The spatial imageries derived from the satellite are in the raw form. Many of the images are from the various satellites and has come in many different positions and is unfiltered. These are normally the digital photos which lack much information in correspondence to the earth’s surface. Since these raw images do not have any location information, hence it is necessary to incorporate the references with respect to the ground so that it can be effectively used and interpreted. The process of referencing these raw satellite images is called “Georeferencing” thereby making each point coordinate with the national coordinate system. And once these raw images are referenced, we can analyze and interpret the data into meaningful information.
Meaningful interpretation of Georeferencing
Georeferencing thereby is the process by which these satellite imageries are mapped through the various process based on the control points of the ground which are known as coordinates. This helps us to recognize the exact location of the satellite imagery. When you get the coordinates of a few of the points, you can easily calculate the other location points. This georeferencing can be done by two methods.
- The first way is by using 3D coordinates where you consider the center of the earth as the point of origin for all the three axes. Although it is one of the most popular methods, still it is not considered feasible on the earth’s surface for applying to the points.
- The second way is through the projection of the points. This process is expressed from a height above the 3D coordinates. In this technique from a small region, the curved area is being flattened for referencing and plane coordinates are being projected towards it. The distance and the direction are being then measured.
There are many ways in which the satellite imageries can be mapped into meaningful interpretations. With the help of the software’s, it is pretty much easy to map the satellite raster images. There are many software’s that are now available. Few of them are as below:
- MapInfo Professional
- MapViewer and Surfer
- AutoCAD Map 3D
- Micro Images
With the help of these above few software’s, the satellite images can be mapped, georeferenced, created and edited using different techniques. With reference to the ground details, various interpretations and assessments are now possible.
How and where is mapping and imaging of satellite imageries used?
Satellite mapping and imagining data is widely used for various fields. It is beneficial in forestry, agriculture, weather, hazards and disasters, governments, military, vegetation and many more. With many of the techniques of mapping the satellite imageries, assessments and predictions can be easily achievable.
- Mapping and imaging in Agriculture: With the satellite imageries, once georeferenced, you can distinguish the different patterns of crop cultivation. for paddy, wheat, rice cultivation you will be able to identify in the images patterns of rectangular or square shape. Reason being, the rice or paddy cultivation is done as beds in the soil. If you check for tea cultivation, from the satellite imageries itself you will be able to identify the terrain cuts in the hilly places. Also, with the help of GIS ground data, authentication and practical implementation can be made. Moreover, with the soil nutrients, different maps can be assessed and advised which would surely benefit our farmers and agriculture at a large scale.
- Mapping and imaging in forestry: Mapping is also widely used as you can easily assess the deforestation as part of the present global warming. It is very evident that the abrupt decrease in forestry and the increase in settlements is the main reason behind the destruction of the present world of global warming. Mapping with the data and comparative analysis of the satellite data of few decades with help the people in being more cautious and help the government take necessary measure.
- Natural disasters and hazards imaging interpretations: With the comparative analysis of the satellite mapping of a particular region along with the previous GIS data, it can very well be assessed the hazard and natural disasters. For example, a natural disaster like drought, floods can be predicted well in time with the interpretation of satellite mapping and imaging.
- Vegetations interpretations with satellite mapping: Carbon sequestration is one of the most required and popular interpretations which can be achieved with the help of satellite images. With a comparative analysis from the data derived from different ages of satellite mapping, the consumption and release of carbon dioxide can be assessed.
Let us now look at a few of the techniques used to map and imagine satellite data:
- NDVI: NDVI stands for normalized difference vegetation index which is used for analyzing the difference between the reflection of vegetation absorption to vegetation reflection. And for this, near-infrared and red lighted wavelengths are used. There is a formula used to calculate NDVI which is -NDVI= (NIR-Red)/ (NIR+Red). The values of NDVI ranges from -1 to +1. If the value is negative, then it can mostly be water. Whereas, if the value is near to +1, it can be inferred that it has dense green leaves in that area.
- Change detection studies: Through change detection analysis you can easily measure how the change in the attributes has taken place in a particular area over the time. It basically is the comparison from the satellite imaging in due time. Moreover, change detection is widely used for assisting the difference or shifting of deforestations, cultivation, land use and land covered, and the impact left behind by the natural calamities like the earthquake, tsunamis.
- Classification methods: Classification method is one of the most important functions of GIS and remote sensing. It is used widely in the field of land use and land cover mapping. There are many ways through which the classification can be done. Some of them are the supervised, unsupervised, hybrid, parametric, non- parametric, pre-pixel etc. However, supervised and unsupervised methods are widely used.
- PCA: Principal component analysis is a very widely used tool used mainly for transforming the input data from the different bands. This PCA is done to compress the data by eliminating redundancy and explaining the variation in a sample.
- Digital elevation models: The digital elevation models are mainly raster GIS layers which correspond to its elevation of any location. These models help to assists the elevation of any particular place. The data which are captured with airplanes, satellites are originally DSMs.
- Terrain model: Terrain model is also a popular technique in which the satellites mapping is widely used. Mainly for the multiresolution and TIN-based surface, the features in a geodatabase are used. The terrain model is made from the sonar, photogrammetric sources and lidar.
Thus, we can conclude that the satellite mapping is used in a vast area of remote sensing and GIS. With the above mentioned different areas and uses of techniques of satellite mapping, you can now get to know the details and the process on the use of satellite mapping.
Also Read: Remote Sensing and GIS