Representing major soil variability at regional scale by constrained Latin Hypercube Sampling of remote sensing data
Mulder, V.L. ; Bruin, S. de; Schaepman, M.E. - \ 2013
International Journal of applied Earth Observation and Geoinformation 21 (2013). - ISSN 0303-2434 - p. 301 - 310.
design-based estimation - spatial prediction - classification tree - optimization - landscape - attributes - strategies - variables - desert - model
This paper presents a sparse, remote sensing-based sampling approach making use of conditioned Latin Hypercube Sampling (cLHS) to assess variability in soil properties at regional scale. The method optimizes the sampling scheme for a defined spatial population based on selected covariates, which are assumed to represent the variability of the target variables. The optimization also accounts for specific constraints and costs expressing the field sampling effort. The approach is demonstrated using a case study in Morocco, where a small but representative sample record had to be collected over a 15,000 km2 area within 2 weeks. The covariate space of the Latin Hypercube consisted of the first three principal components of ASTER imagery as well as elevation. Comparison of soil properties taken from the topsoil with the existing soil map, a geological map and lithological data showed that the sampling approach was successful in representing major soil variability. The cLHS sample failed to express spatial correlation; constraining the LHS by a distance criterion favoured large spatial variability within a short distances resulting in an overestimation of the variograms nugget and short distance variability. However, the exhaustive covariate data appeared to be spatially correlated which supports our premise that once the relation between spatially explicit remote sensing data and soil properties has been modelled, the latter can be spatially predicted based on the densely sampled remotely sensed data. Therefore, the LHS approach is considered as time and cost efficient for regional scale surveys that rely on remote sensing-based prediction of soil properties.
Sand transport dynamics after a foredune breach: a case study from Schoorl, the Netherlands
Meerkerk, A. ; Arens, B. ; Lammeren, R.J.A. van; Stuiver, H.J. - \ 2007
Geomorphology 86 (2007)1-2. - ISSN 0169-555X - p. 52 - 60.
sediment transport - aeolian processes - transverse dunes - natural tracers - profile - models - desert - island - inlet - wind
Near Schoorl in The Netherlands a gap was created in the foredunes during a nature development project in 1997. This resulted in considerable aeolian sand transport and allowed the sea to enter the swale valley behind the foredunes during storm events. From 1997 to 2002 a monitoring program was carried out and various data sets were collected. This study used a part of those data to investigate the effects of a foredune breach on sand transport dynamics. The main focus was on the aeolian transport of sediment through the gap in the dunes. After the breach calcareous beach sand was transported into the swale valley where exclusively decalcified sand was present. This enabled a study of the spatial aspects of transport based on six data sets of carbonate content that were collected during the 1997¿2002 period. Grids of carbonate content were interpolated and analysed together with data on geomorphology, topography and wind characteristics. The results provided insight on the displacement speed of the deposition front of calcareous sand, the influence of transport barriers and the correlation of transport directions with wind data. In addition, the study led to the observation that the trend of increase of available digital data during the last two decades is significant in facilitating the study of sand transport at the landscape scale. This is encouraging given the fact that the practical use of existing sand transport models in this context remains limited.
Effect of rock fragment embedding on the aeolian deposition of dust on stone-covered surfaces
Goossens, D. - \ 2005
Earth Surface Processes and Landforms 30 (2005)4. - ISSN 0197-9337 - p. 443 - 460.
cima volcanic field - semiarid region - spatial-distribution - eolian deposition - atmospheric dust - gravel mulch - pebble mulch - desert - soil - china
Many stone-covered surfaces on Earth are subject to aeolian deposition of atmospheric dust. This study investigates how the deposition of dust is affected when rock fragments become gradually more embedded in the ground or, inversely, become more concentrated on the surface. Experiments were executed in an aeolian dust wind tunnel with eight different types of pebbles. The following parameters were measured: dust deposition on the pebbles, dust deposition between and underneath pebbles, total dust deposition (pebbles + inter-pebble space), and the fraction, of total deposition, of dust caught by the pebbles alone. The absolute amount of dust deposition and the dust deposition density (dust deposition per unit surface) were studied for each parameter. The effects exerted by pebble size, pebble flattening, pebble elongation and wind speed were also investigated. Dust patterns on and around pebbles were also studied via flow visualization.The absolute amount of dust settling on pebbles decreases the more that the pebbles become embedded. Dust deposition density on pebbles, on the other hand, increases with embedding. The more pebbles become embedded in the soil, the more efficient the process of dust deposition on pebbles becomes. Dust deposition between and underneath pebbles increases with pebble embedding. Dust deposition density between and underneath pebbles is maximum at 50 per cent embedding, showing that in this area dust deposition is most efficient when pebbles are halfway embedded. Total deposition slightly decreases the more pebbles become embedded, but total dust deposition density increases with embedding. Aerodynamic flow separation and diverging and converging airflow play an important role in the process of dust deposition on stone-covered surfaces. The more pebbles protrude above the soil, the more they act as an obstacle and the more they disturb the air and dust flow creating scouring zones, flow separation bubbles and shelter areas for the dust. All these effects diminish as pebbles become more embedded in the soil. However, perturbations in dust patterns remain visible until pebbles have disappeared entirely
Evapotranspiration components determined by stable isotope, sap flow and eddy covariance techniques
Williams, D.G. ; Cable, W. ; Hultine, K. ; Hoedjes, J.C.B. ; Yepez, E.A. ; Simonneaux, V. ; Er-Raki, S. ; Boulet, G. ; Debruin, H.A.R. ; Chehbouni, A. ; Hartogensis, O.K. ; Timouk, F. - \ 2004
Agricultural and Forest Meteorology 125 (2004)3-4. - ISSN 0168-1923 - p. 241 - 258.
water-vapor - soil-water - flux measurements - carbon-dioxide - forest canopy - gas-exchange - leaf water - heat - surface - desert
Understanding and modeling water exchange in and and semiarid ecosystems is complicated by the very heterogeneous distribution of vegetation and moisture inputs, and the difficulty of measuring and validating component fluxes at a common scale. We combined eddy covariance (EC), sap flow, and stable isotope techniques to investigate the responses of transpiration and soil evaporation to an irrigation event in an olive (Olea europaea L.) orchard in Marrakech, Morocco. The primary goal was to evaluate the usefulness of stable isotope measurements of water vapor in the turbulent boundary layer for partitioning evapotranspiration under Such dynamic conditions. The concentration and deuterium isotope composition (delta(2)H) of water vapor was collected from different heights within the ecosystem boundary layer of the olive canopy before and over several days following a 100mm surface irrigation. 'Keeling plots' (isotope turbulent mixing relationships) were generated from these data to estimate the fractions of evaporation and transpiration contributing to the total evapotranspiration (ET) flux. Transpiration accounted for 100% of total ET prior to irrigation, but only 69-36% of ET during peak midday fluxes over the 5-day period following irrigation. The rate of soil evaporation and plant transpiration at the stand level was calculated from eddy covariance measurements and the evaporation and transpiration fractions from isotope measurements. Soil evaporation rate was positively correlated with daily atmospheric vapor pressure deficit (D), but transpiration was not. Component fluxes estimated from the isotope technique were then compared to those obtained from scaled sap flow measurements. Sap flow in multiple-stemmed trees increased following the irrigation, but large single-stemmed trees did not. We matched the source area for eddy covariance estimates of total ET fluxes with scaled sap flow estimates developed for the different tree types. Soil evaporation was determined from the difference between total ET and the scaled sap flow. Ecosystem-level transpiration and soil evaporation estimated by the isotope approach were within 4 and 15% of those estimated by scaled sap flow, respectively, for periods of peak fluxes at midday. Our data illustrate the utility of the isotope 'Keeling plot' approach for partitioning ET at the ecosystem scale on short time steps and the importance of accurate spatial representation of scaled sap flow for comparison with eddy covariance measurements of ET. (C) 2004 Elsevier B.V. All rights reserved.
Remote sensing parameterization of land surface heat fluxes over arid and semi-arid areas
Ma, Y.M. ; Wang, J.M. ; Huang, R.H. ; Wei, G. ; Menenti, M. ; Su, Z. ; Hu, Z.Y. ; Gao, F. ; Jiang, W. - \ 2003
Advances in atmospheric sciences 20 (2003)4. - ISSN 0256-1530 - p. 530 - 539.
heterogeneous landscape - oasis - heife - index - desert - field - ndvi
Dealing with the regional land surfaces heat fluxes over inhomogeneous land surfaces in arid and semi-arid areas is an important but not an easy issue. In this study, one parameterization method based on satellite remote sensing and field observations is proposed and tested for deriving the regional land surface heat fluxes over inhomogeneous landscapes. As a case study, the method is applied to the Dunhuang experimental area and the HEIFE (Heihe River Field Experiment, 1988¿1994) area. The Dunhuang area is selected as a basic experimental area for the Chinese National Key Programme for Developing Basic Sciences: Research on the Formation Mechanism and Prediction Theory of Severe Climate Disaster in China (G1998040900, 1999¿2003). The four scenes of Landsat TM data used in this study are 3 June 2000, 22 August 2000, and 29 January 2001 for the Dunhuang area and 9 July 1991 for the HEIFE area. The regional distributions of land surface variables, vegetation variables, and heat fluxes over inhomogeneous landscapes in arid and semi-arid areas are obtained in this study.