Rb. Grayson et Aw. Western, TOWARDS AREAL ESTIMATION OF SOIL-WATER CONTENT FROM POINT MEASUREMENTS - TIME AND SPACE STABILITY OF MEAN RESPONSE, Journal of hydrology, 207(1-2), 1998, pp. 68-82
Areal estimates of soil moisture over large areas are required for the
ground truthing of remotely sensed measurements and for establishing
catchment-wide antecedent conditions for runoff simulations. There is
a mismatch in scale between field (point) measurements and the areal e
stimates from both remote sensing and simulation modelling, so attenti
on must be focused on developing sampling strategies that are able to
determine accurate areal estimates of soil moisture using present (ess
entially point) techniques. In this paper, we use the concepts of time
stability, applied to catchments with significant relief, to investig
ate the existence of certain parts of the landscape which consistently
exhibit mean behaviour irrespective of the overall wetness. We denote
these as catchment average soil moisture monitoring (CASMM) sites. Fo
ur data sets from three catchments (Tarrawarra, R5-Chickasha and Locky
ersleigh) are examined. The catchments range in size from 10.5 ha to 2
7 km(2). Soil moisture measurements are made using time domain reflect
rometry (TDR) or neutron moisture meters (NMMs), over depths from 30 t
o 120 cm. Time-stable locations representing mean areal moisture conte
nt are found in each catchment, i.e. CASMM sites exist. Although this
analysis is preliminary, it points towards the possibility of a method
ology for determining a sampling regime that could provide reliable es
timates of areal mean soil moisture in complex terrain from a limited
number of sample locations. (C) 1998 Elsevier Science B.V. All rights
reserved.