Nugget effect

[Shakil_Romshoo]

Hello, May somebody please tell me how to interpret the negative nugget effect? I mean when the semi-variance is negative at h=0. I was doing variogram analysis of soil moisture data derived from remotely sensed data and I do observe this trend in a few variograms. I don't know exactly how to interpret it. A few comments would be highly appreciated. With regards, Shakil --