Full transcript of “Lecture 1 : Rudiments of Remote Sensing and Advantages”. Click a timestamp to open the video at that moment. Need another video? Use the YouTube transcript generator.
0:24 Hello everyone, and I am Arun Saraf from IIT Roorkee. And we will be discussing in this course essentials of remote sensing which I have given name is remote sensing essentials. Basically we will be looking in this course about the basics that is rudiments of remote sensing advantages and also various applications which we will be ahh discussing in due course of time. So, this is 30 hours ahh course, which we are going to have. So in this series of lectures and I am going for first one, that is rudiments of remote sensing and advantages. So, very briefly in this lecture we will be going to discuss what exactly remote sensing
1:15 and especially the formal formal definition of remote sensing as well. And then and different platforms and other things. And we will be also discussing. So let us start first with the word basically remote sensing, in the books or literature, this is how it is defined. That is remote sensing is the technology of acquiring information about the Earth's surface without actually being in contact with it. And that that means if I say in simple words, that anything which we can sense film, our eyes or cameras or sensors, without basically coming into physical contact of it, and then we can say as a ahh this that we are doing remote sensing.
2:05 As you know that our eyes are very sensitive. And though they work in the very limited part of EMF spectrum, which we will be discussing in detail that is only visible part of the spectrum, but it is a very efficient ahh remote sensor or a similarly, there are some ahh other you know animals are also having different kind of or similar or different kind of capabilities of sensing things. And because human has designed sensors, which can not only work with the invisible part of EMF spectrum. But they can work in the infrared thermal infrared, even in microwave regions and not
2:52 only active microwave, but in passive microwave also. So, a large part of EMF spectrum wherever atmosphere windows are available instruments are sensors have been developed, some are ground ways, some are aerial based, and many, many of them are a spacecraft based on based on satellites. And also you know that now we are going for extraterrestrial ahh remote sensing like going on moon putting satellites around the moon or Mars and so on. So, all these things will be also discussing in brief in this course, ahh this is the remote sensing as you know is done by sensing and recording. And that is a recording what recording that is the reflection or emitted energy, which
3:42 is coming out of the surface of the Earth. And then we process it and analyze it and up and then use this data, these images for different applications. But as I gave the example of human eyes, we do not have that that kind of recording facilities only it goes in memories, but we cannot replay, ahh but using instruments or sensors it is possible to require record the reflection or emitted energy of the surface of the Earth. And it is also possible to acquire that information or that data which has been sense by satellite, which is based ahh which is in orbiting around the Earth or moon.
4:29 And to Earth ahh by through satellite Earth stations. So, in this course also very briefly we will be also touching that aspect that how data is acquired from satellites and then they send the signals and so on. And then of course, whatever the data or images which we get generally are in raw form. So, we need to do the image processing a lot of corrections are also performed. And we also analyze interpret the images and then use for different application. So, this is what is basically ahh remote sensing in this one. if we if we see different parts of remote sensing or different components of remote sensing, so, we will go a step by step that the the E which is which you see here is the
5:18 energy source or illumination, this is very much required that is essential especially for the reflected energy which we have just discussed in the definition of remote sensing that you need either illumination source or illumination or reflection that is possible in daytime or you need to imitate emittance that is any object which is above absolute 0 will also emit energy. That energy can be also detected by satellite. So, this is what it is is shown here, that E is the illumination source, B is the radiation and the atmosphere, so that the energy which is coming from ahh sun reaches towards the Earth, which is a C here and then some of this energy is reflected or emitted and then
6:10 it reaches to the satellites and another D is also shown, because this is shown for the microwave and satellites. In our sensors that the satellite itself they send the microwave signals towards the Earth and then whatever the work is capturing ahh or the energy which goes back again is recorded by the satellite. So, that is why here B is also shown. So, then the C part is the interaction with the target or the surface of the Earth in case of passive remote sensing and recording of energy by the sensor. Whatever the signals which reaches or energy which reaches to the sensor, it is recorded by the satellites which are orbiting and the Earth, moon or Mars and then the transmitter
7:00 this in ahh these signals, whatever the data which they have acquired or satellite images they transferred towards the Earth. So, this is the satellite Earth station and so these the receiving is done some ahh first level or second level of processing is also done. And then it is recorded here and then of course, it goes for processing analysis and interpretation. So, that part comes the ahh the G that is the application also. It is also possible that a the satellite which is which has recorded a scene or an image can also transmit to some other satellite which might be orbiting over ahh a satellite particular satellite Earth station.
7:45 So, almost in a real time that data though the satellite might be safe flying over ahh over India. But ahh the Earth station might be new is so through a satellite that transmission goes from one satellite to another and then and that signal goes to ahh that station where it is located. So, all kinds of ahh possibilities are there for data recording as well as all kinds of possibilities are there for sensing ahh these signals either illuminated or emitted. So, this is all what we are having in remote sensing. Now, there are different types of platforms which are discussed in remote sensing which
8:33 are considered as part of remote sensing. And this is a ahh changing at a quite fast rate I would say that because initially we started remote sensing with ahh balloons, so, some cameras were put on balloons, and though in this diagram is not soon because I am discussing here only the present day remote sensing platforms, and then later on then it came on the aircraft but this these aircrafts are having their own limitations, helicopters are also their aircrafts are there. So they can fly up to 1.3, 1.5 or maybe 10 kilometer ahh in the in the air or in the atmosphere. But the more robotic platforms are the satellites which are very far around the 700 to 900 kilometer,
9:23 these these satellites I am talking about the remote sensing satellites roughly they are somewhere 840 50 kilometer + - 10 kilometer, these remote sensing polar orbiting or near polar satellites, these are the satellite which I am talking here. Though there are different types of orbits are also they are in in due course and time we will be might be also discussing some basic types of orbits which are used in a space or in satellite remote sensing. But the the remote sensing which we discuss or I am going to discuss mainly will focus on the data or images which are acquired by these polar orbiting satellites, which are around 840 or 50 kilometer in space.
10:10 It is also possible to acquire data it has been done on the past using space shuttles, like one of the examples of through space shuttles or missions are there ahh like a shuttle radar topography mission, which was done using the space shuttle. So, that is also possible, they fly somewhere between 185 to ahh 576 kilometer above the Earth and then there are also possibility of airborne SAR, airborne aircraft are also shown here. But air bornes are ahh they fly much higher above the ground and the latest the new edition in remote sensing platforms is a this is what is UAB and unmanned aerial vehicles which
10:57 are becoming very popular for ahh for different kinds of photography or imaging, and all kinds of payloads can be put depending on the capability of these drones. And though they cannot fly very high, they cannot cover a very large area. But if somebody is looking for a very high resolution images and almost in real time and they would like to have the full control over it, then you will be can be one of the options and this is being used in case of disasters in agriculture and a lot of resources management also, currently you UAVs are being used, very popular in, very cost effective also sometimes. So, the different platforms are there at different heights to cover the various parts of the
11:46 Earth. And as you know that then there are 100 of satellites orbiting and and different depth in the space. And there are the satellites which before we will be focusing as I have already mentioned, near polar orbiting satellites which are shown in these ahh red color orbits, there are satellites which are ahh as jewel geostationary satellites, which are shown here like INSAT series of India. These are the geostationary satellites. We are also having like these polar orbiting satellites, like IRS satellite, landsat and meteosat and NOAAVHR, NOAA satellite, there are many such satellite which are orbiting
12:36 in polar orbits. And there are some other different types of orbits are they ahh, so very not all satellites are shown but many, many such satellites are shown ahh which which have which have been put by different countries in different orbits for completely, sometimes different purposes. But most of the time, we are going to discuss about the polar orbiting or near near polar orbiting and sun synchronous satellites, which are around 850 kilometer away from us. So as you as we have just discussed that remote sensing is the process which involves an interaction between incident radiation and the targets of interest. And this is exemplified by the use of imaging systems or sensors where the ahh these following
13:29 7 elements are involved. What are those 7 elements as we start with the satellite. So, there is a very important component of satellite based remote sensing, if it is drone, then drone is the some vehicle is required on which a payload can be put. So, that is what is required. So, instead of satellite we can say vehicle then of course the there is a Earth and different objects on the Earth whether the water body is there, forest is there, grass is there, bare soil and so and so forth. Of course, you need a energy source. So, we are having sun here illumination source. And then in between you are having atmosphere in between means, the between sun and Earth
14:15 and between satellite and Earth and this atmosphere plays a very important role in in field of remote sensing. And because ahh though the solar energy is coming through the atmosphere, so, the entire energy is not reaching towards the Earth. And the same way when it is reflected back and say to the satellite, then again entire reflection or emission is not reaching towards the Earth because in between there is atmosphere and this atmosphere while ahh the energy or signals which are going back ahh through the atmosphere there are a lot of distortions are created, and errors are introduced and we try to minimize by through our processing or techniques which are available currently.
15:03 We try to minimize these atmospheric errors as well. So that our images becomes much more useful quantitatively and qualitatively as well. So, the 7 components are here, ahh which are key elements in remote sensing also ahh one by one we will be discussing these elements ahh like a first as A is here shown also that energy source illumination, that is the first requirement for remote sensing is to have an energy source and which illustrates or provide electromagnetic energy to the target of interest. And that the second element or second important component of remote sensing is the radiation
15:48 and atmosphere. Of course, atmosphere is there, but if we talk about remote sensing of Mars or moon, then in those ahh extraterrestrial bodies like Mars, Mars has a very thin atmosphere. And therefore, the distortions or errors or you know the blurriness which might come in case of Earth images, that is not very common in case of Mars. So, that atmosphere there is thin and has got less role to play as compared to the Earth. But, when we are on the Earth or we are talking about satellite images or remote sensing of the Earth, then atmosphere plays a very important role as as we know that when the energy travels
16:33 from its source to the target, it will come in contact with ahh atmosphere and interact with it ahh and it passes through also some part of energy and this interaction ahh may take place a second time as the energy travels from the target to the sensor. By second time is I have already said that when it is coming from Sun to the Earth, it has to travel through atmosphere, which is in between, and when it goes back after illuminating the surface or image and energy, then again it has to pass through the atmosphere that is ahh that is why it is second time. So, second time is more important in case of remote sensing of the Earth.
17:21 Then comes the C part that is the interaction with the target or interaction with the surface of the Earth. So, once that energy ahh reaches ahh its way through the atmosphere to the target through illumination source like sun and then it interacts with the target depending on the properties of both the target and the radiation. Here the properties means that target might be a water body might be ocean, or a land or a desert, or a dense forest, or a building or a similar objects or a mountain or a snow peaks or glaciers. So, different objects which are present on the surface of the Earth will interact differently with the signals which are coming ahh or the energy which is coming to the sun and then
18:13 they will behave differently the radiation is will be going to be different and then whatever is reflected back or reaches to the satellite, that is what it is recorded ahh by the sensor which are on board of the satellites, that is the D ahh component. And after the energy has been scattered or emitted ahh from the target in between with the of course, it has gone through also and absorption or scattering within the atmosphere as well. And so, we require a sensor that maybe a remote sensor and maybe own board of satellite or aircraft or helicopter to collect and record the electromagnetic radiation which has reflected
19:01 or scattered back from the Earth. So, you record a recording system also with that sensor and this transmission and then of course, then whatever is recording is done either it should be transmitted live that is by direct broadcasting or recording in direct broadcasting, all kinds of options are available with different types of sensors. So, transmission is also important component or remote sensing and these whatever the data it has collected, whatever the image is has collected, it has to transmit towards the satellite Earth station like soon shown here. Then these restrictions received the data. So, the reception part and then of course processing first level processing, second
19:47 and then ahh satellite analysis, image analysis interpretations and of course applications. So, the energy recorded by the sensor has to be transmitted, of in in form of electronic form and basically be receiving digital form. So, all the remote sensing images recorded in digital form not analog form nowadays. And then processing stations or satellite this systems receives this these data sets or images and then processing will take place and generally the outputs nowadays is very common is the digital one, but hard copies can also be prepared. And then of course, after all this then we come to the interpretation and analysis part
20:35 ahh that is here and that is mainly in the lab work also. So, the processed image is interpreted by experts or for application scientists for different purposes. If one is civil engineer, then he might be using that image for civil engineering purposes. If somebody is geologists then he would be using for identification of some mineral deposits or ahh coal or oil or gas or whatever. And similarly for a scientists will be looking at different density of for us maybe different species of plants and so on. So the interpreting and the same image can be interpreted for different purposes. That is why also it is said that the remote sensing is a generic technology that means
21:23 it can be applied in various applications of various domains. And then interpretation can be visually interpretations can be ahh digitally based on the softwares or maybe more recent tools like neural network and basically classification based on fuzzy logic and other things. And then ahh ultimate purpose is to extract information of the Earth objects from these images for different applications. So that is the main purpose. And then finally comes the applications that the final element remote sensing process is achieved when we apply the information, we have been able to extract from imagery about
22:09 the target in order to better understand it reveal some few new information or assist in solving a particular problem. You know that nowadays remote sensing images, though it is need not to be everyone is expert on remote sensing. But, from in day to day life we have started using remote sensing. For example, when we see the weather forecast is so whoever in the television or on net when it is displayed the satellite image is also displayed and clouds and if there are some cyclones are developing or other thing, they are also ahh shown through these images. So we start seeing images for different, so it can be also used for weather forecasting
22:57 or natural disaster management and various other applications. So, these satellite images are becoming very common Google Earth is another ahh product, which provides lot of images. And you can zoom it and as soon as you zoom it, you get higher and higher spatial resolution images of any location of the world. So, because thousands and millions of images have been put in that Google Earth database, which can be accessed by very easily by the users of their ahh area of interest. Now, what are the advantages, some you might have realized by seeing or while going through this discussion is the synoptic view that is the biggest advantage but because generally
23:47 remote sensing is done from a distance. So when you go from from an object away from object to the distance, you start covering a large area and so in one go you can cover a very large area of course, it depends on the spatial resolution of the sensor. But nonetheless, ahh it will provide a synoptic view. So, a large area can be covered in one go that is what meaning here is. So, suppose if I take example of NOAA AVHRR, NOAA is the name of satellite AVHRR is the advanced very high ahh resolution radiometer and that having a spatial resolution about 1.1 kilometer and that covers about 2800 kilometer wide swath.
24:36 So, in one image in one go you can cover a 2800 kilometer ahh swath or a strip of the part of the Earth. So, it provides a very large coverage, but as you go higher and higher spatial resolution, the size of this swath, the breadth of the swath reduces and if I take example of one meter resolutions say ikonos images, then the swath reduces to 11 kilometer. So, from 1 clue 1.1 kilometer spatial resolution and 28 2800 kilometer swath you reduce to 11 kilometers swath, but the spatial resolution you are getting all 1 meter. So, as you go for higher spatial resolution, the breadth of the swath reduces, but it is
25:25 still that higher spatial resolution image will provide a synoptic view. So that is the one of the biggest advantages and the remote sensing in day to day nowadays, we are seeing these drones have become very common and whether it is a marriage or some function or some large programs there ahh these videographers have started to have using these ahh drones. And why they use to cover a large area. So they provide also the synoptic view, global coverage. When you are going for satellite based remote sensing, not drone based of course, then satellite based remote sensing, then you can cover the entire globe is basically I am talking about
26:10 a polar orbiting satellite like IRS LANSAT port or many, many such satellites. So, they provide a completely global coverage sometimes except for ahh polar regions, but otherwise they provide a complete global coverage. Repeatability that is another best advantages with satellite based remote sensing, that each satellite will be coming or revisiting the same part of the Earth, maybe after a few hours like in case of new NOAA VHRR or maybe after 30 days, 16 days, 18 days depending on the resolution and depending on the distance from the Earth. So, these repeatability is another best advantage of remote sensing satellite based remote sensing.
26:59 So you can have coverage like that, and then you are having multispectral sensors, that is another very good advantage because in the beginning I mentioned that our eye work only in the visible part of EMF spectrum. But if we if I want to scan a part of the earth, using infrared or thermal infrared and of course visible as well, then I can have different you know, bands or channels, then we call it the multispectral. So, these sensors can be designed and been designed, they are already there are lot of different types of sensors are there, which can sense or measure the energy at different parts of EMF spectrum, beyond the range of as mentioned, human vision.
27:47 Multi resolution images are now possible. Within even 1 satellite different sensors are installed. Like I give the example of IRS so earlier in IRSV IRS-1Z 1D satellites. We had ahh 3 types of sensor, we have panchromatic sensors, which was giving black and white images. Then we have multispectral sensors sensors like LISS 2, LISS 3, LISS 4 and so on, so forth. So, within one platform you can have different payloads and multi resolution images can also be acquired, it is it is a very common thing nowadays with satellite based remote sensing, it is also possible to have images data in near real time. Once the satellite has acquired and there are satellites which can directly transmit
28:37 towards the Earth. So, if you are having your own satellite Earth station in real time you can acquire the data, though the satellite is scanning of the sensor is just scanning that part of the Earth. If it is in range of your ahh satellite Earth station or antenna, then in real time you can get the images and then systematic data collection because the repeatability is fixed and the the coverage is fixed. So, you get a complete ahh sequence of data. So, the time series analysis is become very possible very much possible with the satellite based remote sensing. So, since the data collection is very systematic, it is not common the drone or any such or
29:25 aerial or airborne remote sensing but mainly with satellite based remote sensing. The only solution sometimes for otherwise inaccessible areas. This is another important point, because there are many power there are many parts in the world which are inaccessible to human, not easily reachable, but the satellites can reach that means they can acquire the data and provide to ahh whoever needs for that time and especially in case of natural disasters, and satellite remote sensing plays a very important role. And finally, the generic data which I have already mentioned that one data set one image can be used by 10 or 20 types of applications.
30:12 So, there are multi purposes are associated with a single remote sensing data sets and that is another very big advantage like the first one the synoptic view, the last one the generic data and in between all are a big advantages with remote sensing and that is why remote sensing is being used from agriculture to natural disaster from civil engineering to ahh our sciences or in a on the Earth or moon on Mars or explore the ahh universe. So, for all kinds of such missions remote sensing techniques are being used. Another few more advantages of remote sensing and which is when we go at the processing
30:58 level because data being acquired by these satellites, which is in digital form and therefore lot of processing either can be done in automatic manner or semi automatic manner. So, analysis and processing becomes very fun because originally generically the data in digital form. If we are working in microwave region, then microwave advantage with microwaves that it can penetrate through the clouds. Because the the waves or bender which we are covering in microwave, the waves are having a larger and you know larger ahh wave length and therefore, they can penetrate the clouds and also sometimes in dry sand and then it can be used.
31:48 This microbial remote sensing has been used in India ahh to identify or locate the old lost courses of social theory in Rajasthan desert because the dry sand was there. So, as soon as the moisture comes that can be imaged or mapped by these microwave sensors. And of course in a natural disaster conditions especially in flooding, and sometimes there are clouds or enduring flooding most of the time there are clouds. So, if we imply the remote microwave remote sensing, then these can penetrate the optical remote sensing may not work the thermal may not work in flood and may not work, but microwave remote sensing can work in such conditions. It also optimizes field investigations it it will note, it can never replace the field
32:37 investigations, the field work or field investigates, site investigation have to be there a ground routing have to be there, but one can plan very well using remote sensing, one can optimize and one can take field investigation at a very fast rate by implying the remote sensing technology as it is happening in geological map or mineral exploration or in civil engineering. First people nowadays starts exploding or seeing things on Google Earth, then the plan many many field investigation side investigations just based on Google Earth data, which are the high resolution images, and then they go to that specific point which need to be checked on the ground.
33:23 And therefore, it optimizes field investigations, updating or revision of existing maps is expensive and faster. So, it is inexpensive that whenever there are old maps are there if you want to upgrade and then you imply the high resolution satellite images, and then these can be upgraded like survey of India, have you started doing this thing that they are now using in order to update the topographic maps they are using now satellite images to upgrade and that process become because if everything has to be checked in the field and it is upgraded. Then it is very expensive, but employing remote sensing data becomes inexpensive inexpensive and faster and color composites because we are talking about multispectral remote sensing.
34:13 So, therefore color composites can be created and they ensures the details of the area that we can I can identify very easily the water bodies, I can identify the turbidity in water, in pollution in water or forest I can identify density of forest. I can identify different species of forests or if I talk in case of our sciences or in geology, then I can to some extent I can identify different types of rocks and geological structures if they are of larger scale. And then and there are advantages with remote sensing is in natural disasters studies and rescue missions. And then based remote sensing based rescue missions can become easier and fast and this
35:01 is has become a this has become a normal practice. And extensively it is being used when in 2015 Nepal earthquake occurred and people or different countries shared their whatever the satellite data, current satellite data they had, which was covering and and the area which got affected by those series of earthquakes. And these rescue missions, ahh use the data and could prepare a lot of plans and maps and then these operations were done like that. And of course, so overall it is cost effective. And because they are doing things in the field getting updating information in the field
35:50 is very expensive. And where is using remote sensing data, it becomes very much possible earlier when remote sensing is starting the real remote sensing like lens at one in 1972 at that time, the satellite life of the satellite used to be say 3 years, 4 years like that. But nowadays, the the technology has improved, electronics has improved, the solar panels have improved, the batteries have improved. And now a satellite when it is known sometimes they are lasting for more than 10 years. So, they are becoming further cost effective. So, these are the various advantages of remote sensing which can be ahh used implied and
36:38 lot of work can be done implying remote sensing data. Now, there are some other little bit more discussion on this advantages that remote sensing is on obviously, on unobtrusive that is it is a passive thing. It does not destroy anything. So it records the reflected or emitted ahh energy by an object and a passive it is most of the passive except that some part of microwave remote sensing which is active, but still it does not destroy anything of the object. So, in that way it is unobtrusive that passive remote sensing does not disturb the object
37:25 or area of interest, I can say overall the entire remote sensing does not not disturb the objects or area of interest. So, in that way, it is also non invasive and advantages remote sensing devices may be programmed to collect the data systematically and such as within say 10 by 10 kilometer frame, vertical aerial photography. And this systematic data collection can remove the sampling bias interlude in some institute investigations. Nowadays, a drones are also these UAVs are also being programmed and they are they too have started collecting data very systematically.
38:10 So, the satellites and in between the platforms between say Earth and satellite that you are having drone, helicopters, aircraft and then different satellites in different heights. And under controlled conditions remote sensing can provide fundamental biophysical information including x by location, z location, and that is these other types of satellites or navigation satellites. Also we can get the biomass, temperature and moisture content. Whatever the research currently which is going on on climate change, large part of or larger data huge data or big data is coming from remote sensing sensors be the temperature
38:59 or say moisture content or say vegetation cover or a pollutants, aerosols. All that information is coming from different types of satellites. So lot of the data input in ahh these climate changes studies and modeling, all the data is coming from remote sensing or from different platforms. So this brings to the end of this initial discussion on remote sensing essentials, I try to cover in this one, what exactly remote sensing is, and what are different platforms. And how this whole thing works, starting from sun to satellite in between Earth and atmosphere. And then very briefly, I have told what are ahh the other processes involved and finally,
39:49 I have also discussed in detail the advantages of remote sensing for various purposes. So this brings to the end of this discussion. Thank you very much.
