Naturally occurring greenhouse gases (not fluorinated gases) are good in naturally occurring amounts; it’s when people start contributing excessive amounts of them that greenhouse gases become a problem.  With excessive greenhouse gas buildup, the earth’s atmosphere warms to unnatural temperatures which causes, among other things, sea level to rise.  Global warming also causes sea surface temperatures to rise, precipitation patterns to change, etc.. (NASA, 2002)

Remote Sensing Platforms

Environmental remote sensing devices can be mounted on a variety of platforms. Hand-held cameras can be used to acquire (usually) oblique photo images and hand-held radiometers can be used to measure the reflectance characteristics of a surface. If a wider field of view is required, the camera, radiometer or scanner can be mounted on a tower or cherry picker (trucks used by hydro department to repair electrical lines or replace burnt out street lamps). These platforms are commonly used to collect radiometer data representing the reflectance of different surfaces or land cover types. For mapping and analysis of spatil patterns, however, we usually rely on remote sensing devices mounted on low or high altitude aircraft or on satellites. In general, the higher the altitude of the platform, the smaller the scale of the resulting remote sensing imagery, although scale is also dependent on the configuration of the remote sensing device.

CAMERAS

Photographic Camera/Film Systems

The term “photographic” refers to systems that use films coated with photo-sensitive silver halide emulsions to record an image. Silver halide crystals are structurally changed when exposed to light, producing a latent image on the film. When the exposed film is placed in a developer solution, the silver halide crystals turn to black metalic silver. The speed of this transformation depends upon the intensity of light striking the silver halide crystals at the instant of exposure: crystals exposed to intense light turn black very quickly while crystals exposed to less intense light turn black more slowly. The development process can be arrested by rinsing the film to remove all traces of the developer solution. The result is a continuous tone negative (bright spots appear black and vice versa) image..

Photographic camera/film systems have been used since the first decades of the 20th century to collect spatial data. Aerial photographs are the primary data input for production of topographic maps, although various types of “ground truth” information are needed to verify interpretation of the airphoto imagery and to ensure accurate transformation of the image data into map or GIS database format. Photographic films are sensitive to reflected EMR in wavelengths ranging from the mid-ultraviolet to the near-IR. The camera’s entire field of view is recorded instaneously. The film detects and records the EMR reflected from surfaces within the field of view as a continuous tone image.

Digital Cameras

Digital cameras are a recent development. Like the traditional photgraphic camera, they use a lens to focus reflected EMR but use an array of EMR sensors rather than photographic film to record the image. Sensor arrays can have different spatial resolutions, ranging from 512 by 512 for a 35 mm equivalent image up to 2048 by 2048 for applications requiring finer spatial detail. The sensors detect reflected EMR for each wavelength for which they are calibrated. The resulting image is comprised of picture elements or pixels, each of which records a brightness value for the spatial field of view it detects. A 2048 by 2048 pixel image contains 4.2 million pixels!

Trimetregon Cameras

A trimetregon camera is acutally an array of three cameras that take simultaneous overlapping images of the terrain. This type of camera is used to take airphotos in areas of mountainous terrain. The central camera in the array takes a vertical airphoto while the left and right cameras record oblique images of adjacent terrain. This type of camera is used to obtain images of steep valleys. By flying along the valleys and collecting overlapping images of the floor and sides of the valleys, trimetregon cameras can overcome the problems that are associated with normal parallel traverse airphoto coverage in areas with high local relief.

Optical-Electrical Scanners

Electro-optical scanners used in both airborne and satellite remote sensing are somewhat similar to digital cameras in that they use an array of electronic sensors, in combination with mirror/lens optical devices to scan a scene and record an image. Each sensor in the array produces an electrical signal for each wavelength detected. The electrical signals can be recorded on magnetic tape. In the case of satellite sensors, the continuous electrical signals are usually converted into digital numbers representing up to 256 gray levels before being transmitted to Earth-based receiving stations. Optical-electrical scanners offer the potential of real time data acquistion since there is no delay while film is being developed and prints produced for distribution.

Remote sensing devices can be classified according to whether they are active or passive devices. Passive remote sensing devices detect reflected EMR while active remove sensing devices emit a signal and detect the intensity of the signal reflected back off an object. A photographic camera used with available light and Landsat MSS, Landsat Thematic Mapper, or SPOT satellite imagary are examples of passive remote sensing systems. A photographic camera used with a flash attachment, radar and sonar are examples of active remote sensing systems.

SEE MORE