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First off, you need to realize that the landsat program goes back a _long_ ways (the first generation was launched in the late 70's). Have a look at the Wikipedia article for more details: http://en.wikipedia.org/wiki/Landsat_program Most of the imagery you're looking at is probably from Landsat 7, which launched in 1999 and is still (partially) functional and active today. (Edit: scratch that, it looks to be all very recent Landsat 8 data.) Due to the need to have comparable datasets over multiple generations of satellites, newer platforms (e.g. the recently launched Landsat Data Continuity Mission, a.k.a. Landsat 8) deliberately target similar spatial resolutions as the older platforms (This is a good thing!). Next, Landsat as a program is focused on uses like landcover classification, monitoring broad changes over time, etc. There's a higher-resolution 15m pan-chromatic band on the past few generations, but the real value is in the lower-resolution (30m, 60m, or 100m) multispectral bands. The visible bands are just the tip of the iceberg, and they actually aren't the most useful for the "main" purposes of landsat (land cover classification, etc). For many uses cases in remote sensing, we're much more interested in having good spectral coverage and a long record of changes than in having very high spatial resolution. Landcover classification has always been a key use case for the Landsat missions. Most of the information is in the spectral signature of a given pixel. (Some recent methods use texture, etc, but it's less useful than you'd think.) There's a trade-off between the wavelength being observed, the spatial resolution, and the exposure time. Because all bands need to be acquired in a similar amount of time, longer wavelength bands (e.g. mid-far infrared) will always have a lower spatial resolution than panchromatic or visual bands. (The transparency of the atmosphere is actually the main player here, but I'll skip the details.) The Landsat program has been invaluable in documenting and understanding human, ecologic, geologic, and hydrologic changes over the past >30 years. We don't have anything comparable! It's really, really incredible imagery. |