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[ai-geostats] Re: Nugget effect...

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  • Rajni Gaur
    Dear Mam and List members, Sorry I could not get to your mail early. I must clarify that every time the number of observations are the same. Iam measuring the
    Message 1 of 6 , Oct 1, 2005
      Dear Mam and List members,
      Sorry I could not get to your mail early. I must clarify that every time the number of observations are the same. Iam measuring the values at the same place and exactly at the same point but the vary in time and not in space. everytime of measurement the X and Y remains same.
      So with time Iam getting the same number of observations.
      Iam sorry If  I have misunderstood your point.
       
      One more querry I have regarding the coefficient of variation. How the changes in coefficient of variation effect the semivariogram?
       
      Thanks in advance
      Regards
      Rajni

       
      On 9/5/05, Isobel Clark <drisobelclark@...> wrote:
      Rajni
       
      The nugget effect is the variance of the difference in values at very short distances. Your calculated nugget effect is an estimate of a true variance.
       
      To start with, you have few observations and therefore few degrees of freedom. A confidence interval in your estimated variance is going to be hugely wide around your estimate. Since your first period of observations are very close together, this reduces the degrees of freedom even further. In short, your early estimates of variance could be widely different from the real value.
       
      As time goes on, two things happen: you get more observations and (more importantly) they are more widely separated. Your confidence in the estimated nugget effect will increase dramatically as the extent of your observations increases relative to your range of influence.
       
      Isobel


      Rajni Gaur <rajni.geophy@...> wrote:
      Dear list members,
      I have a querry regarding the presence of nugget effect. I have brought to the notice of my seniors before that iam working on the variography of the resistivity data.
      I have been monitoring the resisivity variations at a fixed point from past many months with a frequency of 7 days or sometimes 14 days. I have come across the remarkable changes in the resitivity values. Simultaneously i have been incorporating the variograms on the acquired values of resitivity. As the time is passing by the nuggest effect is decreasing witht the changes in the resistivity values. though it is not sure the resistivity increase or sometimes it decrease also but nugget effect is showing a decline in the value. Iam not able to interpret this change in the nugget effect. though it is good but in the initial value the nugget effect comes to be 1500 and then after 1 month the value reduces to 300.
      It would be help to me if list suggest me some thing better for my interpretation work.
      thanks in advance to all of you who consider me seriously.
      regards
      Rajni
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