Dear Maureen,
I have dealt with the same problem. The basic approach is to transform
your coordinates as Warren suggested. If you only have one measurement
per transect, than it is as simple as working with distance from a set
point such as the last or first sampling point, and your variogram and
kriging is one-dimensional. If you need a 2-dimensional transformation,
than it gets much more complicated. There are different approaches
possible, such as normalizing to distance from one bank or from the
center of flow. Then, regardless of how wide the stream is, two points
1/3 of the way into the stream will have the same lateral coordinates. You
also have to account for angles to the bank or center line.
I used a grid generation approach in my case. You can use commercial
software or write your own code. I settled for the latter, the commercial
software (Gridgen from Pointwise) is for much more complicated problems.
Look at this reference for a general description:
Barabas N, Goovaerts P, Adriaens P (2001) Geostatistical Assessment and
Validation of Uncertainty for Three-Dimensional Dioxin Data from Seidments
in an Estuarine River. Environ. Sci. Technol. 35, 3294-3301.
Noemi
Noemi Barabas
PhD Candidate
The University of Michigan
Dept. Civil and Environmental Engineering
1351 Beal Avenue (13 EWRE)
Ann Arbor, MI 48109-2125
Phone: (734) 615-5905
On Thu, 2 May 2002, Warren Schlechte wrote:
> Maureen,
>
> I believe we met in Savannah a couple of years ago. If you don't mind,
> could you send me any responses you get as a summary? Such seems useful to
> know - how to best deal with boundary conditions. It would seem from my
> neophyte position that such would be easy to do. First, you don't provide
> any data from the adjacent land. Hence the estimation of the variogram won't
> take anything but stream readings into account. Second, when you provide a
> grid to estimate over, only provide points that lay within the stream. One
> item you will want to consider is how you portray your grid. Since a stream
> is a self-contained entity, I would think that distance should be portrayed
> as distance within the stream, distance as the water flows, not distance as
> the crow flies. Another aspect you may wish to consider is that streams
> have direction. Hence, it would seem unusual (with the exception of large
> inflows) for downstream sites to ever have an effect on upstream sites.
> This would suggest all sites should only look upstream for temperature
> information. The final item that comes to mind quickly is the influence of
> inflow. These will be sources of different temperatures than exist in the
> main stream basin. As such, it would seem that any major inflows should be
> measured.
>
> Hope that my thought help, and that you get the help you need from this
> group.
>
>
> Warren Schlechte
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf
> Of Maureen Walsh
> Sent: Wednesday, May 01, 2002 9:35 PM
> To: [EMAIL PROTECTED]
> Subject: AI-GEOSTATS: Kriging a stream surface
>
> << File: vcard.vcf >> I am interested in using kriging to interpolate
> temperature surfaces for
> a stream that I work on, based on data from fixed point temperature
> loggers along the length of the stream. However, I am unsure if it is
> possible to constrain the analysis within the stream boundaries. I was
> wondering if anyone with experience conducting these types of analyses
> would have any suggestions about how to address this problem.
> Thank you very much,
> Maureen Walsh
>
>
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