Daily discharge estimation at ungauged river sites using remote sensing

A methodology is developed to estimate daily river discharge at an ungauged site using remote sensing data. Use is made of ERS‐2 and ENVISAT satellite altimetry to provide a time series of river channel stage levels and longitudinal channel slope and Landsat satellite imagery to provide a range of channel widths over a 50 km reach of river. The data are substituted into the Bjerklie et al. ( 2003 ) equation, which is based on the Manning's resistance equation and has been developed using a global database of channel hydraulic information and discharge measurements. Our methodology has been applied at three locations on the Mekong and Ob Rivers and validated against daily in situ discharge measurements. The results show Nash–Sutcliffe efficiency values of 0.90 at Nakhon Phanom and 0.86 at Vientiane on the Mekong, and 0.86 at Kalpashevo on the Ob. Copyright © 2012 John Wiley & Sons, Ltd.     

Using satellite altimetry data to augment flow estimation techniques on the Mekong River

Satellite altimetry is routinely used to provide levels for oceans or large inland water bodies from space. By utilizing retracking schemes specially designed for inland waters, meaningful river stages can also be recovered when standard techniques fail. Utilizing retracked waveforms from ERS‐2 and ENVISAT along the Mekong, comparisons against observed stage measurements show that the altimetric measurements have a root mean square error (RMSE) of 0·44–0·65 m for ENVISAT and 0·46–0·76 m for ERS‐2. For many applications, however, stage is insufficient because discharge is the primary requirement. Investigations were therefore undertaken to estimate discharges at a downstream site (Nakhon Phanom (NP)) assuming that in situ data are available at a site 400 km upstream (Vientiane). Two hypothetical, but realistic scenarios were considered. Firstly, that NP was the site of a de‐commissioned gauge and secondly, that the site has never been gauged. Using both scenarios, predictions were made for the daily discharge using methods with and without altimetric stage data. In the first scenario using a linear regression approach the altimetry data improved the Nash‐Sutcliffe r² value from 0·884 to 0·935. The second scenario used known river cross‐sections while lateral inflows were inferred from a hydrological model: this scenario gave an increase in the r² value from 0·823 to 0·893. The use of altimetric stage data is shown to improve estimated discharges and further applications are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Mid-ir imaging polarimetry and circumstellar magnetic fields

We have obtained diffraction-limited images of the mid-infrared emission and polarization patterns in a number of southern-sky objects. By mapping the polarization produced in absorption or emission by aligned aspherical dust grains, we have been able to trace the detailed spatial structure of magnetic fields in the warm circumstellar material of young molecular-outflow sources and HII regions, in the expanding dust shell of the mass-losing star Eta Carinae, and in the inner parsec of the Galactic Centre.     

Transient response of reservoir–dam–soil systems to earthquakes

A direct time-domain numerical procedure is proposed to analyse the transient dynamic response of two-dimensional reservoir–dam–soil systems. The reservoir extends to infinity and the dam is supported by an unbounded soil. The structure with either linear or non-linear material properties is modelled by the Finite Element Method (FEM). The soil is assumed to be an elastic, isotropic and homogeneous half-space represented by a boundary condition in the form of generalized impedance determined by the transient Lamb's solution due to a uniformly distributed traction imposed on the free surface, Guan and Novak.¹ Moreover, a technique is developed to include the influence of the reservoir on the dam in terms of nodal accelerations along their interface at different time steps. The advantages of the proposed procedure are obvious. For example, it avoids any additional discretization of the boundaries except the soil–dam interface, and the influence matrix of the fluid is obtained explicitly using shape functions defined at the upstream face of the dam without the finite analysis of the reservoir so that it works very efficiently. Numerical results for a system consisting of reservoir, elastic dam and foundation subjected to the San Fernando, 1971 earthquake ground motion are presented.     

SULFUR IN ACHONDRITIC METEORITES

Total sulfur abundances have been measured for 48 achondrites. For twenty eucrites they ranged from 370 to 3700 μgS/g with a median sulfur content of 1180 μgS/g. Sulfur abundances for howardites ranged from 1490 to 3240 μgS/g and had a median sulfur concentration of 2340 μgS/g. Diogenites' sulfur abundances ranged from 130 to 3170 μgS/g, with a median value of 1280 μgS/g. Four shergottites had a median sulfur content of 1940 μgS/g and ranged from 740 to 2540 μgS/g. Enstatite achondrites contained the greatest sulfur abundances of any achondrite group. They ranged from 2450 to 8580 μgS/g and had a median sulfur content of 6020 μgS/g. A single Chassignite had a sulfur concentration of 360 μgS/g. The wide variations in sulfur concentrations for the achondrites reflect the small scale heterogeneous nature of these unique extraterrestrial materials due in large part to discrete sulfide mineral grains.