A reader here also asked about the pre-1979 satellite data over at my question place. The thing is, we do have pre-1979 satellite sea ice data -- the ESMR (Electrically Scanning Microwave Radiometer) 1973-1976. It was a much simpler instrument than the SMMR, SSMI, SSMI-S, and AMSR which started flying in 1978 and since. The more recent ones have two very important improvements over the ESMR -- they use multiple channels (think of it as colors) and they use both horizontal and vertical polarizations rather than just total power.
Ok, translation to English. Our eyes look in three channels -- red, green, and blue. Different creatures use different numbers of channels. Dogs use only one, black and white (as we do if the lighting is very low). Mantis shrimp use 10 channels. Bees use ultraviolet. And so forth. The key is that the eyes respond to some number of colors. Numbers vary, and what color band also varies.
The other thing about electromagnetic radiation is that it can be polarized -- vibrating in one way versus another. The two linear polarizations are horizontal and vertical. ESMR just lumped them together and measured total power. SMMR and the rest measure horizontal and vertical polarization separately at most of the channels. Basically, SMMR and all the more recent instruments have high quality color vision versus ESMR being a rather fuzzy black and white.
But ... black and white is still better than not being able to see at all. The question then arises in retrospect whether we can use the black and white instrument, ESMR, like our more recent color vision instruments. Now, in part, I know the answer already -- you can't. More precisely, you can't do it well enough to satisfy my colleagues at NASA-Goddard. Perhaps, though, it can be done accurately enough to answer some questions of interest, even if not accurately enough to be entirely comparable to the modern instruments.
I have some ideas, naturally, and have been been pursuing them a bit -- enough to know that there's a fair chance of getting useful answers. Whether it's useful enough to answer questions of interest ... well, I'll also invite questions you all find of interest.
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