Just like our comparison of April 2011 to November 2011, we are going to interpret color as a pattern of change over time, but now the change is over years rather than between seasons. Since 1984 NDVI is assigned to Red, 1996 NDVI is assigned to Green, and 2011 NDVI is assigned to Blue, our map could have any of the more than 16 million RGB colors on it, but you can use this table to give you some guidance about interpreting the colors in terms of patterns of change in NDVI.
| Red (1984) | Green (1996) | Blue (2011) | Color | Land cover change indicated | Likely cause? |
| High | High | High | No change - green in all three years | Green vegetation all three years | |
| Low | Low | Low | No change - not green in all three years | Lack of vegetation all three years | |
| High | High | Low | Vegetated areas became un-vegetated between 1996 and 2011 | Loss of vegetation (due to development or fire) shortly before 2011 | |
| High | Low | Low | Vegetated areas became un-vegetated between 1984 and 1996 | Loss of vegetation due to development after 1984 (probably not fire, or vegetation would have recovered by 2011). | |
| Low | Low | High | Un-vegetated areas grew vegetation between 1996 and 2011 | New park, new agricultural field, new golf course - artificial, irrigated vegetation | |
| Low | High | Low | Un-vegetated areas grew vegetation between 1984 and 2011, then became un-vegetated in 2011 | Possibly due to fire before 1984, then again before 2011, with recovery in between. | |
| Low | High | High | Un-vegetated areas grew vegetation between 1984 and 1996 | Fire recovery after 1984, or new artificial vegetation | |
| High | Low | High | Vegetated area became un-vegetated between 1984 and 1996, then became vegetated between 1996 and 2011 | Fire just before 1996, or development followed by new artificial vegetation |
Fire is a part of our ecosystems, and after a fire land will be un-vegetated. However, vegetation usually re-grows after fire, so low NDVI due to a fire should be temporary.
Permanent loss of habitat happens because of human development. The two colors that are most likely to indicate permanent development are thus shades of red or yellow.
Development before 1984 is hard to judge for sure from the colors in this composite, but would most likely show as white, black, or a shade of gray. White areas will usually be golf courses or other large, irrigated lawns. Black areas that are not water bodies will generally be roads or extensively paved urban areas, like shopping malls. Intermediate shades of gray are harder to interpret - they could be older housing areas with mature landscaping, or they could be vegetated areas that have stayed the same vegetation type for the whole period. Look at some white, black, and gray areas and see if you can figure out what they are now to help you see what the color indicates (for example, a gray area that is currently vegetated has probably been vegetated consistently since 1984).
Pan, zoom, and swipe your way around the image looking for:
You should also look at the map as a whole and get an impression of how much development has happened in this 27 year period - how much red and yellow is there on the map? How much black and white? Think about this both in terms of reduction in the amount of habitat, and in terms of breaking up patches of habitat into smaller pieces (that is, habitat fragmentation).
That's it for the activities - we will finish up with some discussion before you head back to MHHS.