Distributed velocity method of solving the convective-dispersion equation: 2. Error analysis and comparison with other methods

This is the second part of a two-part paper presenting a new method for treating convective-dispersive transport. The motivation for developing this technique arises from the demands of performing a risk assessment for a nuclear waste repository. These demands include computational efficiency over a relatively large range of Peclet numbers, the ability to handle chains of decaying radionuclides with rather extreme contrasts in both solution velocities and half lives and the ability to treat leach- or solubitity-limited sources. To the extent it has been tested to date, the distributed velocity method (DVM) appears to satisfy these demands. This part presents an error analysis employing statistical sampling and regression analysis techniques, and comparisons of DVM with other methods for convective-dispersive transport.     

Surface soil moisture parameterization of the VIC-2L model: Evaluation and modification

HAPEX-MOBILHY data, consisting of one year of hourly atmospheric forcing data at Caumont (SAMER No. 3, 43.68°N, 0.1°W) were used repeatedly to run the two-layer Variable Infiltration Capacity (VIC-2L) land-surface scheme until the model reached equilibrium in its water and energy balance. The equilibrium results are compared with one year of weekly soil moisture measurements at different depths, the estimated latent heat fluxes for 35 days of the intensive observation period (IOP), and the accumulated evaporation, runoff and drainage for the entire soya crop season. The latent heat flux comparisons show that VIC-2L tends to underestimate the evaporation due to the low soil moisture in its upper layer. The soil moisture comparison shows that the total soil water content is well simulated in general, but the soil water content in the top 0.5 m is underestimated, especially in May and June. These comparisons suggest that the lack of a mechanism for moving moisture from the lower to the upper soil layer in VIC-2L is the main cause for model error in the HAPEX-MOBILHY application. A modified version of VIC-2L, which has a new feature that allows diffusion of moisture between soil layers, and a 0.1 m thin layer on top of the previous upper layer, is described. In addition, the leaf area index (LAI) and the fraction vegetation cover are allowed to vary at each time step in a manner consistent with the rest PILPS-RICE Workshop, rather than being seasonally fixed. With these modifications, the VIC-2L simulations are re-evaluated. These changes are shown to resolve most of the structural deficiencies in the original version of the model. The sensitivity analysis of the new version of the model to the choices of soil depths and root distribution show that the evapotranspiration and soil moisture at the model equilibrium state are more sensitive to the root distribution than to the soil depth.     

Surface erosion caused on Mars from Viking descent engine plume

During the Martian landings the descent engine plumes on Viking Lander 1 (VL-1) and Viking Lander 2 (VL-2) eroded the Martian surface materials. This had been anticipated and investigated both analytically and experimentally during the design phase of the Viking spacecraft. This paper presents data on erosion obtained during the tests of the Viking descent engine and the evidence for erosion by the descent engines of VL-1 and VL-2 on Mars. From these and other results, it is concluded that there are four distinct surface materials on Mars: (1) drift material, (2) crusty to cloddy material, (3) blocky material, and (4) rock.Work performed as part of NASA contract W 14,575.     

Radar sensing of the ocean

Radar remote sensing of the ocean has been the subject of research for about 20 years. Spaceborne radar altimetry and scatterometry are approaching maturity, and synthetic-aperture radars (SAR) show great promise. The principles of radar scattering from the sea are outlined here, along with some recently discovered questions. For wind-vector scatterometry, the principle is presented, and remaining uncertainties are outlined. Principles of SAR imaging of moving targets, and particularly the ocean surface, are outlined. The theory of SAR wave imaging is the subject of considerable controversy, and some principles that can be used in evaluating the various theories are presented, along with brief outlines of the major conflicting theories. Other uses of SAR images are discussed briefly, with a theory to explain the bathymetric expression outlined.