Introduction to Remote Sensing for Agriculture Geographic Information System- An overview
How is remote sensing useful
Remote sensing is the science and art of obtaining information about a phenomenoa without being in contact with it. Remote sensing deals with the detection and measurement of phenomena with devices sensitive to electromagnetic energy such as:
Light (cameras and scanners)
Heat (thermal scanners)
Radio Waves (radar)
Remote sensing is one of a suite of tools available to land managers that provides up-to-date, detailed information about land condition. Remote sensing uses instruments mounted on satellites or in planes to produce images or 'scenes' of the Earth's surface.
What is Remote Sensing ?
The uniqueness of satellite remote sensing lies in its ability to show large land areas and to detect features at electromagnetic wavelengths which are not visible to the human eye. Data from satellite images can show larger areas than aerial survey data and, as a satellite regularly passes over the same plot of land capturing new data each time, changes in the land use and condition can be routinely monitored In the Land Monitor project, satellite images are being used to provide information on land condition and the changes in that condition through time, specifically salinity and the status of remnant vegetation, to help farmers, environmental managers and planners better manage the land.
The need for Education in Remote Sensing :- Pollution, population growth exceeding the support capability of the land, loss of biodiversity and global climate change are only few of the problems that face today’s and tomorrow’s generations. Remote sensing and related technologies can contribute to our understanding of these problems as well as tot eh implementation of practical solutions
Meanwhile countries are becoming increasingly aware that long term economic viability requires a balanced, informed strategy for the exploitation of natural resources forecasting agricultural yields, and developing new energy sources. In order to meet these challenges, we need professional who are familiar with the capabilities and limitations of the geospatial technologies. This includes researchers who can develop new methodologies and applications, as well as technicians and practitioners who can apply proven techniques to specify problems. Thus, it is more important than ever that remote sensing educational programs provide an adequate exposure to modern technologies, as well as solid grounding in remote sensing theory and principles.
How Satellites Acquire Images :-
Satellite sensors record the intensity of electromagnetic radiation (sunlight) reflected from the earth at different wavelengths. Energy that is not reflected by an object is absorbed. Each object has its own unique 'spectrum . Remote sensing relies on the fact that particular features of the landscape such as bush, crop, salt-affected land and water reflect light differently in different wavelengths. Grass looks green, for example, because it reflects green light and absorbs other visible wavelengths
This can be seen as a peak in the green band in the reflectance spectrum for green grass above. The spectrum also shows that grass reflects even more strongly in the infrared part of the spectrum. While this can't be detected by the human eye, it can be detected by an infrared sensor.Instruments mounted on satellites detect and record the energy that has been reflected. The detectors are sensitive to particular ranges of wavelengths, called 'bands'. The satellite systems are characterised by the bands at which they measure the reflected energy. The Landsat TM satellite, which provides the data used in this project, has bands at the blue, green and red wavelengths in the visible part of the spectrum .
Another feature that characterises each satellite system is its footprint or pixel size. This is the smallest area on the ground for which it can record the reflected energy. For every 30m by 30m plot of land, the Landsat TM scanner records a number for each of the seven bands, which is the average intensity of the reflected energy for the features in that plot of land. The satellite detectors measure the intensity of the reflected energy and record it as a number between 0 and 255.
Satellites are characterised by the
wavelength 'bands' at which reflected energy is measured
the size of the footprint or pixel for which they measure reflected energy
the frequency with which they revisit a particular location
The Land Monitor Project uses Landsat TM images. These images:
have 6 wavelength bands that are routinely used (3 visible, 3 infrared)
have 30m pixels
are acquired every 16 days (provided conditions are cloud-free)
Interpreting Image Displays :-
The satellite images, consist of numbers which are measurements of the amount of energy that has been reflected from the earth's surface in different wavelength bands. Some of these bands, such as the infrared bands which contain so much information about vegetation growth and condition, can't be seen with the human eye The numbers recorded for the different satellite bands are displayed in red, green and blue colour guns on a computer screen.
When the red, green and blue bands of an image are assigned to the same colours on the computer screen, a true-colour image is formed. These images look like aerial photographs, since they indicate the true colours of objects – green trees and grass and brown soil. When mixtures of the visible and infrared bands are assigned to the red, green and blue colours on the computer, false-colour images are formed. In these images, the different colours on the screen represent different intensities in the wavelength bands that are assigned to each screen colour. As well as deciding which image band to assign to which screen colour, choices can be made about how to relate the range of numbers recorded by the satellite to the 256 levels of each colour on the computer screen.0 The way the range of digital numbers in the image is related to the computer colour levels is called 'image enhancement'.
Thermal Remote Sensing :-
Another area of the spectrum that is useful for assessing crop conditions is the thermal portion of the spectrum. Measures of radiance in this area can be used to derive the surface temperature of the crop. Plants take up water from the soil and then release it from their leaves back to the air. As the water transpires from the plant, its leaves are cooled If a crop cannot get enough water, its surface temperature will increase, so the plant's surface temperature can tell us something about how healthy it is .
Introduction to Remote Sensing for Agriculture :- Remote sensing is the ability to measure the properties of an object without touching it. Almost all of the applications of remote sensing to date have been based on observing crops in distinct areas of the electromagnetic spectrum. The spectrum is represented in the figure below. Agricultural remote sensing is commonly done in the visible, near-infrared and thermal infrared portions of the spectrum; however, new applications in the microwave area are under development.
Regions within the Visible and Infrared Spectrum Visible Infrared 0.40-0.45 um Violet 0.7 - 3.0 um Near-Infrared 0.45-0.50 um Blue 3.0 - 14 um Thermal-Infrared 0.50-0.55 um Green 14.0 - 1000 um Far-Infrared 0.55-0.60 um Yellow 0.60-0.65 um Orange 0.65-0.70 um Red
How is remote sensing useful :-
1--It provides a unique perspective from which to observe large regions. 2--Sensors can measure energy at wavelengths which are beyond the range of human vision (ultra-violet, infrared, microwave). 3--Global monitoring is possible from nearly any site on earth. Remotely sensed images can be used for mineral exploration, monitoring ocean currents, land use planning, and monitoring the condition of forest and agricultural areas. The uniqueness of satellite remote sensing lies in its ability to show large land areas and to detect features at electromagnetic wavelengths which are not visible to the human eye.
Example of Satellite Images :-
1. Lake Superior
2. Temperature Maps of the Great Lakes
3. Mississippi River Flood
4. Surface Temperature Map of Lake Superior
5. Three Dimensional Images of Guatemalan Volcanoes
Remote sensing provides a cost-effective method for mapping and monitoring broad areas, and has the advantage that the spread of diseases such as dieback is not enhanced by remote monitoring. Archived data can be used to monitor how areas have changed through time.