[GRASSLIST:4666] Re: uncertainty on spatial aggregation using Thiessen polygons

[Thomas Adams]

Wouter,

I've done extensive work with precipitation data in the Ohio River 
Valley in the U.S. (~450,000 km^2) looking at both raingauge and radar 
derived precipitation accumulations. Generally, I have only looked at 
monthly, seasonal, and annual amounts. In complex terrain I just have no 
feel for the strength of the orographic influence at shorter time 
scales. Having said that, however, from some research that has been 
done, I know that for isolated storms (some flash flood producing 
convective events) there can be terrain focusing of the storm cells.

I have used the techniques suggested by Goovaerts (cited below) using 
ordinary kriging with variable means, but I have not verified the 
estimates independently yet.

I certainly would like to have a better understanding of the orographic 
influence at shorter time scales, especially in the Appalachian 
Mountains of the U.S. which generally have local relief on the order of 
1000 m.

Regards,
Tom Adams


DrakeGis wrote:

>HI,
>  I'm not so sure about using Thiessen is a really good option. I know
>that usually is the easier way, but Goovaerts, P (2000) in
>"Geostatistical approaches for incorporating elevation into the spatial
>interpolation of rainfall (Journal of Hydrology, 228 (1-2):113-129)"
>presents a really good analysis of the different techniques (prior to
>incorporate the elevation data) and some tools to improve the
>estimations, toghether with analysis of accurancy. He also conclude that
>Kriging is a better option.
>
>  D.
>
>  
>
>>Hello,
>>
>>I'm aware that my question is not really GRASS related, but none of our
>>GIS experts can help me, so I hope someone here can point me to a
>>relevant paper or study.
>>
>>I want to aggregate daily rainfall data of 3 rain gauges in a small
>>catchment for input in a lumped hydrological model
>>Herefore, I am using a weighted average, based on the relative area of
>>the respective Thiessen polygons.
>>
>>Now I'm looking for a technique to determine the uncertainty on the
>>result, based on the variability between the 3 rain gauges.
>>
>>If someone can help me, this would be greatly acknowledged!
>>
>>Thanks,
>>
>>Wouter Buytaert
>>
>>
>>    
>>
>
>
>
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-- 
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL:	thomas.adams at noaa.gov

VOICE:	937-383-0528
FAX:	937-383-0033

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