 Good morning everyone, I am Dr. Mohanjit Bordegor, a System Processor, Department of Geography, Cotton University. So, today in this session we are going to discuss GNSS, Global Navigation Satellite System, the working principle of GNSS, the overview of GNSS and the application of GNSS. So, basically knowingly and knowingly we all are familiar with GNSS. So, any location service you are using nowadays in your smart phones are basically a part of GNSS. So, it helps us to locate us on this art service. So, our coordinates that x, y coordinates suppose in geography or in geospatial technologies one of the main questions, major question is where? So, this where to understand the where we are located it is very important to know the latitude and longitude information. And GNSS particularly help us to locate those or to give us their latitude and longitude information on the surface of art. So, GNSS is basically a satellite based navigation system. So, there are number of satellites which are located in the space in the specific orbits and they you know send us some range based measurement through radio signals which help us to get the x, y coordinates. For instance, if you try to see that prior to this invincible you know the navigators, the sailors you know in the medial period or in a later period also they use the celestial observation, celestial measurements looking into the stars they use to you know locate themselves. But, there are some difficulties while you are trying to locate yourself on the basis of the celestial objects because sometimes they may be visible, sometimes they may not be visible due to overcast you know sky and all these things. So, the point is then we have actually replaced those celestial objects from this satellite based navigation system where we have send some man-made satellites into the space and place them in some specific orbits so that they can continuously communicate with the users on the surface of the art and they will be able to locate themselves at any point of time without any interruptions. So, this is the basic idea about GNSS, why GNSS you know how it works actually. So, why GNSS this is the main question why we have to replace those celestial objects with these man-made satellites because we need 24 hours 24 into 7 on weather informations regarding that question of where ok where we are. So, for this you know uninterrupted locational services we need this GNSS global navigation satellite system. Another point is that it is extremely accurate because it is based on the radio signals. So, we can get very precise locations you know up to a sub centimeter level location in some time. So, then you know any point of time you would like to come back to your previous location you will be accurate by the centimeter scale. So, that is the level of accuracy we can achieve. Precise time also it helps us to get the precise time also the precise time which is also known as a coordinated universal time. This mention as UPC in your study material. So, it is within 16 nanosecond to 5 nanosecond that is the accuracy ok 10 to the power 8. So, that is the accuracy of the time we can get with the help of GNSS ok. Why it is so important and why we can get some uninterrupted information regarding our location because this GPS signal is a high frequency radio wave ok which is 3 to 30 gigahertz. So, when you ever get such a high frequency radio waves it can penetrate the clouds. So, that atmospheric disturbance cannot you know stop us getting us our location. So, this is very important ok it can penetrate the clouds. So, in case of your overcast sky or some atmospheric disturbances you will still get your location and information. So, that is why you know we have replaced that celestial object see now we can get uninterrupted information regarding our location ok. Continuous real time information and accessibility to n number of worldwide users. So, if everyone in the world nowadays you can see that any point of time we will we tend to keep our location service on in our smartphones. So, n number of users can access those signals without any interruptions. So, that is why we need this global navigation satellite system. In the global navigation satellite system this is a generic term which includes all such type of you know satellite communication. The pioneering in this field was the GPS global positioning system by US Department of Defense. So, they started this the first of such you know initiative was taken in 1960 by US level when they installed 6 satellites at the heart of 1000 kilometers. So, this was a constellation of 6 satellites. So, 6 satellites were placed in order which is located at 1000 kilometer from the heart surface. So, this was a leading navigation satellite system NNSS. But later on they installed a navstar GPS navigation system with time and ranging global positioning system navstar GPS. So, this is the first of its kind you know GNSS we have. So, it was basically developed by the Department of Defense. Now, if we have a brief look over the history of GNSS. I mean the GPS as it is the first of its kind in global navigation satellite system. So, 1959 US Navy built that transit system which is the level you know of the 6 satellite installation level GPS. 1978 the first prototype satellite of the navstar was launched in 1978. 1983 the president of US needed president of US Ronald Reagan. He affirmed the US policy of civil use of GPS. So, prior to that that was only for the defense use. But in 1983 they promised that it will be allowed for the civilians to use the GPS signals. After that in 1989 the first operational satellite which is also known as block 2 came into existence. And along with that the civilian use was allowed from 1989. So, the Manila was the first company which introduced a handheld GPS. So, handheld GPS is the device which can get the signals and give you the accurate locational services. So, the same technology nowadays there in our smartphones. In our smartphones also now we will be able to identify our locational information the latitude, longitude and the altitude. But in 1990s US just last the sum of this precision of the GPS system ok. It was kind of a selective availability. So, they allowed the high frequency waves to be captured only by the defense US defense. For the civilian use they have reduced at that point of time they reduce the precision of that locational services. But in 2000 they you know remove those kind of you know selective availability. From 2000 the civilians can also get a very precise locational services. And from 2000 to 2007 they have installed many more satellites to make the constellation of this entire GPS system complete. And nowadays we can have an uninterrupted signals and from any location from the on the surface. If you have to see the after you know US many countries initiated their own GNSS global navigation satellite services. Next to US is the Russia ok. So, there this GNSS is known as global navigation satellite system which is GLONASS. Then Europe has its own GNSS it is still in the development it is going on. It is known as a Galileo. China is a bidot ok. And for India started installing their own satellites for navigation in 2013 also this process is going on we do not have a fully operational GNSS here. So, it is known as an economic ok navigation with Indian constellation in Japan also started in 2017 ok. So, this is about the GNSS across the countries. Now, if we have to if we have to understand the working principle of GNSS then we have to see the segments of the GPS ok. So, in case of your global positioning systems basically we have three segments as I have been referring the first segment is your space segment itself the satellites ok. The second segment is the control segment and the third system belongs to us the user segment we are the users ok. So, I am going to discuss them one by one. Now, in case of the space segment to have a full installation of this GNSS the mean the requirement is more than 21 or 24 satellites. So, there are six orbits in which orbits a four satellites. So, total of 24 satellites. So, you have a full installation of this GNSS system. So, more than 20000 sorry more than 20000 kilometer and 24 satellites. Now, even that recently they crossed almost 36 because some of these satellites make it only know due to some technical glitch or the health of the satellite. So, you have to clearly replace. So, they you know install more and more number of satellites to get a worldwide coverage ok. So, six orbital plane most importantly twelve hours return interval for each satellite. So, from a particular location that that particular orbit is set in such a manner I guess it is almost 2.5 kilometer per second that is the speed of the satellite in its orbit. So, it passes through the same location twice day which help the particular from a particular location to visualize a particular satellite or to get not visualize actually to get the signal of a particular satellite for at least 8 to 10 hours in a day ok. So, during that pass the space segment yes visible from any point of on the earth for about 10 hours ok. Because it pass that particular point twice daily ok. With a full constellation 4 to 12 satellites will be visible from any unobstructed locations. So, this is the requirement for which actually we have to or we have been installing more than 24 satellites or 31, 32 satellites US 36 almost satellites they mean stop ok. So, this is because of so that you can we have these satellites in your ephemerie for 4 to 12 satellites ok. The high frequency band this is L1 and L2 ok. There is no much discussion in your syllabus regarding this band and its characteristics and all, but this is a high frequency 3 to 30 gigahertz ok which is more than our radio signals and a normal radio and TV the signal which is more than that it is higher than that the frequencies. Satellite transmit coded signal and navigation message this is very important I am coming to this the coded signal and the message along with the carrier frequencies. But before that you must understand the control segment and its role ok. Now space segment is clear that 20,000 kilometer plus 20,000 kilometer we have installed these satellites a full constellation is 24 satellites in 6 orbits so that we can get an uninterrupted signal. So, that from any specific location we can have these satellites for at least 10 hours in a day ok. So, that total orbital this is 12 hours ok. So, one particular satellite passes through a particular location on the earth twice daily. So, this is the space segment. Now the control segment the master control station basically there are 6 or 5 control stations. The master control station is located in a Colorado stream Raystar, Hawaii, Accination, Diego, Garcia and Sanam. So, these are the control segments ok. Now what is the role of these control segments what they do normally. So, basically they are the monitoring stations for the health of the satellites ok. So, they track the health of the satellites ok. They also provide the data regarding the satellite effemates. Now this particular word it is a new concept the effemates ok. So, I am coming to describe it what is effemates. Now clock offset you see there is a clock offset in the satellite and the user segment because you see the satellite the clock is an atomic clock, but here we have a ordinary clock. So, there is an offset time offset. So, they do take care of their time offset the control segment they correct it ok and sent us the correct it sending signals. Navigation messages are also uploaded by the control segments they monitor the health of the satellites and they also look into the status of the entire satellite constellation which is known as an almanac. So, what is an almanac? Almanac is the entire satellite constellation is known as an almanac. So, you have to understand that the satellite the signals it sends to the master you know control segment basically it sends or to our receivers also we receive basically 2 satellites. One is if satellites sends the data regarding the location of other satellites in the entire constellation and also sends a specific very precise information about its own location I mean the location in its orbit ok. So, this entire constellation is the almanac later the specific location is the effemates data when it is located at a particular point of time. So, these two information are very important for the locational service for the GPS to work the almanac the effemates and the codes the signal the coded signal these three things are very important now I am coming to it. Next is the user segment user segment these are the you know specific hand held GPS nowadays we are having the locational service here we can download some apps which are available in the Google services and from those apps also we can make use of our any normal smartphone as a hand held GPS we can we will be able to locate our XY coordinates with the help of our smartphones also. But these are standard hand held GPS. So, this is the user segment ok. Now, the working principle which is very important to understand the working principle of the GFC three information one is your almanac data effemates data and a signal random phone. So, these are the three basic things you have to understand first is the almanac data. It tells where its GPS satellite should be at any time throughout the day. So, this is the almanac data ok. Each satellite transmits almanac data showing the orbital information for the satellite as I have already mentioned. Apart from its own location each satellite sends the information regarding the other satellites where they are located at a specific time. So, this is your almanac data. Effemaries data these are a precise data for the specific satellite in its position. So, this is the effemaries data and the pseudo random phone it is a signal ok a particular phone why it is known as a pseudo random phone because that particular signal is something like a noise signal. So, that is why it is known as a pseudo random phone not actually a phone pseudo random ok. This is very important very interesting phone I am coming to it again pseudo random phone. Now this is the effemaries ok. So, high orbit very stable orbit no atmospheric drag disturbances because of the you know high frequency you know wavelength we have and from this from the satellites they are sending their effemaries data through the monitoring stations and monitoring stations transmitting the data through the user centers. This is the effemaries data ok. That means the where that particular satellite is located at a particular point of time. And in this standard GPS things in the display you will be able to locate the effemaries also. They send a kind of a graphically map of the effemaries ok in some of this you know handle GPS system not enough. Now this is how GPS works I have already mentioned one specific point you need to remember ok this is tri-intrusion which is I am coming to describe again why this what is tri-intrusion and why is important to have our location on the our service. Res I have already covered like a great clock is required effemaries collected for atmospheric and iron is where disturbances and differential corrections. Now the best part is that we need not to border for all these things. These are taken care of by the control systems ok. So, they are corrected everything and send those corrected message to us to the users. So, users again this is very important the range measurement it is very important to know for the locational information to solve the locational question it is very important to know the range measurement what is the range measurement. You see it is also beautifully explained in your study material like there is a time lag between the sound and light right light travel faster than sound right. Now from a specific point if you would like to see that if you see a thunderstorm and you heard that the sound of the thunderstorm if you can get the time difference ok. And if you multiply it with the speed of time speed of light then you will be able to get your exact distance from that particular point ok. Same same idea that the particular signal from the GPS travels at a speed of light ok speed of light which is 3 into 10 to the power 8 meter per second speed of light ok. Now which is speed of light less by any atmospheric disturbances which is taken care of the control system ok. And speed of light and the travel time if you get the travel time and the speed of light you will be able to get the distance your distance from that particular satellite. So, this is the range measurement it is all about ok. So, why this range measurement is important why this range measurement is important why should we know the why should we know the you know that our distance from the satellite. You see the pseudo random code I have written ok. Our receiver does not receive the pseudo random code ok. The same code is also generated by our receivers same code. Now it actually compares the difference between these two specific nodes of that particular code and that difference is your time difference see pseudo random code from the SB space vehicle that means the satellites and the pseudo random code from the GTS receiver ok. Now can you see there is a time difference of these particular specific code ok. So, that time difference ok into multiplied by the speed of light you will be able to get the distance from the specific satellite ok. So, that is why the pseudo random code is such an important part ok. It matches it gives us the time length ok. The time length it can be due to atmospheric delay also ok. These are the things that the signal takes some time to travel minus your atmospheric delay. So, all these are taken care of and you will be able to understand that particular time length and if you multiply with the speed of light you will be able to get your distance from the satellite. After moving your distance from the satellite this is very easy to solve your x y coordinate information ok. Now this is the method of trial equation. Now you must remember this is very important thing see pseudo random codes we as a part of our syllabus we need not to know much more about the pseudo random codes you know its characteristics and all we only have to understand the time length ok. But this trial equation is very important you see to get a precise location on the earth surface the minimum requirement is the four satellites you must receive at least signals from the four satellites why because in this locational equation you have to solve four things one is your x coordinate one is your y coordinate that means latitude, longitude, altitude and you have to take care of that time length. So, x, y, z and t. So, these are the four things ok for that the minimum requirement is the four satellites ok then what is the process of the private reason. So, the process of private reason is why do we need the fourth satellite actually what is the requirement of the fourth satellite. Now you see suppose we are getting the signal from a single satellite it will help us to solve that we have on the surface of earth somewhere on the surface of earth ok. Now the second satellite will bring us this particular area ok. Now we know that we are located somewhere here this is the role of the second satellite it reduces ok earlier we know that we are somewhere on the surface of the earth. Now our location got reduced to within this zone. Now the third satellite will bring us down to two specific points because the third satellite will cut into two points of this particular surface see. Fourth one will give us our exact location fourth one will gives us our exact location. So, this is a graphical representation of the same thing the fourth one is giving us our exact location here ok. So, that is why we need these four satellites ok more than four it depends but you cannot rely on the locational data if it is given by less than four satellites it will be a wrong answer. If you have to, if you go through that, you know, I am knowing things like x, y, z and t, x, y, z basically, three elements we need to know, that is why we need a force of light, okay. Now, the use of GPS need not to explain, we are using it extensively into our day-to-day from the CV, we use like your aviation, you know, personal aviation, tracking, sipping, surveying, recreation, you know. Nowadays, you always try, if you have to go somewhere, you just take help of the Google Map, but this is a locational service, okay. If you have to order something, you have to call for a cab, or if you have to ask for your dinner or lunch, the Jomato and all these apps are working on the GPS system only, right. So, now tracking in case of the animals, surveying the animals, it is very useful for tracking. Then your navigation, like, you know, the maps we are using for the navigational purposes, okay. The Google Map and other services we are using. Then this is navigation on ground, air, everywhere we can use, okay. So, air navigation is also, you know, it is much easier now with the help of GPS, okay. For field digitization, field survey, like, you know, surveying a railroad or a drainage system, okay, or any roads kind of a thing, it is very useful. Open with my survey precision admittals, okay. Now, I guess we have been using precision admittals also for harvesting, okay. So, this is the robotic harvesting. You need not to go along with the harvesters, okay. You can lay down the track along which you want your harvester to move. The harvester will move on that particular track. And the track will be a line, which is a combination of points, we know, right. That line is a combination of points. So, this GPS information, the locational information, you incorporate in the harvester. The harvester will automatically harvest your editor's product. Very easy, okay, construction, okay. So, these are not really used. But there are some disadvantages of this GPS system, okay. What is the deep GPS, what is the most important disadvantage? That GPS needs to see the sky all the time, okay. Any obstruction is not good, okay. This is the basic thing you have to remember. Like, you are in a middle of a, like, in a city center where there are sky detectors, or you are inside a building. You cannot get a precise locational information. Okay, this is the diesel package. It always needs to see the clear sky. No talent coverage, okay. Underwater, no clear sky. If you do not see the sky, then your, the locational information will be erroneous, okay. It gives us our coordinates in the worldwide data. Data means the reference from point, from where we calculate our altitude. So, have you heard a term like mean sea level? Always, you know, 50 meter from mean sea level. So, that mean sea is a reference, okay. So, this, the World Georetics System 1984. This is a standard data, the reference from where we calculate our altitude, WJ-84. This is a worldwide data. So, it gives us our altitude information in that particular worldwide data. And it is an ellipsoidal data. You understand the ellipsoidal, right? You know, that ellipsoidal, this resembles the same of the earth. It is an ellipsoidal data. What is the problem with the ellipsoidal data? Ellipsoidal data, as I have already mentioned, we are using the GPS for surveying, okay. But for surveying, we need a very precise locational information, okay. This means that very localized, you know, information. These localized information cannot be achieved by the ellipsoidal data, okay. So, it can give us a ellipsoidal heart or orthometric heart. Actually, we know that the surface of the heart is not that smooth, okay. There are ups and downs. There are mountains like Mount Everest, deep trance like Mariana trance, okay. So, which has its own, you know, influence in the plumb walk when you try to locate your particular point where you are standing. So, it doesn't matter. So, if you need a very precision survey, very localized survey, then you have to rely on, you cannot rely on the WGS-84 data, okay, which is a worldwide data given by the WGS-84. So, for that, we need some advanced technologies, okay. So, that would be all for the GNSS file.