Derivation of vegetative variables from a landsat tm image for modelling soil erosion

A study was carried out to assess the potential use of satellite thematic mapper (TM) images to produce maps of vegetation-related variables for erosion modelling. In a Mediterranean study area in southern France the (semi-)natural vegetation was described at 33 field plots using four quantitative methods: the Fosberg structural classification system, the cover and management factor of the Universal Soil Loss Equation, the leaf area index and the total percentage cover. After radiometric correction of the image, the spectral TM bands were processed following three different methods. Each method aimed at combining the data of the six spectral TM bands into a single band in such a way that the resulting image displayed optimal information on green vegetation cover. The algorithms used comprise the normalized difference vegetation index, the conventional ‘tasselled cap’ transformation and a locally tuned tasselled cap transformation. Only slight differences were found between the different methods to calculate spectral vegetation indices for this particular case. Furthermore, the correlations between the field variables and image-derived spectral indices are generally small. The largest correlations were found for the normalized vegetation index and the leaf area index (r + 0·71) and for the normalized vegetation index and Fosberg's structural vegetation classes (r + 0·76). However, Fosberg's method results in very general classes, which are of little use for soil erosion models. Furthermore, the spectral indices appeared to be sensitive for the vitality of the vegetation. Consequently, an area covered by a sensed, senescent vegetation will not yield a large value for the spectral index, but its soil is protected against splash erosion. This might lead to a misinterpretation of the soil protective cover when satellite images are used. A final conclusion is that a balance has to be found between the more accurate, but time-consuming field surveys to gather information on erosion-controlling factors and a certain loss of accuracy associated with the use of quick and easy remote sensing methods.     

Ice-collapse induced waves and graded gravel ridges on a Lake Beach

Ice collapsing into the waters of proglacial Briksdal Lake, western Norway, generates waves which rework shoreline sediments. Swash establishes graded gravel ridges sub-perpendicular to the shoreline, derived from material eroded by backwash. A terminal gravel bar at the lakeward limit of wave-induced transport marks the maximum depth of water surface waves.     

An investigation into thermodynamic consistency of data for the olivine, wadsleyite and ringwoodite form of (Mg,Fe)2SiO4

We have performed a thermodynamic analysis to determine the internal consistency of state-of-the-art experimental data for olivine, wadsleyite, and ringwoodite solid solutions. The analysis has been carried out between 200 and 2200 K and 0 and 20 GPa. We conclude that the volume-pressure-temperature data of wadsleyite and ringwoodite show very large inconsistencies, which hamper the accurate prediction of bulk sound velocities in the transition zone to within tomographic accuracy. Owing to the compositional effect in two-phase regions, thermodynamic properties, crucial for geodynamic modeling, differ up to an order of magnitude relative to values in single-phase regions at conditions prevailing in the earth’s transition zone. Thermal expansivity in the olivine-wadsleyite two-phase region is ∼23 times larger than that in the olivine region. For the wadsleyite-ringwoodite two-phase region, thermal expansivity is ∼6 times larger than that in the wadsleyite region. It may be anticipated that this differential thermal expansivity significantly affects future geodynamic model calculations.     

Bimodal wave spectra in lower Chesapeake Bay, sea bed energetics and sediment transport during winter storms

The transition zone separating estuarine environments from the coastal ocean is characterized not only by distinctive morphological and sedimentary trends but by unique hydrodynamic forces as well. Lower Chesapeake Bay, a large coastal estuary within the Mid-Atlantic Bight of the U.S. East Coast, experiences complex wave and current-induced forces produced during winter storms. Wave and current measurements made near Thimble Shoal Light over five winter seasons show that most storms simultaneously produce both ocean and bay-generated wave trains that appear as distinct bimodal peaks in directional spectra. Analysis of selected storm wave records reveal that lower-frequency ocean waves, although nominally lower in amplitude than higher-frequency bay waves, are roughly equivalent to bay waves in terms of energy expended on beds of fine- to medium-grained sand at either end of the Thimble Shoal Channel. Grain-friction energy dissipation estimates calculated for waves and currents suggest that waves provide more net energy capable of transporting bottom sediment than currents, although strong barotropic flows briefly encountered during a major storm on 13–14 March 1993, exceeded wave energy expended at the bed by almost an order of magnitude. From analyses of wave orbital velocity spectra, it is shown that dual wave trains characterized by differences in peak frequency and direction may assist each other through interactions that increase their combined contribution to frictional energy dissipation and inferred sediment transport at the bed.     

Warming at 18,000 yr B.P. in the Tropical Andes

Palynological, paleopedological, and glacial geomorphological evidence from the area of the high plain of Bogotá in the Colombian Eastern Cordillera indicates a significant climatic warming around 18,000¹⁴C yr B.P. Comparison of dated vegetation changes, pedogenic episodes, and glacier fluctuations provides the basis for defining the so-called “La Laguna Interstadial” that lasted from 19,500 to 17,000 yr B.P. During this interstadial period, mean annual temperatures in the tropical Andes were up to 4°C higher than during the preceding and following stadial periods, when full-glacial conditions prevailed and temperatures were up to 8°C colder than at present.     

3D magnetotelluric modelling including surface topography

An edge finite‐element method has been applied to compute magnetotelluric (MT) responses to three‐dimensional (3D) earth topography. The finite‐element algorithm uses a single edge shape function at each edge of hexahedral elements, guaranteeing the continuity of the tangential electric field while conserving the continuity of magnetic flux at boundaries. We solve the resulting system of equations using the biconjugate gradient method with a Jacobian preconditioner. The solution gives electric fields parallel to the slope of a surface relief that is often encountered in MT surveys. The algorithm is successfully verified by comparison with other numerical solutions for a 3D‐2 model for comparison of modelling methods for EM induction and a ridge model. We use a 3D trapezoidal‐hill model to investigate 3D topographic effects, which are caused mainly by galvanic effects, not only in the Zxy mode but also in the Zyx mode. If a 3D topography were approximated by a two‐dimensional topography therefore errors occurring in the transverse electric mode would be more serious than those in the transverse magnetic mode.     

Integrity Monitoring of IGEX-98 Data,Part I: Availability

The International GLONASS Experiment 1998 (IGEX-98) was the first international tracking campaign of the Russian counterpart to the Global Positioning System (GPS), GLONASS. Started in October 1998, the campaign was originally scheduled to last for three months. However, the launch of additional GLONASS satellites and a widespread enthusiasm among the participants led to an indefinite continuation of the campaign on a “best effort” basis. At the Delft University of Technology, the data of six IGEX-98 stations have been analyzed in detail with integrity monitoring software, developed at the Department of Mathematical Geodesy and Positioning of the University. The software aims to detect outliers and slips in code and phase observations in real time. In addition, the software also allows the validation of the information contained in the broadcast navigation messages. The results of the IGEX-98 data analyses will be presented in a three-part series. In the second part, GLONASS outlier and slips statistics will be discussed, while in the third part the anomaly detection results of the GLONASS and GPS messages will be shown. In this first part of the series, however, the most basic of all statistics will be considered: a simple day-to-day count of the number of GLONASS and GPS observations. Although simple, this statistic yields a surprising amount of information both on the availability of the GLONASS satellites and on the peculiarities of some of the receiver makes participating in the IGEX-98 campaign. ? 2000 John Wiley & Sons, Inc.     

Geochronologic evidence for Early Cretaceous volcanic activity on Barton Peninsula, King George Island, Antarctica

Ages of six volcanic and plutonic rocks on Barton Peninsula, King George Island, were determined using ⁴⁰Ar/³⁹Ar and K-Ar isotopic systems. The ⁴⁰Ar/³⁹Ar and K-Ar ages of basaltic andesite and diorite range from 48 My to 74 My and systematically decrease toward the upper stratigraphic section. Two specimens of basaltic andesite which occur in the lowermost sequence of the peninsula, however, apparently define two distinct plateau ages of 52-53 My and 119-120 My. The latter is interpreted to represent the primary cooling age of basaltic andesite, whereas the former is interpreted as the thermally-reset age caused by the intrusion of Tertiary granitic pluton. The isochron ages calculated from the isotope correlation diagram corroborate our interpretation based on the apparent plateau ages. It is therefore likely that volcanism was active during the Early Cretaceous on Barton Peninsula. When the K-Ar ages of previous studies are taken into account with our result, the ages of basaltic andesite in the northern part of the Barton Peninsula are significantly older than those in the southern part. Across the north-west-south-east trending Barton fault bounding the two parts, there are significant differences in geochronologic and geologic aspects.