BibSonomy publications for /user/jgomezdans/soilFri Aug 15 14:48:39 CEST 2008Agronomy Journal61706-1710Soil Physical Properties Web Database for GOSSYM and GLYCIM Crop Simulation Models962004Soil models agriculture agronomic crops Knowledge of soil physical properties is needed for various kinds of environmental studies, including crop simulation where the intended users are agronomists, consultants, and growers. However, acquiring and tabulating a complete set of soils analysis data for a particular region is expensive and laborious. This paper describes the construction of a web-based soil physical properties database to meet data requirements of users of cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.] crop simulation models (GOSSYM and GLYCIM, respectively) in addition to providing a generic data file of soil physical properties. The data are comprised of undisturbed samples of 1074 soil horizons (or about 300 sample sites) collected from farmers' fields using a tractor-mounted hydraulic probe. Standard laboratory analyses were performed to determine the various soil physical properties. An Oracle8 relational database management system was designed and implemented to store and deliver the soil physical properties using a client/server approach. A Perl database interface was used for the server-side database connectivity to build the soil files. The database accepts queries on several attributes, including sampling location, soil series name, state, county, farm, etc. This web-based database of soil physical properties was successfully implemented and tested and is available online at www.msstate.edu/~ia3/ (verified 11 Aug. 2004) without any restriction of identification or password. Thu Jul 03 18:17:33 CEST 20082002 Soil Moisture Experiment (SMEX02)Remote Sensing of EnvironmentSep4475--482Vegetation water content mapping using Landsat data derived normalized difference water index for corn and soybeans922004satellite reflectance evaporation moisture ndwi vegetation remotesensing drought soilmoisture stress Soil Information about vegetation water content (VWC) has widespread utility in agriculture, forestry, and hydrology. It is also useful in retrieving soil moisture from microwave remote sensing observations. Providing a VWC estimate allows us to control a degree of freedom in the soil moisture retrieval process. However, these must be available in a timely fashion in order to be of value to routine applications, especially soil moisture retrieval. As part of the Soil Moisture Experiments 2002 (SMEX02), the potential of using satellite spectral reflectance measurements to map and monitor VWC for corn and soybean canopies was evaluated. Landsat Thematic Mapper and Enhanced Thematic Mapper Plus data and ground-based VWC measurements were used to establish relationships based on remotely sensed indices. The two indices studied were the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index (NDWI). The NDVI saturated during the study period while the NDWI continued to reflect changes in VWC. NDWI was found to be superior based upon a quantitative analysis of bias and standard error. The method developed was used to map daily VWC for the watershed over the 1-month experiment period. It was also extended to a larger regional domain. In order to develop more robust and operational methods, we need to look at how we can utilize the MODIS instruments on the Terra and Aqua platforms, which can provide daily temporal coverage.Thu May 15 12:42:42 CEST 20082002 Soil Moisture Experiment (SMEX02)Remote Sensing of Environment#sep#4548--559Crop condition and yield simulations using Landsat and MODIS922004modis satellite optical assimilation uncertainty models vegetation crops moisture mapping MODIS Soil application reflectance Crop remotesensing Monitoring crop condition and yields at regional scales using imagery from operational satellites remains a challenge because of the problem in scaling local yield simulations to the regional scales. NOAA AVHRR satellite imagery has been traditionally used to monitor vegetation changes that are used indirectly to assess crop condition and yields. Additionally, the 1-km spatial resolution of NOAA AVHRR is not adequate for monitoring crops at the field level. Imagery from the new MODIS sensor onboard the NASA Terra satellite offers an excellent opportunity for daily coverage at 250-m resolution, which is adequate to monitor field sizes are larger than 25 ha. A field study was conducted in the predominantly corn and soybean area of Iowa to evaluate the applicability of the 8-day MODIS composite imagery in operational assessment of crop condition and yields. Ground-based canopy reflectance and leaf area index (LAI) measurements were used to calibrate the models. The MODIS data was used in a radiative transfer model to estimate LAI through the season. LAI was integrated into a climate-based crop simulation model to scale from local simulation of crop development and responses to a regional scale. Simulations of corn and soybean yields at a 1.6�1.6-km2 grid scale were comparable to county yields reported by the USDA-National Agricultural Statistics Service (NASS). Weekly changes in soil moisture for the top 1-m profile were also simulated as part of the crop model as one of the critical parameters influencing crop condition and yields.Wed May 07 20:18:23 CEST 2008Computers and GeotechnicsSeptember6431--442Prediction of rainfall-induced transient water pressure head behind a retaining wall using a high-resolution finite element model302003soil Retaining walls are used to provide additional support to slopes thought to be at risk of failure. The design of such structures requires the inclusion of pore water head in the appropriate calculations, whilst subsequent construction can have major implications for the overall slope pore water head regime. Despite the obvious importance of pore water head in this context there has been no rigorous model development facilitating the temporal as well as the spatial high-resolution computation of pore water head. This paper reports on the development of a soil water finite element model (ESTEL-2D), which is capable of achieving this. The model is applied to a typical Hong Kong retaining wall scenario where the model is shown to be capable not only of establishing `dynamic steady state initial conditions', but also of illustrating the complexities of the pore water head changes occurring immediately adjacent to a retaining wall. The results suggest that it is entirely appropriate to consider the utilisation of such modelling capability to assess drainage requirements (including optimal drainage locations) and appropriate piezometric monitoring strategies.