The remote sensing has transformed our lives through vast range of its applications. Perhaps we can't live without this revolutionary technology. Name any field we will find some way or the other Remote Sensing is involved.
Electromagnetic spectrum (EMS) represents the continuum of electromagnetic radiation (EMR) arranged on the basis of wavelengths or frequency. Electromagnetic spectrum ranges from shorter wavelengths (gamma rays to x rays) to the longer wavelengths (microwave and radio waves).Most common remote sensing systems operate in one or several of the visible, infrared and microwave portions of the electromagnetic spectrum. Within the infrared portion of the spectrum it should be noted that only thermal infrared energy is directly related to the sensation of heat; not the near and mid infrared ones.Before discussing about EMS with reference to remote sensing it is important to understand it fully.
Different radiations which constitute the EMS are as follows:
Radio waves
These are the longest wavelength (lowest frequency) radiations of the EMS. The wavelength of radio waves is more than 100 cm. These passes through Earth's atmosphere easily. Radio signals are used in radios, televisions, aircrafts, ship etc. These are also emitted by stars.
Electromagnetic Spectrum
MicrowavesTheir wavelength ranges between 1mm & 1m. RADAR (Radio Detection And Ranging) is the most common device used in Microwave Remote Sensing. Other applications are in cooking food (microwave oven), in broadcasting transmissions etc.
Infrared Radiations
When we feel hot it is because of infrared (IR) radiations. For common understanding we can call them as 'Heat'. The wavelength of IR is longer than visible light and shorter than microwaves approximately ranges between 1micron to 100 microns. These are very useful radiations for remote sensing. Thermal Imaging Systems detect objects by recording their temperature (infrared emissions).
Visible Radiations
As their name itself suggests these are the EMRs which are visible to our eyes in different colours. These ranges between 700nm to 400nm. Most of the remote sensing systems and camera records images in this range.
Ultraviolet (UV) Radiations
These radiations have wavelength shorter violet colour of visible light and longer than X-rays. UV radiations can be divided into near UV (400–200nm), far UV (200–10) and extreme UV 1–31 nm.
X-rays
These are very short length electromagnetic radiations wavelength in the approximate range from 0.01 to 10 nanometers. In EMS these falls between UV radiations and Gamma-rays. Mostly used in medical sciences.
Gamma-raysGamma-rays are the electromagnetic radiations with shortest wavelength in the range of the range of 10^-11 m to 10^-14 m. Their very high energy can cause serious damage to living cells.
Global Positioning System (GPS) is satellite-based navigation system which records and displays location of an object on earth (in terms of coordinates, e.g. latitude and longitude). It also shows height of a place above mean sea level.
Like many other remote sensing and GIS devices, application of GPS devices was also first started for military and defense purposes. Slowly these devices made entry into public domain for various civilian uses. Now GPS has become so popular that it is being integrated in new generation mobile phones.
A GPS device receives signals from satellites and these signal codes are processed & converted into values showing position, time and velocity (what we see on screen of GPS device). The instrument to which we generally call ‘GPS’ is basically a GPS receiver and it is a small part of a large system. A complete Global Positioning System consists of three segments- space segment, control segment and user segment.
A Handheld GPS
Space Segment
Space segment consists of dedicated satellites for Global Positioning System and are referred as space vehicles (SVs). There are twenty four satellites in a nominal GPS constellation. Out of these twenty four satellites three are spare satellites which start operating if some of the functional twenty one satellites have some operational problem.
These satellites remain in six orbital planes (four in each) and are positioned such that five to eight of these SVs visible from any place on the earth at a given point of time.
Control Segment
The control segment consists of tracking stations located around all over world. There are master control station and monitoring stations in control segment.
User Segment
User segment of GPS is what we uses i.e. GPS receiver. It also includes the GPS user community. A GPS receiver consists of a screen for displaying information, buttons to operate it and antenna to receive signals from satellites.
The antenna may be in-built in receiver instrument or it may be externally attached to it.
Signals from minimum four satellites are required for a GPS receiver to compute location (x, y & z) and time (t). GPS receivers are essential part of navigation system of air crafts and ships. Now-a-days these are also being integrated in surface-based navigation (trains, buses, cars & other vehicles).
Geographic Information System (GIS) is becoming more & more popular amongst decision makers as it enables them to quickly refer the GIS outputs which help them in solving problems and making right decisions. Visualization of features, converting data into need-based maps (thematic maps) and capability of providing solutions by taking into account overall scenario of an area are some of the virtues of GIS due to which it is being implemented across a number of sectors and departments (e.g., transportation, forestry, environment, disaster management, urban planning, health etc).
We often feel difficulty to understand and visualize a problem just by seeing data or figures. We are more comfortable with visual representation of a problem that’s what GIS is giving to us (that too with the true representation of real-world).
Definition
GIS is made up of three terms- Geographic, Information and System. In literal meaning Geographic Information System is a System containing Information which is geographic in nature.
GIS can be defined as - A System which involves collecting/capturing, storing, processing. manipulating, analyzing, managing, retrieving and displaying data (information) which is, essentially, referenced to the real-world or the earth (i.e. geographically referenced).
Explanation of the Definition
We have used many term in the definition of GIS mentioned above. It is necessary to discuss each term for getting an idea - what actually GIS is?
Collection/Capturing
The dataset collected for GIS may be in the form of hard copy maps, satellite images, survey data or other data obtained from other primary and secondary sources. Collection of data depends on the objective of the assignment. Data capturing involves digitization of hard copy maps and satellite images.
Storage
In GIS Storage means not merely storing whatever data we have collected. The collected data is converted in usable GIS format and then finally stored for further use either on computer hard disk or in other storage devices (CD, DVD, magnetic tapes etc.)
Processing and Manipulation
The collected and stored dataset is imported and converted into layers. Then required attributes are attached. Then data is processed for refinement, removing errors and preparing it for further GIS-based analysis. Data manipulation is essential so that it can be represented in proper understandable form.
Analysis
Analysis of GIS data is required to convert it into desired outputs. There are many type of analysis in GIS which is (or are) to be done is objective dependant. The analysis may be statistical, spatial or specialized (like network analysis, utility analysis etc. Need not to say GIS analysis requires skilled professionals.
Management
Data management is essential and very important part of GIS for storing, managing and properly maintaining GIS database.
Retrieval
In GIS, data can be retrieved through SQL or spatial queries. Some software provide tools to retrieve data by simply selecting the features. Retrieval is used for getting information about the features of our interest.
Display
Displaying of final output may in many forms. These may be hard copy printouts, on-screen display of maps, internet-based map display (through Internet Map Servers) or in the form of presentation (like power point).
Following is a good video explaining GIS in simple way. (Please note that this is just for learning purpose, we do not endorse any product)
I am sharing👇 a very good video for GIS users who want to learn and explore QGIS software. It is an easy guide which tells about basic features of the software. Starting from adding data to creating a layout.. you can a have fair idea of all this. It's for beginners for getting acquainted with QGIS..
It covers following features-
Start using QGIS, the GUI, Adding some built in data, navigate the map, Projections and coordinate systems Adding OpenStreetMap, Save and open projects, Create your own first data, Make temporary layers permanent in GeoPackage format, Style a polygon layer, Adding a Label to your objects, Attributes and tables, Empty project and add your own data, Make a layer style the default for a data source, Using "inverted polygons" and style layers, Adding roads and use "snapping", Styling lines, Adding points to your map, Styling the points and Creating a Layout.
