satellite images
Remote sensing
Remote sensing is used for Earth observation. This is a technique that allows you to acquire information on a ground target from a satellite.Information received by satellites is digitally recorded using electronic sensors.
The information is then recorded as an image and transmitted to receiving stations on the ground. Onboard satellites, the sensor records images in the form of spectral bands.
Each of the spectral bands gives a black and white image, where the shades of grey vary.
By superimposing three spectral bands with color filters, it is possible to obtain a color image or a color compound.
Each colored compound gives different information on land use.
Landsat-TM satellite image at 25 m resolution Sheet 35E
Landsat-ETM satellite image at 15 m resolution Sheet 31H-no. Montreal
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Landsat-TM satellite image at 25 m resolution Sheet 22A
Gaspé (Eastern Quebec)
The three satellite images presented above are also called spatial maps because they are accentuated, geo-referenced, and represented according to a cartographic breakdown. Based on the colors, textures, and shapes presented on these spatial maps, the satellite image gives the main classes of land use, namely:
- the forest domain: hardwood, mixed, softwood, and forest cuts;
- the agricultural domain: maize, potatoes, hay, cereals, wasteland, pastures;
- hydrography and major roads;
- urban agglomerations;
- peat bogs.
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The resolution of the images
The sensors onboard the satellites each have their spatial characteristics for recording images. In remote sensing, we do not speak of scale as in aerial photography, but of spatial resolution, which gives the accuracy of images.
The resolution of an image is determined by the smallest area that the satellite can detect on the ground. This surface is expressed in the image by pixels, an acronym formed by the words "picture element". A series of pixels make up a satellite image. This is also the case for a photo scanned by a computer.
Thus, the example opposite of a small red fox shows that the more a photo is degraded, the more blurry it becomes until it perceives the pixels.
Thus, when we say that an image has a resolution of 30 meters, it means that each pixel that constitutes the image represents an area of 30 meters by 30 meters on the ground.
So, the higher the resolution of an image, the more accurate the image.
However, the higher the resolution, the smaller the area covered by the image. So, what we gain inaccuracy, we lose in the big picture. The example of a baseball field in images of the La Baie region in the Saguenay region illustrates this phenomenon:
- the image taken by a satellite at a resolution of 10 meters makes it possible to observe the location of the land and its environment;
- the image taken by an aircraft at a resolution of one meter allows the baseball field to be circumscribed and details to be seen within the field itself.
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Why use satellite images?
Satellite images are very rich in information of all kinds. The information obtained from satellite images not only makes it possible to produce and update maps but also to analyze various aspects of the territory. Satellite images are generally not as accurate as aerial photographs, but they cover large areas and allow for regional analysis.
- agriculture
- forestry
- geology
agriculture
Satellite imagery allows agricultural producers to obtain information on their territory to manage crops more effectively.
This technology allows them to plan operations and anticipate risks that could threaten their production. For example, they can use it to predict the risks associated with insect infestations, bad weather, droughts, etc. In agriculture, satellite images are used, among other things, to:
- classify the main types of culture;
- assess crop health;
- estimate the total production of a crop;
- map soil management practices;
- monitor compliance with laws and treaties.
forestry
Satellite images are used to obtain information on forest cover types (inventory of large groups and sometimes species), on vegetation density, and the decrease or state of resource regeneration.
They are used to observe the harvests carried out and to monitor the quality, health, and diversity of forests. These tools are very useful for forest resource management and for improving mapping on the subject.
geology
Studies in this area focus on landforms, structures, and the earth's crust to facilitate understanding of the physical processes that modify the earth's crust.
Satellite imagery is an interesting tool in this field since it allows to extract of information on structure, for example, faults and folds. This information is often combined with other data sources to obtain additional measures.
Satellite imagery also allows for planning and logistics, such as planning field campaigns or access roads in a mining area, monitoring projects, and creating base maps on which geological data can be overlaid.
Here is a list of the main applications of satellite images in geology:
- mapping of surface deposits;
- mining and petroleum exploration;
- environmental geology;
- mapping and monitoring.
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