 Good morning everybody, I am Ruchan Mistry from Manchin Institute of Technology, Sholapur and I will be continuing from where we left off in the last session and discuss about rain sensing using time of life measurement. Now, the learning outcomes for this session are you should be able to describe rain sensing with T of measurement that is time of life measurement and then comment on applications and features of these techniques. So, reviewing what was non-contact rain sensing, remember we had taken different types of non-contact rain sensing the last time and one more technique that comes into the picture is actually triangulation and it is very popular using even the existing type of rain sensors and also with rain sensors using video system that is camera based rain sensing. But by far time of flight is the most preferred way of rain sensing and it typically includes intensity measurement, phase modulation or frequency modulation. Another technique is also interferometry and then you have other vision based techniques which include measurement by using binocular vision and structured light approach and other techniques as well. Now, non-contact ranging if you recall, we there were different types of rain sensing such as LIDAR, RADAR and even SONA in which LIDAR typically measures phase shift, RADAR measures the return signal intensity, phase shift and frequency modulation they all widely used. So, the reason why phase shift is preferred in RIDAR you have to understand is the speed of light is actually very significant, RADAR typically uses sound waves where the speed is significantly slower than that compared to light and you need very sophisticated equipment actually to measure time of light when it comes to light. So, it is more prudent actually to use techniques which measure phase shift and these are very accurate techniques. LIDARs let me tell you by the way very sophisticated LIDARs are very expensive as for example, the ones which are used on autonomous vehicles they are upwards of $30,000 so that will give you an idea of what is the quality of these particular equipment. And typically time of light like I said involves intensity measurement, phase modulation and obviously frequency modulation and then you have interferometry and vision based systems as well. Remember, we have other techniques as well we just tend to prefer time of light measurement. So, how is this typically implemented? One is it is simple it is based on physics of wave propagation and most sensors involved in range of type measurement are active sensors not that passive sensors are not used, but if you want to have greater control of it then active sensors are definitely preferred. So, the process is very simple a wave is emitted at the object from the sensor and then the range is calculated based on the time taken by the signal to return to the source or by measuring the intensity of this return signal. So, even though we say time of light typically it is implicit that even the other techniques such as phase modulation and intensity measurement are also included in that particular definition. So, this basically shows you a picture of how things are towards the left as you can see you have an emitter which is typically the sensor which emits a certain energy source at the target which may be light like a microwave or ultrasonic that signal then bounces of the target which is then measured. Now, the measurement like you can say but towards the left the first image over here it can be at the point where you can detect the signal coming back. So, you can consider this as the time of light. Since you want a better accuracy because this can be due to noise as well you can actually measure the peak of the return signal and then you can estimate obviously the range. So, all different techniques are used more sophisticated equipment can use actually all of the above techniques. So, ranging using type of life measurement typically like I said involves in which a wave burst is emitted which bounces back from the target and is then detected at the receiver which is often located at the emitter as well. The emitter and receiver may be physically the same package or the receiver may be mounted on the target as well in certain cases it is mounted on the target as well. So, that depends upon entirely the configuration and the setup. The time of light is the time elapsed from the beginning of the signal transmission to the beginning of the return signal and hence we can calculate it as now if D is the distance between the emitter and the target and if C is the speed of light then that into half the time of light gives you an idea for the distances or if the receiver is attached to the target then obviously the distance equals the speed of light into the time of light. So, that is a very simple arithmetic that is involved in this. The critical aspects in this are actually the quality of the instruments and the sophistication of the increments the signal condition circuitry which is associated with it. So, that is actually the more you can say the more technical aspects of the physics involved is relatively simple. Now like based on the previous discussion that you had what do you think affects the range and accuracy of these particular devices. So, we will try to have a discussion on the same see if you can recall a few things from the previous class and we can continue with the discussion. Now let us continue with our discussion and obviously we are looking at ranging using time of line measurements. So, we discussed what how is this range defined what does the range depend upon. So, one obviously is the wavelength that is used the other is again simple logical you know common sense involved here that is signal intensity third like I mentioned is instrument quality resolution of the instrument signal processing capability all that is called propagation momentum and then the last aspect is of you know electromagnetic noise. So, these significantly affect the range at which an object can be detected and also in a in a very in an appropriate way. So, the issue here is when we see electromagnetic rise one thing would be one thing is obvious like for example, lightning and storms that very significantly affects the range and quality when it comes to radars and it is a that is a known fact and even dust particles tends to obscure lights and lead are is very much affected by the quality of the air qualities are already good. Another thing also on which range depends upon is the cross sectional area and also the reflectivity of the target and the direction of the reflected phase. This typically was is very important when it comes to radars and this is how your stealth aircraft actually have been determined. So, what stealth aircraft basically do is they actually have a very small cross section for a given size. So, a comparable aircraft is non non stealth typically has a larger cross sectional area as seen on the radar compared to a stealth aircraft and this is obviously achieved using one is the direction altering the direction of the reflected wave which is what some of the oldest stealth aircraft like the F 117 did and then what the other techniques used typically involved absorption of the radio waves. So, all these factors like the cross sectional area reflectivity of the target and direction of the waves affect the range at which the object can be detected. And so, this is this you can say is just an introduction to you what what stealth technology is right now at the moment. Then what are the issues now when it comes to time of flight measurement? Like I said range also depends upon all those factors which we discussed in the previous slide and error typically depends upon what are uncertainties in determining the exact time of flight. And these uncertainties are also based on what you choose to define as the return signal like if you want to define it at the beginning of the signal then definitely there is a higher chance that certain uncertainties are there. If you take a look at the peak signal then obviously if your accuracies are much better, but then you will have to compensate for whatever the differences that may arise because of it. Then limitations of electronic circuitry is another issue which introduces error in time of flight measurement. Instrument quality obviously the kind of circuits that you use, the propagation medium, the electromagnetic noise and any other wave interference all this together typically affect time of flight measurement in when it comes to rain sensing. I definitely recommend that you need mechatronics handbook by Bishop and that by Bolton covers significant aspect of time of flight measurement. Handbook definitely is a better choice it has an extensive discussion on range of flight measurement using different techniques including the ones that we haven't discussed. So that is I definitely ask you to look this particular thing out. Thank you. If you have any questions please let me know about it.