Minimum_ScanAngle_selection: Finally, data with minimum scan angle is selected for composite to minimize the influence of atmosphere, bi-directional reflection and size of footprint.

Figure 2. Definition of value DIFF to evaluate "Speckle" in this study.
This method is applied for global product generated in CEReS and the result is compared with the MVC. The period of the composite is 10 days from 80th to 89th day of the year 1993. Comparison is done for pixels that selected by different composite method (i.e., by maximum_NDVI_selection in the MVC and maximum_ch.4_selection and Minimum_ScanAngle_selection in the N4SC). The points of evaluation are as follows: 1) Histograms of NDVI and reflectance. 2) Histogram of scan angle. Point 2 and 3 aim at evaluating "speckle" (i.e., higher local variance in image) and at evaluating whether the image is approximate the single data, near-nadir image.

3. Results and Discussion
Each composite result is shown in figure 3. N4SC and MVC look similar, however, 72 percent of pixels ware passed Maximum NDVI selection and proceeded to NDVI_range_check in N4SC, and in 43 percent of the passed pixels, different day is selected for composite.

(a) N4SC


(b) MVC
Figure 3. Composite results (channel 1:2:1 =R:G:B)



Figure 4. Histograms of NDVI and reflectance of channel 1 and 2. The vertical axis is frequency in percent.       -:N4SC       : MVC



(a) N4SC



(b) MVC
Figure 5. Composite images around Taklimakan desert (channel 1:2:1 -= R:G:B)
Histograms of NDVI and reflectance for channel 1 and 2 are shown in figure 4. The N4SC has high frequency in the minus range in NDVI, while the MVC has a peak around zero. In reflectance, the N4SC has frequencies higher than the MVC around 10 percent, but opposite situation in reflectance over 60 percent. This indicates that the N4SC could avoid the clouds over the low NDVI region like desert DUE TO brightness temperature, as shown in figure 5, though the MVC selected clouds.