we have now finally reached the last major heading in chapter two remote sensing of the environment what's remote sensing well it means sensing collecting information about the earth remotely from a distance without actually going there no direct contact aerial photography is a form of remote sensing we've been doing that for years and years and years but more recently and over the last 30 maybe 40 years becoming more and more important is gathering information from orbiting satellites in space above the earth one conspicuous advantage of orbiting satellites is that there are no political barriers no go areas no fly zones in space we can image the whole world traditionally we've always captured images by recording them on photographic film and with aerial photography that works perfectly fine the plane lands you have your films once we start using orbiting satellites in space it's trickier how do we retrieve the film when an astronaut goes up to the space station or used to take a flight in the space shuttle point the camera out the window take images again the guy's coming home the film comes home with him satellites aren't coming home when they reach the end of their life 20 50 years from now they dive into the atmosphere and burn up in the early years of space some pretty amazing solutions were developed one or two of the early early russian spy satellites the satellite was launched loaded with rolls of film it was directed from the ground what to take pictures of and once a roll of film was completed it was actually ejected from the satellite in a small capsule which fell down through the atmosphere um using a parachute to slow its descent it had a radio beacon so it was emitting if you like radio beeps and the russians sent out a fighter plane trailing a large net behind to scoop the falling capsule out of the air i mean how amazing does that sound and how irrelevant almost with today's technology but yes film impractical in that environment and that has led us to move more and more into digital imaging when you want to take photographs today you don't use film anymore it's all done digitally have you noticed every time you go into a camera or electronic store and look longingly at the latest equipment even if you only just bought a new camera a few months ago the ones they're selling now have more megapixels why forever more and more and more megapixels finer resolution records more detail why do we keep adding more and more and more haven't we got there yet well the fact is the digital still hasn't caught up with phil in terms of resolution in terms of analyzing fine detail photographic film still wins but digital is so much more convenient you can take the digital data and manipulate it you can adjust improve color balance all the rest of it your pictures and perhaps perhaps the most important here of all you can then electronically in basically real time transmit them to friends family or anybody anywhere in the world and it's that advantage in particular which makes digital imaging so important in remote sensing we don't have to worry about getting the data home we ship it electronically we code it on radio waves and send it from the orbiting spacecraft back to planet earth in essentially more or less real time another important advantage of digital imaging relates to the kinds of data that we can collect photographic film records visible light some ultraviolet that is near to visible light and some shortwave infrared that is very near to visible light and that's it all the data that we record in remote sensing is what is called electromagnetic radiation that is light and its relatives waves traveling at the speed of light either emitted from the ground or reflected bounced off surfaces on the ground and coming up to be recorded at the satellite or airplane moving over the above the earth's surface we have designed and built sensors scanners that can pick up all kinds of wavelengths of electromagnetic radiation far beyond that limited narrow range visible light and nearby on both ends far beyond that shorter waves longer waves and so there's a much greater wealth of data types that we can obtain using digital scanning and then transmitting those digital images here's a look at the part of the electromagnetic spectrum relevant to remote sensing these are wavelengths ranging from short getting longer longer longer there's kind of a break here and getting much longer over here the names that we apply up here and this shows photography is visible light plus a little bit of ultraviolet plus a little bit of near-infrared we can get near-infrared from photography thermal scanners over here those pick up temperatures temperature contrasts radar another useful technique and then multi-spectral scanners which can gather any wavelengths desired within this range including visible light including near-infrared including thermal expanding to a bigger picture visible light of course has the full range of colors within it red at the longer wavelength end shorter shorter shorter to violet at the short end the electromagnetic spectrum ranges far beyond the parts that we use in remote sensing up to these high energy shortwave radiation at this end and going off in the other direction to longer and longer waves used in radio and television there are four particularly useful wavelengths frequency bands whatever you want to call them slices of that electromagnetic spectrum categories of data that we collect recapping those are near-infrared thermal infrared radar and multi-spectral scanning and we'll look at each of these and what is good for in turn so there are four principal types of remote sensing that we need to know about the first of those was near infrared or n i r okay near infrared means near in wavelength to the wavelength of visible light it is not the same thing as the temperature related thermal infrared it reflects well from chlorophyll the green pigment in healthy plants so how does this work plants as i'm sure you know take in energy from sunlight and use it to power photosynthesis plants look green does that mean that the green light is what they're using for photosynthesis no exactly the opposite green light is no use to them so it's bouncing off and coming to your eyes so that you see green okay now it turns out the plants actually reflect bounce away light even more strongly in what is called the near infrared those are the waves that are just a little bit too long for our eyes to see there's still light but not light that we can see and that means that a sensor or photographic film set to pick up those near infrared wavelengths gets a much brighter crisper better image of plants than visible light provides now since we can't see near infrared the word color doesn't mean anything color is how our brain processes the wavelengths that we can see if we can't see it there's no such thing as color so really that near infrared data comes in as a black and white image ranging essentially from dark no reflection to bright powerful reflection but we like color so we tend to colorize that image and since near infrared is very close to visible red it's become a tradition to colorize near-infrared data in shades of red so that means that healthy plants instead of looking green in near infrared look bright red take a look at the diagram in the textbook figure 2 37 on or around page 50 in your textbook here is the version in the 10th edition it depicts the southern tip of florida and the nearby florida keys the regular light image on the left has varying greens and browns that represent different kinds of vegetation and shallow water in the ocean you can't really tell them apart easily in the near infrared image on the right the bright red here represents mangroves trees with broad green leaves the brownish red above that is the grasses in the everglades and the shallow water in the ocean now looks totally different from the land vegetation much clearer the version of this image in the ninth edition the free pdf is of the bayous in louisiana it's not quite as clear but you can get the same idea from it so near-infrared useful for [Music] different types of vegetation grass trees riverbed vegetation that kind of thing useful for agriculture health and state of growth of crops the different shades of red in the image on the right show how well the crops are growing in different fields whether you've fertilized them satisfactorily or not that kind of thing military application identifying camouflage because camouflage is dead or fake vegetation and doesn't look like the real thing in near-infrared the second important kind of remote sensing is called thermal infrared and that's covered in the next video you