I was/is an avid radar watcher since living in tornado alley for a good bit.
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An infrared image shows temperature differences.
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Apologies for not answering your query earlier! I was busy, putting together a big archeological presentation for a meeting today...
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I'll use current imagery from both systems in Miami,FL, tonight, Saturday September 9, to illustrate the differences
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RADAR (capitalized because it's an acronym...) is basically an image generated by reflections from raindrops of radio pulses that are sent out in a circular "sweep. (Analogy: You don't actually "see: an object illuminated by a flashlight -- you see the light reflected back from that object. "RADAR "illuminates" with radio waves instead of light beams...)
As shown below, each RADAR station has a discrete limited coverage range; things beyond that range are, in essence "invisible" to that specific RADAR station. Notice that, even as Irma is approaching Miami, the "eye" is not yet within the range of Miami's RADAR. To lessen that weakness, composite images from multiple, overlaping RADAR stations are often displayed. If, for example. this display included the RADAR on Key West, the eye would be visible. Back when IRMA was over Cuba, it didn't even show up on Miami RADAR...
In IRMA's case, the value of RADAR is that can show rainfall intensity, and can give a measure of how fast those rain bands are moving horizontally. And, importantly, it can sometimes give an indication and warning of tornadoes embedded in those rain bands
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Satellite Infrared images are photos taken using the "long" (low frequency) wavelengths beyond red in the light spectrum. They are basically images of the temperature of clouds. Sometimes, they are color-coded to reflect temperature (or, more accurately, heat content) of clouds. Just as important, since they are taken by satellites far out in space, they can show weather features that are well beyond the range of land-based RADAR:
IR images are just photos of cloud tops viewed with sensors tht are receptive to heat, rather than to visible light...
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Hope this is helpful -- and not too late...! '-)
TXnMA