There are 2 similar numbers for SD data, but 2 different for RMS, in my AFM analysis data, from 2 samples, I thought they were equal!
I think the RMS is a measure of the square root of the means gotten from several samples, meanwhile the SD shows how distributed or how scatter a particular variable or sets of variables is from an original set of data. It is a measured for a single sample space.
Surface roughness[ Rq(RMS)] is defined as the SD of the Z values within the given area and is calculated using the formula: Zrms=sqrt(sum from i to N ((Zi-Zavg)^2)/N)
where: Zavg is the average of the Z values within the given area, Zi is the current Z values, and N is the number of points within the given area.
http://www.formatex.org/microscopy3/pdf/pp758-769.pdf
http://www.iovs.org/content/41/3/680.full
Rms roughness represents the entire surface as Dr. Hajji mentioned. Nevertheless you must consiider the physical meaning of the values you get from your images if the values are as different as you mention. Could you tell what are you measuring and how do the images look like? What deposition gechnique
Niusha, please get these links , hope they are useful for your research
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