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4. Make a first guess for T cold by looking at some fully covered agricultural fields (darkgreen). Insert a color gradation around the selected temperature.5. View the colored T s image and select a point that represents a “cold” (wet)agricultural field. Do not select an extreme cold point but one that is representativeof a well-watered full cover crop. For the best results, the cold pixel should have asurface albedo in the range of 0.22 to 0.24 (corresponding to a full coveredreference alfalfa field). It should have a Leaf Area Index in the range of 4 to 6(corresponding to full covered agricultural field). Finally, the cold pixel should belocated nearby the weather station so that the weather conditions are similar.6. Observe other areas of the image for similar temperatures.7. Select T cold from a pixel in the center of the chosen field that represents a very cold,but not extremely cold, point in the image.8. Record the coordinates and temperature of the “cold” pixel.Illustrative Example (Landsat 7 ETM+, 4/8/2000)The following example illustrates some of the thought processes employed during selectionof a cold pixel.In the following example, many well-watered agricultural fields, during an initial viewing, arefound to have surface temperatures of around 290 K. This can serve as an initial guess forthe cold pixel temperature.Next, we create a graduated color map for T s over a range of 284-295 K (Figure 1) thatincludes the 290 K temperature. In this picture, the blue colored pixels are near 284 K andthe red pixels are near 295 K. The image in Fig. 1 is an early April image, and not manyfields are well-watered for this period in this region. One can see that most of theagricultural fields are still bare fields and cultivation has not been started. In the colored T simage, bluish fields are more likely to be well-watered fields having some vegetation cover.67