Adequate knowledge of soil moisture storage as well as evaporation and tran
spiration at the land surface is essential to the understanding and predict
ion of the reciprocal influences between land surface processes and weather
and climate. Traditional techniques for soil moisture measurements are gro
und-based, but space-based sampling is becoming available due to recent imp
rovement of remote sensing techniques. A fundamental question regarding the
soil moisture observation is to estimate the sampling error for a given sa
mpling scheme [G.R. North, S. Nakamoto, J Atmos. Ocean Tech. 6 (1989) 955-9
92; G. Kim, J.B. Valdes, G.R. North, C. Yoo, J. Hydrol., submitted]. In thi
s study we provide the formalism for estimating the sampling errors for the
cases of ground-based sensors and space-based sensors used both separately
and together. For the study a model for soil moisture dynamics by D. Entek
habi, I. Rodriguez-Iturbe [AJv. Water Res. 17 (1994) 35-45] is introduced a
nd an example application is given to the Little Washita basin using the Wa
shita '92 soil moisture data. As a result of the study we found that the gr
ound-based sensor network is ineffective for large or continental scale obs
ervation, but should be limited to a small-scale intensive observation such
as for a preliminary study. (C) 2001 Published by Elsevier Science Ltd.