The optical spectrum (red-green-blue to the mid-infrared) looks different for the three basic land-cover types (water, vegetation and soil). The first three "thematic" bands of Landsat are for red, green and blue, are bands 3,2 and 1 respectively (or TM3, TM2 and TM1). Sometimes the contrast between these bands is not very useful in highlighting the differences between the landcovers (see figure below).
Using the graph from the figure, calculate the ratio of reflectivity (reflection percent) of band 2 to band 1 for Water, Vegetation and Soil (approximate the graph as being constant within the bands). Call these variables, R
water 21 ,R veg 21 , and R soil 21.